ADT7461AR-REEL View Datasheet(PDF) - Analog Devices

Part Name

Description

Manufacturer

ADT7461AR-REEL

±1°C Temperature Monitor with Series Resistance Cancellation

Analog Devices 

The user may switch between measurement ranges at any time.

Switching the range will also switch the data format. The next

temperature result following the switching will be reported back

to the register in the new format. However, the contents of the

limit registers will not change. It is up to the user to ensure that

when the data format changes, the limit registers are repro-

grammed as necessary. More information on this can be found

in the Limit Registers section.

ADT7461 REGISTERS

The ADT7461 contains 22 8-bit registers in total. These regis-

ters are used to store the results of remote and local temperature

measurements and high and low temperature limits and to confi-

gure and control the device. A description of these registers fol-

lows. Additional details are given in Table 7 through Table 11.

Address Pointer Register

The address pointer register itself does not have or require an

address, as the first byte of every write operation is automa-

tically written to this register. The data in this first byte always

contains the address of another register on the ADT7461, which

is stored in the address pointer register. It is to this register

address that the second byte of a write operation is written to or

to which a subsequent read operation is performed.

The power-on default value of the address pointer register is

0x00, so if a read operation is performed immediately after

power-on, without first writing to the address pointer, the value

of the local temperature will be returned, since its register

address is 0x00.

Temperature Value Registers

The ADT7461 has three registers to store the results of local and

remote temperature measurements. These registers can only be

written to by the ADC and can be read by the user over the

SMBus. The local temperature value register is at Address 0x00.

The external temperature value high byte register is at

Address 0x01, with the low byte register at Address 0x10.

The power-on default for all three registers is 0x00.

Configuration Register

The configuration register is Address 0x03 at read and Address

0x09 at write. Its power-on default is 0x00. Only four bits of the

configuration register are used. Bits 0, 1, 3, and 4 are reserved

and should not be written to by the user.

Bit 7 of the configuration register is used to mask the ALERT

output. If Bit 7 is 0, the ALERT output is enabled. This is the

power-on default. If Bit 7 is set to 1, the ALERT output is

disabled. This only applies if Pin 6 is configured as ALERT. If

Pin 6 is configured as THERM2, then the value of Bit 7 has no

effect.

ADT7461

If Bit 6 is set to 0, which is power-on default, the device is in

operating mode with the ADC converting. If Bit 6 is set to 1, the

device is in standby mode and the ADC does not convert. The

SMBus does, however, remain active in standby mode, so values

can be read from or written to the ADT7461 via the SMBus in

this mode. The ALERT and THERM outputs are also active in

standby mode. Changes made to the registers in standby mode

that affect the THERM or ALERT outputs will cause these

signals to be updated.

Bit 5 determines the configuration of Pin 6 on the ADT7461. If

Bit 5 is 0, (default) then Pin 6 is configured as an ALERT output.

If Bit 5 is 1, then Pin 6 is configured as a THERM2 output. Bit 7,

the ALERT mask bit, is only active when Pin 6 is configured as

an ALERT output. If Pin 6 is setup as a THERM2 output, then

Bit 7 has no effect.

Bit 2 sets the temperature measurement range. If Bit 2 is 0

(default value), the temperature measurement range is set

between 0°C to +127°C. Setting Bit 2 to 1 means that the

measurement range is set to the extended temperature range.

Table 7. Configuration Register Bit Assignments

Bit Name

Function

Power-On

Default

7

MASK1

0 = ALERT Enabled

1 = ALERT Masked

0

6

RUN/STOP

0 = Run

1 = Standby

0

5

ALERT/THERM2

0 = ALERT

1 = THERM2

0

4–3 Reserved

0

2

Temperature

Range Select

0 = 0°C to 127°C

1 = Extended Range

0

1–0 Reserved

0

Conversion Rate Register

The conversion rate register is Address 0x04 at read and

Address 0x0A 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 0x0A) to 16 seconds

(Code 0x00). For example, a conversion rate of 8 conversions

per 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 0x08, giving a rate of

16 conversions per second. Use of slower conversion times

greatly reduces the device power consumption, as shown

in Table 8.

Rev. A | Page 11 of 24

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