bq24630 - P/G LED flashing during charge

Thank you for coming back on this Wang.

The input voltage is 28V with a current max 2.6A from the adaptor. This P/G flashing condition exhibited in the first batch of 10 pcbs. The charge voltage reached the pre-programmed value (R2 was 1378K) and charge termination succeeded in 5 out of 10 boards, with a trickle maintenance where cut-off was in the range of 25.23V to 26.15V and cut-in was approximately 0.5V lower. I cannot give you waveforms because these units have been shipped out. However the issue concerned me because of a problem with the second batch of 10 boards (same gerber set) which I would like to discuss with you. Of the remaining 5 boards from the first batch 3 suffered from Q5 and bq24630 catastrophic failure, and most interesting two failed to terminate charge ending in two more catastrophic failures whilst evaluating possible causes.

However the second set of boards, which have had some adjustments as follows: R2 reduced from 1378K to 1300k for Vbatt of 24.5V, R4 has been reduced from 32K to 9K1 for a reduction of adaptor regulation current from 4A to 1.38A, R6 left at 5K6 to maintain a termination current o 0.18A, and R8 reduced from 22.2K to 12K  to reduce fast charge level from 3A to 1.75A. Having set up 4 of the ten second batch boards, I have four boards that charge, but P/G LED is on with STAT1 LED and now no longer flashes, adaptor current is maxed out until Vfb reaches 1.8V then falls slowly whilst battery is charging close to adaptor voltage (ie no termination). I have reduced adaptor volts to 27.5V on account of earlier failures and possible transient over-voltages on Q5 and or bq24630.

My current concern is that I might lose more PCBs, if I am not careful, without learning anything about the problem, so any experience input on this would be useful. I have an operating board I can take values from.

Dick

Reducing adapter regulation current can reduce the voltage drop on 28V input cable and other circuit.

Reducing R2 (lower down charging Vref) can give more headroom from Vbatt to Vin. So, Vcc_ SRN sleep comparator will have more margin to avoid the PG pin flashing.

According to datasheet typical application circuit, Q5 is low side switching FET. What is the voltage rating for that FET?

Thanks,

Wang

Hi Wang,

The adaptor regulation current I set at 1.38A and fast charge current is set to 1.75A. I understand this is supposed to limit the amount of current that the charger draws from the adaptor. This circuit does not seem to know this and initially draws the maximum adaptor current which is 2.7A. It does however reduce towards the end of charge which I guess is due to the battery reaching 27.66V, ie no charge termination.

I reduced R2 from 1M3 to 1M2 but there was no change, because the charge did not terminate. This particular circuit did initially charge to Vfb of 1.8V then terminated charge correctly, the second and subsequent tests did not

Q5 is aSiS412 which has a Vds max of 30V and a Vgs max of +/-20V

Wang,

Further to the last reply, I omitted the fact that the first test of this board when charge did terminate correctly, the P/G LED was flashing during charge. In subsequent charges and no termination the P/G LED was on continuously.

Is it correct that the P/G LED should not flash during charging?