ADT7481ARMZ ON Semiconductor, ADT7481ARMZ Datasheet - Page 7

• Manufacturer Part Number: ADT7481ARMZ
• Description: IC SENSOR TEMP 2CH ALARM 10MSOP
• Manufacturer: ON Semiconductor

Specifications of ADT7481ARMZ

• Function: Temp Monitoring System (Sensor)
• Topology: ADC, Comparator, Multiplexer, Register Bank
• Sensor Type: External & Internal
• Sensing Temperature: -40°C ~ 120°C, External Sensor
• Output Type: SMBus™
• Output Alarm: Yes
• Output Fan: Yes
• Voltage - Supply: 3 V ~ 3.6 V
• Operating Temperature: -40°C ~ 120°C
• Mounting Type: Surface Mount
• Package / Case: 10-MSOP, Micro10™, 10-uMAX, 10-uSOP
• Full Temp Accuracy: +/- 2.5 C
• Digital Output - Bus Interface: Serial (2-Wire)
• Maximum Operating Temperature: + 127 C
• Minimum Operating Temperature: 0 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Theory of Operation
sensor and over/under temperature alarm. When the
ADT7481 is operating normally, the on−board ADC
operates in a free−running mode. The analog input
multiplexer alternately selects either the on−chip
temperature sensor to measure its local temperature, or
either of the remote temperature sensors. The ADC digitizes
these signals and the results are stored in the local, Remote 1,
and Remote 2 temperature value registers.
with the corresponding high, low, and THERM temperature
limits, stored in on−chip registers. Out−of−limit comparisons
generate flags that are stored in the status register. A result that
exceeds the high temperature limit, the low temperature limit,
or remote diode open circuit will cause the ALERT output to
assert low. Exceeding THERM temperature limits causes the
THERM output to assert low. The ALERT output can be
reprogrammed as a second THERM output.
controlled and configured via the serial SMBus. The
contents of any register can also be read back via the SMBus.
the device between normal operation and standby mode,
selecting the temperature measurement scale, masking or
enabling the ALERT output, switching Pin 8 between
ALERT and THERM2, and selecting the conversion rate.
Temperature Measurement Method
the negative temperature coefficient of a diode, measuring
the base−emitter voltage (V
constant current.
Temperature Measurement Results
measurements are stored in the local and remote temperature
value registers and are compared with limits programmed
into the local and remote high and low limit registers.
The ADT7481 is a local and dual remote temperature
The local and remote measurement results are compared
The limit registers can be programmed, and the device
Control and configuration functions consist of switching
A simple method of measuring temperature is to exploit
The results of the local and remote temperature
NOTE:
CAPACITOR C1 IS OPTIONAL. IT IS ONLY NECESSARY IN NOISY ENVIRONMENTS. C1 = 1000pF MAX.
TRANSISTOR
SENSING
REMOTE
BE
) of a transistor operated at
C1
D–
D+
Figure 14. Input Signal Conditioning
I
http://onsemi.com
DIODE
BIAS
N ×I
7
absolute value of V
in V
measure the output of a remote temperature sensor. This
figure shows the remote sensor as a substrate transistor, but
it could equally be a discrete transistor. If a discrete
transistor is used, the collector is not grounded and is linked
to the base. To prevent ground noise 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. C1 may optionally be added
as a noise filter with a recommended maximum value of
1,000 pF.
sensor is switched among two related currents. The currents
through the temperature diode are switched between I, and
N x I, giving DV
using the DV
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 producing a temperature
measurement. To reduce the effects of noise, digital filtering
is performed by averaging the results of 16 measurement
cycles for low conversion rates. At rates of 16, 32, and 64
conversions/second, no digital averaging takes place.
temperature sensor is performed in the same manner.
measurement with 1°C resolution. The remote temperature
measurements are 10−bit measurements, with the 8 MSBs
stored in one register and the 2 LSBs stored in another
register. Table 1 is a list of the temperature measurement
registers.
I
BIAS
This technique requires calibration to null the effect of the
The technique used in the ADT7481 measures the change
Figure 14 shows the input signal conditioning used to
To measure DV
The resulting DV
Signal conditioning and measurement of the local
The local temperature measurement is an 8−bit
BE
f
C
when the device is operated at two different currents.
V
= 65kHz
DD
BE
BE
measurement.
. The temperature can then be calculated
BE
BE
BE
, the operating current through the
, which varies from device to device.
waveforms pass through a 65 kHz
TO ADC
V
V
OUT+
OUT–
BE
.