UCD9090A: Power sequence, PMbus signals

Oba

Genius 17295 points

Part Number: UCD9090A

Hello,

I have a question about power sequence of UCD9090A, specially PMbus.

Due to thesystem requirement, PMbus pull-up power is powered up before V33D/V33A powering up.

(When powering down, V33D/V33A are shutdowned before PMbus pull-up power rail.)

So PMbus signals inputs go to 3.3V before V33D/V33A powering up.

Usually, digital device doesn’t accept higher voltage input than the device VDD.

Does this condition damage the device or cause any reliability issue?

Regards,

Oba

over 7 years ago

0 yihe over 7 years ago

TI__Guru 65830 points

Hi Oba

We recommend to use the same V33D/A to pull up the I2C as much as can.

UCD9090A has a internal ESD diode to protect on all IO pins and MON pins. when the device is not power on, if a positive voltage is applied to a pin, the ESD diode will be forward biased and a leakage current may be observed. If such a scenario can be anticpated, the current shall be below 1mA.

Regards

Yihe