Maxim Integrated MAXQ7666 - Manual (Page 126)

MAXQ7665/MAXQ7666 User’s Guide
3-36
Figure 3-15 shows the nominal transfer function for temperature conversions. Output coding is two’s complement with 1 LSB =
+0.125°C.
3.4.3 Internal Temperature Sensor
The MAXQ7665/MAXQ7666 perform local die temperature measurements with an internal diode-connected transistor. The diode bias
current is changed from 68µA to 4µA (4.096V reference; for 5V use 74.7µA and 4µA) to produce a temperature-dependent bias volt-
age difference. The on-chip ADC is used to measure the voltage generated at different drives. The ADC conversion result at 4µA is
subtracted from the first at 68µA to calculate a digital value that is proportional to absolute temperature. The final result output is the
previously mentioned digital code minus an offset to adjust from Kelvin to Celsius.
The reference voltage used for the temperature measurements is derived from the external ADC reference source to ensure that 1 LSB
corresponds to 1/8th of a degree. The internal temperature sensor does not use any analog input channel.
The temperature measurement process is fully automated in the MAXQ7665/MAXQ7666 ROM utility routine "tempConv." All the required
setup and temperature measurement algorithm steps are handled in the utility routine and it returns the local or remote temperature
result. See the utility ROM section (
Sections 15 and 16) for details of the routine.
3.4.4 Remote Temperature Sensor Driver
The MAXQ7665/MAXQ7666 temperature sensor supports remote temperature sensor driver on two input channels. The device sup-
ports both singled-ended and differential temperature measurements. Remote temperature sensor in differential mode uses analog
input channel pairs AIN2/AIN3 and AIN0/AIN1. In single-ended mode, only channels AIN2 and AIN0 are used. The superior common-
mode rejection and lower noise of the differential mode reduces measurement errors and provides higher accuracy, while single-ended
measurements require a lower number of connections, resulting in a simpler implementation.
Figure 3-15. Temperature Transfer Function
800
801
FFE
001
000
FFF
7FE
7FF
-256 0 +255.875
OUTPUT CODE (hex)
TEMPERATURE ( °C)
Maxim Integrated