ASC7531A ETC2 [List of Unclassifed Manufacturers], ASC7531A Datasheet - Page 4

• Manufacturer Part Number: ASC7531A
• Description: LOW-VOLTAGE 1-WIRE DIGITAL TEMPERATURE SENSOR AND VOLTAGE MONITOR
• Manufacturer: ETC2 [List of Unclassifed Manufacturers]

SST Sensors
The SST voltage and temperature sensor provides a means for
an analog signal to travel over a single-wire digital bus
enabling remote voltage and temperature sensing in areas
previously not monitored in the PC. The temperature sensor
supports an internal temperature sensor and external thermal
diodes.
This section outlines general requirements for Simple Serial
Transport (SST) sensors intended for use in PC desktop
applications that conform to SST Version 1.0 specification.
The aSC7531 is a Combination Voltage and Temperature
Sensor. It reports external temperature sensed by a remote
diode-connected transistor and an internal temperature
measurement. It also has five voltage measurements: 2.5V,
3.3V, 5V, 12V, and V
Addressing
The aSC7531 complies with the address range set aside for
fixed-address, discoverable devices as defined in the SST
Specification Version 1.0. Combination voltage and
temperature sensors use fixed addresses in the range of 0x48
to 0x4A. The aSC7531 may be programmed to any of these
addresses via the address select pin AD0.
Frame Check Sequence (FCS)
Each message requires a frame check sequence byte to
ensure reliable data exchange between host and client. The
message originator and client both make an FCS calculation.
One FCS byte must be returned from the message target to
the originator after all bytes including the header and the data
block are written. If data is read from the target, a second FCS
byte must follow the data block read.
The FCS byte is the result of an 8-bit cyclic redundancy check
(CRC) of the each data block preceding the FCS up to the
most recent, earlier FCS byte. The first FCS in the message
does not include the two address timing negotiation ‘0’ bits that
precede the address byte or the message timing negotiation bit
after the address byte. The first FCS does include the address
byte in its computation. The FCS is initialized at 0x00 and is
calculated in a way that conforms to a CRC-8 represented by
the CRC polynomial, C(x) = x
Bus Voltage
All SST sensor devices used for PC applications must be
capable of operating the SST interface portion of the sensor
device at 1.5 volts as defined in 1.5 Volt Static (DC)
Characteristics section of the SST Version 1.0 specification
Bus Timing
All SST sensor devices must be able to negotiate timing and
operate at a maximum bus transfer rate of 2-Mbps. If the bus
address timing is negotiated at a lower rate due to the
performance limitations of other devices on the bus, the sensor
device will operate at that lower rate.
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Device Power-on Timing
Following a power-on reset, such as a system transitioning
from S3-S5 to S0, the aSC7531 will be able to participate in
the address and message timing negotiation and respond to
required SST bus commands such as respond to a GetDIB()
command within 10ms of the device’s V
The aSC7531 has an internal power on reset and will be fully
functional within 50ms of power on.
The aSC7531 does not employ any device power
management.
Voltage and Temperature Sensor Data
Little Endian Format
The bit level transfer is defined in the SST specification. The 2-
byte data values are returned in little Endian format, in other
words, the LSB is sent first followed by MSB.
For multi-function devices that allow access to multiple
sensors, the data is returned LSB followed by the MSB for the
first sensor, LSB followed by the MSB for the second sensor,
and so on. The specific order is explicitly specified in the
command description.
Atomic Readings
The aSC7531 ensures that every value returned is derived
from a single analog to digital conversion and is not skewed
(e.g. the MSB and the LSB come from two different
conversions).
Conversion Time
The maximum refresh time for all voltage and temperature
values is 200ms. The aSC7531 provides the logic to ensure all
readings meet the conversion time requirements.
There are 7 channels (5 voltage and 2 temperature) channels
which must be measured every 250ms.
Temperature Data
Data Precision, Accuracy and Resolution
The temperature data meets the following minimum
requirements:
Temperature Data Format
The data format is capable of reporting temperature values in
the range of +/-512°C. The temperature sensor data is
returned as a 2’s complement 16-bit binary value. It represents
the number of 1/64°C increments in the actual reading. This
allows temperatures to be represented with approximately a
0.016°C resolution.
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Operational Range: -40°C to +125°C
Internal Sensor Accuracy:
Remote Sensor Accuracy (when TA is from 0°C to
70°C):
Resolution: 0.125°C
o
o
o
o
aSC7531A / aSC7531B
+/- 3°C over operational range
+/- 2°C over 40°C to 70°C
+/- 3°C over operational range
+/- 1°C over 50°C to 70°C
December
DD
rail reaching 90%.
2006 - 70A05012