ADT7473ARQZ-1 ON Semiconductor, ADT7473ARQZ-1 Datasheet - Page 16

• Manufacturer Part Number: ADT7473ARQZ-1
• Description: IC THERM MON FAN CTRLR 16-QSOP
• Manufacturer: ON Semiconductor
• Series: dBCool®r

Specifications of ADT7473ARQZ-1

• 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: 16-QSOP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

and should be linked to the base. If a PNP transistor is used,
the base is connected to the D– input and the emitter is
connected to the D+ input. If an NPN transistor is used, the
emitter is connected to the D– input and the base is
connected to the D+ input. Figure 25 and Figure 26 show
how to connect the ADT7473/ADT7473−1 to an NPN 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.
sensor is switched among three related currents. N1 x I and
N2 x I are different multiples of the current I, as shown in
Figure 24. The currents through the temperature diode are
switched between I and N1 x I, giving DV
between I and N2 x I, giving DV
then be calculated using the two DV
method can also cancel the effect of any series resistance on
the temperature measurement.
65 kHz low−pass filter to remove noise and then to a
chopper−stabilized amplifier. This amplifies and rectifies
the waveform to produce a dc voltage proportional to DV
The ADC digitizes this voltage, and a temperature
If a discrete transistor is used, the collector is not grounded
To measure DV
The resulting DV
Figure 25. Measuring Temperature Using an NPN
Figure 26. Measuring Temperature Using a PNP
2N3904
2N3906
NPN
PNP
BE
BE
, the operating current through the
TRANSISTOR
Figure 24. Signal Conditioning for Remote Diode Temperature Sensors
Transistor
Transistor
waveforms are passed through a
SENSING
REMOTE
ADT7473−1
ADT7473−1
D+
D–
BE2
D+
D–
ADT7473/
ADT7473/
D+
D–
BE
. The temperature can
I
measurements. This
N2 y I
BE1
, and then
N1 y I
http://onsemi.com
I
BIAS
BE
f
V
C
.
DD
= 65kHz
LPF
16
measurement is produced. To reduce the effects of noise,
digital filtering is performed by averaging the results of 16
measurement cycles.
stored in 10−bit, twos complement format, as listed in Table
10. The extra resolution for the temperature measurements
is held in the Extended Resolution Register 2 (0x77). This
gives temperature readings with a resolution of 0.25°C.
Noise Filtering
previous practice was to place a capacitor across the D+ pin
and the D− pin to help combat the effects of noise. However,
large capacitances affect the accuracy of the temperature
measurement, leading to a recommended maximum
capacitor value of 1000 pF. This capacitor reduces the noise,
but does not eliminate it, making use of the sensor difficult
in a very noisy environment.
other devices for eliminating the effects of noise on the
external sensor. Using the series resistance cancellation
feature, a filter can be constructed between the external
temperature sensor and the part. The effect of any filter
resistance seen in series with the remote sensor is
automatically canceled from the temperature result.
ADT7473−1 and the remote temperature sensor to operate
in noisy environments. Figure 27 shows a low−pass R−C
filter with the following values:
differential noise.
Series Resistance Cancellation
D− inputs (seen in series with the remote diode) is caused by
a variety of factors including PCB track resistance and track
The results of remote temperature measurements are
For temperature sensors operating in noisy environments,
The ADT7473/ADT7473−1 has a major advantage over
The construction of a filter allows the ADT7473/
This filtering reduces both common−mode noise and
Parasitic resistance to the ADT7473/ADT7473−1 D+ and
Figure 27. Filter Between Remote Sensor and
R + 100 W, C + 1 nF
TEMPERATURE
REMOTE
SENSOR
ADT7473/ADT7473−1
V
V
OUT+
OUT–
TO ADC
100Ω
100Ω
1nF
D+
D–
(eq. 1)