BQ24133: BQ24133 charges to 12V and stops for 3 Cell setting

In the schematic R8 and R10 is NC.
The circuit charges the battery to about 12 V and then stops with STAT blinking and then ON for a few seconds(charging) then blinking again.

I notice that VREF changes from 3.3V when not charging to 3.55V when charging.

I am still trying to find what issue on the design.

Hi Kok Keong Neo,

What is the voltage on AVCC, ACN, SRN, REGN and VREF at the pin of the QFN package. If you can provide scope waveforms, that would be better.

Also, add more resistance on R27 (1k-3k?), the LED may be taking too much current.

Regards,
Steven

Hi Steven

Thank for the feedback. I have change R27 to 1.5K.

I still have the same behaviour. STAT blinking and then ON for a few seconds(charging) then blinking again when VBAT is near 12V

Below are the scope signals

ACN = 15.2V

AVCC = 14.96V

REGN=6.525V

SRN = 12.19V

VREF= 3.579V

Hi,

Is there anything else connected to the VREF and REGN nets of our charger apart from what you already have on the schematic attached? REGN should be 6V and VREF should be 3.3V.

Regards,
Steven

VREF and REGN connected as in the schematic shown.

VREF=3.3V and REGN=6.0V when the board is not charging.

When the board is in charging(STAT LED ON), VREF=3.57V and REGN=6.5V as in the scope signals.

When VREF voltage increase, it will cause ISET, ACSET to increase.

I have 3 prototype boards built and all the boards shows the same result

Hi Steven

See below for the ISET and ACSET signals which I think is abnormal

I seems to have some interference when charging

ISET when Charging

ISET when not charging

ACSET when charging

ACSET when not charging

It looks like your GND is very noisy. If the GND reference has any offset, this will happen. Make sure you separate the power ground from the analog ground, or at least use a different GND path for the power and for analog.

Regards,
Steven

Hi Steven,

I am using a separate power gnd plane.
Can it be that if the thermal pad of the chip which is not soldered properly causing this GND drift.

Regards
Kok Keong

Kok Keong,

If the pad is not soldered properly, the unit may be overheating and we cant really guarantee specs if the layout is not per our recommendation on the layout guidelines on page 30 of the datasheet.

Regards,
Steven

attached is the PCB printout. 

Please if there is any placement error on the PCB. Thank you very muchCharger-1-0-A_final.pdf

Have send you the altium pcb file.
Please advise for anything that I should correct in the placement.
Thank you.

Hi Kok Keong,

Sorry for the delay. Here are a few notes on the layout and schematic review:

1. You need to combine both analog and power ground together on one point under the IC power pad. Use a net tie to connect them.
2. Connect ACP and ACN to R2, SRP and SRN to R15 with a kelvin connection, to not use a power trace to track voltage on the sense resistor.
3. C13 and R20 need to be much closer to the chip.
4. Try to create a short path for GND on the C7 and C8 input caps to the GND of the IC. Looks like the trace for C13 and R20 is preventing this. Also, connect the vias under the IC to Bottom GND layer (light blue) to shorten the path to the IC ground.
5. C1, C3, C7, C8, C22, C14, C15, C16 should be on power ground.
6. R26, R24, C24, C19, R32, R18 should be on analog ground.
7. Pins 22 and 23 should be on power ground.

Regards,
Steven

Hi Steven

Thank you for your reply.

I have updated the pcbdoc according to your notes.

Please see the attached and advise if it is correct. Thank you

Charger-1-0-A_pcbdoc.zip

Regards

Kok Keong