BQ24171: System power selector problem

Sivaraj T

Part Number: BQ24171

Hi,

I am facing an issue when using BQ24171 with 12V input and single cell 4.2V battery.

When System output switches from Battery power to input DC power or from input DC power to battery power, there is a voltage dip occurs and causes the system to reset.

When switching from input DC to Battery, the system voltage stays at 3V for 8ms, Attached scope shot for voltage at ACDRV, BATDRV, and Vsys(system voltage) when switching from DC to battery.

When switching from Battery to input DC, the system voltage stays at 3V for 1.5ms. Attached scope shot for voltage at ACDRV, BATDRV, and Vsys(system voltage) when switching from battery to DC.

over 7 years ago

0 Steven Bangdiwala over 7 years ago

TI__Expert 8690 points

Hi Sivaraj,

Could you provide the schematic here? Or are you using our EVM?

Regards,
Steven

0 Sivaraj T over 7 years ago in reply to Steven Bangdiwala

Prodigy 190 points

Hi Steven,

Please refer to the following schematic.

Thanks,

Sivaraj. T

0 Steven Bangdiwala over 7 years ago in reply to Sivaraj T

TI__Expert 8690 points

Sivaraj,

Remove the C206 cap and try again. It may improve the timing on the turn on/turn off of ACFET.

Regards,
Steven

0 Sivaraj T over 7 years ago in reply to Steven Bangdiwala

Prodigy 190 points

Steven,

There is no improvement in ON/OFF timing after removing C206.

Thanks,
Sivaraj

0 Steven Bangdiwala over 7 years ago in reply to Sivaraj T

TI__Expert 8690 points

Sivaraj,

Alright, also change R304 to 10k and place a resistor 100k at C204. Change R305 to 5 ohms. Remove D3 and short VCHG to R305 with 0 ohms. Remove C217.

Regards,
Steven

0 Sivaraj T over 7 years ago in reply to Steven Bangdiwala

Prodigy 190 points

Hi Steven,

I have made the changes you mentioned and following are my observation.
When switching from input DC to Battery, the system voltage stays at 3V for 520us and When switching from Battery to input DC, the system voltage stays at 3V for 1ms.

I also tried to reduce the above timing by removing C200.
Then the above timings are reduced to 120us and 46us respectively.

Thanks
Sivaraj

0 Steven Bangdiwala over 7 years ago in reply to Sivaraj T

TI__Expert 8690 points

Hi Sivaraj,

Good to note that C200 changes the timings drastically. If you modify the resistor R299, you could reduce the timing further.

Regards,
Steven

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BQ24171: System power selector problem