Research Article A High Efficiency Li-Ion Battery LDO-Based Charger for Portable … · 2019. 7. 31. · Active and Passive Electronic Components PTAT CV M1 M2 End of charge Li-ion

Research ArticleA High Efficiency Li-Ion Battery LDO-BasedCharger for Portable Application

Youssef Ziadi and Hassan Qjidaa

CED-ST, LESSI, Faculty of Sciences Dhar el Mahraz, Sidi Mohamed Ben Abdellah University, BP 1796, 30003 Fez, Morocco

Correspondence should be addressed to Youssef Ziadi; [email protected]

Received 2 June 2015; Revised 2 August 2015; Accepted 12 August 2015

Academic Editor: Yuh-Shyan Hwang

Copyright © 2015 Y. Ziadi and H. Qjidaa. This is an open access article distributed under the Creative Commons AttributionLicense, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properlycited.

This paper presents a high efficiency Li-ion battery LDO-based charger IC which adopted a three-mode control: trickle constantcurrent, fast constant current, and constant voltage modes. The criteria of the proposed Li-ion battery charger, including highaccuracy, high efficiency, and low size area, are of high importance. The simulation results provide the trickle current of 116mA,maximum charging current of 448mA, and charging voltage of 4.21 V at the power supply of 4.8–5V, using 0.18 𝜇m CMOStechnology.

1. Introduction

As we know, portable devices have become the main appli-cations of advanced technical products. Due to their smallsize, light weight, and recharge ability, Li-ion batteries arewellsuited to portable electronicmanufactures such as cell phonesand PDAs [1] because of their high energy density, long cyclelife, high voltage, and absence of memory effects. But the lifeof a rechargeable battery depends not only on charging time,but also on overcharging control and charging strategies [2].To avoid the battery from overcharging, the charging processneeds a specificmethod supporting the constant current (CC)and the constant voltage (CV) modes in order to charge thebattery by a degrading current [3–5].

In literature, there are several architectures of batterychargers with different approaches of power control methodsin order to adapt the supply voltage. The same are char-acterized by high efficiency such as the DC/DC converter,switching-capacitor, or switching mode power supply [1, 6–8], but they are not suitable for single chip integration and,sometimes, they have low accuracy despite their efficiency.On the other hand, the same are using charge pump as anadaptive supply voltage [3]; however this one is distinguishedby its high current ripple and low efficiency. LDO-basedcharger is characterized by a low current ripple and it canbe integrated into the chip without descript components [9],

but itsmajor problem is the low efficiency. In thisworkwewillimprove the efficiency of an LDO-based charger, using thepower transistor as a variable current source and minimizingits dropout.

One of the important missed criteria in several works[1, 3, 6, 8–12] is the control of temperature during chargingand the lack of trickle current charge mode in [1, 13] whichis necessary for the battery protection when it is fullydischarged. That makes this work a complete battery chargerchip with respect to all charge procedures and the batteryprotection.

This paper describes the architecture and simulationresults of a three-mode control high efficiency battery chargerintegrated circuit for Li-ion batteries with charging currentsfrom 116mA up to 448mA. In Section 2 we describe thetypical charging method of Li-ion battery. The architectureand the functionality of major blocks of the proposed inte-grated circuit are illustrated in Section 3. Simulation resultsare shown in Section 4. Finally, the conclusion is remarked inSection 5.

2. Li-Ion Battery Charger Method

Amongst the important criteria of Li-ion battery charger issafety of charging. Yet there are some limitations for the

Hindawi Publishing CorporationActive and Passive Electronic ComponentsVolume 2015, Article ID 591986, 9 pageshttp://dx.doi.org/10.1155/2015/591986

2 Active and Passive Electronic Components

End of chargeCV

VoltageCurrent

4.2

Fast CCTrickle CC

2.9

C/40

0

Char

ging

vol

tage

(V)

Char

ging

curr

ent (

A)

Charging time

Ifcc

Itcc

Figure 1: Typical charging process of a Li-ion battery.

Charging start

Detect battery

YesTrickle currentcharging

NoYesFast constant

current charging

NoConstant voltage

charging

No

Yes Yes

End of charge

Over temperature?

voltage (Vbat)

Vbat < 2.9V?

Vbat < 4.2V?

Ichg < C/40

Figure 2: Battery charging flowchart.

current and voltage of charging; thus, the battery temperaturewill augment severely causing fatal troubles due to some ofthese limitations.

Notably, the typical charging current is 1C, in which thecurrent can completely charge a battery in one hour [14].

The typical charging profile of Li-ion batteries shownin Figure 1 is needed to achieve three fundamental modes:trickle constant current, fast constant current, and constantvoltage modes.

So far as the first trickle constant current mode is con-cerned, when the battery voltage (𝑉bat) is less than 2.9V,the internal resistance of Li-ion battery is getting larger; theLi-ion battery, accordingly, has to be charged by a trickleconstant current phase; this strategy is called an “overnightcharger” [15]; as for the second phase, once the value of𝑉bat is

larger than 2.9V, the process switches from the trickle currentto the fast constant current phase.

Ultimately, we use constant voltage to charge the batterywhen the battery voltage is greater than 4.2V, whilst thecharger is operating within constant voltage mode.

There are twomethods to terminate the charging process,the first of which is monitoring the minimum chargingcurrent at the CV stage. The charger terminates the chargingprocess when the charging current shrinks to the specifiedrange. To finish the charging process, the other one is basedon the maximum charging time [16].

In the proposed design, we have adopted the first methodto terminate the charging process; the battery is charging untilthe charging current is less than 1C/40.

The whole charging flow of our Li-ion battery charger isdesigned as shown in Figure 2.

Active and Passive Electronic Components 3

PTAT

CV

M1

M2

End of charge

Li-io

n ba

ttery

Level shifter

2.9V comparator

4.2V comparatorIref2Iref1

A2

A3

A4

A0

Vref2

Vref1

R1

R2

R3

Vfb1

Vfb2

A1

1 : N

Vbat

Ichg

Vadapt

−+

−+

−+

−+

−+

Rsens

M1

M2

MP ≡Mcs

Mm

Figure 3: Simplified diagram of the proposed Li-ion battery charger.

3. Circuit Descriptions

Contrary to the other architectures which use a microproces-sor to control the differentmodes of the charge, our proposedarchitecture is a purely analogic support of the threemodes ofLi-ion battery charging, trickle constant current, fast constantcurrant, and constant voltage, as shown in Figure 3. It ismade of many blocks: LDO, current generator, current sense,temperature sense (PTAT circuit), and bandgap multioutput.The supplying tension 4.8V–5V is adapted by LDO regulatorbefore generating 𝑉adapt. The power transistor MP is equiva-lent to a variable current source; this technique has been usedin [10] with flyback converter. The MP control made by twocurrent sources 𝐼ref1 and 𝐼ref2 passed through a shifter levelcomposed of𝑀1, 𝑀2, 𝑀1, and𝑀2, so that the transistorMP provides a constant current order of 116mA and 448mAto order the trickle constant current and the fast constantcurrent modes. We use the integrator to control the constantvoltage mode. These modes are switched by Op 𝐴

2and 𝐴

3

that compares tensions 𝑉fb1 and 𝑉fb2 with 𝑉ref1. We use theoutput of 𝐴

1and 𝐴

4to stop charging when the battery is

full or when the temperature detected by the PTAT circuitexceeds 115 degrees.

Figure 4 shows the complete architecture of the proposedLi-ion battery charger. What distinguishes our architectureis the use of current like a parameter of command toswitch the power transistor MP between different modesof charge, and it is utilized like a variable current source.The current generator furnishes two reference currents 𝐼ref1and 𝐼ref2 which are copied by current mirror (𝑀4 and 𝑀3)to command the MP gate with level shifter (this currentgenerator will be discussed in Section 3.1). Unlike trickle

constant current and fast constant current (CC mode) witchare under the control of 𝐼ref1 and 𝐼ref2, CVmode is controlledby an integrator, following its principles [10]; when 𝑉fb1 isgetting larger gradually, the integrator output is decreasing,so the MP furnishes a current decrease until the end ofcharge; we could make use of voltage-to-current conversionto generate CV current.

The end of charge occurs when the current sense detectsthat 𝐼chg (charge current) equals 20mA or when the dietemperature transpasses 115∘C switching off PMOS (𝑀eoc)integrated into the current generator.

3.1. Current Generator. The current generator furnishes thereference currents, 𝐼ref1 and 𝐼ref2, to control the trickle CC andfast CC modes. We have opted for utilizing this architecture,as shown in Figure 5, which is not influenced by the tempera-ture variation [17]. It is formed by a conventional architecture(𝑀6-𝑀6-𝑀9-𝑀10) where the passive resistor is changedwith a PMOS transistor𝑀18 and its gate bias generator.Thereare two diode-connected NMOS transistors and one PMOStransistor that make up the gate bias generator, for eachmode(𝑀11, 𝑀12, and 𝑀7 for 𝐼ref1 mode and 𝑀13, 𝑀14, and 𝑀8for 𝐼ref2 mode). Whereas𝑀7 copies the reference current 𝐼,the gate voltage of𝑀18 is generated by the diode-connectedtransistors 𝑀11 and 𝑀12 to generate 𝐼ref1. We can generatethe reference current 𝐼ref1 or 𝐼ref2 by the control switches𝑀15and 𝑀16. We integrate a transistor 𝑀eoc switcher to cancelthe generation of 𝐼ref1 and 𝐼ref2 to end the charging process.

3.2. Bandgap Reference Multioutput. In our proposed design,four reference tensions would be prerequisite (𝑉ref1, 𝑉ref2,


M1

M2

PTATcircuit

M3M4

M17

LDO

Current generator

M18

M6M5

M9 M10

M15

M7

M11

M12

M16

M8

M13

M14

End of charge

CV integrator

Li-io

n ba

ttery

2.9V comp

4.2V comp

A2

A3

A5

A6

A4

A0

Vref2

Vref1

Vref3

Vref4

R1

R2

R3

Vfb1

Vfb2

A1

1 : N

Vbat

Ichg

VsupVadapt

Vdd

−+

−+

−+−

+

−+

−+

−+

Rsens

M1

M2

MP ≡

C1

C2

Mcs

Mm

Meoc

Figure 4: Complete architecture of the proposed Li-ion battery charger.

End of charge

M18

M5 M6 M7 M8

M9 M10

M11

M14M12

M13M15 M16

I

Iref2 modeIref1 mode

Iref

Vdd

2.9V compMeoc

Figure 5: Current generator circuit.


A B

M1 M2 M3 M4 M5 M6M8M9M7

M10M11M12

M14M15M16

M13

Vdd

Vref2 Vref3Vref1 Vref4

C1R8

R1R2

R3

R4 R5 R6 R7

A0

Q1 Q2

I1

I11 I12 I21

I22

I2 I3 I4 I5 I6− +

Figure 6: Bandgap reference multioutput.

𝑉ref3, and 𝑉ref4), hence making use of multioutput bandgapreference tensions. Figure 6 shows a high precision tempera-ture compensates CMOS bandgap reference [18].This latter isimproved in order to generate𝑉ref1 = 1.3 V,𝑉ref2 = 1.4V,𝑉ref3 =0.53mV, and 𝑉ref4 = 0.99mV reference voltages by means ofadding four out-stages.

The equation of the two generated currents, which areproportional to𝑉EB andΔ𝑉EB, to bias these four added stages,is the following equation:

𝐼1= 𝐼2= 𝛼𝐼3= 𝛽𝐼4= 𝛾𝐼5= 𝛿𝐼6. (1)

As shown in Figure 6, each current is divided into twoother currents passing through two branches containingresistor and bipolar transistor in such a way that

𝐼11= 𝐼22;

𝐼12= 𝐼21.

(2)

We made 𝑅2= 𝑅3, to make the voltage of 𝐴 equal to 𝐵.

The inputs of the operational amplifier are equalized.From Figure 6, 𝑉

𝐴= 𝑉EB1. Consider

𝑅3𝐼11= 𝑅2𝐼22,

𝑉𝐴= 𝑉𝐵,

𝑅2𝐼22= 𝑉𝐴= 𝑉𝐵= 𝑉EB1,

𝐼22=𝑉EB1𝑅2

,

𝐼21𝑅1= 𝑉𝐵− 𝑉EB2

= 𝑉𝐴− 𝑉EB2

= 𝑉EB1 − 𝑉EB2 = Δ𝑉EB,

𝐼21=Δ𝑉EB𝑅1

.

(3)

So, the outputs reference voltages of the proposed multi-output BGR can be obtained as

𝑉ref1 = 𝑅4𝐼5 =𝑅4𝐼2

𝛼

=𝑅4(𝐼21+ 𝐼22)

𝛼

=𝑅4

𝛼(Δ𝑉EB𝑅1

+𝑉EB1𝑅2

) ,

𝑉ref2 =𝑅5

𝛽(Δ𝑉EB𝑅1

+𝑉EB1𝑅2

) ,

𝑉ref3 =𝑅6

𝛾(Δ𝑉EB𝑅1

+𝑉EB1𝑅2

) ,

𝑉ref4 =𝑅7

𝛿(Δ𝑉EB𝑅1

+𝑉EB1𝑅2

) .

(4)

Unlike 𝑉EB1, which has a negative TC, Δ𝑉EB has a positiveTC. So, all outputs (𝑉ref1, 𝑉ref2, 𝑉ref3, and 𝑉ref4) becomealmost autonomous from temperature. Figure 7 shows thesimulation of these aforementioned output reference voltagesas a function of temperature over the range −40∘C to 120∘C.

3.3. Current Sense. To sense the current on power transistorMP we have used the 𝑀cs transistor in the current sensecircuit shown in Figure 8 to make the voltage of 𝑉sd of 𝑀cs


V(V

)V

(V)

V(V

)V

(mV

)

1.391.3851.38

1.371.375

1.365

545.0540.0

530.0535.0

1.4351.425

1.411.41.0

0.9980.9960.9940.992

−50.0 −25.0 0.0 50.025.0 75.0 100.0 125.0

Temp. (∘C)Vref1Vref3

Vref2Vref4

Figure 7: Reference voltages versus temperature.

MP

Vbat

Ichg

Isens

Vadapt

Rsens

A0−

+

Mcs

Mm

Figure 8: Current sense circuit.

and MP equal. We have used the OP. The current of𝑀cs MPcan be described as the following equation:

𝐼𝑀cs=1

2𝜇𝑛𝐶𝑜𝑥

𝑊cs𝐿cs[2 (𝑉SG −

𝑉thp) 𝑉SD − 𝑉SD

2]

= 𝐼sens,

𝐼MP =1

2𝜇𝑛𝐶𝑜𝑥

𝑊𝑝

𝐿𝑝

[2 (𝑉SG −𝑉thp) 𝑉SD − 𝑉SD

2]

= 𝐼chg.

(5)

𝐼chg and 𝐼sens are proportional to their aspect ratios.Their ratiocan be described as

𝐼sens𝐼chg≅𝑊cs/𝐿cs𝑊𝑝/𝐿𝑝

=1

𝑁. (6)

Figure 9 shows the simulation results of sensing currents.

4. Simulation Results

The results simulation waveforms of the proposed Li-ionbattery charger are presented in Figure 10. The reference


A(m

A)

A(𝜇

A)

500.0

400.0

300.0

200.0

100.0

0.0

−100.0

250.0

200.0

150.0

100.0

50.0

0.0

−50.0

0.0 2.0 4.0 6.0 8.0

Time (ks)

IchgIsens

Figure 9: Simulation results of sensing currents; from top to bottom, the waveforms are the charging current 𝐼chg and the sensed current 𝐼sens,respectively.

Ichg

Vbat

0.0 2.0 4.0 6.0 8.0

Time (ks)

A(m

A)

500.0

400.0

300.0

200.0

100.0

0.0

−100.0

V(V

)

4.25

4.0

3.75

3.5

3.25

3.0

2.75

2.5

4.21V

2.89V

20mA

Figure 10: Simulation results of output voltage and current; from top to bottom, the waveforms are the battery voltage 𝑉batt and the chargingcurrent 𝐼chg, respectively.

currents are, respectively, 116mA and 448mA for workingat the trickle constant current and fast constant currentmodes. The range voltages are presented as 2.5 V and 4.2 V,correspondingly. The stop current is 20mA that is equal toaround 1C/40 that we have defined. The transition between

CC and CV mode occurs, as shown in Figure 11. And as canbe observed in Figure 12, the system is stable.

Figure 13 shows a layout of the battery charger integratedcircuit. As expected, the Li-ion battery charger was designedusing 0.18𝜇m technology; most of the area is occupied by


4.199V

VbatIchg

2.5

2.75

3.0

3.5

3.75

4.0

4.25

3.25V(V

)

A(m

A)

−100.0

10.0

120.0

230.0

340.0

450.0

8.07.5 8.257.25 7.75

Time (ks)

Figure 11: Transition from CC to CV mode.

V(d

eg.)

10−3 10−2 10−1 100 101 102 103 104 105

25.0

25.0

−100.0

−75.0

−50.0

−25.0

0.0

−100.0

−75.0

−50.0

−25.0

0.0

V(d

B)

Freq. (Hz)

Figure 12: Frequency response of battery charger.

the power PMOS pass device, in which the effective die areais 1.172mm2.

Table 1 summarizes the performance characteristics of theproposed battery charger IC herein presented. Apparently,this work presents an average power efficiency up to 87% andbetter performance in terms of maximum current charge andvery small chip size.

5. Conclusion

The presented Li-ion battery charger has been designed with0.18 𝜇m CMOS processes. The proposed charger is operating

Table 1: Summary of simulation results.

Topology Adaptive LDOTechnology 0.18𝜇mSupply voltage (V) 4.8–5

Efficiency (%) 87 at 4.8 V84 at 5VOutput voltage (V) 2.5–4.2Maximum charging current 448mAChip area 1.172mm2


Power MOS

MP LDOControl

Figure 13: Layout of proposed charger.

within trickle constant current, fast constant current, andconstant voltage triple mode with high power efficiency of87%, small chip size, and low consumption and it is suitablefor portable system as battery charger.

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper.

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Research Article A High Efficiency Li-Ion Battery LDO-Based Charger for Portable … · 2019. 7. 31. · Active and Passive Electronic Components PTAT CV M1 M2 End of charge Li-ion