Power Battery Charger Application Notes - Dual OPA Architecture

AN0497E V1.10 1 / 5 April 3, 2019

Power Battery Charger Application Notes - Dual OPA Architecture

D/N: AN0497E

Introduction A battery charger generally refers to a device that converts alternating current into

low-voltage direct current to recharge and manage the battery. Chargers are widely used

in various applications and can be divided into two types, digital type chargers and power

battery chargers depending on the type of application. In the traditional type of battery

charger, as there is no MCU for charging management, it is not possible to accurately

control the battery charging curve, which may cause the battery to overcharge or to be

not fully charged, situations which can affect the battery life.

HOLTEK has an ASSP MCU, the HT45F5Q-2, which is especially designed for power

battery chargers. As well as solving the problem of poor control of the charging curve, the

integrated Battery Charge Module can accurately control both charging voltage and

current and replace the usual external circuit which requires an external OPA and other

components such as a TL431. In the charger production process a fixture can store the

charging voltage and current correction parameters into the integrated EEPROM, thus

eliminating the need for traditional manual calibration and improving the production

efficiency. The following takes the HT45F5Q-2 as an example and shows the advantages

of the power charger application architecture and the HOLTEK MCU.

Functional Description The HT45F5Q-2 Battery Charge Module, which has a double OPA Architecture, has three

OPAs (OPA0~2), an 8-bit DAC (DAC0) and a 12-bit DAC (DAC1). The open drain OPA0~1

along with DAC0~1 are used together for CV and CC signal control. The OPA output can

directly drive an optocoupler connected to a primary side PWM IC to implement power

adjustment. OPA2 is used to implement a gain of 10 to amplify the current signal to improve

the current resolution and reduce power losses in the sense resistor. The following

describes the operating principles of the constant voltage mode, constant current mode, the

10 times signal amplification and improved constant voltage and constant current resolution

methods.

Power Battery Charger Application Notes - Dual OPA Architecture

AN0497E V1.10 2 / 5 April 3, 2019

HT45F5Q-2 Battery Charge Module

Operating principles

Constant Voltage Mode - CV Mode

Constant voltage charging is where a battery is charged using a fixed voltage irrespective

of the internal resistance of the battery. The principle is that the charging voltage (B+) is

divided by the resistor dividers R3 and R4, the centre point of which is transmitted to the

negative terminal of OPA1. The error signal between OPA1N and DAC1 is amplified by

OPA1 which appears on OPAE and which is then transmitted to the PWM IC via the

optocoupler. If the OPA1N voltage is lower than the DAC1 voltage, the PWM IC increases

the PWM duty cycle, otherwise the PWM duty cycle is reduced. If the OPA1N voltage is

equal to DAC1, then the PWM duty cycle will remain the same.

Example: If it is required to set the charger CV to 55V, since the DAC1 is preset to 2048

and the output is 2.5V (VDD is 5V), R3 and R4 can be chosen to be 82K and 3.9K. In this

way the R3 and R4 voltage drop will be 2.5V (2048 ÷ 4096 × 5V = 2.5V). Now the 55V

output can be measured at B+.

Note: When changing the value in DAC1, the values in the DA1L and DA1H registers

need to be changed in the correct sequential order to enable the value in DAC1 to be

properly updated.

Constant Current Mode - CC Mode

Constant current charging is where the battery is charged using a fixed current

irrespective of the internal resistance of the battery. Here the charging current will

generate a voltage (V=I×R) on the current detect resistor R1 which is then transmitted via

OPA0N to the negative terminal of OPA0. The OPA0N and DAC0 error signal is amplified

by OPA0 and appears on OPAE where it is transmitted to the PWM IC via the optocoupler.

If the OPA0N voltage is lower than the DAC0 voltage, the PWM IC will increase the PWM

U2 PC817

R9

D1

C2 Battery1

R1

Rectifier/Filter/Regulator

Q1Current Mode PWM IC

R3

R4

R6

AC DC

5V LDO

C3 C4

5VD2 B+

5VR2

C6

5V

B+

AC_N

AC_L

C5

R5 C7

R7 C9

R8 C8

VDD

VSS

OPA2P

OPA0N

OPA1NOPAE

C1

DAC1 12Bit

DAC0 8Bit

ADC

OPA0

OPA1

OPA2

9R

R

U1 HT45F5Q-2

Power Battery Charger Application Notes - Dual OPA Architecture

AN0497E V1.10 3 / 5 April 3, 2019

duty cycle, otherwise the PWM duty cycle will be reduced. If the OPA0N voltage is equal

to DAC0, the PWM duty cycle will remain the same.

Example: Suppose that the charger current sense resistor is 0.1Ω and VDD is 5V. If the

charger CC is designed to be 2A, then the feedback voltage will be 0.1Ω×2A=0.2V. DAC0

can be set to 10 (0.2V×256÷5V≒10), so that the maximum output current of the charger

is 2A.

Note: DAC0 is preset to 64. If the current sense resistor is 0.1Ω, then the CC will be 12.5A

(64÷256×5V÷0.1Ω≒12.5A). Therefore first change DAC0 before the charger switch is

turned on to avoid a charger overcurrent causing battery damage.

10 Times Amplifier OPA2 Circuit OPA2 amplifies the current signal by a factor of 10, reducing the power consumption of

the current sense resistor. The offset voltage of OPA2 can be calibrated through the

register OPVOS from ±15mV to ±2mV. The OPA2 calibration method is as follows:

1. Set OOFM to 1: Select Offset Calibration Mode.

2. Adjust OOF [5:0] from low to high until OPO changes state, this value is now the

correction value VOS1.

3. Adjust OOF [5:0] from high to low until OPO changes state, this value is now the

correction value VOS2.

4. Adjust the OOF [5:0] value to VOS=(VOS1+VOS2)/2.

5. Set OOFM to 0, select the Normal Mode to complete the calibration procedure.

Improving the constant voltage and constant current resolution

The OPA0 and OPA1 positive input signals, as well as being input from the DAC can be

input through the OPA0P and OPA1P inputs. If the user has higher resolution

requirements, the preset value can be set by a resistor divider method via these pins, and

the OPA0N or OPA1N voltage can be adjusted by changing the DAC value to improve the

input voltage and current resolution.

PCB Layout Guidelines Charger CV and CC control is implemented using feedback of the voltage and current

signals through the Battery Charger Module. Therefore, the PCB layout of the module

peripheral components is extremely important. If the PCB layout has not been properly

implemented, then the possibility of CV and CC instability as well as noise problems may

occur. It is necessary to pay special attention to the distance between the optocoupler

and the external components (red parts) of the battery charger module and the MCU. The

following figure shows the schematic diagram and PCB layout for a HT45F5Q-2 three-cell

lithium battery charger. For feedback optimisation, the secondary side components, with

the exception of the power components, are located around the MCU.

Power Battery Charger Application Notes - Dual OPA Architecture

AN0497E V1.10 4 / 5 April 3, 2019

HT45F5Q-2 3-cell Lithium Battery Charger Circuit Diagram

HT45F5Q-2 3-cell Lithium Battery Charger PCB Layout

Conclusion

The HT45F5Q-2 ASSP MCU is a highly integrated charger device that can provide CV or

CC operation using optocouplers and PWM ICs. As it is implemented solely in hardware,

it is not subject to software interference thus improving product safety. It includes a UART

communication interface for increased security and flexibility. The device is available in a

20NSOP package that meets industry specifications (-40°C to 85°C) and has high noise

immunity, making it ideal for smart multi-function charger applications.

D1KBP210

F1 250V/3A

C310uF/400V

R41.2M

R51.2M

R6160K

D4SFR107

R8160K

C42.2nF/630V

T1

D3 SFR107R2 5.1

CY12.2nF/400V

VDD

GNDFBRI NC

NCWENSE

GATE

U1 OB2263AP

Q1K3567

R3 470

D2 1N4148W

C110uF/50V

C20.1uF

R1 100K

C140.1uF

C10680uF/35VC6

471/1KVR1547

IN OUTGND

U4 LP2950CZ-5

C90.1uF

5V

C11680uF/35V

Q2AP9565BGH

R1610K

R91.2

R71.2

HV

HV

B-

R23 10

Q3SI2300

R2210K

R21 0.1

B+

NTC

B-

R2533K

R268.2K

C150.1uF

R2833K

R2710K

R298.2KC17

0.1uF

C160.1uF

NTC5VHVB+

GLED

R17 1.3K

R18 700

RLED

5V

5V

PA7

OPA1N

OPAE

OPA0N

VDD

VSS

PB1

PA1/OPA2P

PA4/CTPB

PB4/AN4

PB3/AN3PB0/AN0

U3 HT45F5Q-2

U5SBD10CU2

SBD10C

0.1uFC5

10uFC7

12KR10

200KR19

0.1uFC12

0.1uFC13

75KR20

10KR13

33KR11

0R14

8.2KR12

0.1uFC8

510R24

U6PC817

Power Battery Charger Application Notes - Dual OPA Architecture

AN0497E V1.10 5 / 5 April 3, 2019

References

1. HT45F5Q-2 Datasheet.

2. Power Charger Calibration Platform Application Note (AN0516E)

For more information refer to the Holtek’s official website www.holtek.com.

Versions and Modification Information Date Author Issue

2018.05.21 李昱緯(Tooker Lee) V1.00.

2019.03.26 王駿維 V1.10 – Add a new application note as a reference.

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