ADM1026JST ON Semiconductor, ADM1026JST Datasheet - Page 19

• Manufacturer Part Number: ADM1026JST
• Description: IC CNTRL SYS REF/EEPROM 48LQFP
• Manufacturer: ON Semiconductor

Specifications of ADM1026JST

• Rohs Status: RoHS non-compliant
• Function: Hardware Monitor
• Topology: ADC, Comparator, Multiplexer, Register Bank
• Sensor Type: External & Internal
• Sensing Temperature: 0°C ~ 100°C, External Sensor
• Output Type: SMBus™
• Output Alarm: No
• Output Fan: Yes
• Voltage - Supply: 3 V ~ 5.5 V
• Operating Temperature: 0°C ~ 100°C
• Mounting Type: Surface Mount
• Package / Case: 48-LFQFP

unconnected. Do not connect V
capacitor. The internal output buffer on the voltage reference
is capacitively loaded, which can cause the voltage reference
to oscillate. This affects temperature readings reported back
by the ADM1026. The recommended interface circuit for
the V
Temperature Measurement System
Local Temperature Measurement
sensor whose output is digitized by the on−chip ADC. The
temperature data is stored in the local temperature value
register (Address 1Fh). As both positive and negative
temperatures can be measured, the temperature data is stored
in twos complement format, as shown in Table 4.
Theoretically, the temperature sensor and ADC can measure
temperatures from −128°C to +127°C with a resolution of
1°C. Temperatures below T
the operating temperature range of the device; however, so
local temperature measurements outside this range are not
possible. Temperature measurement from −128°C to
+127°C is possible using a remote sensor.
Remote Temperature Measurement
remote diode sensors, or diode−connected transistors,
connected to Pins 25 and 26, or 27 and 28.
Pins 27 and 28 can be configured to measure a diode sensor
ADM1026
Figure 32. V
If the V
The ADM1026 contains an on−chip band gap temperature
The ADM1026 can measure the temperature of two
Pins 25 and 26 are a dedicated temperature input channel.
V
REF
REF
output is shown in Figure 32.
REF
24
REF
10kΩ
output is not being used, it should be left
0.1μF
Interface Circuit for V
TRANSISTOR
SENSING
REMOTE
Figure 33. Signal Conditioning for Remote Diode Temperature Sensors
MIN
and above T
50Ω
REF
+12V
C1*
D+
D–
NDT3055
REF
to GND using a
*
CAPACITOR C1 IS OPTIONAL. IT IS ONLY NECESSARY IN NOISY ENVIRONMENTS.
C1 = 2.2nF TYPICAL, 3nF MAX.
MAX
0.1μF
Loads > 2 mA
I
are outside
10μF
http://onsemi.com
DIODE
BIAS
N x I
V
REF
I
BIAS
19
LOW−PASS FILTER
by clearing Bit 3 of Configuration Register 1 (Address 00h)
to 0. If this bit is 1, then Pins 27 and 28 are A
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, so the
technique is unsuitable for mass production.
change in V
currents, given by:
carrier, T is the absolute temperature in Kelvins, and N is the
ratio of the two currents.
measure the output of a remote temperature sensor. This
figure shows the external sensor as a substrate transistor
provided
microprocessors, but it could equally well be a discrete
transistor such as a 2N3904.
and should be 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.
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.
operating currents of I and N × I. The resulting waveform is
passed through a 65 kHz low−pass filter to remove noise,
and to a chopper−stabilized amplifier that performs the
functions of amplification and rectification of the waveform
to produce a DC voltage proportional to DV
is measured by the ADC to give a temperature output in
8−bit, twos complement format. To further reduce the
effects of noise, digital filtering is performed by averaging
the results of 16 measurement cycles. A remote temperature
measurement takes nominally 2.14 ms.
f
C
= 65kHz
The forward voltage of a diode or diode−connected
The technique used in the ADM1026 is to measure the
where K is Boltzmann’s constant, q is the charge on the
Figure 33 shows the input signal conditioning used to
If a discrete transistor is used, the collector is not grounded
To prevent ground noise from interfering with the
To measure DV
V
DD
for
be
DV
when the device is operated at two different
be
temperature
+ K
be
, the sensor is switched between
be
q
varies from device to device, and
T
log n ( N )
monitoring
V
TO ADC
V
OUT+
OUT–
be
IN8
. This voltage
on
and A
(eq. 10)
some
IN9
.