ASC7521A 查看數據表（PDF） - Unspecified

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ASC7521A

LOW- OLTAGE 1-WIRE DIGITAL TEMPERATURE SENSOR

Unspecified 

aSC7521A

Values that would represent temperatures below -273.15°C (0

K or absolute zero) are reserved and are not be returned

except as specifically noted.

For the aSC7521A the required resolution is 0.125°C. Bits

[2:0] will be defined but they are beyond the required

resolution. The sign bit will indicate a negative temperature

except when reporting an error condition (see Sensor Error

Condition).

Temperature

80°C

79.875°C

1°C

0°C

-1°C

-5°C

2’s complement representation

0001 0100 0000 0000

0001 0011 1111 1000

0000 0000 0100 0000

0000 0000 0000 0000

1111 1111 1100 0000

1111 1110 1100 0000

Table 1. Temperature Representation

Sign

Integer Temperature 0°C to 512°C

15 14 13 12 11 10 9 8 7

Fractional

Temperature

LSB 0.125°C

6●5 4 3

Always Zero

210

Figure 2. Temperature Reading

A to D Converter Resolution and Mapping

The mapping of the A-D converter bit values is a two’s

complement representation with the binary point between bits

5 and 6 of the 16-bit data word. Bit 15 is the sign, bits 14

through 6 are integer temperature in degrees, bits 5 down to

3 are the fractional part with 0.125°C as the LSB. The lowest

3 bits are set to zero.

Temperature Inputs

The simple temperature sensor has an internal thermal

sensor plus an external sensor using a remote diode. Both

temperature readings are internally corrected for lead

resistance and non-ideality for the thermal diode of a

Pentium™ 4, 65nM process (1.009 non-ideality, 4.35Ω lead

resistance). The range of measurement currents falls within

the Intel recommended range of 10μA and 170μA to

minimize the impact of Beta variation in the CPU substrate

thermal diode. Note that Pentium 4, 90 nM process is 1.011

non-ideality and series resistance of 3.33Ω.

If a diode connected discrete transistor is used instead of a

CPU diode, a correction must be applied to the reading to

compensate for the difference in non-ideality. A 2N3904 NPN

transistor has a non-ideality (η) factor of approximately 1.04.

To correct the value reported to the actual temperature use

the following formula:

TACTUAL = TREPORTED x ηTransistor / 1.009

It is recommended that the actual transistor type and

manufacturers chosen for the remote sensor be

characterized for non-ideality as part of system qualification.

Sensor Error Condition

The aSC7521A has the capability to detect and report open

or shorted external diode inputs per Sensor Error Condition.

When an error or failure condition is detected, the sensor

device must return a large negative value in response to

either the GetIntTemp() or GetExtTemp() command. In this

manner software is provided with a means to determine

whether or not the sensor is working normally and that the

data returned is good.

The aSC7521A will write one of the values from the table

below to appropriate memory locations for GetIntTemp()

and/or GetExtTemp().

The aSC7521A uses the OEM defined values of 0x8102

(open) and 0x8103 (short) rather than the generic errors

defined for codes 0x8000 to 0x8003.

Error Code

0x8000 to 0x80FF

0x8102

0x8103

0x8100-0x81FF

Description

Reserved

Remote Diode Open

Remote Diode Short

Reserved

Table 2. Error Codes

© Andigilog, Inc. 2006

-5-

www.andigilog.com

October 2006 - 70A05011

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