UCD90910: UCD90910 Fan control IO pins

Peter Redmond

Part Number: UCD90910

The PWM fan controller ports on the UCD90910 can be setup as 'open collector' outputs - what is the voltage limit on these.

I want to PWM control a 24V fan - can the open collector output cope with this?

The PWM fan input is connected to a FET gate pulled up to the 24V by a 10k resistor. See image of PWM Fan input.

Thanks

0 yihe over 2 years ago

No, All the IOs are limited at 3V3 even with open drain.

Regards

Yihe

0 Peter Redmond over 2 years ago

Thanks YiHi for the prompt reply.

I guess the 3V3 limit is due to the internal ESD protection diodes?

Its unfortunate as I now have to add two external transistors on each fan control to ensure the signal is not inverted.

As the PWM IO's are low at startup I need to make sure the fans don't turn on during this time.

Regards

Peter

+1 yihe over 2 years ago in reply to Peter Redmond

Yes, the internal ESD diode forces the limit.

FPWM pins are default at LOW output.

Regards

Yihe

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