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ASC7531A

LOW-VOLTAGE 1-WIRE DIGITAL TEMPERATURE SENSOR AND VOLTAGE MONITOR

Unspecified 

aSC7531A / aSC7531B

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 aSC7531 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

Figure 2. Temperature Reading

Always Zero

210

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 aSC7531A has an internal thermal sensor plus an

external sensor using a remote diode. The remote sensor is

calibrated for a 2N3904 NPN transistor that has a non-

ideality (η) factor of approximately 1.0046. Use of the remote

diode is discussed in the Applications Information section.

The aSC7531 will write one of the values from the table

below to appropriate memory locations for GetIntTemp()

and/or GetExtTemp().

The aSC7531 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

The aSC7531B also has an internal thermal sensor plus an

external sensor using a remote diode however the remote

sensor is calibrated for an Intel CPU (Pentium 4, 65nM) that

has a non-ideality (η) factor of approximately 1.009. Use of

the remote diode is discussed in the Applications Information

section.

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 aSC7531 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.

Voltage Data

Accuracy and Resolution

The aSC7531 measures the following voltages:

• Measured voltages:

o 12V

o 5V

o 3.3V

o 2.5V

o VCCP

• Measurement Error: +/- 2% of full scale

• Resolution: 7.8 mV

Voltage Data Format

The data format used to report voltage allows values in the

range of +/-32V. The voltage sensor data is returned as a 16-

bit 2’s complement binary value. It represents the number of

1/1024 volts in the reading if extended the full 16-bits. This

allows voltages to be represented with approximately a 1mV

resolution.

© Andigilog, Inc. 2006

-5-

www.andigilog.com

December 2006 - 70A05012

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