ADM1031ARQZ Datasheet ADM1031ARQZ, ADM1031ARQ, ADM1031ARQ-REEL | P7-P9

ADM1031

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Functional Description

The ADM1031 is a temperature monitor and dual PWM

fan controller for microprocessor-based systems. The

device communicates with the system via a serial System

Management Bus (SMBus). The serial bus controller has a

hardwired address pin for device selection (Pin 13), a serial

data line for reading and writing addresses and data (Pin 15),

and an input line for the serial clock (Pin 16). All control and

programming functions of the ADM1031 are performed

over the serial bus. The device also supports Alert Response

Address (ARA).

Internal Registers

Brief descriptions of the ADM1031’s principal internal

registers are given below. For more detailed information on

the function of each register, see Table 18 through Table 33.

Configuration Register

This register controls and configures various functions on

the device.

Address Pointer Register

This register contains the address that selects one of the

other internal registers. When writing to the ADM1031, the

first byte of data is always a register address, which is written

to the address pointer register.

Status Registers

These registers provide status of each limit comparison.

Value and Limit Registers

Theses registers store the results of temperature and fan

speed measurements, along with their limit values.

Fan Speed Configuration Register

This register is used to program the PWM duty cycle for

each fan.

Offset Registers

These registers allow the temperature channel readings to

be offset by a 5-bit twos complement value written to these

registers. These values are automatically added to the

temperature values (or subtracted from if negative). This

allows the systems designer to optimize the system if

required, by adding or subtracting up to 15C from a

temperature reading.

Fan Characteristics Registers

These registers are used to select the spin-up time, PWM

frequency, and speed range for the fans used.

THERM Limit Registers

These registers contain the temperature values at which

THERM

is asserted.

MIN

RANGE

Registers

These registers are read/write registers that hold the

minimum temperature value below which the fan does not

run when the device is in automatic fan speed control mode.

These registers also hold the temperature range value that

defines the range over which auto fan control is provided,

and hence determines the temperature at which the fan is run

at full speed.

Serial Bus Interface

Control of the ADM1031 is carried out via the SMBus.

The ADM1031 is connected to this bus as a slave device,

under the control of a master device, for example, the 810

chipset.

The ADM1031 has a 7-bit serial bus address. When the

device is powered up, it does so with a default serial bus

address. The five MSBs of the address are set to 01011; the

two LSBs are determined by the logical state of Pin 13

(ADD). This is a three-state input that can be grounded,

connected to V

, or left open-circuit to give three different

addresses. The state of the ADD pin is only sampled at

powerup, so changing ADD with power on has no effect

until the device is powered off, then on again.

Table 5. ADD PIN TRUTH TABLE

ADD Pin A1 A0

GND 0 0

No Connect 1 0

0 1

If ADD is left open-circuit, then the default address is

0101110. The facility to make hardwired changes at the

ADD pin allows the user to avoid conflicts with other

devices sharing the same serial bus; for example, if more

than one ADM1031 is used in a system.

Serial Bus Protocol

1. The master initiates data transfer by establishing a

START condition, defined as a high-to-low

transition on the serial data line SDA while the

serial clock line SCL remains high. This indicates

that an address/data stream follows. All slave

peripherals connected to the serial bus respond to

the START condition, and shift in the next eight

bits, consisting of a 7-bit address (MSB first) plus

an R/W

bit that determines the direction of the

data transfer, that is, whether data is written to or

read from the slave device.

The peripheral whose address corresponds to the

transmitted address responds by pulling the data

line low during the low period before the ninth

clock pulse, known as the Acknowledge Bit. All

other devices on the bus now remain idle while the

selected device waits for data to be read from or

written to it. If the R/W

bit is a 0, then the master

writes to the slave device. If the R/W

bit is a 1,

then the master reads from the slave device.

2. Data is sent over the serial bus in sequences of

nine clock pulses, eight bits of data, followed by

an acknowledge bit from the slave device.

Transitions on the data line must occur during the

low period of the clock signal and remain stable

ADM1031

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during the high period, as a low-to-high transition

when the clock is high can be interpreted as a stop

signal. The number of data bytes that can be

transmitted over the serial bus in a single read or

write operation is limited only by what the master

and slave devices can handle.

3. When all data bytes have been read or written,

stop conditions are established. In write mode, the

master pulls the data line high during the tenth

clock pulse to assert a stop condition. In read

mode, the master device overrides the

acknowledge bit by pulling the data line high

during the low period before the ninth clock pulse.

This is known as No Acknowledge. The master

then takes the data line low during the low period

before the tenth clock pulse, then high during the

tenth clock pulse to assert a stop condition.

Any number of bytes of data can be transferred over the

serial bus in one operation, but it is not possible to mix read

and write in one operation, because the type of operation is

determined at the beginning and cannot subsequently be

changed without starting a new operation.

In the case of the ADM1031, write operations contain

either one byte or two bytes, and read operations contain one

byte, and perform the functions described next.

Writing Data to a Register

To write data to one of the device data registers or read

data from it, the address pointer register must be set so that

the correct data register is addressed; data can then be

written to that register or read from it. The first byte of a

write operation always contains an address that is stored in

the address pointer register. If data is to be written to the

device, the write operation contains a second data byte that

is written to the register selected by the address pointer

This is illustrated in Figure 15. The device address is sent

over the bus followed by R/W

set to 0. This is followed by

two data bytes. The first data byte is the address of the

internal data register to be written to, which is stored in the

address pointer register. The second data byte is the data to

be written to the internal data register.

Reading Data from a Register

When reading data from a register there are two

possibilities:

1. If the ADM1031’s address pointer register value is

unknown or not the desired value, it is first

necessary to set it to the correct value before data

can be read from the desired data register. This is

done by performing a write to the ADM1031 as

before, but only the data byte containing the

to the register. This is shown in Figure 16.

A read operation is then performed consisting of

the serial bus address, R/W

bit set to 1, followed

by the data byte read from the data register. This is

shown in Figure 17.

2. If the address pointer register is known to be

already at the desired address, data can be read

from the corresponding data register without first

writing to the address pointer register, so Figure 16

can be omitted.

NOTES:

1. Although it is possible to read a data byte from a data

if the address pointer register is already at the correct value,

it is not possible to write data to a register without writing to

the address pointer register. This is because the first data

byte of a write is always written to the address pointer

2. In Figure 15, Figure 16, and Figure 17, the serial bus

address is shown as the default value 01011(A1)(A0),

where A1 and A0 are set by the three-state ADD pin.

3. The ADM1031 also supports the Read Byte protocol, as

described in the system management bus specification.

Figure 15. Writing a Register Address to the Address Pointer Register,

then Writing Data to the Selected Register

R/W

SCL

SDA

ACK. BY

ADM1031

START BY

MASTER

191

ACK. BY

ADM1031

ACK. BY

ADM1031

STOP BY

MASTER

SCL (CONTINUED)

SDA (CONTINUED)

FRAME 1

SERIAL BUS ADDRESS BYTE

FRAME 2

ADDRESS POINTER REGISTER BYTE

FRAME 3

DATA BYTE

ADM1031

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Figure 16. Writing to the Address Pointer Register Only

SCL

SDA

ACK. BY

ADM1031

START BY

MASTER

ACK. BY

ADM1031

STOP BY

MASTER

FRAME 1

SERIAL BUS ADDRESS BYTE

FRAME 2

ADDRESS POINTER REGISTER BYTE

R/W

Figure 17. Reading Data from a Previously Selected Register

SCL

SDA

NO ACK.

BY MASTER

START BY

MASTER

ACK. BY

ADM1031

STOP BY

MASTER

A1 A0

FRAME 1

SERIAL BUS ADDRESS BYTE

FRAME 2

DATA BYTE FROM ADM1031

R/W

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 6.

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 V

, 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 V

when the device is operated at two different

currents.

This is given by:

(eq. 1)

+ KTńq ln(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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ADM1031ARQZ

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Motor / Motion / Ignition Controllers & Drivers 2 CH TDM PWM FAN CTRL IC

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ADM1031ARQZ

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