TPS650864: Re-boot issue due to unused LDOA3 on TPS650864

Akshay S

Part Number: TPS650864
Other Parts Discussed in Thread: TPS650861

Tool/software:

Hi Team,

We have design a custom design using the Zynq MPSoC and TPS6508641RSKT PMIC, in which the LDOA3 output is unused and connected with a 4.7 µF output capacitor. After several days of testing in some board, we observed that the board began rebooting continuously upon power-up. To resolve this, we added a 1 kΩ resistor in parallel with the LDOA3 output capacitor, which successfully eliminated the reboot issue. Although we attempted to mask the LDOA3 fault using the PWR_FAULT_MASK2 register, this was ineffective because the register resets to its default OTP configuration on each power cycle.
Kindly let us know the recommended method to permanently resolve the booting issue.

Thank You

1 month ago

0 Akshay S 1 month ago

Prodigy 10 points

Hi,

Wanted to add one more observation.

After the board boots up, we are reading the PWR_FAULT_STATUS register via I2C from the PMIC and observe that a fault is being reported on the LDOA3 rail.

Please find the logs for the same.

root@Demo:~# i2cget -y 0 0x5e 0xb2
0x00
root@Demo:~# i2cget -y 0 0x5e 0xb3
0x01
root@Demo:~# i2cget -y 0 0x5e 0xb3
0x01

0 Sathish Vallamkonda 1 month ago in reply to Akshay S

TI__Expert 6225 points

Hi Akshay,

LDO stability is worse under no load condition. LDO with required output cap should be sufficient and can be left un-used. But, what is changed with several days of testing?

Could you capture LDOA3 output with and without 1k resistor and see the change in output voltage?

You can try increasing the capacitance see if that helps too.

Sathish

0 Akshay S 1 month ago in reply to Sathish Vallamkonda

Prodigy 10 points

We also tried using a higher value capacitor (10 µF) on the LDOA3 rail, but the issue is still not resolved

Initially, the reboot issue was not observed; however, it started appearing after a few days of testing.

Please find below the captured waveform of the LDOA3 output with a 4.7 µF capacitor.

Below waveform shows the LDOA3 output when a 1 kΩ resistor is connected in parallel with the 4.7 µF capacitor.

0 Sathish Vallamkonda 1 month ago in reply to Akshay S

TI__Expert 6225 points

Hi Akshay,

Looks like LDO output overshoots and shuts down. This is typical on older LDOs. The newer LDOs are much better even under no load condition.

The only solution is to add a bleeder resistor. If 1k is working, i would go with it.

Sathish

0 Akshay S 1 month ago in reply to Sathish Vallamkonda

Prodigy 10 points

Hi Sathish,

Can you suggest an alternative solution, since we don’t have a placeholder for the resistor on our board.

0 Akshay S 1 month ago in reply to Akshay S

Prodigy 10 points

Hi Sathish

Could you please confirm whether the PMIC version mentioned below is the latest one, and if it performs better even under no-load conditions.

0 Sathish Vallamkonda 1 month ago in reply to Akshay S

TI__Expert 6225 points

Hi Akshay,

Can you solder the resistor on top of the output cap?

What kind of testing was done that started showing this behavior?

Out of how many boards this issue happening?

Sathish

0 Akshay S 1 month ago in reply to Sathish Vallamkonda

Prodigy 10 points

Hi Sathish,

We have observed issues on 2–3 boards after conducting over an hour of rigorous testing.

Could you please confirm which is the latest version of the PMIC.

0 Sathish Vallamkonda 1 month ago in reply to Akshay S

TI__Expert 6225 points

Hi Akshay,

Yes, i confirmed this is the latest version.

0 Akshay S 1 month ago in reply to Sathish Vallamkonda

Prodigy 10 points

Hi Sathish,

We do not have a placeholder for the resistor on our board.

If the board is able to boot and we can access the PMIC, is there any option to modify the OTP settings to permanently disable or Mask LDOA3 ?

0 Sathish Vallamkonda 1 month ago in reply to Akshay S

TI__Expert 6225 points

Hi Akshay,

TPS6508641 device OTP is factory programmed, so it can not be re-programmed in the field.

We have a user programmable TPS650861 device but all the OTP in that device need to be matched and programmed similar to TPS6508641, except disabling LDOA3.

Sathish

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TPS650864: Re-boot issue due to unused LDOA3 on TPS650864