Compal LA-3571P Charging Circuit Analysis

Last time I promised to have time to make up the charging circuit. Today I will talk about the charging circuit of F41 with you. The charging chip used in F41 is Fujitsu's MB39A126PFV. Let's explain it in several parts.

First understand the pin definition

1.-INC2: current detection amplifier 2 inverting input terminal
2.OUTC2: current detection amplifier 2 output terminal
3.+INE2: error amplifier 2 non-inverting input terminal
4.-INE2: error amplifier 2 inverting Input terminal
5.ACOK: Output terminal of the power adapter voltage detection module. When ACOK is low, ACIN is high.
When ACOK is in a high-impedance state, ACIN is low and CTL is low.
6.VREF: 5V reference voltage output terminal
7.ACIN: Power adapter voltage Detection module input terminal
8.-INE1: error amplifier 1 inverting input terminal
9.+INE1: error amplifier 1 non-inverting input terminal
10.OUTC1: current detection amplifier output terminal
11.SEL: charging voltage setting terminal, used when it is high 16.8V charging voltage, when it is low, use 12.6V charging voltage
12.-INC1: current detection amplifier inverting input terminal
13 .+INC1: current detection amplifier non-inverting input terminal
14.CTL: power supply control terminal, when the chip is low Standby state
15.FB123: error amplifier 1 2 3 output terminal
16.-INE3: error amplifier 3 inverting input terminal
17.RT: triangular wave oscillation frequency setting resistor connection terminal
18.XACOK: power adapter voltage detection module output terminal, XACOK When ACIN is high, XACOK is high impedance, CTL is low, when XACOK is low, ACIN is low
19.VH: MOS tube drive circuit power supply terminal VH=VCC-6V
20.OUT: External MOS tube gate drive output terminal
21.VCC: Reference voltage, control circuit, power supply terminal of output circuit
22.CS: Soft start setting capacitor connection terminal
23: GND: Ground wire connection terminal
24: +INC2 : Current sense amplifier non-inverting input

 

 

Simple understanding of the internal structure

1. Current detection amplifier 1: the amplification factor is 20 times, used to detect the charging current in this machine, PR56, connected to a 20 milliohm current-limiting resistor. 2. Current detection amplifier

2 : the magnification is 20 times, used to detect the adapter current in this machine, connected to PR45, 20 milliohm current limiting resistor.

3. The internal oscillator generates a 1.5V-2.5V triangular wave, and the frequency is calculated to be 395KHZ , (the highest frequency is 500KHZ). Interested friends can test whether it is this value, which can be measured on the resistance of pin 17.

4. Error amplifier 1: The non-inverting terminal is the IREF sent by EC, the amplitude is between 0.574V-2.56V, the voltage of this signal directly affects the maximum charging current. After PR60 and PR63, the highest value is approxim ately equal to 1.1V, and the reverse terminal is connected to the current detection amplifier 1. The principle is: the charging current will generate a voltage drop on the PR56, which is amplified 20 times by the current detection amplifier 1 and compared with the IREF after the voltage division. When 8PIN is higher than 9PIN, it means that the charging current has exceeded the maximum value set by EC. recharging current. The PWM module will reduce the on-time of PQ13, thereby reducing the charging current.

5. Error amplifier 2: The non-inverting terminal is VREF, which is divided by PR54 and PR53. You can see that according to the different power of the adapter, PR54 will take different values. We calculate by 90W, and +INE2 is also about 1.6V. The working principle is the same as charging current detection. The maximum current of the adapter is limited to 4A. If it exceeds 4A, the charging current will also be reduced to reduce the system current. Here also send ADP_I to EC, it should be that after the voltage of OUTC2 reaches a certain range, EC will find a way to reduce the system current after receiving ADP_I exceeding the threshold.

 

6. Error amplifier 3: The SEL of this machine is grounded and uses a charging voltage of 12.6V. The reverse terminal is formed by the charging voltage after being divided by a resistor, and the same phase terminal is fixed at 3.15V. When The charging voltage is too high and exceeds the After 3.15V, the output of the amplifier will be low, which will also reduce the conduction time of the external MOS tube, so as to stabilize the charging voltage. This is for constant voltage charging . Similarly, when the charging voltage is too low, the tube conduction time, increasing the charging voltage will also prolong the MOS and other modules, so I won't go into details here.

Three: The actual circuit of F41
I have not actually measured the charging circuit of this machine, the following contents are all theoretical values. Everyone can verify.

1. Charge control
    CTL is the main switch of MB39A126. If it is low, even VREF will not be generated. Here, it is controlled by two signals (ACON is open circuit). EC_ON: Through the last analysis, you should know that This signal is before pressing the switch and letting go. The EC is issued.

    FSTCHG: Literally, it means fast charging, and you can also understand it as a charging enable signal. The EC reads the battery information from the 5 and 6-pin SM bus of the battery interface, sends out FSTCHG when charging is required, and sends it all the way to the CTL of MB39A126, and controls the CS through PQ19 and PQ18 all the way. We can know from the pin definition that here CS is used as Soft-start pin, if FSTCHG is invalid, then CS will be directly pulled to the ground, soft-start cannot be completed, and the charging voltage cannot be generated. All FSTCHG also serves as an important condition for generating charging voltage.

 

2. The power supply of MB39A126
    is 21-pin VCC, which is 19V power supply. P2 is directly added to 6-pin VREF on the chip through PR49. After CTL and VCC are normal, there will be 5V output 19-pin VH , which is powered by the gate driver of charging tube PQ13. Let VCC-6V be VH, which means that the gate voltage of PQ13 ranges from 13V-19V. Of these three voltages, only VCC is supplied externally, and the other two should be output after the chip works normally, so it can be used as The basis for judging whether the chip is good or bad, but it can only be used as a reference, because VREF will be turned off after the chip is protected. In addition , the external timing resistor of the chip must be normal.

 

2. Start charging
    . If the above conditions are met, MB39A126 should start working. The EC sends an IREF with a minimum of 0.574V and a maximum of 2.56V to control the charge current. The error amplifier 1 is used to control the const ant current charging until the battery voltage is close to 12.6V, and then it will be converted to 12.6V constant voltage charging. You can think about it. If you don't do this, if you directly use 12.6V to charge the battery from the beginning, if the battery is discharged to a relatively low voltage, this will cause damage to the battery, so it must be charged to close to 12.6V before starting constant voltage charging.

 

    The maximum current during constant current charging (CC mode) is 2.56A, the second CP POINT=2.8AI don't know what it means, but the formula in the box calculates the upper limit of the system current, which should be the maximum limit of the adapter The power is about 53W. As you can imagine, the 65W adapter is limited to about 53W. Therefore, it is impossible to provide the maximum charging current when the machine is running, and the maximum charging current of 2.56A can only be achieved during standby. The third box means that SEL is charged with 12.6V and constant current-constant voltage for low voltage.

    To understand the charging circuit, it is necessary to read its internal block diagram. In addition, the settings of the chip are different from those of ordinary switching power supplies. There are more settings for charging current, charging voltage, etc., and the system current must be detected. MB39A126 also has adapter detection function, which is not used in F41. Today, I will talk to you here first. If you have any questions, you can discuss them together. The charging circuit is actually not difficult to repair, as long as you have a good grasp of its working principle and working conditions.