Z8 Encore! XP® F08xA Series
Product Specification
124
Temperature Sensor
Overview
The on-chip Temperature Sensor allows the user the ability to measure temperature on the
die to an accuracy of roughly ±7°C over a range of -40 to +105°C. Over a reduced range,
the accuracy is significantly better. This block is a moderately accurate temperature sensor
for low power applications where high accuracy is not required. Uncalibrated accuracy is
significantly worse, therefore the temperature sensor is not recommended for untrimmed
use.
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On-chip temperature sensor
±7°C full-range accuracy for calibrated version
±1.5°C accuracy over the range of 20°C to 30°C
Flash recalibration capability
Operation
The on-chip temperature sensor is a PTAT (proportional to absolute temperature) topology
which has provision for zero point calibration. A pair of Flash option bytes contain the cal-
ibration data. The temperature sensor can be disabled by a bit in the Power Control Regis-
ter 0 (page 29) 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 115.) The value read back from the ADC
is a signed number, although it is always positive.
Maximum accuracy can be obtained by customer re-trimming the sensor using an external
reference and using a high-precision external reference in the target application.
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.
PS024705-0405
P R E L I M I N A R Y
Temperature Sensor
ZILOG [ ZILOG, INC. ]
