HT8 MCU OPA Application Descriptions

HT8 MCU OPA Application Descriptions

AN0521EN V1.10 1 / 13 August 30, 2020


D/N：AN0521EN

Overview

In this application note the integrated operational amplifiers within four MCUs are introduced. The

MCUs in question are the HT66F45x0 series, HT45F56, HT45F5Q-2, and HT66FM(5230, 5240,

5242, 5440) series.

The HT66F45x0 series op-amp features include multiple switch and input path selections, multiple

reference voltage selections, multiple internal software gain controls, debounce time control,

hysteresis, input offset voltage calibration and four-bandwidths of 5kHz, 40kHz, 600kHz and 2MHz.

Software control allows users to adjust the op-amp bandwidth based on the required application

response speed. The device power consumption can also be optimisied by selecting a suitable

bandwidth. These features combine to enhance the circuit flexibility allowing them to be widely

used in a variety of applications such as smoke detectors and other related products.

The HT45F56 MCU contains an internal vibration detection circuit. In order to detect a tiny

vibration external analog signal, it integrates a 1~1000 gain PGA, a comparator and a 6-bit DAC

which can internally set a threshold voltage. This can then switch the input comparison path

multiplexer through an internal register. An external circuit can be matched with a variety of sensors

such as piezoelectric vibration sensors, magnetic induction vibration sensors, etc.

The HT45F5Q-2 MCU contains a charging management module which is divided into two parts. The

first part contains two OPAs and DACs for controlling the charging voltage and current. The charger's

constant voltage mode (CV) and constant current (CC) mode upper limit can be setup using the

programmable DAC. The CV control uses a 12-bit DAC while the CC control uses an 8-bit DAC. The

second part is a set of fixed gain OPAs which can be used to increase the current resolution and reduce

any power losses in the current detect resistor.

The HT66FM series of MCUs include a fully integrated phase current sensing circuit for motor

protection drive circuits.

The application note also describes the application and characteristic parameters of other common

op amp functions, such as non-inverting amplifiers, inverting amplifiers and voltage followers,

adders and subtractors, etc. The two OPA principles which are most important are those of the

virtual short and virtual open. For the virtual short point of view the two input terminals appear to

be short-circuited, that is they remain at the same potential. For the virtual open, the input

impedance appears as infinite, which is equivalent to the open circuit. This is to imply that the

current flowing into the positive and negative input terminals is effectively zero.


AN0521EN V1.10 2 / 13 August 30, 2020

OPA Basic Concepts

Signal amplification is one of the most basic signal processing functions. Whenever a signal provided

by a sensor is very weak, for example, in the microvolt or millivolt range and whose energy is low,

signal amplification is required. Because the signal is weak, the reliability of the MCU signal

processing is poor, however if the signal amplitude is increased then signal processing becomes much

easier. When the signal is amplified, issues of linearity need to be considered. When considering signal

amplification, it is also necessary to pay attention to the OPA characteristics to avoid distortion in the

amplified signal, a phenomenon that no designer wishes to witness.

Functional Description

HT66F45x0 Series OPA Application Description

The internal OPA structure of the HT66F45x0 series is shown below. These MCUs also include a 12-

bit ADC. Both OPAs have a function whereby the input offset voltage can be adjusted. The devices

also have three 8-bit DACs. The two OPAs can be set to operate as unity gain buffers by the application

program as shown in Fig. 1 and Fig. 2. The OPA input offset voltage adjustment range can be set

according to user application requirements. Refer to the datasheet (VOS parameters in the OPA

characteristics table) to see how to adjust the internal offset. The offset voltage in the general

applications will be close to 0V.

Basic OPA application

OPA0: Can be used for current signal conversion or amplification, such as infrared signal detection

of smoke detectors or current detection of induction cookers.

OPA1: This is a programmable gain amplifier, PGA. The positive input can control the DC bias

through the internal 8-bit DAC or from an external resistor divider. It can also select the first stage

OPA0 output signal, OPA0O. The internal software program selects the (positive/negative) input of

OPA1 and then sets the second-stage either non-inverting or inverting amplification through the

internal switching circuit. The negative input of OPA1 can be controlled by internal software to set

the gain (as shown below), or an external resistor divider can be used to set the gain. The output of

both OPAs can be converted using a software control A/D channel input. For a wider range of

applications refer to the working principles of the HT66F45x0 series.


AN0521EN V1.10 3 / 13 August 30, 2020

A0NI

A0PI

A1PI

A1NI

OPA0-

+A0O

R2

OPA0O

SDDAC0O

OPA1+

-A1O

8BitDAC0

OPA0O

SDDAC0O

OPA1O

(To A/D Converter)

(To A/D Converter)

SDA0OFMSDA0O

SDA1OFMSDA1O

HT66F45x0 Series Internal OPA Structure

A0NI

A0PI OPA0

-

+A0O

R2

8BitDAC0

OPA0O

SDDAC0O (To A/D Converter)

SDA0OFMSDA0O

Fig.1 OPA0 setup for voltage follower

A1PI

A1NI

OPA0O

SDDAC0O

OPA1+

-A1O

OPA1O (To A/D Converter)

SDA1OFMSDA1O

Fig.2 OPA1 setup for voltage follower

Example: For OPA1, when an inverting/non-inverting amplifier is setup, use the internal gain to

amplify the input signal

OPAMP1-

+

SDA1EN

SDS4

A0O

SDS3

SDS5

SDS6A1PI

SDS2

R1 R2A1NI

SDDAC0O

SDS7

SDPGA[2:0]

A1O

SDA1BW[1:0]


AN0521EN V1.10 4 / 13 August 30, 2020

Circuit connections:

Inverting Amplifier Non-Inverting Amplifier

A1NI connected to VIN - A1PI connected to GND A1NI connected to GND - A1PI connected to VIN

OPA-

+VO

VIN

R1

R2

VO = −

R2

R1VIN

OPA-

+VIN

VO

R1

R2

VO = (1 +

R2

R1)VIN

HT45F56 OPA Application Description

The internal structure of the HT45F56 is shown below. The integrated PGA (x1~1000) is used to

amplify smaller analog input signals such as those from vibration sensors. The integrated CMP and

6-Bit R-2R DAC (DAC0) are then used to form a complete vibration sensing structure. For signal

amplification and comparison circuit details, refer to the HT45F56working principles.

DAC0

MUX

SENSORAnalog Inputs

Analog InputsAN1 / NA2

+

-CMP

MCU I/O

Gain:1~1000 15-level programmable gain

6 bis

-+PGA

HT45F5Q-2 OPA Application Description

The HT45F5Q-2 MCU has three integrated OPA structures as described below:

OPA0 and the 8-bit DAC0 are combined into a current error amplifier for charger constant

current control

OPA1 and the 12-bit DAC1 are combined into a voltage error amplifier for charger constant

voltage control

For detailed constant current and constant voltage operation, refer to the HT45F5Q-2 working

principles

OPA2 is a x10x non-inverting amplifier for current signal amplification to improve current

resolution to allow the use of lower value current sense resistors


AN0521EN V1.10 5 / 13 August 30, 2020

OPA0E

DAC0EN

+-

OPA0N

D[7:0]

10KOPA0P

OPA0

AVDD

OPA1E

DAC1EN

+-

OPA1N

D[11:0]

10KOPA1P

AVDD

OPA1

OPA2-+OPA2P

10xA2P

R

9R

SAOPIN OP2EN

OOFMOPO

OOF[5:0]

OOFM

12-bit DAC1Ro=13K

8-bit DAC0Ro=10K

HT66FM Series OPA Application Description – HT66FM5230/5240/5242/5440

These MCUs include an overcurrent detection module that consists of an amplifier OPA0 (Av is

about 1/5/10/20 times), a 12-bit ADC, an 8-bit DAC, and a CMP0. If an overcurrent condition is

detected, the external motor drive circuit will be turned off in real time to avoid the motor being

damaged.

Two interrupts are used to detect overcurrent conditions:

1. ADC Interrrupt - Int_AHL_Lim

The Int_AHL_Lim interrupt has higher flexibility and can be selected by a software ADR value

and the ADLVD/ADHVD interrupt trigger condition. After comparison, the range can be used as

a buffer protection action.

2. CMP0 Interrupt - Int_Is

Int_Is can be used as a hardware emergency trigger interrupt protection where the external motor

drive circuit can be turned off immediately.

+

-

OPCM

Int_Is AP

OPA0 : Av=1/5/10/20

8-bitDAC

OPA0CMP0

Int_AD_EOC or int_AD_ISEOC

Int_AHL_ Lim

ADC

ADR

EOCB or ISEOCB

AD HL/LVTrigger

IntTrigger

ADLVD/ADHVD

OPA0 Output

PB0/OPA0O

PB0S[2:0]12-bit ADC

C0BPEComparator 0

Int A/D

Int_Is


AN0521EN V1.10 6 / 13 August 30, 2020

Operating Principles

HT66F45x0 Series Operating Principles

The HT66F45x0 series is an MCU that can be applied for use in smoke detection. The external DC

bias voltage on the OPA0 positive input is supplied by an external resistor divider. When the IR

receives a signal, the current-to-voltage conversion is implemented by the R12 resistor. The converted

signal is transmitted via the AC coupling capacitor. After this, the second-stage OPA1 non-inverting

amplifier circuit receives this input and can set the input offset and the gain by the R14 resistor. The

second-stage amplification OPA1 outputs the amplified signal to the internal A/D. The analog signal

then triggers the interrupt to initiate the following on processing. In this way a full smoke detection

function can be implemented.

HT66F45x0 Series Smoke Detector

HT45F56 Operating Principles

The HT45F56 is an MCU which includes a vibration detection function. The device can detect small

external analog signals, amplify them using a PGA with a 15-level programmable gain of 1-1000 and

then compare them using a CMP and an internal 6-bit DAC threshold. The vibration sensitivity can be

determined by the internal PGA gain and the 6-bit DAC. The CMP digital signal output can directly

trigger an interrupt, or the number of pulses can be monitored to determine the vibration signal

magnitude. A single resistor can be connected in series at one end of the sensor to prevent voltages

which might be too large. The external circuit can be matched with a variety of sensors, such as

piezoelectric vibration sensors, magnetic induction vibration sensors, etc.

0.1µF

S N

Magnet Sensor

AD1AD2

+

−

CMPEN

CMPOP Debounce Circuit

DebounceInterrupt

CMPHY[1:0]

Pin-shared select

MUX

6-bitD/ADA[5:0]

CNSEL[1:0]

MUX

CPSEL[1:0]

SENOPA

GAS[3:0]

OPAEN

DSTAG[2:0]ComparatorInterrupt

HT45F56 Sensor Module


AN0521EN V1.10 7 / 13 August 30, 2020

HT45F5Q-2 Operating Principles

The HT45F5Q-2 has an internal charge management module, which includes three OPAs (OPA0~2),

an 8-bit DAC (DAC0) and a 12-bit DAC (DAC1). The Open Drain OPA0 ~1 and DAC0~1 are used

for CV and CC signal control. The OPA output can be directly connected to an optocoupler, so that

the primary side PWM IC can adjust the output power. The integrated 10x signal amplification OPA

(OPA2) is used to amplify the charging current signal, improve current resolution and reduce power

losses in the current detect resistance. The following describes the CV mode, CC mode and 10 times

signal amplification OPA usage.

HT45F5Q-2 Battery Charging Module

Note: 1. OPA0 and OPA1 have no input offset calibration function (hardware limit).

2. OPA2 has an input offset calibration function (accuracy ±2 mV).

3. OPA0 and OPA1 are open-drain output types.

Constant Current Mode – CC

Constant current charging means charging at a fixed current regardless of how the internal

resistance of the battery changes. The principle is that the charging current generates a voltage

(V=I×R) through the detecting resistor R1. This is transmitted from the OPA0N to the negative end

of the OPA0. The OPA0N and DAC errors are amplified by the OPA0 output OPAE (NMOS) and

transmitted to the PWM IC via the optocoupler. If the OPA0N voltage is lower than the DAC (DA0)

voltage, the PWM IC increases the PWM duty cycle, otherwise it reduces the PWM duty cycle.

Note: DAC0 (8-bit DAC) (DA0) is the maximum current threshold.

Constant Voltage Mode – CV

Constant voltage charging is a fixed voltage charging regardless of the internal resistance of the battery.

The principle is that the charging voltage (B+) is divided by the resistor dividers R4 and R5 and is

transmitted from the OPA1N to the negative terminal of OPA1. The OPA1N and DAC errors are

amplified by the OPA1 output OPAE (NOMS) and transmitted to the PWM IC via the optocoupler. If

the OPA1N voltage is lower than the DAC voltage, the PWM IC increases the PWM duty cycle,

otherwise it reduces the PWM duty cycle.

Note: DAC1 (12-bit DAC) (DA1H and DA1L) is the maximum voltage threshold.


AN0521EN V1.10 8 / 13 August 30, 2020

HT66FM Series Operating Principles Description –

HT66FM5230/5240/5242/5440

The HT66FM series of MCUs contain an overcurrent detection circuit, including an integrated OPA0

amplifier circuit (Av about 1, 5, 10 or 20 times), can be selected by PB0S whether to output through a

pin-sharing configuration and through a high-speed (2μs) 12-bit ADC, 8-bit DAC and CMP circuit to

monitor the presence or absence of overcurrent during motor driving. If an overcurrent situation should

occur, then immediately turn off the external gate drive circuits to avoid the motor being damaged.

HT66FM5440 Brushless Motor Control Driver Circuit

Over Current Protection – OCP

Motor current sampling is obtained using a current sampling resistor. When the current flows through

R_Shunt, a small voltage signal is generated. It needs to be amplified by the OPA in the OCP circuit

and then the ADC measured value or the DAC is used together with the CMP to determine whether

an overcurrent situation exists.

Characteristics and Parameter Description

Ideal OPA Characteristics

An ideal operational amplifier (ideal OP-AMP) should have the following characteristics:

● Infinite input impedance (ZIN=∞): The input of an ideal op amp does not allow any current

to flow in, that is, the input impedance is infinite.

● Output impedance close to zero (ZOUT = 0): The output of an ideal op amp is a perfect voltage

source. The output voltage of the amplifier is always constant regardless of the current flowing

to the amplifier load. Therefore its impedance is zero.


AN0521EN V1.10 9 / 13 August 30, 2020

● Infinite open-loop gain (Ad=∞): An important property of an ideal op amp is that it has an

infinite voltage gain on the differential signal in the open-loop state. This feature makes the

op amp suitable for negative feedback configurations in actual applications.

● Infinite common-mode rejection ratio (CMRR=∞): An ideal op amp can only react to the

difference between the positive and negative input voltages. The same voltage on both of

the two-input signals (ie, the common-mode signal) will be completely ignored.

● Power supply voltage rejection ratio (PSRR=∞): This refers to the ability of the OPA to

maintain its output voltage when its DC supply voltage changes.

● Infinite bandwidth (BW=∞): An ideal op amp will amplify the same differential gain for any

frequency input signal and not be affected by changes in signal frequency.

● Offset is zero (OFFSET=0): The output is also zero when the input is zero.

OPA D.C Characteristic Description

There is no single OPA specification standard, therefore the behavior of a specific OPA should be

based on the corresponding specification. Detailed characteristic parameters are as follows.

OPA Characteristic Characteristic Description

VDD

OPA operating voltage range: This means that the OPA can meet the following characteristics within the working voltage range. If this voltage range does not match the MCU voltage range (for example, the MCU operating voltage range is 2.2V~5.5V), then pay attention to the actual voltages verified and used.

IQ OPA static current consumption (IOUT=0), specified as the current under no-load conditions

IOPA OPA operating power consumption, IOPA, specified as the power consumption of MCU when OPA on – power consumption current of MCU when OPA off

VOS

Input offset voltage (VOS) definition: In order to make the output voltage of the op amp equal to 0, it is necessary to add a small voltage to the two input terminals of the op amp. The small voltage that needs to be added is the input offset voltage VOS at the input end. This is mainly due to the mismatch between the differential input stage of the op amp. The smaller the VOS, the higher the matching degree of the OPA positive and negative input. Due to the limitations of the layout and the process, a perfect match is not possible. VOS=negative input voltage – positive input voltage (ideally zero)

IOS Input Offset Current (IOS) Definition: When the output DC voltage of the op amp is zero, the difference between the bias currents of the two inputs is IOS.

VCM

Common Mode Input Range (VCM) Definition

VCM = �(VIN+)+(VIN−)2

� (the lower the better)

Common mode input voltage is when the op amp's common-mode rejection ratio is significantly degraded when the op amp is operating within the linear region. Generally the CMRR is reduced to a certain value, such as 60dB.

CMRR(dB) = 20log �Gain×VCMVOUT

�

Gain is the differential mode gain of the amplifier, VCM is the common mode voltage present at the input and VOUT is the result of the input common mode voltage at the output.

VOR

The maximum output range (VOR) of the OPA is defined as the maximum voltage amplitude that the op amp can output when the current supply voltage is supplied under the specified load (VOR is the maximum and minimum voltage that the output MOS transistor can output. The result should be very close to the power supply.)


AN0521EN V1.10 10 / 13 August 30, 2020

OPA A.C. Characteristic Description

OPA Characteristic Functional Description

AOL

Differential Mode Open Loop DC Voltage Gain (AOL): Defined as the ratio of the op amp output voltage to the differential mode input voltage when the op amp is operating in the linear region. Here open loop means operating without feedback. The amplification factor of the operational amplifier is called open loop gain. AOL=20log (△VOUT÷△VOS)

SR The conversion rate, also called slew rate, is defined as the output rise rate of the op amp measured from the output of the op amp when the op amp is in a closed loop condition and the input has a large signal which can include step signals.

GBW Gain bandwidth product definition: For an op-amp with a closed loop gain of 1 a small sinusoidal signal is input to the input of the op amp. The frequency corresponding to the 3dB point is then measured.

OPAMP Characteristic Description

OPA Characteristic Functional Description

PSRR

Power Supply Rejection Ratio (PSRR) Definition: The ratio of the op amp's input offset voltage to the power supply voltage when the op amp is operating in the linear region. (PSRR=20log(△VOS÷△VDD)) PSRR: For the noise immunity value of the power supply (the larger the value, the better), the smaller the output signal is affected by the power supply, the lower the noise/ripple. The calculation result of this equation is generally zero. For example, for an amplifier PSRR = 100dB, when applied to an application with a closed loop gain = 40dB, the overall circuit PSRR is: 100dB - 40dB = 60dB Thus, when the power supply has 1V of noise, the output noise is: 1V×10-60⁄20= 0.001V=1mV

CMRR

Common Mode Rejection Ratio (CMRR) Definition: The ratio of the op amp's differential mode gain to the common mode gain when the op amp is operating in the linear region (CMRR=20log(△VIN÷△VOS))

RO

The output impedance (RO) is defined as: ROUT = RO⁄(1+AO /β). The RO is determined by the internal output stage of the op amp and does not vary with the closed loop gain. It can be seen as a parameter inherent within the op amp. ROUT is different. This is the impedance that the op amp sees from the output after it forms a closed-loop amplifier circuit. It needs to be measured at the output. It will change as the closed loop gain changes.

OPA Basic Circuits

A variety of amplifier circuits can be formed by externally connecting different resistors and capacitors.

The following figure shows several practical amplifier circuits and formulas.

Inverting Amplifier Non-inverting Amplifier

OPA-

+VO

VIN

R1

R2

VO = −R2

R1VIN

OPA-

+VIN

VO

R1

R2

VO = (1 +R2

R1)VIN


AN0521EN V1.10 11 / 13 August 30, 2020

Adder Subtractor

-

+OPA

RFR1

R2

R3

RN

VA

VB

VC

VN

Vo

VO = (−RF)[VAR1

+VBR2

+VCR3

+VNRN

]

-

+OPA

R2

R1

R2

VA

VB

R1

VO

VO = (VB−VA)[R2

R1]

Voltage Follower Low Pass Filter/Integrator

OPA-

+VIN

VO

VO = VIN

-

+OPA

RF

VINR1

VO

C

T = RC = RFC

VO = VIN �−RF

R1×

1RFCS + 1

�

High Pass Filter/Differentiator

-

+OPA

RF

VIN

R1

VO

C

VO = VIN �−RF

RIN×

RINCSRINCS + 1

�

Precautions when using the op amps

1. Note whether the amplified signal is a DC signal or an AC signal.

2. Note whether it is non- inverting amplification or inverting amplification.

3. It is necessary to pay attention to whether the maximum value of the input signal multiplied by

the amplification factor exceeds the power supply voltage of the OPA.

OPA Input Voltage Range

For operational flexibility, the input voltage can be positive or negative in different PGA operation modes.

When the input voltage VIN > 0, the PGA is set to operate in the non-inverting mode and the OPA

output VOUT = (1 + R2R1

)VIN.

When the input voltage VIN < 0, the PGA is set to operate in the inverting mode and the OPA output

VOUT = −(R2R1

)VIN.


AN0521EN V1.10 12 / 13 August 30, 2020

Note: If the input voltage is negative, its value should not be less than -0.2V to avoid current leakage

which will affect the OPA normal performance.

Application Range

1. HT66F45x0 series is used in smoke detectors, handheld measuring tools, environmental

monitoring, voice which can be used for audio, OCP, OVP and other applications.

2. The HT45F56 can be applied for small signal amplification, such as piezoelectric vibration

sensors, magnetic induction vibration sensors and so on.

3. The HT45F5Q-2 is used in a variety of charging systems.

4. The HT66FM (5230, 5240, 5242, 5440) series has a phase current detection module for motor

protection.

Conclusion

This application note has introduced the operational amplifiers within four MCUs. It has described

the internal OPA functions and also notes for their practical application. What has been described

here can be used for similar OPAs within other MCUs.

Reference Material

For more information consult the HT66F45x0 series, HT45F56, HT45F5Q-2 and

HT66FM5230/5240/5242/5440 series datasheets.

For more information consult the Holtek website: www.holtek.com.

Version and Modification Information

Versions Information Date Author Issue

2020.07.23 吳嘉乾 V1.10

2019.01.29 蔡俊男 V1.00

Modification Information

V1.10：Title modified.

http://www.holtek.com/


AN0521EN V1.10 13 / 13 August 30, 2020

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Documents

HT8 MCU OPA Application Descriptions