Datasheet

MAX6653/MAX6663/MAX6664
Temperature Monitors and
PWM Fan Controllers
______________________________________________________________________________________ 21
the highest expected temperature must be greater than
0.25V at 10µA, and at the lowest expected tempera-
ture, the forward voltage must be less than 0.95V at
100µA. Large power transistors must not be used. Also,
ensure that the base resistance is less than 100Ω. Tight
specifications for forward current gain (50 < ß <150, for
example) indicate that the manufacturer has good
process controls and that the devices have consistent
V
BE
characteristics.
Manufacturers of discrete transistors do not normally
specify or guarantee ideality factor. This is normally not
a problem since good-quality discrete transistors tend
to have ideality factors that fall within a relatively narrow
range. We have observed variations in remote tempera-
ture readings of less than ±2°C with a variety of dis-
crete transistors. Still, it is sound design practice to
verify good consistency of temperature readings with
several discrete transistors from any manufacturer
under consideration.
16
1
2
3
4
5
6
PWM_OUT
SMBCLK
MAX6653
TACH/AIN
CRIT0
V
CC
CRIT1
+3.3V
10k
Ω
10k
Ω
10k
Ω
NDT3055L
THERM SIGNAL
TO THROTTLE
CPU CLOCK
FAN _FAULT
TO SIGNAL
FAN-FAILURE
CONDITION
10k
Ω
+3.3V
+3.3V
3-WIRE
FAN
+5V+3.3V
+3.3V
GND
THERM
FAN_FAULT
7
8
15
SMBDATA
10k
Ω
2.2k
Ω
2.2k
Ω
+3.3V
+3.3V
+3.3V
14
13
INT
ADD
10k
Ω
2.2nF
CPU
SYSTEM
SHUTDOWN
INTERRUPT
TO
µ
C
CLOCK
DATA
+3.3V
12
SDR
11
SDL
10
DXP
9
DXN
Typical Operating Circuits