ADT7483A(2012) Ver la hoja de datos (PDF) - ON Semiconductor

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ADT7483A
(Rev.:2012)

Dual Channel Temperature Sensor and Over Temperature Alarm

ON Semiconductor 

ADT7483A

remains low, the master will send the ARA again,

and so on, until all devices whose ALERT outputs

were low have responded.

Masking the ALERT Output

The ALERT output can be masked for local, Remote 1,

Remote 2, or all three channels. This is done by setting the

appropriate mask bits in either the Configuration 1 register

(read address = 0x03, write address = 0x09) or in the

consecutive ALERT register (address = 0x22)

To mask ALERTs due to local temperature, set Bit 5 of the

consecutive ALERT register to 1. Default = 0.

To mask ALERTs due to Remote 1 temperature, set Bit 1 of

the Configuration 1 register to 1. Default = 0.

To mask ALERTs due to Remote 2 temperature, set Bit 0 of

the Configuration 1 register to 1. Default = 0.

To mask ALERTs due to any channel, set Bit 7 of the

Configuration 1 register to 1. Default = 0.

Low Power Standby Mode

The ADT7483A can be put into low power standby mode

by setting Bit 6 (Mon/STBY bit) of the Configuration 1

register (read address = 0x03, write address = 0x09) to 1.

When Bit 6 is 0, the ADT7483A operates normally. When

Bit 6 is 1, 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 5 mA.

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

initiate a one-shot conversion of both channels by writing to

the oneshot register (Address 0x0F), after which the device

will return to standby. It does not matter what is written to

the one-shot register, all data written to it is ignored.

It is also possible to write new values to the limit register

while in standby mode. If the values stored in the

temperature value registers are now outside the new limits,

an ALERT is generated, even though the ADT7483A is still

in standby.

Sensor Fault Detection

The ADT7483A has internal sensor fault detection

circuitry located at its D+ input. This circuit can detect

situations where a remote diode is not connected, or is

incorrectly connected, to the ADT7483A. A simple voltage

comparator trips if the voltage at D+ exceeds VDD − 1 V

(typical), signifying an open circuit between D+ and D−.

The output of this comparator is checked when a conversion

is initiated. Bit 2 (D1 OPEN flag) of the Status Register 1

(Address 0x02) is set if a fault is detected on the Remote 1

channel. Bit 2 (D2 OPEN flag) of the Status Register 2

(Address 0x23) is set if a fault is detected on the Remote 2

channel. If the ALERT pin is enabled, setting this flag will

cause ALERT to assert low.

If a remote sensor is not used with the ADT7483A, then

the D+ and D− inputs of the ADT7483A need to be tied

together to prevent the OPEN flag from being continuously

set.

Most temperature sensing diodes have an operating

temperature range of −55C to +150C. Above 150C, they

lose their semiconductor characteristics and approximate

conductors instead. This results in a diode short, setting the

OPEN flag. The remote diode in this case no longer gives an

accurate temperature measurement. A read of the

temperature result register will give the last good

temperature measurement. The user should be aware that,

while the diode fault is triggered, the temperature

measurement on the remote channels may not be accurate.

Interrupt System

The ADT7483A has two interrupt outputs, ALERT and

THERM. Both outputs have different functions and

behavior. ALERT is maskable and responds to violations of

software programmed temperature limits or an open-circuit

fault on the remote diode. THERM is intended as a fail-safe

interrupt output that cannot be masked.

If the Remote 1, Remote 2, or local temperature exceeds

the programmed high temperature limits, or equals or

exceeds the low temperature limits, the ALERT output is

asserted low. An open-circuit fault on the remote diode also

causes ALERT to assert. ALERT is reset when serviced by

a master reading its device address, provided the error

condition has gone away and the status register has been

reset.

Similarly, the THERM output asserts low if the Remote 1,

Remote 2, or local temperature exceeds the programmed

THERM limits. The THERM temperature limits should

normally be equal to or greater than the high temperature

limits. THERM is automatically reset when the temperature

falls back within the (THERM − Hysteresis) limit. The local

and remote THERM limits are set by default to 85C. An

hysteresis value can be programmed, in which case,

THERM resets when the temperature falls to the limit value

minus the hysteresis value. This applies to both local and

remote measurement channels. The power-on hysteresis

default value is 10C, but this may be reprogrammed to any

value after power-up.

The hysteresis loop on the THERM outputs is useful when

THERM is used for on/off control of a fan. The user’s

system can be set up so that when THERM asserts, a fan can

be switched on to cool the system. When THERM goes high

again, the fan can be switched off. Programming an

hysteresis value protects from fan jitter, wherein the

temperature hovers around the THERM limit and the fan is

constantly being switched.

Table 18. THERM HYSTERESIS

THERM Hysteresis

Binary Representation

0C

1C

10C

0 000 0000

0 000 0001

0 000 1010

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