UCD90910: UCD90910 Fan control IO pins

Peter Redmond

Part Number: UCD90910

Your technical department has confirmed the Fan drive 'FPWM' outputs are limited to 3v3 due to the internal protection diodes.

Just to mention - the data sheet is a bit misleading as it shows a direct PWM fan drive from the IC to the 12V fan PWM input.

I now have to add 2 transistors to the output drive of each of the 10 fans.

Two transistors are needed to ensure the signal is not inverted.

Instead of the transistor PWM drive can I use a series resistor to reduce the voltage back into the IC.

I have included an image of the Fan PWM input and the transistor drive circuit I have initially used.

0 yihe over 3 years ago

The PWM is a output signal you can not reduce its voltage back to device.

Do you mean the voltage back to the MONx Pin to monitor the temperature？

If so, yes, the MON support up to 2.5V. you have to properly configure the temperature gain based on the divider.

Regards

Yihe

0 Peter Redmond over 3 years ago

These are the PWM outputs of the UCD9091 driving each fan PWM input.

Each IO will be configured as open collector outputs.

The fan is 24V and the PWM input of each fan has (internally) a FET with the gate pulled up to 24V with a 10k resistor.

The 10k resistor will limit the current sink to 2.4mA.

Can I therefore drive the fan PWM input directly?

0 yihe over 3 years ago in reply to Peter Redmond

that shall be fine.

There is a limit on how many current can be sinked on the data sheet.

Regards

Yihe

0 Peter Redmond over 3 years ago in reply to yihe

Thanks Yihe

I couldn't find this limit on the datasheet - could you let me know where to find this.

Regards

Peter

0 yihe over 3 years ago in reply to Peter Redmond

Please see below

Regards

Yihe

+1 Peter Redmond over 3 years ago in reply to yihe

Ok Thanks

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