Sendyne SFP200 IC for Precision Automotive Grade Current

1Preliminary Rev 1.0 © 2017 Sendyne Corp.

Sendyne SFP200

Applications ― Battery monitoring for industrial, automotive,

railroad and utility scale storage

DescriptionThe Sendyne SFP200 IC is a high precision sensing

IC addressing the unique requirements of electrical

energy storage and monitoring. The IC is rated for the

automotive temperature range of -40 °C to +125 °C.

It simultaneously measures bi-directional DC current

through a resistive shunt and is capable of sensing

three voltages with flexible range.

For current sensing, the SFP200 achieves an un-

calibrated maximum offset error of less than 200

nanovolts when measuring the voltage drop across

the shunt. This performance extends throughout the

entire automotive temperature range. With an ap-

propriate shunt, the IC can accurately measure a wide

dynamic range of currents from tens of thousands of

amperes to milliamperes.

Sendyne’s proprietary, patented “Continuous Cali-

bration” technology allows the IC to compensate for

thermal drifts including those arising from external

interface circuitry such as EMI/RFI/anti-aliasing fil-

ters. The IC provides internally-accumulated coulomb

counting information. Communications are achieved

via an isolated CAN 2.0B interface (500 kbaud). The

SFP200MOD is an implementation of the reference

design contained in this document.

Sendyne® Sensing Products Family

Sendyne SFP200 IC for Precision Automotive Grade Current and Voltage Measurements

Operating Specifications with Suggested Circuit and the Sendyne SFP Shunt

Parameter Value

Power supply +5.5~+6.5 V Isolated - See suggested schematics

Interface CAN 2.0B isolated, termination per user’s application, 120 Ω suggested

Current measurement range ±600 A continuous / ±1250 A (220 s), <±1.0 % error, using Sendyne SFP

Shunt attached to 108 mm2 busbars

Voltage measurement range 3 Channels: ±800 V nominal, ±1000 V/channel max, <±1.0 % error

Rating Automotive

Power consumption < 350 mW

IC operating temperature range -40 °C to +125 °C

2 Preliminary Rev 1.0 © 2017 Sendyne Corp.

Sendyne SFP200

― High precision current and voltage sensing IC

― Pre-programmed, no additional firmware required

― Achieves an offset error of less than 200 nanovolts

― Systems using the SFP200 IC need only be calibrated at a single room temperature point

― Accurate voltage measurement with flexible range

― Automotive temperature range, –40 °C to +125 °C

― Low power consumption

― “High” or “Low” side current sensing and voltage sensing reference point with isolated front end

― Patented zero offset functionality

― Automatically compensates for the shunt’s varying resistance relative to temperature (Gain Error)

― Built-in calibration for voltage measurements

― Separate charge, discharge, and total Coulomb counters

― Automotive rated, AEC-Q100

― Reference design as described in this, and related documents, allows for configurability based on system specific

needs (e.g. different input power supply, different full-scale voltages, no voltage measurement, etc.)

― Isolated CAN2.0B interface (500 kbaud)

Features


Sendyne SFP200

SFP200 IC Pin Description LQFP64

Pin Number Pin Name Pin Function1 S4 One of the digital input pins for selection of the CAN address,

40 kΩ (typical) built-in pull-up

2 S3 Same as above

3 S2 Same as above

4 S1 Same as above

5-6 NU - Not used, do not connect

7 DVDD Positive supply voltage for the digital circuits in the IC. DVDD

pin 7 must be connected to DVDD pin 41

8 AVDD Positive supply voltage for the analog circuits in the IC and

voltage reference for the ADC. AVDD voltage must be within

±300 mV of the DVDD voltage

9-10 AVSS Negative supply voltage for the analog circuits in the IC. AVSS

pins must be connected to DVSS pin

11 XIN Input to the built-in crystal oscillator circuit; to be connected

to the external feedback resistor and 16 MHz crystal with

built-in load capacitors

12 XOUT Output from the built-in crystal oscillator circuit; to be con-

nected to the external feedback resistor and 16 MHz crystal

with built-in load capacitors

13 NU - Not used, do not connect

14 CH2S2 Digital output pin controlling cross-bar switch for CH2

current sensing

64 63 62 61 60 59 58 57 56 55 54 53 52 51 50 49

48474645444342414039383736353433

NUNUNUNUNUNUNU

DVDDDVSS

NUNUNUNUNUNUNU

17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

HB

2C

H1S

2C

H1S

1V

TH1

ZRE

FZD

RV

NU

NU

CU

R2N

CU

R1P

VX

4V

X3

VX

2V

X1

CU

R2P

CU

R1N

123456789

10111213141516

S4S3S2S1NUNUDVDDAVDDAVSSAVSSXINXOUTNUCH2S2CH2S1HB1

RIO

3R

IO2

RIO

1N

UN

UN

UN

UN

UN

UN

UN

UN

UC

AN

_R

XC

AN

_TX N

UN

U

PIN 1

SFP200


Sendyne SFP200

Pin Number Pin Name Pin Function

15 CH2S1 Digital output pin controlling series-disconnect switch for

CH2 current sensing

16 HB1 Optional Heartbeat outputs; see design notes section

17 HB2 Optional Heartbeat outputs; see design notes section

18 CH1S2 Digital output pin controlling cross-bar switch for CH1

current sensing

19 CH1S1 Digital output pin controlling series-disconnect switch for

CH1 current sensing

20 VTH1 Analog input pin for thermistor sensing

21 ZREF Analog input pin for analog-zero reference voltage sensing

22 ZDRV Digital output pin for analog-zero reference voltage control


25 CUR2N Negative analog input for CH2 current sensing

26 CUR1P Positive analog input for CH1 current sensing

27 VX4 Analog input for voltage measurements, referenced to VX1

pin 30


pin 30


pin 30

30 VX1 Analog input, reference for voltage measurements on VX2,

VX3, and VX4

31 CUR2P Positive analog input for CH2 current sensing

32 CUR1N Negative analog input for CH1 current sensing


40 DVSS Negative supply voltage for the digital circuits in the IC. DVSS

pin must be connected to AVSS pins.

41 DVDD Positive supply voltage for the digital circuits in the IC. DVDD

pin 41 must be connected to DVDD pin 7


51 CAN_TX Digital output pin for the CAN interface data stream

52 CAN_RX Digital input pin for the CAN interface data stream

53-61 NU- Not used, do not connect

62 RIO1 Reserved digital I/O pin, factory test only; do not connect,

keep open

63 RIO2 Same as above

64 RIO3 Same as above

NU pin name means Not Used pin. These pins are electrically connected to the silicon chip via bonding wires, there-fore they should be left as electrically open on the PCB, i.e. not connected to any potential on the board.


Sendyne SFP200

Absolute Maximum Ratings

TA= -40 °C to +125 °C

Parameter RatingAVSS to DVSS ±0.05 V

AVDD to DVDD ±0.3 V

Input lines VSS -0.3 V to

DVDD +0.3 V

DVDD -0.3 V to 6.0 V

ESD (human body model)

all pins

±6 kV

ESD (charged-device model) ±500 V

Storage temperature -55 °C to +150 °C

Lead temperature

soldering reflow

260 °C Max,

per J-STD-020

Stresses above those listed under Absolute Maximum

Ratings may cause permanent damage to the device.

This is a stress rating only; functional operation of the

device at these or any other conditions above those

indicated in the operational section of this specifica-

tion is not implied. Exposure to absolute maximum

rating conditions for extended periods may affect

device reliability.

ESD CAUTION

ESD (electrostatic discharge) sensitive device.

Electrostatic charges readily accumulate on the

human body as well as test equipment, and can

discharge without detection. Although this product

features protection circuitry, damage may occur in

devices subjected to high energy ESD. Proper ESD

precautions should be taken to avoid performance

degradation or loss of functionality.


Sendyne SFP200

Electrical Specifications

These specifications are based on the performance of Sendyne SFP200MOD units

Parameter Min Typ Max Units Conditions/CommentsPower and GeneralIC operating

temperature range

-40 +125 °C

IC Supply Voltage 5.95 5.00 5.05 V Regulated supply voltage for the IC

Supply Voltage 5.5 6 6.5 V Unregulated supply voltage for isolated

part of the circuit

Supply Current 40 mA Nominal load of the isolating DC/DC con-

verter, consumption of the whole isolated

circuit

Start-up time 0.5 0.75 s After initial application of power and

power supply stabilization

Current MeasurementNominal full-scale current ±500 A Continuous rating in still air at room

temperature of 25 °C with module

connected to busbars of at least 108 mm2

cross-section (the same cross-section as

the shunt)

Peak full-scale current ±1250 A Maximum current value that is measured

without clipping; less than 5 s duration,

the same conditions as above

Current offset error* -50 <±20 +50 mA Uncalibrated performance, applies over

the full operating temperature range

Current noise error* <25 50 mARMS 1 Hz reporting rate

Current value error* -0.25 +0.25 % Room temperature, test current ±20 A or

higher

-0.5 +0.5 % 0 oC to +50 oC, test current as above

-1 +1 % -40 oC to +125 oC, test current as above

±1 % End of life, test current as above

Current measurement

resolution

<100 μA Minimum discernible current change; cor-

responds to one count of Analog to Digital

Converter (ADC), 1 Hz current report rate

Charge measurement

resolution

<1 μC Minimum discernible amount of charge

change,100 Hz report rate

Technical Specifications

* The combined Total Current Error is the ±sum of Current offset error, Current noise error, and

[Current value error] x [measured value]. For currents over 100 A the Current offset error and the Current noise error

could be omitted from the calculation since they will typically contribute less than 0.05 % to the error.


Sendyne SFP200

Electrical Specifications

These specifications are based on the performance of Sendyne SFP200MOD units

Parameter Min Typ Max Units Conditions/CommentsVoltage MeasurementNominal Full-scale voltage

range

±800 V In reference to negative terminal

of the shunt

Maximum transient voltage ±982 ±1002 V Maximum voltage value measured and

reported without clipping or distortion

Voltage offset error -300 <±50 +300 mV VX = 0 V, applies over the full ambient

operating temperature range,

TA = -40 °C to +125 °C

Voltage gain error <±1 % Over full operating temperature range,

TA = -40 °C to +125 °C

Voltage noise error <12 20 mVRMS 1 Hz reporting rate

Voltage measurement

resolution

<1 mV Minimum discernible voltage change;

corresponds to one count of ADC, voltage

report rate of 10 Hz or lower

Impedance of the voltage

measurement inputs

12 MΩ Resistive dividers utilized for the volt-

age inputs consist of four (4) elements

connected in-series. Combined Limiting

Element Voltage is 2 kV, and combined

Maximum Overload Voltage is 4 kV.

Temperature Measurement (For shunt temperature measurement) Absolute temperature

measurement error

-5 ±0.5 +5 °C Built-in temperature sensor for shunt

temperature measurements

Temperature measurement

resolution

10 m°C Practical temperature measurement

granularity

IsolationTest voltage 3 kVDC CAN interface to SHUNT.

1 min duration

Communication

Interface Spec Speed TerminationNumber of units in the same CAN branch

CAN 2.0B 500 kbit/s *None or

120 Ω

16 (DIP switch or wires/jumpers selects

one of sixteen CAN address sets)

* When two or more devices are connected to the same CAN branch, only a single device may have the termination.


Sendyne SFP200

Measured Performance Data (based on Sendyne SFP200MOD units)

Current magnitude error over temperature range of –40 °C to +125 °C

Cur

rent

mag

nitu

de e

rror

(%)

Temperature (oC)

-40 -20 0 20 40 60 80 100 120 140

3.0

2.5

2.0

1.5

1.0

0.5

0

-0.5

-1.0

-1.5

-2.0

-2.5

-3.0


Sendyne SFP200

Performance data provided in this datasheet assumes the combined use of Sendyne’s SFP200 IC and SFP 18 µΩ shunt

(please see separate Sendyne SFP Shunt datasheet). Automatic compensation for changes in resistance due to tem-

perature fluctuations (Gain Error) is pre-set in the SFP200 IC for use with Sendyne’s RoHS compliant SFP Shunt. If a

shunt other than the Sendyne SFP Shunt is selected for use, the automatic compensation feature must be disabled, or

alternatively, another compensation table can be loaded in its place. Both options can be achieved through the CAN

interface. No firmware changes are needed. For more detailed information, including instructions instructions on how

to create an appropriate compensation table please see “Notes on Automatic Calibration for Systems Using Shunts

Other Than the Sendyne SFP Shunt”.

A Note About ShuntsThe Sendyne IC can work with any shunt of any material of any resistance, including, for example, a copper busbar, as

long as that material remains reasonably consistent throughout production. For optimal performance, an appropriate

compensation table must be loaded onto the IC through the CAN 2.0B interface. The SFP200 IC ships as default with

a compensation table for the Sendyne SFP Shunt. For instructions on creating an appropriate compensation table

please refer to “Notes on Automatic Calibration for Systems Using Shunts Other Than the Sendyne SFP Shunt”.

SFP200 IC and SFP Shunt


Sendyne SFP200

Table for selection of the CAN address set

Switch 1 (IC pin 4)

Switch 2 (IC pin 3)

Switch 3 (IC pin 2)

Switch 4 (IC pin 1)

Address set Notes

Off Off Off Off 1 Default

Off Off Off On 2

Off Off On Off 3

Off Off On On 4

Off On Off Off 5

Off On Off On 6

Off On On Off 7

Off On On On 8

On Off Off Off 9

On Off Off On 10

On Off On Off 11

On Off On On 12

On On Off Off 13

On On Off On 14

On On On Off 15

On On On On 16

“Off” signifies a sensing pin is not connected / floating; “On” signifies a sensing pin is shorted to IC’s DVSS (local logic GND) potential.

The IC can operate with sixteen (16) different sets of CAN addresses, thus 16 modules based on the SFP200 IC can

simultaneously reside on the same CAN bus stub. When two or more devices are connected to the same CAN branch,

only a single device may have the 120 Ω suggested termination between the two CAN communications lines (assum-

ing that the Host has the termination at the other end of the transmission line).

Selection of a specific set of addresses is performed by the activation of one or more switches from the four individual

switches on the quad-switch unit (or selectively cutting the traces on the PCB, as shown below). After the state of any

of the switches is changed, it is required that the module is powered-down (supply voltage is removed) for 10 seconds,

in order for the new settings to be accepted. In other words, any changes made while the unit is powered on will be

ignored until the next power-up.

Selected address set follows the switch settings shown in the table below:

CAN Addresses Selection


Sendyne SFP200

S1 S2 S3 S4

DVS

S

IC

Address selection with switches

The Host (controller) communicates with the SFP200 via the CAN interface using the request-response method.

The Host issues a message requesting the specific data, and SFP200 responds with that data. For details on the com-

position of these messages, please see the following Communications section. Requests for data from the Host and

the response of the SFP200 are sent using different Extended Message ID values. These values are shown in the table

below for the sixteen (16) address sets supported by the IC.

Table for SFP200 supported Message ID sets

Address Set Request Message ID Response Message ID Notes

1 0xA100201 0xA100200 Default Address Set

2 0xA100211 0xA100210

3 0xA100221 0xA100220

4 0xA100231 0xA100230

5 0xA100241 0xA100240

6 0xA100251 0xA100250

7 0xA100261 0xA100260

8 0xA100271 0xA100270

9 0xA100281 0xA100280

10 0xA100291 0xA100290

11 0xA1002A1 0xA1002A0

12 0xA1002B1 0xA1002B0

13 0xA1002C1 0xA1002C0

14 0xA1002D1 0xA1002D0

15 0xA1002E1 0xA1002E0

16 0xA1002F1 0xA1002F0


Sendyne SFP200

Communications

Features

― CAN2.0B extended frame format

― 500 kbaud

― Polling mechanism allows host to determine the rate of incoming data

Registers The SFP200 provides Current, Voltage, Shunt Temperature and Coulomb-count registers, mapped in memory space

as shown in Table 3. Registers can only be accessed one at a time. All other addresses are reserved; any writes outside

of the defined register address range are ignored.

Message Frames Access to the registers of the SFP200 is accomplished through polling by the host. When operated with the Default

Address Set, the SFP200 listens for extended ID 0xA100201 with data length of 1. Data byte 0 of the message carries

the requested register address. If the message data length is greater than 1, the message is ignored and discarded. The

simple structure of the message is demonstrated in Table 1.

Host Request for Data, Default Address Set

Request message ID Data byte 00xA100201 Register Address

When operated with the Default Address Set, the SFP200 returns data using message ID 0xA100200. Byte 0 of the

returned message is the requested register, followed by the data with the most significant byte first. See Table 2 for

details.

SFP200 Response, Default Address Set

Response Message ID

Data byte 0 Data byte 1 Data byte 2 Data byte 3 Data byte 4

0xA100200 Register Address MSB data byte Data byte Data byte LSB Data byte

Register Map

Register address Description0x00 Reserved

0x20 Current, μA

0x40 Coulomb Count Low, μC

0x41 Coulomb Count High, μC * 232

0x60 Voltage 0, μV

0x61 Voltage 1, μV

0x62 Voltage 2, μV

0x80 Temperature, m°C

Table 1

Table 2

Table 3


Sendyne SFP200

Data format

All data returned by the SFP200 is in a 32-bit signed integer format (2’s complement signed data). Divide the signed

data by 106 (1000000) to get the values in Amperes or Volts. For Temperature, divide the signed data by 103 (1000) to

get the values in degrees Celsius.

Coulomb counts are split into two registers, Coulomb Count High and Coulomb Count Low. The data is a combined

64-bit signed integer value (2’s complement signed data). Divide the signed data by 106 to get the value expressed in

Coulombs. Register Coulomb Count Low should always be read first. Read of this register causes Coulomb Count High

to latch and remain unchanged until Coulomb Count Low is read again.

Example Communications, Default Address Set

Origin Message ID Byte 0 Byte 1 Byte 2 Byte 3 Byte 4Host 0xA100201 0x60

SFP200 0xA100200 0x60 0xFF 0x45 0xA1 0x34

Example walkthrough1. Host sends a request message with ID 0xA100201 (extended), byte 0 set to 0x60 (voltage) and message

length set to 1.

2. The SFP200 receives the message and responds with the requested register address and contents using

extended ID 0xA100200.

3. Host receives the message and checks byte 0 to determine if the correct register address has been received.

4. Host re-assembles the bytes into a signed integer, and then divides by 106 to scale the value.

Pseudo-code for Current and Voltage received data reassembly by the host:// Example raw data from SFP module

unsigned char byte1 = 0xFF;

unsigned char byte2 = 0x45;

unsigned char byte3 = 0xA1;

unsigned char byte4 = 0x34;

// Assembling to 32 bit unsigned integer

unsigned int reassembled_data = 0;

reassembled_data |= byte1 << 24;




// Converting to volts

float voltage = (int)(reassembled_data) / 1000000.0f;

// Calculated value is -12.213964 Volts

Table 4


Sendyne SFP200

SHU

NT

x1

x1

x1

x1

Current Sensing

Voltage sensing

HEARTBEATLEDs(optional)

ADC

t

21

22

32

26

19

18

AVDD

GND

20

28

30

29

SW SW

GND

SW SW

GND

GND

Temperature sensing

51

8

AVDD

GND

7 41

9 10 40

DVDD

Control Logic

Communications Logic

52

11

12

CLOCK

16

17

CAN_TX

CAN_RX

CRYSTAL 16 MHz

14

15

31

25 G

G

x1

x1

ZDRVControl

ZREF

x1

27

x1

GND GND

CAN

VREF

GND

HV1

HV2

HV3

4

3

2

1

GND

CAN Address Selection

Nonvolatile memory for

calibration data

Calibration controls

Block Diagram in Application Circuit


Sendyne SFP200

Suggested Schematic

J2J1

0J1

1J4

J3J1

J12

J9

Sen

dyne

18

µΩ s

hunt

(SFP

SH85

36-1

-8P1

8U)

NU

NU

NU

NU

NU

NU

NU

NU

NU

NU

NU

CA

N_

RX

CA

N_

TX

RI0

3R

I02

RI0

1

NUNUNUNUNU

NUNUNU

NUNUNU

NU

DVSSDVDD

ZDR

VN

UN

U

ZRE

FV

TH1

CH

1S1

CH

1S2

CU

R2N

CU

R1P

VX

4V

X3

VX

2V

X1

CU

R1N

CU

R2P

NUNU

DVDDAVDDAVSSAVSS

NUXOUT

XIN

CH2S2CH2S1

S1S2S3S4

SFP2

0058596061626364 51525354555657 4950

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10111213141516

23222120191817 292827262524 323130

39383736353433

46454443424140

4847

To/F

rom

isol

ated

C

AN

tran

scie

ver

U1

GN

DG

ND

GN

D

+5V

+5V

A +5V

C16

C17 C15

100n

F

100n

F

10uF

L5FBEAD

R23

1M 1

%

X1

16M

Hz

CAN address select

GN

D

C9100nF

R12

10k

1%

R13

1M 1

%

R38

1M 1

%

R11

10k

1%

ZREF

+5V

GN

D

GN

DC14

100n

F

C10 C12

C13

R19R18

C11 R17

R16

30k

1%

30k

1%

30k

1%

30k

1%

100n

F

100n

F

100n

F

100n

F

T1TE

ST_

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DC8

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R15

10k

1%

R14

1M 1

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ND

U2

MCP6234

DM

G69

68U

DM

DM

G69

68U

DM

R6

R7

499

1%

499

1%

GN

D

C2

100n

F

C3

100n

F

C6

100n

F CH

2P

CH

2N

ZRE

F

CH

1P

CH

1N

C7

100n

F

C4

100n

F

C5

100n

F

R8

R9

499

1%

499

1%

GN

D

+5V

A R5

10k

1%

10k @ 23C

TH1

GN

DG

ND

C1

100n

F

1234567

12111098

1314

VOUTB

VINB -

VINB +

VDD

VINA +

VINA -

VOUTA

VOUTC

VINC -

VINC +

VSS

VIND +

VIND -

VOUTD

+5V R27

1M 1

%

SHU

NT

SHU

NT

SHU

NT

SHU

NT

J10

J11

J12

J9

Q1

1 2 3

6 5 4

Q2

1 2 3

6 5 4

R4

10k

1%

R3

10k

1%

R2

10k

1%

R1

10k

1%

CH

2S2

CH

1S1

CH

1S2

CH

2S1

R20

R24

R28

R31

3M 1

%3M

1%

3M 1

%3M

1%

VSE

NSE

J6

R21

R25

R29

R32

3M 1

%3M

1%

3M 1

%3M

1%

VSE

NSE

J7

R33

R30

R26

R22

3M 1

%3M

1%

3M 1

%3M

1%

VSE

NSE

J8

Full

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le ±

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e 12

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ors

have

a v

alue

of

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1%

for

full-

scal

e in

put ±

247

V

J1 J2 J3 J4TIE

DO

WN

TIE

DO

WN

TIE

DO

WN

TIE

DO

WN

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NU

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t sw

itch

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plifi

ers

Clo

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ypas

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tage

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ing

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t Tem

p.Se

nsin

g


Sendyne SFP200

Suggested Schematic Isolated DC/DC and CAN communication

Isolation

Isolated powersupply 5.5-6.5 V

CAN_RXCAN_TX

GND

GND GND

GND

ISOLATED

ISOLATED

+5V

ISOLATED

12345678

131211109 161514

213

456

32

123

4

5

C28

10uFC29

100nF

C20

100nF

GNDPWR GNDPWR GNDPWR

GNDPWR

GNDPWR

GNDPWR

GNDPWR GNDPWR GNDPWR GNDPWR GNDPWR

GNDPWR

BA

V70

W76

0390

014

R36

1VDD

FBE

AD

L1

TX1

D1

U3

SI86

22_

WB

1234

8765

TJA1051T

U4

C1810uF

C19100nF

1234

NUP2105L

CONN_01X04

1

23

D2P1

R39

120

CANHCANL

C311uF 100V

R421

U5

SN6501-Q1

TXDGNDVCC RXD

SCANHCANL

NC

GND

GND

D

D2VCC

GN

D2

NC

NC

B2

B1

VD

D2

NC GN

D2

NC

GN

D1

NC

A2 A1

VD

D1

NC

GN

D1

XM

ITR

RC

VR

RC

VR

XM

ITR

C22 47pF

R37

100C21

100n

F

1

Isolated DC/DC

CAN Tranceiver

Isolated Digital I/O

Supply VoltageFiltering & Current Limit

GND

GND

GNDC271uF

C2410uF

FBE

AD

L3

GNDGND

C2310uF

VO

UT

VIN

GN

DU6

+5 V

MC

P170

3AT-

5002

E

LDO & Reference


Sendyne SFP200

SFP200 IC Packaging

12

10

6 5

PIN 11

16 33

48

64 49

12° (4X)

seating plane 12° (4X)

1.60 MAX

0.270.17

(64X)

0.5(60X)

PITCH

LQFP6410 x 10 x 1.4 P 0.5All dimensions are in millimeters

5 6

10 12

17 32


Sendyne SFP200

Design Notes for SFP200 Circuit

General Background Information The SFP200 is a precision mixed-signal analog-digital

IC that provides measurements for current (by sensing

the voltage drop across a shunt), voltage and shunt

temperature.

Measurements of large currents are difficult due to

high heat generation (Joule heating) in the shunt. In

order to provide sufficient accuracy and negate the

effects of various errors, the voltage drop across the

shunt must be adequately large. However, the heat

production resulting from the passage of the current

is linearly dependent on that voltage drop. The only

solution for limiting the heat is to lower the resistance

of the shunt, thus limiting the voltage drop across the

shunt.

When dissimilar materials are jointed together, and

when the assembly is heated (due to environment

and/or Joule heating), there are so-called thermoelec-

tric voltages generated; these are commonly known as

resulting from Seebeck / Peltier / Thomson (Kelvin)

effects. The value of these errors in the carefully con-

structed devices may be in the range of single micro-

volts (10-6 V) to as much as several tens of millivolts.

These error voltages will manifest themselves as large

offset (deviation from zero) errors in the measured

current.

Sendyne’s proprietary and patented method reduces

the errors associated with sensing of the low-level

voltages, and enables measurements of the large cur-

rents with shunts having extremely small resistance.

This is achieved with the proprietary circuit that

reduces voltage-sensing errors at the shunt to below

200 nV (0.0000002 V), independent of the ambient/

environment or shunt’s operating temperature, and

operating within the whole specified temperature

range of –40 °C to +125 °C.

The Standard Sendyne shunt utilized in the

SFP200MOD devices have a nominal resistance value

of 18 µΩ; maximum voltage drop at the declared

maximum full-scale (unclipped) currents of ±1250 A

is ±22.5 mV and nominal voltage drop at the currents

of ±500 A (that are rated for continuous operations)

is ±9 mV, with resulting Joule heating (power loss) of

only 4.5 W.

In addition, Sendyne’s circuit allows the use of RC

filtering for the reduction of the RFI/EMI-induced

noise, specifically without any detrimental effects to

the quality and accuracy of the current measurements.

Any errors resulting from thermoelectric effects in the

elements of the filters are completely eradicated.

Furthermore, SFP200 utilizes redundant sensing of

two independent current measurement channels (with

two independent sets of sensing contact on the shunt).

The SFP200 is capable of sensing arbitrary-large volt-

age potentials in reference to the negative terminal of

the shunt. The magnitude of the sensed voltage only

depends on the capabilities of the voltage dividers

used for the purpose. Care in designing of the PCB

artwork should be exercised in order to guarantee

sufficient minimum clearance and creepage distances

between the parts of the circuit energized with high

voltage potentials; an example of such design is shown

later in this document.


Sendyne SFP200

PCB Artwork Design Guidelines In order to achieve minimal levels of the current offset

errors, there are specific guidelines to be followed in

the design of the artwork for the PCB.

Referring to Fig. 1 below, the copper artwork nets

between the sensing pins of the shunt (J9, J10, J11,

and J12) and the pins of the input-switching MOSFET

transistors (Q1 and Q2) must NOT have vias (plated

pass-troughs from one side of the PCB to the other).

These four (4) nets and the transistors Q1/Q2 must

be located on the same external copper layer on the

PCB, and must be routed on the same single layer, as

outlined in dashed black lines in Fig 1.

The artwork shown below resolves the whole low-level

signal chain on a single layer without the use of vias.

However, this is not strictly required, the signal nets

to the right of Q1 (to resistors R7/R6) and all nets

after that, following to OpAmp U2 and including the

circuitry around U2, can have vias without any detri-

mental effects on the circuit’s operations. The same is

true for the nets to the left of Q2 (to resistors R8/R9)

and all nets after that.

The rest of the artwork for the PCB should be designed

utilizing good practices; ground plane under the

amplifying components (shown in light blue in Fig 1),

stitching vias between the ground planes on the top

and bottom of the PCB, close location of the bypass

capacitors to their respective ICs.

The high-voltage sensing lines and associated PCB art-

work is shown below in Fig 2. Design considerations

and spacing between the connectors and between

components in this part of the circuit depend on the

level of the voltages being sensed, and on the particu-

lar safety standards followed. On the SFP200MOD

assemblies, the rating for the voltage sensing is ±1 kV

measurement range, and ±4 kV momentary overload.

As can be seen, an utmost care has been taken in order

to have the clearance and creepage distances as large

as possible; two slots have been cut into the PCB in

order to provide better creepage, with possibility to

improve clearance, if an external plastic case is de-

signed with vertical “walls” that fit into the slots.

This part of the layout does not have any copper pours

(on both sides of the PCB) in order to promote large

clearance and creepage distances; the ground planes

start just past the edge of the leftmost terminals of

the bottom resistors of the voltage dividers, where the

maximum voltage levels are already small.

Do not place any components of the voltage dividers

in the areas of the PCB that may experience flexing, as

this may degrade the sensing accuracy (due to resis-

tance changes of the SMD resistors with mechanical

stress).

The rationale for using multiple series-connected

resistors is explained in the following section of this

document describing the voltage sensing and voltage

dividers.Figure 1: Example of PCB artwork for the connection to

the shunt’s sensing pins.


Sendyne SFP200

For proper functioning, the SFP200 circuit requires a

galvanically isolated power supply and digital I/O.

Example of the PCB layout of the circuit implemented

on the SFP200MOD assembly is shown in Fig 3.

The clearance and creepage between the isolated parts

is 7.3 mm, mostly due to the spacing of the (SMT WB

SOIC-16) PCB footprint for the digital signal isola-

tor. The clearance between the copper pours (ground

planes) for the two isolated sections is slightly larger.

It is important not to place any copper within the

isolation gap; a specific note to the PCB fabricator

should be made, as they often place manufacturing lot

numbers and/or other data within seemingly empty

areas, on the copper layers, thus defeating the original

design intentions of keeping these areas completely

clear of the copper tracks.

For the shape of the copper pours in the lower-left

corner of Fig 3 (indicated with an arrow), the spacing

is maintained (to preserve the clearance distance) de-

spite the presence of the cut into the PCB outline (that

is made for unrelated mechanical reasons, but does

improve the creepage in that specific area).

7.3

mm

7.

3 m

m

Circuit Operations and Selection of Components

Current-sensing

Looking at the schematic of the circuitry around the

SFP200 IC, the components Q1/Q2, R6, R7, R8, and

R9 together with C2, C3, C4, C5, C6, and C7 form two

input switching circuits and two EMI/RFI RC filters.

The topology of these filters enables rejection of both

common-mode and differential-mode high-frequency

interference.

Quad OpAmp U2 with the surrounding components

R12, R13, R14, R15, R27, and R38 form the two dif-

ferential amplifiers for the two current-measurement

channels.

Figure 2: Example of PCB artwork for high voltage

sensing Figure 3: Example of PCB artwork for the galvani-

cally isolated power and digital I/O.


Sendyne SFP200

A local bypass capacitor (100 nF, C9) for the OpAmp

U2 must be located close to its supply pins, pin 4 and

pin 11.

As shown on the schematics, the values of the resistors

around the OpAmp U2 provide the differential gain of

201 for each of the channels. If the value of the gain

has to be changed (for example, if a different range of

currents need to be measured with the same shunt, or

a shunt with different resistance is utilized), then the

values of resistors can be adjusted, considering that

R13=R38=R14=R27 and R12=R14, and their ratio

determines the gain value. These resistors should be

1 % low-noise metal film units. The value of the dif-

ferential gain (for example, for channel 1) is equal to

[(2*R14/R15) + 1]. The maximum voltage drop across

the shunt (for the full-scale unclipped readings) mul-

tiplied by the gain should be less than approximately

4.6 V.

Resistors R1, R2, R3, and R4 provide protection of

both transistors Q1/Q2 and the pins of SFP200 IC

from the fast voltage transients or ESD overvoltages

on the shunt, as well as reduce possible contamination

of the low-level signals (via parasitic capacitances of

the transistors Q1/Q2) with digital noise originating

on the switch-control digital pins of the SFP200 IC

(pins 14, 15, 18, and 19).

Analog “Zero” Reference

The common analog “zero” reference point for the

shunt-sensing circuits is the net ZREF that provides a

potential that is roughly 1/2 of the +5 V analog supply

voltage of the SFP200 IC (VZREF≈2.5 V), as measured

in reference to net GND, that is the most-negative

supply voltage for the IC. All ground plains (copper

pours) on the board are also the part of the net GND,

however it is not a reference potential for any external

measurements.

The signal ZREF is generated on capacitor C8 with

the action of resistor R11. The values and properties

of these two components (C8 = 10 µF ±10 % X7R and

R11 = 10 k 1 %) should not be changed; there is an in-

tentional triangular waveform, roughly 100 mV pk-pk,

generated on C8 that is important for the operations

of the circuit and for improvement of the statistical

properties of the measured and reported values.

ZREF net absorbs the minute leakage currents from

the gates of transistors Q1/Q2 as well as provides

return path for the bias currents originating from the

inputs of the OpAmp U2.

In addition, capacitor C8 couples any fast transients

and ESD overvoltages from the shunt to the common

ground plane (local GND, that is the most-negative

supply voltage of the SFP200 IC).

Selecting this specific potential for the “zero” analog

reference net ZREF provides the most-advantageous

conditions for operations of the current-sense

amplifiers and of the SFP200 IC; furthermore, it

makes possible the sensing of bipolar currents and

bipolar voltages.

All measurements are done in respect to the potential

of the net ZREF; for the external (high-voltage) sens-

ing inputs the “0 V” reference is effectively the nega-

tive terminal of the shunt (that has an independent

connection to the net ZREF via the shunt’s pin J3).

However, in order to enable proper operations of the

whole SFP200 circuit, it must have galvanic isolation

from any and all potentials in the target system that is

being measured, including its own power supply rails,

system commons/grounds and CAN communications

lines.

In an isolated (floating) SFP200 circuit, there are

never any (DC) currents in the ZREF line, except for

the above-mentioned leakage and bias currents, as


Sendyne SFP200

well as some possible leakage current in the isolation

circuit; the total sum of these current is always less

than several microamperes (µA, 10-6 A).

Please note that the currents in the high-voltage divid-

ers flow through the dividers and exit from the shunt’s

negative terminal; again – these currents do not flow

by the way of the ZREF line to the SFP200 IC.

Voltage Sensing

In order to enable the measurements of high poten-

tials on the voltage sensing inputs, the SFP200 circuit

utilizes HV-capable voltage dividers, consisting of

resistors R16 – R22, R24 – R26, and R28 - R33;

capacitors C10 – C13 provide noise and anti-aliasing

filtering for the sensed voltages (with a time constant

of approximately 3 ms and the equivalent bandwidth

of 53 Hz at –3 dB point).

The resistors form three simple resistive dividers, with

the upper resistors of the dividers specifically made-

up from several equal units connected in series. This

follows industry practices for handling high voltage

signals, increasing the reliability, since a shorting fault

in one of the resistors will not cause a catastrophic

malfunction and/or smoke/fire. The measured voltage

divides equally among the series-connected units, al-

lowing safe operations within the continuous working

voltage capabilities of the individual low-cost resis-

tors. Alternatively, a single HV-rated resistor can be

utilized for the upper resistor in the voltage divider.

The tolerance of the resistors in the dividers does not

appreciably change the accuracy of the measurements,

since the units are calibrated on the voltage-sensing

lines (and retain calibration parameters in a nonvola-

tile memory); the initial errors due to inaccuracy of

the individual resistors are zeroed out. However, these

resistors should have reasonably good thermal stabil-

ity (i.e. low and equal TCR – Temperature Coefficient

of Resistance), and thermal tracking between the units

composing each divider (specifically between the “up-

per” resistors and the “lower” resistor, so that the divi-

sion ratio stays relatively constant with temperature).

Components R19 and C13 create a compensation

point for negation of the effects from the bias and

leakage currents that are originating at the SFP200

voltage-sensing inputs (pins 27, 28, and 29); these

components must not be removed from the design.

Temperature Measurement

Resistor R5 and NTC (Negative Temperature Coef-

ficient) thermistor TH1 create a simple circuit for

estimation of the temperature of the shunt. The small

thermistor (SMD 0402 size) is placed near (but with-

out electrical contact) to one of the shunt’s pins, as

shown in Figure 4; all the shunt’s pins have solid elec-

trical and thermal connection to the shunt, and convey

the shunt’s temperature to the immediate areas of the

PCB near the pins’ soldering sites.

Figure 4: Example of artwork for thermistor placement

on the PCB

By measuring the voltage at the junction of R5 and

TH1, the present resistance value of the thermistor is

calculated; then an application of the Steinhart–Hart

equation yields the estimated temperature of the

thermistor.

Please note that the coefficients for the Steinhart–

Hart model are specifically tailored to the particular

J2

TH1


Sendyne SFP200

thermistor used (Murata NCP15XH103F03RC,

a 0402-sized miniature surface-mount device,

10 k ±1 % at 25 °C and B25-50 = 3380 K ±1 %). Capacitor C1 provides filtering of the RFI/EMI.

Voltage Regulator and Reference

The analog supply voltage of the SFP200 IC is effec-

tively a Voltage Reference for all measurements. It is

important that this voltage is stable and has predict-

able behavior due to temperature changes.

Absolute initial accuracy of this voltage is not as im-

portant, as both current-measurement channels and

voltage-measurement channels are typically calibrated

at least at a single (room) temperature; all calibration

parameters are retained by the SFP200 IC indefinitely

in the dedicated nonvolatile memory and automati-

cally applied to the measurements.

Sendyne characterized a family of specific low-cost

micropower Voltage Regulator (LDO) devices for uti-

lization in the SFP200 circuit (Microchip Technology

Inc. MCP1703AT-5002E).

Please note that the supply voltage at the input of the

LDO must always be higher than the regulated output

voltage; this requires that the raw isolated power sup-

ply voltage must be higher than +5 V nominal regu-

lated operating voltage. For the LDO mentioned above

at the required supply current levels for the SFP200

circuit, the minimum headroom can be as small as

50 mV - 100 mV; however, considering the variations

of the raw isolated voltage at low operating tempera-

tures (mostly due to changes in forward-voltage-drop

of the silicon diodes), we recommend a minimum

room-temperature raw supply voltage of 5.5 V.

There is no point in providing the raw isolated voltage

of above 6.5 V; this will simply result in additional

heating without providing any benefits.

The regulated voltage from LDO supplies the digi-

tal portion of the SFP200 IC directly, utilizing both

bulk 10 µF (C23) and local 100 nF (C14/C15) bypass

capacitors; the local bypasses must be positioned close

to the respective supply pins (pin 7 and pin 41) as

shown on schematics.

The analog supply rail is developed by filtering the

digital rail through a ferrite bead with another set of

bypass capacitors, bulk 10 µF (C26) and local 100 nF

(C17); again the local bypass must be located as close

as possible to the IC (pin 8).

Isolated power supply

A DC/DC converter consisting of a driver IC U5 and

isolation transformer TX1 provides the isolated power

supply for the floating SFP200 circuit.

The whole solution was selected for the lower-price

(vs integrated AEC-Q100 qualified DC/DC and Digital

Isolator) and for the ability to reliably operate the

circuit to the temperature limits of -40 °C to +125 °C.

Specifically, ordinary silicon diodes (not the Schottky

type) are used as the full-wave rectifiers (dual-unit

D1) from the outputs of the transformer. Schottky

diodes, while providing smaller forward voltage

drop, have prohibitively high reverse leakage at high

temperatures; for a low-power circuit like the SFP200

their leakage may reach and many times exceed the

power requirements of the circuit itself, overloading

the DC/DC driver IC.

The DC/DC converter circuit is a so-called push-pull

forward architecture; is does not provide any voltage

regulation or adjustments, the ratio of input/output

voltages is fixed. A transformer with the secondary


Sendyne SFP200

windings that have more turns than the primaries,

provides a slight voltage step-up in order to satisfy the

requirements of the LDO, as discussed previously.

Isolated digital communications

A Digital Isolator based on the capacitively-crossed

isolation barrier (U3) provides isolation for the

buffered CAN communications signals; a CAN-rated

transceiver U4 directly interfaces to the CAN trans-

mission lines.

It is strongly recommended to include the transient-

suppressor D2 (a unit that is specifically rated for CAN

operation); it will protect from possible transients on

the CAN wires, as well as from possible ESD discharg-

es during the installation of the whole circuit.

A terminating resistor R39 of 120 Ω is connected

between the CAN lines; please assure that if several

units operate “parallel-connected” on the same CAN

branch then only a single unit from the group has the

terminating resistor.

The power supply line on the entry to the circuit is

filtered by the capacitor C31. Intentionally, this device

has the voltage rating that seems overly high; how-

ever, this is done to enable the device to survive volt-

age transients that can be present at the end of a long

cable, in a high electrical noise environment.

Supply voltage on C31 is then distributed through

current-limiting 1-Ω resistors and a ferrite bead to the

rest of the circuit.

Optional Heartbeat Indicator

It is recommended to utilize the optional Heartbeat

Indicator LEDs, at least in the initial prototyping

and testing stages. By alternatively energizing one of

the two LEDs, the IC provides a clear visual indica-

tion that the unit is powered and operating, without

requiring any information from the CAN Host or the

Sendyne GUI / Software Application. This is very use-

ful during set-up of the testing and/or calibrations.

It is recommended to design the PCB to include these

Heartbeat indicators, and simply do not populate

(DNP) their locations if they are not required; alter-

natively, two test points can be incorporated into the

design, and external “off-board” components could be

attached to provide Heartbeat functionality.

The Heartbeat drivers are on pins 16 and 17 of the IC.

They source the current (meaning the LEDs and their

current-limiting resistors would terminate into the

GND net).

These pins are typically shown as NU (Not Used)

pins on schematics, since these components are not

required for the mass-production units.

Both LEDs must be used if the Heartbeat indication

is desired; this is to make the current consumption of

the circuit constant and independent of the state of a

single LED; the alternating pattern of the LEDs

consumes a constant level of the supply current,

resulting in no variations of the supply voltage (that in

turn is used as the Reference voltage inside of the IC).

The circuit for the Heartbeat LEDs is shown in

Figure 5.


Sendyne SFP200

Low-current LEDs. These two devices must be the same part number

GNDGND

DVSS

SFP200 IC

2.7k to 4.7kBoth resistors must have the same value

16

17

16

Figure 5: Circuit for Heartbeat LEDs


Sendyne SFP200

Additional Documentation

― Sendyne SFP Shunt for Precision Current Measurement

― Sendyne SFP200 IC Reference Design Annotated BOM

― Sendyne SFP200 CAN 2.0B Protocol

― Simple Single Point Room Temperature Current Calibration for Systems Using the SFP200 IC

― Simple Single Point Room Temperature Voltage Calibration for Systems Using the SFP200 IC

― Notes on Automatic Calibration for Systems Using Shunts Other Than the Sendyne SFP Shunt


Sendyne SFP200

Ordering Information

Part Number Description

SFP2001ASTZA SFP200 control IC, tray

SFP2001ASTZAR SFP200 control IC, tape and reel


Sendyne SFP200

Revision History

Revision Table

Revision Number Date Comments

0.1 5/26/2017 Preliminary; Initial release


Sendyne SFP200

Information contained in this publication regarding

device applications and the like is provided only for

your convenience and may be superseded by updates.

SENDYNE MAKES NO REPRESENTATIONS OR

WARRANTIES OF ANY KIND WHETHER EX-

PRESSED OR IMPLIED, WRITTEN OR ORAL,

STATUTORY OR OTHERWISE, RELATED TO THE

INFORMATION, INCLUDING BUT NOT LIMITED

TO ITS CONDITION, QUALITY, PERFORMANCE,

MERCHANTABILITY OR FITNESS FOR PURPOSE.

Sendyne disclaims all liability arising from this in-

formation and its use. Use of Sendyne devices in life

support and/or safety applications is entirely at the

buyer’s risk, and the buyer agrees to defend, indemni-

fy and hold harmless Sendyne from any and all dam-

ages, claims, suits, or expenses resulting from such

use. No licenses are conveyed, implicitly or otherwise,

under any Sendyne intellectual property rights.

PatentsUS Pat. 8,264,216

US Pat. 8,289,030

US Pat. 9,052,343

US Pat. 9,588,144

Other patents pending

TrademarksThe Sendyne name and logo are registered trademarks

of Sendyne Corp.

All other trademarks mentioned herein are properties

of their respective owners.

© 2017 Sendyne Corp.

All Rights Reserved.

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Sendyne SFP200 IC for Precision Automotive Grade Current