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ADM1032ARM

±1°C Remote and Local System Temperature Monitor

Analog Devices 

ADM1032

1. SMBALERT 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 ALERT output is low responds to the Alert

Response Address and the master reads its device address.

As the device address is seven bits, an LSB of ‘1’ is added.

The address of the device is now known and it can be inter-

rogated in the usual way.

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

the lowest device address, will have priority, in accordance

with normal SMBus arbitration.

5. Once the ADM1032 has responded to the Alert Response

Address, it will reset its ALERT output, provided that the error

condition that caused the ALERT no longer exists. If the

SMBALERT line remains low, the master will send ARA again,

and so on until all devices whose ALERT outputs were low

have responded.

LOW-POWER STANDBY MODE

The ADM1032 can be put into a low-power standby mode by setting

bit 6 of the Configuration Register. When Bit 6 is low, the ADM1032

operates normally. When Bit 6 is high, the ADC is inhibited, and

any conversion in progress is terminated without writing the result

to the corresponding value register.

The SMBus is still enabled. Power consumption in the standby mode

is reduced to less than 10 µA if there is no SMBus activity, or 100 µA

if there are clock and data signals on the bus.

When the device is in standby mode, it is still possible to initiate a

one-shot conversion of both channels by writing XXh to the

One-Shot Register (address 0Fh), after which the device will return

to standby. It is also possible to write new values to the limit regis-

ter while it is in standby. If the values stored in the temperature

value registers are now outside the new limits, an ALERT is

generated even though the ADM1032 is still in standby.

THE ADM1032 INTERRUPT SYSTEM

The ADM1032 has two interrupt outputs, ALERT and THERM.

These have different functions. ALERT responds to violations of

software-programmed temperature limits and is maskable. THERM

is intended as a “fail-safe” interrupt output that cannot be masked.

If the temperature goes equal to or below the lower temperature limit,

the ALERT pin will be asserted low to indicate an out-of-limit

condition. If the temperature is within the programmed low and

high temperature limits, no interrupt will be generated.

If the temperature exceeds the high temperature limit, the ALERT pin

will be asserted low to indicate an over temperature condition. A local

and remote THERM limit, may be programmed into the device to set

the temperature limit above which the over temperature THERM

pin will be asserted low. This temperature limit should be equal to

or greater than the high temperature limit programmed.

The behavior of the high limit and THERM limit is as follows:

1. If either temperature measured exceeds the high temperature

limit, the ALERT output will assert low.

2. If the local or remote temperature continues to increase and

either one exceeds the THERM limit, the THERM output

asserts low. This can be used to throttle the CPU clock or

switch on a fan.

A THERM Hysteresis Value is provided to prevent a cooling fan

cycling on and off. The power-on default value is 10°C but this

may be reprogrammed to any value after power-up. This hyster-

esis value applies to both the local and remote channels

Using these two limits in this way allows the user to gain maxi-

mum performance from the system by only slowing it down,

should it be at a critical temperature.

The THERM signal is open drain and requires a pull-up to

VDD. The THERM signal must always be pulled up to the same

power supply as the ADM1032, unlike the SMBus signals

(SDATA, SCLK, and ALERT) which may be pulled to a differ-

ent power rail, usually that of the SMBus controller.

100؇C

90؇C

80؇C

70؇C

60؇C

50؇C

40؇C

TEMPERATURE

LOCAL THERM

LIMIT

LOCAL THERM LIMIT

–HYSTERESIS

THERM

Figure 5. Operation of the THERM Output

Table IX. THERM HYSTERESIS Sample Values

THERM HYSTERESIS

Binary Representation

0°C

1°C

10°C

0 000 0000

0 000 0001

0 000 1010

SENSOR FAULT DETECTION

At the D+ input the ADM1032 has a fault detector that detects

if the external sensor diode is open-circuit. This is a simple

voltage comparator that trips if the voltage at D+ exceeds VDD –

1 V (typical). The output of this comparator is checked when a

conversion is initiated, and sets Bit 2 of the Status Register if a

fault is detected.

If the remote sensor voltage falls below the normal measuring

range, for example due to the diode being short-circuited, the

ADC will output –128 (1000 0000). Since the normal operating

temperature range of the device only extends down to 0°C, this

output code should never be seen in normal operation, so it can

be interpreted as a fault condition. Since it will be outside the

power-on default low temperature limit (0°C) and any low limit

that would normally be programmed, a short-circuit sensor will

cause an SMBus alert.

In this respect the ADM1032 differs from and improves upon,

competitive devices that output zero if the external sensor goes

short-circuit. These devices can misinterpret a genuine 0°C

measurement as a fault condition.

When the D+ and D– lines are shorted together, an ALERT

will always be generated. This is because the remote value regis-

ter reports a temperature value of –128°C. Since the ADM1032

performs a less-than or equal-to comparison with the low limit,

an ALERT is generated even when the low limit is set to its

minimum of –128°C.

–10–

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