laptop battery charging circuit information

Analysis of the laptop battery charging circuit

There are all kinds of laptop battery charging chip, but it can be divided into two categories usually,first,is the old laptop battery charging chip used under the Intel 965 platform, the representative mode l is MAX1772;second,is the new charging chip used above Intel GM45 platform,uses SMBUS to transfer the charging instruction,the representative model are ISL88731 and others.Next,analyze respectively the working principle of two kinds of charging chip.

Analysis of laptop battery charging chip

MAX1772 used usually under Intel 965GM platform

MAX1772 is the charger with high integration density,low cost and more chemical battery brought out by Maxim company of USA,it can form the battery charger with high precision and high efficiency by taking advantage of it.MAX1772 also posses the function of the adapter detection.MAX1772 has the following features:

 MAX1772 

1. Input current limit 
2. The precision of output voltage is about 0.7%;
3. Can provide the charging current more than 4A;
4. The efficiency has a maximum of 95%;
5. The duty cycle has a maximum of 99.99%; 
6. The application range is wide,is suitable for Li+,NiCd,NiMH battery charging;
7. The maximum battery voltage can reach to 8.2V;
8. Low cost;
9. The charging current and the charging voltage can be controlled by the analog input.

MAX1772 uses double row 28 pin packaging, the top view of the pin permutation is shown in figure 20-1.

1.  the power input pin
2.  the linear voltage.It makes the voltage input by DCIN pin to output 5.4V after being adjusted by the linear,during using,it should connect a shunt capacity with 1μF between this pin and the ground.
3. the adapter current limit input
4. 4.096V reference voltage output
5. charge compensation capacitor connection
6. the output current regulation loop compensation end
7. voltage regulation loop compensation end
8. analog ground
9. analog ground
10. the battery charging signal amplification output,when the working mode converts from the voltage model to the current mode,this end can be used to monitor and display the size of the charge current 
11. the adapter voltage detection
12. AC detection output,is the open drain output form.When ACIN voltage is less than REF/2,this pin open drain outputs.
13. the reference input
14. the charging current control.The range of voltage is REFIN/32-REFIN.If its less than REFIN/55.the chip stops charging.
15. the maximum output voltage setting input.The range of voltage is 0-REFIN. 
16. the battery serial number setting end,when this pin connects the ground,setstobe two series,when it connects LDO,sets to be four series,when it connects LDO/2,sets to be three series.
17. the battery voltage output pin
18. the output current detection input negative terminal
19. the output current detection input positive terminal.Dur ng using,it should connect a current detection resistance between CSIN pin.
20. the power ground
21. down tube driving output end.This end connects with the G pole of the down tube
22. the down tube drive power connecting termin l 
23. the power loop end of the top tube.This e d connects with the S pole of the top tube and the inductance.
24. the top tube drive output end.Th s end connects with the G pole of the top tube. 
25. the top tube drive connection end.During using,it should connect a capacitance with 1μF between this pin and LX pin, 
26. the adapter current detection negative terminal 
27. the adapter current detection positive terminal 
28. the adapter input current monitor output  

 Application circuit

In this section, e mainly introduces the application of MAX1772 in Quanta CT6,is shown in figure 20-2

The battery interface signal of CT6 is shown in figure 20-3,the explanation of signal is below. MBDATA,MBCLK:the system management bus data and clock.

TEMP_MBAT : Battery over temperature indicator. I consider : the main voltage of the Battery interface

MBATV:the battery voltage sampling point,the sampling voltage is sent to EC,EC judges the fault.

 The working process:

MAX1772 through CELLS and VCTL sets the charging voltage.EC through the system management bus reads the battery parameter,then sends the charging current setting signal CC-SET to ICTL pin of the charging chip,after MAX1772 receiving ICTL,starts to harge the battery according to the set voltage and current,through charging current detection resistance to detect the charging current.The setting of CELL pin is shown in figure 20-4,when the voltage of CELLS pin is less than 0.2V,sets to be 2 core;when the voltage of CELLS pin s h gher than 0.4V and is less than the voltage reduce 0.5V of LDO pin,sets to be 3 core;when the voltage of CELLS is higher than the voltage reduce 0.25V of LDO pin,sets to be 4 core.

The calculation of the charging voltage:accordi g to the figure 20-2,we can know that CELLS is from the partial pressure of 1772 5.4V,is set to be 3 core,REFIN is connected to 3VPCU(3.3V),VCTL gets 0.848V by the partial pressure of REF4.09.According to the formula(20.1),we can calculate that t e c arging voltage is 12.6V.As the following.

The calculation of the charging current:in the figure 20-2,the charging current detection resistance PR112(is RS2 in the formula(20.2) is 0.05W.According to the formula(20.2),it only needs to change VICTL,then the charging current can be changed.

_ICHG=^VREF  _´^VICTL_´ 1    

RS2V_REFIN   20   

If VICTL sent by EC is 1V voltage,then we can calculate that the charging current is 1.24A.

I	CHG	=	4.096	´	1	x	1
			0.05		3.3		20
I	CHG	=	4.096 x		1
					3.3
I	CHG	= 1.24

       

Analysis of the charging chip ISL88731 used usually by the above Intel GM45

ISL88731 is the lithium ion battery charger controller with highly integrated produced by Intersil company, it can program _through the system management bus. It is different from the traditional charging chip,ISL88731 ough SMBUS communicates with EC to control

charging,SMBUS connects the battery interface, EC and the charging chip at the same time.The charging voltage,charging current, harging enable and other control signals are transmitted through SMBUS,no VCTL,VICTL and other pins.ISL88731 has two functions of the adapter detection and charging control.The main features of ISL88731:

0.5% battery voltage accuracy;

 3% adapter current limiting accuracy;

 3% charging current accuracy;

 2 wire serial interface of SMBUS;

 Battery short circuit protection;

Quick response pulse charging;

Rapid system load transient response;

Adapter detection output,the adapter current monitor output;

The maximum battery charging current 8A;

The maximum current 11A of the adapter;

+8～+28V the range of the adapter voltage.

ISL88731 uses 28 pin TQFN packaging,5mm*5mm,the thickness is only 0.8mm.The top view of ISL88731 pin name is shown in figure 20-5.

The pin definition of ISL88731 is shown in table 20-2.

1             the vacant pin

2          AC adapter detection input end.From the power adapter voltage dividing into voltage through two resistances.

3          the reference voltage output,the standard value is 3.2V.

4              the charging current compensation point and the adapter current regulation loop

5       the vacant pin

6              the compensation point voltage regulation loop

7       the vacant pin

8       inputs the current detection output,the voltage of ICM is equal to 20 times of (VCSSP_VCSSN)

9          the system management bus

10          the system management bus

11          the system management bus module power supply

12             ground   connection

13          the adapter detection output.When ACIN is higher th n 3.2V,ACOK signal open drain outputs the high level,needs for external pulling up.

14          the vacant pin

15             the battery voltage feedback

16          the vacant pin

17          the charging current dete tion negative input terminal

18          the charging current detection positive input terminal

19          ground connection

20          the G pole driver signal of the charging down tube

21          the linear voltage of 5.2V output

22             the main power supply input

23          the phase pin,the top tube driving loop

24          the G pole driver signal of the charging top tube

25             boot-strap send,supplies power to the driver of the top tube

26          internal artificial circuit power supply,through 4.7W resistance connects VCC with VDDP

27             the adapter current detection negative input end

28the adapter current detection positive input end.     

The typical application of ISL88731is shown in figure 20-6.

In the figure 20-6:the explanation of the working process of ISL88731

:

① After the adapter switching in,and through the body diode sends to DCIN pin,supplies main power to the chip;at the same time,through the resista ce dividing into voltage sends to ACIN pin.

②The chip internal linear regulator block outputs 5.2V linear voltage from the chip VDDP,and through the resistance supplies the main power supply to VCC.

③The chip internal produ es the reference voltage with 3.2V.

④ After ACIN being higher than 3.2V,the chip open drain outputs ACOK,is pulled up to be high level by VCC.

⑤ HOST(EC) through SCL,SDA communicate with the battery interface,when the battery is _low,EC through SDA,SCL transmits the charging voltage,the charging current,the charging enable and other control instruction to ISL88731.

⑥ The chip starts to drive the charging top tube and down tube conducted in turn,outputs the voltage to charge the battery.

⑦ ISL88731 through VFB monitors the charging voltage,through CSOP and CSON monitors the charging current.

⑧ The chip through CSSP and CSSN monitors the current RS1 flows,that is the adapter current.Enlarge the value of “CSSP-CSSN”20 times through the chip internal,and outputs from ICM to send to EC,informs EC the size of the complete machine input current at present.

⑨According to the power dissipation of the total power of the adapter and the system peration currently,EC adjusts the size of the charging current properly,to prevent that the charging p wer is too high and exceeds the adapter output limiting,then it will cause the adapter burning because of overload.