AMC6821: RPM Accuracy Issue

arulmani v

Part Number: AMC6821

In our design we are using the AMC6821 Fan controller IC, we are facing issue in RPM measurements,

Please find the attached table, in this table Expected RPM we are not getting, As per datasheet its an +/- 7% accuracy will be acceptable, But in our case we are seeing more.

PERCENTAGE	CONFIGURED DCY-REG VALUE	READ TACH-LOW_BYTE	READ TACH-HIGH_BYTE	READ RPM	EXPECTED RPM
25(%)	0x40	0xa9	0x0a	2198	3275
34(%)	0x57	0xc1	0x06	3470	4454
43(%)	0x6E	0x17	0x05	4604	5633
52(%)	0x85	0xe5	0x03	6018	6812
61(%)	0x9B	0x3d	0x03	7237	7991
70(%)	0xB2	0xc5	0x02	8429	9170
79(%)	0xCA	0x76	0x02	9523	10349
88(%)	0xE1	0x3d	0x02	10471	11528
97(%)	0xF8	0xda	0x01	12658	12707
100(%)	0xFF	0xd4	0x01	12820	13100

over 2 years ago

0 Ren Schackmann over 2 years ago

TI__Mastermind 43785 points

When FDRC is set to Software DCY, the AMC6821 cannot control fan RPM; the feedback loop is disabled. You must use Software RPM mode and write the desired RPM to the TACH-SETTING registers 0x1E-0x1F.

thanks,

ren

0 arulmani v over 2 years ago in reply to Ren Schackmann

Prodigy 70 points

Hi
In DCY mode we are setting the Duty cycle of Fan, We are reading Feedback through TACHOMETER signal, in that TACHOMETER Signal we are not getting accurate RPM, for lower values we are getting more deviation.

0 Ren Schackmann over 2 years ago in reply to arulmani v

TI__Mastermind 43785 points

You must use Software RPM mode. Set FDRC=01 in Configuration Register 0x00. You will not be able to write to DCY in Software RPM mode.

ren

Sensors

Sensors forum

AMC6821: RPM Accuracy Issue