DS125BR820: Impact of SDA pull up before power supply.

Ogoshi Tomoki

Part Number: DS125BR820

Hi,

we plan to use the DS125BR820 in SMBus slave mode, with ENSMB will be pull upped to VDD.

If the SDA pull-up supply (VPULLUP) ramps up before the redriver supply (VREDRIVER), could this cause any issues such as:

- damage to the DS125BR820, or

- reverse current into VDD?

When ENSMB = 0 (pin mode), the SDA pin is used as the 4-level input pin for VODA0 and it’s pull upped to VDD in IC.

If VREDRIVER = 0 V, ENSMB will also be 0, and we are concerned that current could flow back through the path shown in the attached figure.

0 Charles 5 months ago

Hi Tomoki-San,

No damage will occur to DS125BR820 if SMBus pullup voltage is within 3.6V shown in 6.3 Recommended Operating Conditions table.

Best,

Charles

0 Ogoshi Tomoki 5 months ago

Hi Charles

Thanks for your reply.
We’re also concerned about whether any reverse current could occur to VDD, since we’re worried it might damage the DCDC.

Thank you.

0 Charles 5 months ago in reply to Ogoshi Tomoki

Hi Ogoshi,

I will have a response by Wednesday.

Best,

Charles

0 Charles 5 months ago in reply to Charles

Hi Ogoshi,

There is reverse current onto VDD pin. On the DS125BR820EVM, I measure 764 uA with the setup shown below.

Best,

Charles

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