MAX6641AUB94+T Maxim Integrated Products, MAX6641AUB94+T Datasheet - Page 12

• Manufacturer Part Number: MAX6641AUB94+T
• Description: IC TEMP MONITOR SMBUS 10UMAX
• Manufacturer: Maxim Integrated Products

Specifications of MAX6641AUB94+T

• Function: Fan Control, Temp Monitor
• Topology: ADC, PWM Generator, Tach Counter
• Sensor Type: External & Internal
• Sensing Temperature: -40°C ~ 125°C, External Sensor
• Output Type: I²C™/SMBus™
• Output Alarm: Yes
• Output Fan: Yes
• Voltage - Supply: 3 V ~ 5.5 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 10-MSOP, Micro10™, 10-uMAX, 10-uSOP
• Full Temp Accuracy: +/- 4 C
• Digital Output - Bus Interface: Serial (2-Wire)
• Digital Output - Number Of Bits: 8 bit
• Maximum Operating Temperature: + 125 C
• Minimum Operating Temperature: - 40 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

frequency setting is used for controlling fans that have
logic-level PWM input pins for speed control. Duty-
cycle resolution is decreased from 2/240 to 4/240 at the
35kHz frequency setting.
The PWMOUT signal is normally used in one of three
ways to control the fan’s speed:
1)
2)
3)
Whenever the fan has to start turning from a motionless
state, PWMOUT is forced high for 2s. After this spin-up
period, the PWMOUT duty cycle settles to the predeter-
mined value. If spin-up is disabled (bit 2 in the configu-
ration byte = 1), the duty cycle changes immediately
from zero to the nominal value, ignoring the duty-cycle
rate-of-change setting.
SMBus-Compatible Temperature Monitor with
Automatic PWM Fan-Speed Controller
Table 5. PWM Frequency Select (10h)
12
FREQUENCY
______________________________________________________________________________________
PWMOUT drives the gate of a MOSFET or the base
of a bipolar transistor in series with the fan’s power
supply. The Typical Application Circuit shows the
PWMOUT pin driving an n-channel MOSFET. In this
case, the PWM invert bit (D4 in register 02h) is set to
1. Figure 5 shows PWMOUT driving a p-channel
MOSFET and the PWM invert bit must be set to zero.
PWMOUT is converted (using an external circuit)
into a DC voltage that is proportional to duty cycle.
This duty-cycle-controlled voltage becomes the
power supply for the fan. This approach is less effi-
cient than 1), but can result in quieter fan operation.
Figure 6 shows an example of a circuit that con-
verts the PWM signal to a DC voltage. Because this
circuit produces a full-scale output voltage when
PWMOUT = 0V, bit D4 in register 02h should be set
to zero.
PWMOUT directly drives the logic-level PWM
speed-control input on a fan that has this type of
input. This approach requires fewer external com-
ponents and combines the efficiency of 1) with the
low noise of 2). An example of PWMOUT driving a
fan with a speed-control input is shown in Figure 7.
Bit D4 in register 02h should be set to 1 when this
configuration is used.
PWM
(Hz)
100
35k
20
33
50
SELECT A
0
0
1
1
X
SELECT B
0
1
0
1
X
PWM Output
SELECT C
0
0
0
0
1
Figure 5. Driving a P-Channel MOSFET for Top-Side PWM
Fan Drive
Figure 6. Driving a Fan with a PWM-to-DC Circuit
Figure 7. Controlling a PWM Input Fan with the MAX6641’s
PWM Output (Typically, the 35kHz PWM Frequency is Used)
PWMOUT
PWMOUT
PWMOUT
V
V
CC
CC
18k
+3.3V
+3.3V
1 F
10k
27k
500k
4.7k
10k
5V
5V
+12V
0.01 F
120k
1 F
P
TO FAN
V
OUT
P