STUSB4500 – I²C Pullup with No VBUS/VDD Applied

[JBean-IUP]

Hello,

I am currently designing a battery-powered device that incorporates the STUSB4500. I have a question regarding the I²C pins: specifically, whether it is safe for these pins to be pulled up (via the system microcontroller’s pull-ups) when no voltage is present on VBUS or VDD.

In my design, the primary microcontroller can be powered on even when the USB power is absent, which means the I²C lines would be driven high before VBUS or VDD is applied to the STUSB4500. I have reviewed the datasheet, but it does not clearly state whether the operating or maximum ratings for the I²C pins depend on VDD. My assumption is that it should be acceptable, but I wanted to confirm to avoid any potential issues.

Any guidance or confirmation you can provide would be greatly appreciated. Thank you for your time and assistance.

Thanks!

[TDK]

Datasheet says they're pulled down when VDD is not present. Probably this is by a protection diode in which case the system isn't going to be pulling them up without powering VDD. Backpowering through protection diodes should be avoided.

[Didier HERROUIN]

Hello,

You can pulled up these pins (SDA and SCL) up to 6V (4.5V max would be better as a steady state), it will not impact the chipset.

Nevertheless, if the STUSB4500 is not supplied (no charger connected), be aware that you will get a leakage current on SDA and SCL pins (few hundred of µA), it will impact SDA and SCL level (from 3.3V to 2.7V if you use 3.3kohms resistors). You may use smaller pull-up resistors values (1k or 470ohms for instance) to limit this voltage drop.

Best regards,

Didier Herrouin

[JBean-IUP]

Thank you for the reply! I'm glad I asked. Would have definitely given me a headache down the road.