ADT7421
Another feature of the ADT7421 is Series Resistance
Cancellation, where up to 50 W (typical) of resistance in
series with the temperature monitoring transistor can be
automatically cancelled from the temperature result,
allowing noise filtering.
The combination of Beta cancellation and series
resistance cancellation provides critical high accuracy
temperature sensing on 45 nm CPU’s and GPU’s.
The ADT7421 can measure the temperature of a remote
thermal transistor accurate to ±1°C and the ambient
temperature accurate to ±1°C. The temperature measurement
range defaults to 0°C to +125°C, compatible with the
ADM1032, but it can be switched to a wider measurement
range of −40°C to +125°C.
The ADT7421 has a configurable ALERT output and an
extended, switchable temperature measurement range.
The ADT7421 communicates over a 2−wire serial
interface, compatible with system management bus
(SMBus) standards. The default SMBus address of the
ADT7421 is 0x4C. An ADT7421−2 is available with a
SMBus address of 0x4D. This is useful if more than one
ADT7421 is used on the same SMBus.
An ALERT output signals when the on−chip or remote
temperature is out of range. The THERM output is a
comparator output that allows on/off control of a cooling
fan. The ALERT output can be reconfigured as a second
THERM output, if required.
ON−CHIP
TEMPERATURE
SENSOR
CONVERSION RATE
REGISTER
LOCAL TEMPERATURE
VALUE REGISTER
D+ 2
D– 3
ANALOG
MUX
A−TO−D
CONVERTER
BUSY RUN/STANDBY
REMOTE TEMPERATURE
VALUE REGISTER
REMOTE OFFSET
REGISTER
EXTERNAL DIODE OPEN−CIRCUIT
ADT7421
1
VDD
5
GND
STATUS REGISTER
ADDRESS POINTER
REGISTER
LOCAL TEMPERATURE
LOW−LIMIT REGISTER
LOCAL TEMPERATURE
HIGH−LIMIT REGISTER
REMOTE TEMPERATURE
LOW−LIMIT REGISTER
REMOTE TEMPERATURE
HIGH−LIMIT REGISTER
LOCAL THERM LIMIT
REGISTERS
EXTERNAL THERM LIMIT
REGISTERS
CONFIGURATION
REGISTERS
INTERRUPT
MASKING
SMBus INTERFACE
7
SDATA
8
SCLK
Figure 1. Block Diagram
6 ALERT/THERM2
4 THERM
PIN ASSIGNMENT
Pin No.
Mnemonic
1
VDD
2
D+
3
D−
4
THERM
5
GND
6
ALERT / THERM2
7
SDATA
8
SCLK
Description
Positive Supply, 3.0 V to 3.6 V.
Positive Connection to Remote Temperature Sensor. (Anode)
Negative Connection to Remote Temperature Sensor. (Cathode)
Open-Drain Output. Can be used to turn a fan on/off or throttle a CPU clock in the event of an
overtemperature condition. Requires pullup resistor.
Supply Ground Connection.
Open-Drain Logic Output Used as Interrupt or SMBus ALERT. This can also be configured as a
second THERM output. Requires pullup resistor.
Logic Input/Output, SMBus Serial Data. Open-Drain Output. Requires pullup resistor.
Logic Input, SMBus Serial Clock. Requires pullup resistor.
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