ADT7461AARMZ datasheet(14/24 Pages) AD

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ADT7461A

Rev. A | Page 14 of 24

When Flag 1 and/or Flag 0 are set, the THERM output goes low

to indicate that the temperature measurements are outside the

programmed limits. The THERM output does not need to be

reset, unlike the ALERT output. Once the measurements are

within the limits, the corresponding status register bits are

automatically reset and the THERM output goes high. The user

may add hysteresis by programming Register 0x21. The THERM

output is reset only when the temperature falls to limit value

minus the hysteresis value.

When Pin 6 is configured as THERM2, only the high tempera-

ture limits are relevant. If Flag 6 and/or Flag 4 are set, the

THERM2 output goes low to indicate that the temperature

measurements are outside the programmed limits. Flag 5 and

Flag 3 have no effect on THERM2. The behavior of THERM2 is

otherwise the same as THERM.

Table 11. Status Register Bit Assignments

Bit

Name

Function

BUSY

1 when ADC converting

LHIGH1

1 when local high temperature limit tripped

LLOW1

1 when local low temperature limit tripped

RHIGH1

1 when remote high temperature limit tripped

RLOW1

1 when remote low temperature limit tripped

OPEN1

1 when remote sensor open circuit

RTHRM

1 when remote THERM limit tripped

LTHRM

1 when local THERM limit tripped

1 These flags stay high until the status register is read or they are reset by POR

unless Pin 6 is configured as THERM2. Then, only Bit 2 remains high until the

status register is read or is reset by POR.

Offset Register

Offset errors can be introduced into the remote temperature

measurement by clock noise or when the thermal diode is

located away from the hot spot. To achieve the specified

accuracy on this channel, these offsets must be removed.

The offset value is stored as a 10-bit, twos complement value in

justified). Only the upper two bits of Register 0x12 are used.

The MSB of Register 0x11 is the sign bit. The minimum,

programmable offset is −128°C, and the maximum is

+127.75°C. The value in the offset register is added to, or

subtracted from, the measured value of the remote temperature.

The offset register powers up with a default value of 0°C and has

no effect unless the user writes a different value to it.

Table 12. Sample Offset Register Codes

Offset Value

0x11

0x12

−128°C

1000 0000

00 00 0000

−4°C

1111 1100

00 00 0000

−1°C

1111 1111

00 00 0000

−0.25°C

1111 1111

11 00 0000

0°C

0000 0000

00 00 0000

+0.25°C

0000 0000

01 00 0000

+1°C

0000 0001

00 00 0000

+4°C

0000 0100

00 00 0000

+127.75°C

0111 1111

11 00 0000

One-Shot Register

The one-shot register is used to initiate a conversion and

comparison cycle when the ADT7461A is in standby mode,

after which the device returns to standby. Writing to the one-

shot register address (0x0F) causes the ADT7461A to perform a

conversion and comparison on both the internal and the

external temperature channels. This is not a data register as

such, and it is the write operation to Address 0x0F that causes

the one-shot conversion. The data written to this address is

irrelevant and is not stored.

Consecutive ALERT Register

The value written to this register determines how many out-of-

limit measurements must occur before an ALERT is generated.

The default value is that one out-of-limit measurement generates

an ALERT. The maximum value that can be chosen is 4. The

purpose of this register is to allow the user to perform some

filtering of the output. This is particularly useful at the fastest

three conversion rates, where no averaging takes place. This

Table 13. Consecutive ALERT Register Bit

Number of Out-of-Limit

Measurements Required

yxxx 000x

yxxx 001x

yxxx 011x

yxxx 111x

1 x = don’t care bit.

y = SMBus timeout bit.

Default = 0. See the Serial Bus Interface section.

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