Z8F021ASH020SC datasheet(153/276 Pages) ZILOG

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PS022815-0206

Temperature Sensor

Z8 Encore! XP® 4K Series

Product Specification

134

Temperature Sensor

Overview

The on-chip Temperature Sensor allows the user the ability 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 temperature sensor is not recommended for uncalibrated use.

Temperature Sensor Operation

The on-chip temperature sensor is a PTAT (proportional to absolute temperature) topology.

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 (page 30) 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 (See Input Buffer Stage on page 122.) 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 2.0V reference. Unless

the sensor is re-trimmed for use with a different reference, it is most accurate when used

with the external 2.0V reference.

Because this sensor is an on-chip sensor it is recommended 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 will cause a mismatch between

the ambient temperature and that measured by the sensor. For best results, the XP device

should be placed into STOP mode for sufficient time such that the die and ambient tem-

peratures converge (this time will be dependent on the thermal design of the system). The

temperature sensor measurement should 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.

V = 0.01 * T + 0.65 (where T is the temperature in C; V is the sensor output in Volts)

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