ZUSBOPTSC01ZACG datasheet(161/282 Pages) ZILOG

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PS022827-1212

P R E L I M I N A R Y

Temperature Sensor

Z8 Encore! XP® F082A Series

Product Specification

144

Temperature Sensor

The on-chip Temperature Sensor allows you to measure temperature on the die with either

the on-board ADC or on-board comparator. This block is factory calibrated for in-circuit

software correction. Uncalibrated accuracy is significantly worse, therefore the tempera-

ture sensor is not recommended for uncalibrated use.

Temperature Sensor Operation

The on-chip temperature sensor is a Proportional to Absolute Temperature (PTAT) topol-

ogy. A pair of Flash option bytes contain the calibration data. The temperature sensor can

be disabled by a bit in the Power Control Register 0 section on page 33 to reduce power

consumption.

The temperature sensor can be directly read by the ADC to determine the absolute value of

its output. The temperature sensor output is also available as an input to the comparator for

threshold type measurement determination. The accuracy of the sensor when used with the

comparator is substantially less than when measured by the ADC.

If the temperature sensor is routed to the ADC, the ADC must be configured in unity-gain

buffered mode (for details, see the Input Buffer Stage section on page 133). The value read

back from the ADC is a signed number, although it is always positive.

The sensor is factory-trimmed through the ADC using the external 2.0 V reference. Unless

the sensor is retrimmed for use with a different reference, it is most accurate when used

with the external 2.0 V reference.

Because this sensor is an on-chip sensor, Zilog recommends that the user account for the

difference between ambient and die temperature when inferring ambient temperature con-

ditions.

During normal operation, the die undergoes heating that causes a mismatch between the

ambient temperature and that measured by the sensor. For best results, the Z8 Encore! XP

device must be placed into STOP Mode for sufficient time such that the die and ambient

temperatures converge (this time is dependent on the thermal design of the system). The

temperature sensor measurement must then be made immediately after recovery from

STOP Mode.

The following equation defines the transfer function between the temperature sensor out-

put voltage and the die temperature. This is needed for comparator threshold measure-

ments.

0.01

0.65



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