MAX6620_13 Datasheet, PDF (24/30 Pages) Maxim Integrated Products – Quad Linear Fan-Speed Controller

MAX6620
Quad Linear Fan-Speed Controller
Fan_ Target Drive Voltage Registers (28h, 2Ah, 2Ch, 2Eh)—POR = XXXX XXXX
The Fan_ Target Drive Voltage consists of 9 bits con-
tained in two bytes. The two bytes must be written in
order in one or two I²C transactions with no other I²C
writes in between. These target registers are updated
internally at the same time when a second byte (LSB) is
written.
BIT
R/W
FUNCTION
Fan_ Target Drive Voltage D8:D1:
7
This is a 9-bit value that ranges from 0 to 511 and is contained in two bytes. In DAC mode, write the
desired fan drive voltage to these two registers. The MAX6620 will then ramp the fan drive voltage to
this value at a rate determined by the DAC rate-of-change bits.
In RPM mode, the value contained in this register will be the voltage applied to the fan immediately after
6
spin-up or after changing the Fan_ Target TACH Count from 2047 (7FFh) to a value lower than 2047
(7FFh). For example, if the fan is currently stopped with spin-up disabled, and a new Fan_ Target TACH
Count corresponding to 60% of the full-scale fan speed is to be selected, the fan voltage can be
programmed to immediately go to 60% of the full-scale drive voltage when the new Fan_ Target TACH
5
Count is selected from 2047 (7FFh), and then close the RPM control loop starting from that voltage.
The register value is converted to the drive voltage at the fan (or voltage at DACFB_) as follows:
D8:D0
FAN_ DRIVE VOLTAGE (V)
4
DECIMAL
HEX
5V RANGE
12V RANGE
0
R/W
200
3
300
000h
0C8h
12Ch
0.000
1.764
2.646
0.000
4.486
6.729
400
190h
3.527
8.972
480
1E0h
4.232
10.766
2
511
1FFh
4.506
11.462
The value of the Fan_ Target Drive Voltage at POR depends on state of the DAC_START pin, as shown
1
below:
D8:D0
DECIMAL
HEX
DAC_START
0
000h
GND
0
384
180h
Open
511
1FFh
VCC
Fan_ Target Drive Voltage Registers (29h, 2Bh, 2Dh, 2Fh)—POR = X000 0000
Bit
R/W
7
R Fan_ Target Drive Voltage D0
FUNCTION
24
Maxim Integrated