MAX6640
2-Channel Temperature Monitor with Dual
Automatic PWM Fan-Speed Controller
_______________________________________________________________________________________ 5
PIN
TQFN-EP QSOP
NAME FUNCTION
1, 15
3, 1
PWM2,
PWM1
Open-Drain Output to Power Transistor Driving Fan. Connect to the gate of a MOSFET or base of a
bipolar transistor. PWM_ requires a pullup resistor. The pullup resistor can be connected to a
supply voltage as high as 13.5V, regardless of the MAX6640’s supply voltage.
2, 16 4, 2
TACH2,
TACH1
Tachometer Inputs. Connect to the tachometer output of the fan. TACH_ requires a pullup resistor.
The pullup resistor can be connected to a supply voltage as high as 13.5V, regardless of the
MAX6640’s supply voltage.
35FANFAIL Active-Low, Open-Drain, Fan-Failure Output. Open circuit when V
CC
= 0.
46THERM
Active-Low, Open-Drain Thermal Alarm Output. Typically used for clock throttling. Open circuit
when V
CC
= 0.
57OT
Active-Low, Open-Drain Overtemperature Output. Typically used for system shutdown or clock
throttling. Can be pulled up to 5.5V regardless of V
CC
. Open circuit when V
CC
= 0.
68V
CC
Power-Supply Input. 3.3V nominal. Bypass V
CC
to GND with a 0.1μF capacitor.
7 10 GND Ground. Connect to a clean ground reference.
8, 10 9, 12
DXP1,
DXP2
Combined Current Source and A/D Positive Input for Remote Diode. Connect to anode of remote-
diode-connected temperature-sensing transistor. Do not leave unconnected; connect to DXN if no
remote diode is used. Place a 2200pF capacitor between DXP_ and DXN for noise filtering.
9 11 DXN
Combined Current Sink and A/D Negative Input for Remote Diode. Connect cathode of the remote-
diode-connected transistor to DXN.
11 13 I.C. Internally Connected. Connect to V
CC
.
12 14 ALERT Active-Low, Open-Drain SMBus Alert Output
13 16 SCL S M Bus S er i al - C l ock Inp ut. C an b e p ul l ed up to 5.5V r eg ar d l ess of V
C C
. O p en ci r cui t w hen V
C C
= 0.
14 15 SDA
SMBus Serial-Data Input/Output, Open Drain. Can be pulled up to 5.5V regardless of V
CC
. Open
circuit when V
CC
= 0.
——EP
Exposed Pad (TQFN package only). Internally connected to GND. Connect to a large ground
plane to maximize thermal performance. Not intended as an electrical connection point.
Pin Description
Typical Operating Characteristics (continued)
(V
CC
= 3.3V, T
A
= +25°C.)
PWMOUT FREQUENCY
vs. DIE TEMPERATURE
MAX6640 toc10
TEMPERATURE (°C)
PWMOUT FREQUENCY (Hz)
85603510-15
31
32
33
34
35
30
-40 110
PWMOUT FREQUENCY
vs. SUPPLY VOLTAGE
MAX6640 toc11
SUPPLY VOLTAGE (V)
PWMOUT FREQUENCY (Hz)
5.04.54.03.5
31
32
33
34
35
30
3.0 5.5
