ADM1031ARQZ datasheet(9/30 Pages) ONSEMI

Il numero della parte	ADM1031ARQZ

Spiegazioni elettronici	Intelligent Temperature Monitor and Dual PWM Fan Controller

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Produttore elettronici	ONSEMI [ON Semiconductor]

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ADM1031

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Figure 16. Writing to the Address Pointer Register Only

Figure 17. Reading Data from a Previously Selected Register

STOP BY

MASTER

ACK. BY

ADM1031

ACK. BY

ADM1031

START BY

MASTER

SCL

11

9

FRAME 1

SERIAL BUS ADDRESS BYTE

FRAME 2

ADDRESS POINTER REGISTER BYTE

0

1

0

1

A1

A0

R/W

D7

D6

D5

D4

D3

D2

D1

D0

SDA

STOP BY

MASTER

ACK. BY

ADM1031

NO ACK.

BY MASTER

START BY

MASTER

SCL

11

9

FRAME 1

SERIAL BUS ADDRESS BYTE

FRAME 2

DATA BYTE FROM ADM1031

0

1

0

1

A1

A0

R/W

D7

D6

D5

D4

D3

D2

D1

D0

SDA

Alert Response Address

Alert Response Address (ARA) is a feature of SMBus

devices that allows an interrupting device to identify itself

to the host when multiple devices exist on the same bus.

The INT output can be used as an interrupt output or can

be used as an SMBALERT. One or more INT outputs can be

connected to a common SMBALERT line connected to the

master. If a device’s INT line goes low, the following

procedure occurs:

1. SMBALERT is pulled low.

2. Master initiates a read operation and sends the

Alert Response Address (ARA = 0001 100). This

is a general call address that must not be used as a

specific device address.

3. The device whose INT output is low responds to

the alert response address, and the master reads its

device address. The address of the device is now

known and can be interrogated in the usual way.

4. If more than one device’s INT output is low, the

one with the lowest device address has priority, in

accordance with normal SMBus arbitration.

5. Once the ADM1031 has responded to the alert

response address, it resets its INT output.

However, if the error condition that caused the

interrupt persists, then INT is reasserted on the

next monitoring cycle.

Temperature Measurement System

Internal Measurement

The ADM1031 contains an on−chip bandgap temperature

sensor. The on−chip ADC performs conversions on the

output of this sensor and outputs the temperature data in

10−bit twos complement format. The resolution of the local

temperature sensor is 0.25

°C. The format of the temperature

data is shown in Table 2.

External Measurement

The ADM1031 can measure the temperatures of two

external diode sensors or diode−connected transistors,

connected to Pins 9 and 10, and Pins 11 and 12.

These pins are dedicated temperature input channels. The

function of Pin 7 is as a THERM input/output and is used to

flag overtemperature conditions.

The forward voltage of a diode or diode−connected

transistor, operated at a constant current, exhibits a negative

temperature coefficient of about –2 mV/

°C. Unfortunately,

the absolute value of VBE, varies from device to device, and

individual calibration is required to null this out. As a result,

the technique is unsuitable for mass production.

The technique used in the ADM1031 is to measure the

change in VBE when the device is operated at two different

currents.

This is given by:

DVBE = KT/q × In (N)

where:

K is Boltzmann’s constant.

q is charge on the carrier.

T is absolute temperature in Kelvins.

N is ratio of the two currents.

Figure 18 shows the input signal conditioning used to

measure the output of an external temperature sensor. This

figure shows the external sensor as a substrate transistor,

provided

for

temperature

monitoring

on

some

microprocessors, but it could equally well be a discrete

transistor.

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