Z8F1680SH020SG Datasheet, PDF (285/412 Pages) Zilog, Inc. – High-Performance 8-Bit Microcontrollers

Z8 Encore! XP^® F1680 Series
Product Specification
260
Chapter 19. Temperature Sensor
The on-chip Temperature Sensor allows you to measure temperature on the die to an accu-
racy of roughly ±7° C over a range of –40° C to +105° C. Over a reduced range, the accu-
racy is significantly better. This block is a moderately accurate temperature sensor for
low-power applications where high accuracy is not required. Uncalibrated accuracy is sig-
nificantly worse, therefore the temperature sensor is not recommended for untrimmed use:
• 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
19.1. Operation
The on-chip temperature sensor is a Proportional To Absolute Temperature (PTAT) topol-
ogy which provides 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
Register 0 (see page 44) 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. Maximum accuracy can
be obtained by customer retrimming the sensor using an external reference and a high-pre-
cision 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 should be measured immediately after recovery from STOP Mode.
The following two equations define the relationship between the ADC reading and the die
temperature. In each equation, T is the temperature in degrees Celsius, and ADC is the 10-
bit compensated ADC value.
Equation #1. If bit 2 of TEMPCALH calibration option byte is 0, then:
T = (25/128) * (ADC + {TEMPCALH_bit1, TEMPCALH_bit0, TEMPCALL}) – 77
Equation #2. If bit 2 of TEMPCALH calibration option byte is 1, then:
T = (25/128) * (ADC – {TEMPCALH_bit1, TEMPCALH_bit0, TEMPCALL}) –77
PS025015-1212
PRELIMINARY
Temperature Sensor