ADT7421

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2

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.

Figure 1. Block Diagram

A−TO−D

CONVERTER

RUN/STANDBY

BUSY

REMOTE OFFSET

REGISTER

STATUS REGISTER

INTERRUPT

MASKING

REMOTE TEMPERATURE

VALUE REGISTER

LOCAL TEMPERATURE

VALUE REGISTER

ON−CHIP

TEMPERATURE

SENSOR

ANALOG

MUX

EXTERNAL DIODE OPEN−CIRCUIT

SMBus INTERFACE

ADT7421

3

2

8

4

1

57

GND

SDATA

SCLK

THERM

6

D+

D–

ALERT/THERM2

CONFIGURATION

REGISTERS

EXTERNAL THERM LIMIT

REGISTERS

LOCAL THERM LIMIT

REGISTERS

REMOTE TEMPERATURE

HIGH−LIMIT REGISTER

REMOTE TEMPERATURE

LOW−LIMIT REGISTER

LOCAL TEMPERATURE

HIGH−LIMIT REGISTER

LOCAL TEMPERATURE

LOW−LIMIT REGISTER

CONVERSION RATE

REGISTER

ADDRESS POINTER

REGISTER

PIN ASSIGNMENT

Pin No.

Mnemonic

Description

1

Positive Supply, 3.0 V to 3.6 V.

2

D+

Positive Connection to Remote Temperature Sensor. (Anode)

3

D−

Negative Connection to Remote Temperature Sensor. (Cathode)

4

THERM

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.

5

GND

Supply Ground Connection.

6

ALERT / THERM2

Open-Drain Logic Output Used as Interrupt or SMBus ALERT. This can also be configured as a

second THERM output. Requires pullup resistor.

7

SDATA

Logic Input/Output, SMBus Serial Data. Open-Drain Output. Requires pullup resistor.

8

SCLK

Logic Input, SMBus Serial Clock. Requires pullup resistor.