ADT7421ARMZ-2RL View Datasheet(PDF) - ON Semiconductor

Part Name

Description

MFG CO.

ADT7421ARMZ-2RL

Precision Temperature Sensor with Beta Compensation (for <45 nm Geometries)

ON Semiconductor 

ADT7421

Offset Register

Offset errors can be introduced into the remote

temperature measurement by clock noise or when the

thermal transistor 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 Register 0x11 (high byte) and Register 0x12 (low

byte, left 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 6. Sample Offset Register Codes

Offset Value

−128°C

−4°C

−1°C

−0.25°C

0°C

+0.25°C

+1°C

+4°C

+127.75°C

0x11

1000 0000

1111 1100

1111 1111

1111 1111

0000 0000

0000 0000

0000 0001

0000 0100

0111 1111

0x12

00 00 0000

00 00 0000

00 00 0000

11 00 0000

00 00 0000

01 00 0000

00 00 0000

00 00 0000

11 00 0000

One−Shot Register

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

comparison cycle when the ADT7421 is in standby mode,

after which the device returns to standby. Writing to the

one−shot register address (0x0F) causes the ADT7421 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 register is at Address 0x22.

Table 7. Consecutive ALERT Register 0x22

Bits

Value†

Number of Out−of−Limit

Measurements Required

<3−0>

000x

1

001x

2

011x

3

111x

4

†x = Don’t care bit.

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