MAX6620ATI MAXIM [Maxim Integrated Products], MAX6620ATI Datasheet - Page 24

• Manufacturer Part Number: MAX6620ATI
• Description: Quad Linear Fan-Speed Controller
• Manufacturer: MAXIM [Maxim Integrated Products]

Quad Linear Fan-Speed Controller
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 I
24
BIT
Bit
7
6
5
4
3
2
1
0
7
______________________________________________________________________________________
R/W
R
R/W
R/W
Fan_ Target Drive Voltage Registers (28h, 2Ah, 2Ch, 2Eh)—POR = XXXX XXXX
Fan_ Target Drive Voltage Registers (29h, 2Bh, 2Dh, 2Fh)—POR = X000 0000
Fan_ Target Drive Voltage D0
2
Fan_ Target Drive Voltage D8:D1:
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
spin-up or after changing the Fan_ Target TACH Count from 2047 (7FF) to a value lower than 2047 (7FF).
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 Count is
selected from 2047 (7FF), 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:
The value of the Fan_ Target Drive Voltage at POR depends on state of the DAC_START pin, as shown
below:
C transactions with no other I
DECIMAL
DECIMAL
200
300
400
480
511
384
511
0
0
D8:D0
D8:D0
0C8h
12Ch
000h
190h
1E0h
1FFh
HEX
000h
180h
HEX
1FF
2
C
5V RANGE
FAN_ DRIVE VOLTAGE (V)
writes in between. These target registers are updated
internally at the same time when a second byte (LSB) is
written.
0.000
1.764
2.646
3.527
4.232
4.506
FUNCTION
DAC_START
FUNCTION
Open
GND
VCC
12V RANGE
10.766
11.462
0.000
4.486
6.729
8.972