12 V
8
V
DD
FanM
BIAS
3 TRSOUT
D
R
BIAS
A
Digital
Integrator
Fan M
6
Logic Unit
R
VCO
1 FCin
7 NTC
Speed Value
Generator
+ OTP
In Case of OTP
VCO
1 mA
RC-VCO 5
C
VCO
R
NTC
2 RSin
R
RSin
Filter
Amplifier
Pulse
Detection
V
DD
GND
4
Block Diagram
FCin
V
DD
R
FC
CON1
FAN+
FAN-
10 kΩ
C
FAN
100 nF
Q1
C
FC
100 nF
TDA 21801
1
FCin
V
DD
2
NTC
RSin
3
TRSOUT FanM
4
RC-VCO
GND
8
7
6
5
R
VCO
220 kΩ
R
BIAS
3.6 kΩ
FanM
To OVP
DOVP
Fan Speed Controller
R
RSin
0.5
Ω
C
VDD
100 nF
C
VCO
3.3 nF
C
NTC
100 nF
R
NTC
22 kΩ
Typical Application Circuit
7
Fan Speed Controller
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