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)
PS022815-0206
Temperature Sensor
ZILOG [ ZILOG, INC. ]
