LM25066A: Sometime cannot read controller status by SMBus when the controller is disabled by UVLO/EN pin

Stan Wu

Part Number: LM25066A
Other Parts Discussed in Thread: LM25066

Hello TI,

We need to read the LM25066A status by SMBus after we performing the TVS1 short (kind of SPOF test).

After F1 burned out by the short current of TVS, the UVLO/EN should be low state( pulled low by R1, enable pin still is high)

But reading of 79h is "NACK" on our system board, seems cannot communicate with LM25066A.

By the description on pg.23 in datasheet, the SMBus should keep alive no matter the status of UVLO/EN and OVLO.

I got another pure mother board which has no CPU and other main chipsets, only some DCDC regulators and LM25066A.

I can read the controller status after performing TVS1 short or leave F1 opened directly.

Just wonder if you our your customer had ever encountered the similar situation?

Stan.

over 5 years ago

0 Praveen GD over 5 years ago

TI__Guru 57737 points

Hi Stan,

I have checked on EVM the condition that you have mentioned. I disabled the IC, applied 12V at Vin. I was able to read the PMBus registers of the IC.
Have you checked the I2C Bus signals on your Board ? It might be better to isolate each chipset to find which IC is causing problem on the I2C Bus.

0 Praveen GD over 5 years ago in reply to Praveen GD

TI__Guru 57737 points

Hi Stan,

Do you have any other questions? If not, can we close this thread?

0 Stan Wu over 5 years ago in reply to Praveen GD

Intellectual 580 points

Hi Praveen,

Yes I isolated the I2C bus than was able to read the PMBus register as you did. But we still not sure why we cannot read the register when LM25066 is disabled.

We can read it during system normal operation.

BR.

Stan.

Power management

Power management forum

LM25066A: Sometime cannot read controller status by SMBus when the controller is disabled by UVLO/EN pin