Z8F042AHJ020SG Datasheet, PDF (161/282 Pages) Zilog, Inc. – High-Performance 8-Bit Microcontrollers

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.
V = 0.01  T + 0.65
PS022827-1212
PRELIMINARY
Temperature Sensor