ADT7476AARQZ-REEL ON Semiconductor, ADT7476AARQZ-REEL Datasheet - Page 17

• Manufacturer Part Number: ADT7476AARQZ-REEL
• Description: IC REMOTE THERMAL CTRLR 24-QSOP
• Manufacturer: ON Semiconductor
• Series: dBCool®r

Specifications of ADT7476AARQZ-REEL

• Function: Fan Control, Temp Monitor
• Topology: ADC, Comparator, Fan Speed Counter, Multiplexer, Register Bank
• Sensor Type: External & Internal
• Sensing Temperature: -40°C ~ 125°C, External Sensor
• Output Type: SMBus™
• Output Alarm: No
• Output Fan: Yes
• Voltage - Supply: 3 V ~ 3.6 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 24-QSOP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

and is linked to the base. If a PNP transistor is used, the base
is connected to the D– input and the emitter to the D+ input.
If an NPN transistor is used, the emitter is connected to the
D– input and the base to the D+ input. Figure 26 and
Figure 27 show how to connect the ADT7476A to an NPN
Table 6. Twos Complement Temperature Data Format
1. Bold numbers denote 2 LSB of measurement in the Extended
Table 7. Extended Range, Temperature Data Format
1. Bold numbers denote 2 LSB of measurement in the Extended
If a discrete transistor is used, the collector is not grounded
Resolution Register 2 (0x77) with 0.25°C resolution.
Resolution Register 2 (0x77) with 0.25°C resolution.
Temperature
Temperature
+10.25°C
+50.75°C
+25.5°C
–128°C
+100°C
+125°C
+127°C
–50°C
–25°C
–10°C
+75°C
–64°C
100°C
125°C
191°C
–1°C
10°C
25°C
50°C
75°C
0°C
0°C
1°C
TRANSISTOR
Digital Output (10−Bit) (Note 1)
Digital Output (10−Bit) (Note 1)
SENSING
1000 0000 00 (diode fault)
1100 1110 00
1110 0111 00
1111 0110 00
0000 0000 00
0000 1010 01
0001 1001 10
0011 0010 11
0100 1011 00
0110 0100 00
0111 1101 00
0111 1111 00
0000 0000 00 (diode fault)
0011 1111 00
0100 0000 00
0100 0001 00
0100 1010 00
0101 1001 00
0111 0010 00
1000 1001 00
1010 0100 00
1011 1101 00
1111 1111 00
REMOTE
Figure 25. Signal Conditioning for Remote Diode Temperture Senors
CPU
THERMDA
THERMDC
D+
D–
I
DIODE
BIAS
http://onsemi.com
N
×
I
I
BIAS
LOW−PASS FILTER
17
f
V
C
DD
= 65kHz
Remote Temperature Measurement
remote diode sensors or diode-connected transistors
connected to Pin 17 and Pin 18, or Pin 15 and Pin 16.
transistor operated at a constant current exhibits a negative
temperature coefficient of about –2 mV/°C. Unfortunately,
the absolute value of V
individual calibration is required to null this out. As a result,
this technique is unsuitable for mass production. The
technique used in the ADT7476A is to measure the change
in V
This is given by:
measure the output of a remote temperature sensor. This
figure shows the external sensor as a substrate transistor,
which is provided on some microprocessors for temperature
monitoring. It could also be a discrete transistor such as a
2N3904/2N3906.
or PNP transistor for temperature measurement. To prevent
ground noise from interfering with the measurement, the
more negative terminal of the sensor is not referenced to
ground, but is biased above ground by an internal diode at
the D– input.
The ADT7476A can measure the temperature of two
The forward voltage of a diode or diode-connected
Figure 25 shows the input signal conditioning used to
BE
where:
when the device is operated at two different currents.
k is the Boltzmann’s constant.
q is the charge on the carrier.
T is the absolute temperature in Kelvin.
N is the ratio of the two currents.
DV
BE
BE
+ KT q
V
varies from device to device, and
V
OUT+
OUT–
TO ADC
In ( N )
(eq. 1)