MAX6643LBBAEE+ Maxim Integrated Products, MAX6643LBBAEE+ Datasheet - Page 8

• 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

Figures 3–6 show various configurations.
When using an external thermal diode, temperature
accuracy depends upon having a good-quality, diode-
connected, small-signal transistor. Accuracy has been
experimentally verified for a variety of discrete small-
signal transistors, some of which are listed in Table 5.
The MAX6643/MAX6644/MAX6645 can also directly
measure the die temperature of CPUs and other ICs
with on-board temperature-sensing diodes.
The transistor must be a small-signal type with a rela-
tively high forward voltage. This ensures that the input
voltage is within the ADC input voltage range. The for-
ward voltage must be greater than 0.25V at 10µA at the
highest expected temperature. The forward voltage
must be less than 0.95V at 100µA at the lowest expect-
ed temperature. The base resistance has to be less
than 100 . Tight specification of forward-current gain
(+50 to +150, for example) indicates that the manufac-
turer has good process control and that the devices
have consistent characteristics.
Automatic PWM Fan-Speed Controllers with
Overtemperature Output
Table 3. Configuring the FAN_IN_ Inputs with TACHSET
Table 4. Setting the Overtemperature
Thresholds (T
High-Z = high impedance
8
_______________________________________________________________________________________
TACHSET
MAX6643
MAX6644
MAX6645
High-Z
High-Z
High-Z
OT2
0
0
0
1
1
1
Applications Information
Remote-Diode Considerations
OVERT
Tachometer
Tachometer
Tachometer
FAN_IN1
)
High-Z
High-Z
High-Z
OT1
(MAX6643 and MAX6644)
0
1
0
1
0
1
VDD
Tachometer
Tachometer
Tachometer
FAN_IN2
T
OVERT
L SUFFIX
100
60
65
70
75
80
85
90
95
(°C)
Do not connect
Current sense
Current sense
FAN_IN1
to GND
The accuracy of the remote temperature measurements
depends on the ideality factor (n) of the remote diode
(actually a transistor). The MAX6643/MAX6644/MAX6645
are optimized for n = 1.01, which is typical of many dis-
crete 2N3904 and 2N3906 transistors. It is also near the
ideality factors of many widely available CPUs, GPUs, and
FPGAs. However, any time a sense transistor with a differ-
ent ideality factor is used, the output data is different.
Fortunately, the difference is predictable. Assume a
remote-diode sensor designed for a nominal ideality fac-
tor n
diode with a different ideality factor, n
temperature T
where temperature is measured in Kelvin.
As mentioned above, the nominal ideality factor of the
MAX6643/MAX6644/MAX6645 is 1.01. As an example,
assume the MAX6643/MAX6644/MAX6645 are config-
ured with a CPU that has an ideality factor of 1.008. If
the diode has no series resistance, the measured data
is related to the real temperature as follows:
For a real temperature of +60°C (333.15K), the mea-
sured temperature is 59.33°C (332.49K), which is an
error of -0.66°C.
Table 5. Remote-Sensor Transistor
Manufacturers
T
Central Semiconductor (USA)
Rohm Semiconductor (USA)
Samsung (Korea)
Siemens (Germany)
ACTUAL
GND
NOMINAL
Do not connect
Current sense
Current sense
MANUFACTURER
FAN_IN2
to GND
T
M
T
M
M
is used to measure the temperature of a
can be corrected using:
n
NOMINAL
T
ACTUAL
n
1
failure detection
Effect of Ideality Factor
Disables fan-
Locked rotor
Locked rotor
FAN_IN1
n
T
NOMINAL
M
UNCONNECTED
n
1
1.008
1.01
1
. The measured
failure detection
MODEL NO.
KST3906-TF
Disables fan-
CMPT3906
SMBT3906
Locked rotor
Locked rotor
SST3906
FAN_IN2
T
M
. 1 00198