ADM1022 datasheet(7/19 Pages) AD

7 / 19 page

REV. 0

ADM1022

–7–

FREQUENCY – Hz

50M

500

50k

500k

10mV SQ. WAVE

100k

25M

Figure 8. Temperature Error vs. Differential-Mode Noise

Frequency

TEMPERATURE – C

1.7

–40

VDD = 3.0V

–20

100

130

1.8

1.9

2.0

2.1

2.2

2.3

VDD = 3.3V

VDD = 5.5V

110

–10

–30

120

Figure 9. Standby Supply Current vs. Supply Voltage

TEMPERATURE – C

100

150

200

250

300

350

400

RST1

RST2

–40

–20

2040

6080

100

130

110

–10

–30

120

Figure 10. Power-up Reset vs. Temperature

GENERAL DESCRIPTION

The ADM1022 is a low-cost temperature monitor and fan con-

troller for microprocessor-based systems. The temperature of

one or two remote sensor diodes may be measured, allowing

monitoring of processor temperature in single- or dual-processor

systems. The chip also contains an on-chip sensor to allow

ambient temperature to be monitored.

Measured values can be read out via a serial System Manage-

ment Bus, and values for limit comparisons can be programmed

in over the same serial bus.

The ADM1022 also contains a DAC for fan speed control.

Automatic hardware temperature trip points are provided for

fault tolerant fan control and the fan will be driven to full speed

if they are exceeded. Two interrupt outputs are provided, which

will be asserted if the software or hardware limits are exceeded.

Finally, the chip has two supply voltage monitors for brownout

detection. These drive two reset pins, one of which is bidirec-

tional. A manual reset input is also provided.

INTERNAL REGISTERS OF THE ADM1022

A brief description of the ADM1022’s principal internal regis-

ters is given below. More detailed information on the function

of each register is given in Tables IV to IX.

Conﬁguration Register: Provides control and conﬁguration.

Address Pointer Register: This register contains the address that

selects one of the other internal registers. When writing to the

ADM1022, the ﬁrst byte of data is always a register address, which

is written to the Address Pointer Register.

Interrupt (

INT) Status Register: This register provides status

of each Interrupt event. It is also mirrored by a second register

at address 4Ch.

Interrupt (

INT) Mask Register: Allows masking of individual

interrupt sources.

Value and Limit Registers: The results of temperature measure-

ments are stored in these registers, along with their limit values.

Analog Output Register: The code controlling the analog out-

put DAC is stored in this register.

SERIAL BUS INTERFACE

Control of the ADM1022 is carried out via the serial bus. The

ADM1022 is connected to this bus as a slave device, under the

control of a master device, e.g., the PIIX4.

The ADM1022 has a 7-bit serial bus address. When the device is

powered up, it will do so with a default serial bus address. The ﬁve

MSBs of the address are set to 01011, the two LSBs are deter-

mined by the logical states of Pin 13 (ADD/NTEST_OUT).

This is a three-state input that can be grounded, connected to VCC

or left open-circuit to give three different addresses. The state of

the ADD pin is only sampled at power-up, so changing ADD

with power-on will have no effect until the device is powered

off then on again.

Table I. ADD Pin Truth Table

ADD Pin

GND

No Connect

VCC

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