LM87: FAN RPM Error

Hi Oba,

Below is my feedback:

Oba said:

1)
The datasheet defines "FAN RPM Error" as +-10%, +-15% and +-20% for each temperature range.
I think the main factor of this error is frequency accuracy of the internal 22.5KHz ocsillator that is used for FAN counter?
Is it correct?

This spec would include all errors in the device including resolution, oscillator, etc...

Oba said:

2)
What is the definition of this "FAN RPM Error" ?
Does it mean just oscillator accuracy of the internal 22.5KHz oscillator?
Or does it mean RPM error at a certain RPM input like nominal input RPM? (including both oscillator accuracy and error caused by resolution).

FAN RPM Error spec would would mean RPM input like nominal input RPM.  For example at 118°C when the fan is rotating at 1000 RPM the reading could be in the range of  800-1200 RPM.  

Oba said:

3)
The customer would like to know "FAN RPM Error" at 20 deg C.
From the datasheet, it is 10% at +25C < TA < +75C and 15% at -10<TA<+100.  So from the datasheet, it is within 10% - 15% at 20 deg C.
But they would like to know more detail value at 20 deg C. Do you have any data at 20 deg C?

We can only guarantee the specs that are in the datasheet which would be the ±15% at 20 °C.

Thanks,

David