BQ25120A: SYS is too high when VIN is not connected

L Z

Part Number: BQ25120A

Tool/software:

Hello,

I am working on a device which uses the BQ25120A and shows unexpected behaviour: SYS VOUT is configured to 3.3 V, but during regular operation (Hi-Z mode) I get about 3.4 V. Only when I connect VIN (5 V USB voltage), SYS goes to 3.3 V (and also unexpectedly gets more stable).

The screenshots show SYS (yellow, offset -3.45 V) and filtered SYS (blue, offset -3.15 V) while LS/LDO (purple, offset -1.5 V) is being turned on.

no VIN:

no VIN

VIN:

VIN

What could be the cause of this?

2 months ago

0 Juan Ospina 2 months ago

TI__Genius 17855 points

Hi,

Can you confirm if this is the case with a load applied to SYS?

Best Regards,

Juan Ospina

0 L Z 2 months ago in reply to Juan Ospina

Prodigy 20 points

Yes, SYS is powering an MCU and some modules on the board. Except for VIN, the conditions are the same in the 2 screenshots.

0 Juan Ospina 2 months ago in reply to L Z

TI__Genius 17855 points

Hi,

Let me try to recreate the behavior and see if I can't identify the cause and how you might mitigate it.

Best Regards,

Juan Ospina

0 Juan Ospina 2 months ago in reply to Juan Ospina

TI__Genius 17855 points

Hi,

I'm unable to recreate this behavior on an EVM. In both scenarios the average VSYS voltage is about 3.3V. I have the following set up:

- VIN = 0V; VBAT = 4V; SYS_VOUT = 3.3V; LDO = 3.3V; SYS_Load = 10mA

- VIN = 5V; VBAT = 4V; SYS_VOUT = 3.3V; LDO = 3.3V; SYS_Load = 10mA

Can you please share your schematics?

Best Regards,

Juan Ospina

0 L Z 2 months ago in reply to Juan Ospina

Prodigy 20 points

Thank you for testing. Here are the schematics for the PMIC:

0 Juan Ospina 2 months ago in reply to L Z

TI__Genius 17855 points

Thank you. Some of the behavior might be improved by increasing the capacitance to VINLS. Additionally, it looks like a PMID capacitor has not been populated, this might help with stability.

Can you try recreating the test but having the LSLDO configured to a 3.3V LDO rather than a load switch?

Best Regards,

Juan Ospina

0 L Z 2 months ago in reply to Juan Ospina

Prodigy 20 points

I will get back to you with the results of setting the LDO to 3.3 V on Monday. Although currently the LSLDO is already configured as LDO (2.8 V), not as a load switch.

Could the missing capacitor on PMID and/or a high load on the LDO (about 85 mA at 3.0 V) be responsible for undefined faults in the status register? I sometimes get a fault in the status registers without any of the fault flags set during charging. This happens in either of these cases, although not always and seemingly random:

- only for the duration of LDO enabled, fault clears after LDO is disabled

- at any point during charging; persistent and doesn't clear when toggling CD_N pin

0 Juan Ospina 2 months ago in reply to L Z

TI__Genius 17855 points

Hi,

I believe this is typically due to VIN ILIM fault. Does the fault also happen if you increase the ILIM setting on the device?

Best Regards,

Juan Ospina

0 L Z 1 month ago in reply to Juan Ospina

Prodigy 20 points

Sorry for the very late response. This issue could to be related to another one I have: BQ25120A: Unexpected behavior with external load directly on VBAT

SYS is higher when the load on VBAT is higher.

+1 Juan Ospina 1 month ago in reply to L Z

TI__Genius 17855 points

Hi Liz,

For the sake of continuity it might be best to continue on the other thread.

Best Regards,

Juan Ospina

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BQ25120A: SYS is too high when VIN is not connected