BQ24770: BQ24770 BATFET on but no charge current

Hi Star,

I noticed several things in the schematic that are unusual:

1) What is the adapter voltage (BQ_VBUS)? The ACDET resistor divider is 430 kΩ/430 kΩ, so ACDET is half of the adapter voltage. However, the absolute maximum rating for the ACDET pin is only 7 V. Please let me know the adapter voltage so we can determine the ACDET pin voltage.

2) How many cells is the battery? The CELL pin has a 100 kΩ/100 kΩ resistor divider biased by REGN. Since REGN is 5.4 V, the CELL pin is 2.7 V (logic high), which indicates a 3s or 4s battery.

3) Is the connection between power ground (BQ_GND) and analog ground (BQ_GND_IN) a 1 kΩ resistor, or is it a net tie? Power ground and analog ground should be connected at the thermal pad, as described below:

4) Please change the BAT cap (C24) to 0.1 uF.

Please also share the register settings. Thanks!

Best regards,

Angelo

Hi Angelo

Thanks for your reply.

1, BQ_VBUS is 19V, and the voltage divider resistance has been changed from 430k/430k to 430k/66.5k;

2, The CELL pin is connected to GND;

3, BQ_GND and BQ_GND_IN are connected together through a 0ohm resistor.

4, Register setting as below

BQ24770 BQ24770_REG_ChargeOption0 is 0x634e
BQ24770 BQ24770_REG_ChargeOption1 is 0x0a11
BQ24770 BQ24770_REG_ChargeOption2 is 0x0040
BQ24770 BQ24770_REG_ProchotOption0 is 0x4b54
BQ24770 BQ24770_REG_ProchotOption1 is 0x8120
BQ24770 BQ24770_REG_MaxChargeVoltage is 0x1010
BQ24770 BQ24770_REG_MinSystemVoltage is 0x0f00
BQ24770 BQ24770_REG_InputCurrent is 0x0800
BQ24770 BQ24770_REG_ChargeCurrent is 0x0f00 

Now the charge current is only 6mA.

Please give some suggestion.

Thanks

Star

Hi Star,

Thanks for making the schematic changes in 1), 2), and 3). Your register settings look fine. Please resend the schematic so I can check the updated version.

First, let's check whether the ACFET and RBFET are turned on. Please use a multimeter to measure the following voltages: BQ_VBUS, ACN, ACDRV, CMSRC, ACDET, and ACOK.

If possible, please use an undamaged board with a new BQ24770 IC for this test. The ACDET resistor divider in the old schematic caused the ACDET voltage to exceed the 7 V absolute maximum rating, so it's possible that this may have damaged the ACDET pin.

Lastly, please note that for 1s applications, we typically recommend one of our dedicated single-cell chargers, such as the BQ2560x family or the BQ2589x family. These chargers allow a simpler, more integrated solution for 1s applications. The BQ24770 can also be used to charge a 1s battery, but this is a more complicated solution, and you also need to verify that the BATFET can be fully turned on, as described below:

Best regards,

Angelo