MAX6643LBBAEE+ Maxim Integrated Products, MAX6643LBBAEE+ Datasheet - Page 5

• Manufacturer Part Number: MAX6643LBBAEE+
• Description: IC CNTRLR FAN SPEED 16-QSOP
• Manufacturer: Maxim Integrated Products

Specifications of MAX6643LBBAEE+

• 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: PWM
• 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: 16-QSOP
• Full Temp Accuracy: +/- 3.5 C, +/- 3 C
• Digital Output - Bus Interface: Serial (2-Wire)
• Maximum Operating Temperature: + 125 C
• Minimum Operating Temperature: - 40 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

The MAX6643/MAX6644/MAX6645 measure temperature
and automatically adjust fan speed to ensure optimum
cooling while minimizing acoustic noise from the fan.
The MAX6643/MAX6644/MAX6645 generate a PWM
waveform that drives an external power transistor,
which in turn modulates the fan’s power supply. The
MAX6643/MAX6644/MAX6645 monitor temperature and
adjust the duty cycle of the PWM output waveform to
control the fan’s speed according to the cooling needs
of the system. The MAX6643 monitors its own die tem-
perature and an optional external transistor’s tempera-
ture, while the MAX6644 and MAX6645 each monitor
the temperatures of one or two external diode-connect-
ed transistors.
The pn junction-based temperature sensor can mea-
sure temperatures up to two pn junctions. The
MAX6643 measures the temperature of an external
diode-connected transistor, as well as its internal tem-
perature. The MAX6644 and MAX6645 measure the
temperature of two external diode-connected transis-
tors. The temperature is measured at a rate of 1Hz.
If an external “diode” pin is shorted to ground or left
unconnected, the temperature is read as 0°C. Since the
larger of the two temperatures prevails, a faulty or
unconnected diode is not used for calculating fan
speed or determining overtemperature faults.
The larger of the two measured temperatures is always
used for fan control. The temperature is compared to
three thresholds: the high-temperature threshold (T
MAX6643
13, 14
12
16
Automatic PWM Fan-Speed Controllers with
_______________________________________________________________________________________
MAX6644
13, 14
PIN
12
16
Detailed Description
Temperature Sensor
MAX6645
10
—
9
PWM Output
PWM_OUT
OT2, OT1
HIGH
NAME
V
DD
),
Overtemperature Output
PWM Output for Driving External Power Transistor. Connect to
the gate of an n-channel MOSFET or to the base of an npn.
PWM_OUT requires a pullup resistor. The pullup resistor can
be connected to a supply voltage as high as 5.5V, regardless
of the supply voltage.
Overtemperature Threshold Inputs. Connect to V
leave unconnected to select the upper-limit OT fault output trip
temperature, in 5°C increments. See Table 4.
Power-Supply Input. 3.3V nominal. Bypass V
0.1µF capacitor.
the low-temperature threshold (T
perature threshold, OT. The OT comparison is done once
per second, whereas the comparisons with fan-control
thresholds T
The duty-cycle variation of PWM_OUT from 0% to 100%
is divided into 64 steps. If the temperature measured
exceeds the threshold T
is incremented by one step, i.e., approximately 1.5%
(100/64). Similarly, if the temperature measured is below
the threshold T
one step (1.5%). Since the T
isons are done only once every 4s, the maximum rate of
change of duty cycle is 0.4% per second.
Tables 1 and 2 show the °C value assigned to the TH_
and TL_ input combinations.
Table 1. Setting T
(MAX6643 and MAX6644)
High-Z = High impedance.
High-Z
High-Z
High-Z
TH2
0
0
0
1
1
1
High-Z
High-Z
High-Z
Pin Description (continued)
HIGH
TH1
0
1
0
1
0
1
LOW
and T
, the duty cycle is decremented by
FUNCTION
LOW
HIGH
T
HIGH
L SUFFIX
HIGH
20
25
30
35
40
45
50
55
60
are done once every 4s.
, the PWM_OUT duty cycle
(°C)
HIGH
LOW
and T
), and the overtem-
DD
to GND with a
DD
LOW
T
H SUFFIX
HIGH
, GND, or
40
45
50
55
60
65
70
75
80
compar-
(°C)
5