ADT7461AR datasheet(12/24 Pages) AD

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ADT7461

Table 7. Configuration Register Bit Assignments

Bit

Name

Function

Power-On

Default

MASK1

0 = ALERT Enabled

1 = ALERT Masked

RUN/STOP

0 = Run

1 = Standby

ALERT/THERM2

0 = ALERT

1 = THERM2

4–

Reserved

Temperature

Range Select

0 = 0°C to 127°C

1 = Extended

Range

1–

Reserved

Conversion Rate Register

The conversion rate register is Address 0×04 at read and

Address 0×0A at write. The lowest four bits of this register are

used to program the conversion rate by dividing the internal

oscillator clock by 1, 2, 4, 8, 16, 32, 64, 128, 256, 512, or 1024 to

give conversion times from 15.5 ms (Code 0×0A) to 16 seconds

(Code 0×00). For example, a conversion rate of 8 conver-

sions/second means that beginning at 125 ms intervals the

device performs a conversion on the internal and the external

temperature channels.

This register can be written to and read back over the SMBus.

The higher four bits of this register are unused and must be set

to 0. The default value of this register is 0×08, giving a rate of 16

conversions per second. Use of slower conversion times greatly

reduces the device power consumption, as shown in

Table 8

Table 8. Conversion Rate Register Codes

Code

Conversion/Second

Average Supply

Current µA Typ

at VDD = 5.5 V

0×00

0.0625

121.33

0×01

0.125

128.54

0×02

0.25

131.59

0×03

0.5

146.15

0×04

169.14

0×05

233.12

0×06

347.42

0×07

638.07

0×08

252.44

0×09

417.58

0×0A

816.87

0×0B to 0×FF

Reserved

Limit Registers

The ADT7461 has eight limit registers: high, low, and THERM

temperature limits for both local and remote temperature

measurements. The remote temperature high and low limits

span two registers each, to contain an upper and lower byte for

each limit. There is also a THERM hysteresis register. All limit

registers can be written to and read back over the SMBus. See

for details of the limit registers’ addresses and their

power-on default values.

Table 12

When Pin 6 is configured as an ALERT output, the high limit

registers perform a > comparison while the low limit registers

perform a ≤ comparison. For example, if the high limit register

is programmed with 80°C, then measuring 81°C will result in an

out-of-limit condition, setting a flag in the status register. If the

low limit register is programmed with 0°C, measuring 0°C or

lower will result in an out-of-limit condition.

Exceeding either the local or remote THERM limit asserts

THERM low. When Pin 6 is configured as THERM2, exceeding

either the local or remote high limit asserts THERM2 low. A

default hysteresis value of 10°C is provided that applies to both

THERM channels. This hysteresis value may be reprogrammed

to any value after power up (Register Address 0×21).

It is important to remember that the temperature limits data

format is the same as the temperature measurement data

format. So if the temperature measurement uses default binary,

then the temperature limits also use the binary scale. If the

temperature measurement scale is switched, however, the

temperature limits do not switch automatically. The user must

reprogram the limit registers to the desired value in the correct

data format. For example, if the remote low limit is set at 10°C

and the default binary scale is being used, the limit register

value should be 0000 1010b. If the scale is switched to offset

binary, the value in the low temperature limit register should be

reprogrammed to be 0100 1010b.

Status Register

The status register is a read-only register, at Address 0×02. It

contains status information for the ADT7461.

Bit 7 of the status register indicates that the ADC is busy con-

verting when it is high. The other bits in this register flag the

out-of-limit temperature measurements (Bits 6–3 and Bits 1–0)

and the remote sensor open circuit (Bit 2).

If Pin 6 is configured as an ALERT output, the following applies. If

the local temperature measurement exceeds its limits, Bit 6 (high

limit) or Bit 5 (low limit) of the status register asserts to flag this

condition. If the remote temperature measurement exceeds its lim-

its, then Bit 4 (high limit) or Bit 3 (low limit) asserts. Bit 2 asserts to

flag an open-circuit condition on the remote sensor. These five flags

are NOR’d together, so if any of them is high, the ALERT interrupt

latch will be set and the ALERT output will go low.

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