4 temperature sensor -34, 4 temperature sensor – Maxim Integrated MAXQ7666 User Manual
Page 124
MAXQ7665/MAXQ7666 User’s Guide
3-34
3.4 Temperature Sensor
The MAXQ7665/MAXQ7666 support an internal temperature sensor for local die temperature measurement and a remote temperature
sensor drive to measure outside temperature. The internal temperature sensor performs local die temperature measurements with an
internal diode-connected transistor. In the remote temperature sensor drive configuration, the device provides the proper bias neces-
sary to measure outside temperature with up to two external diode-connected transistor sensors. Figure 3-14 shows a simplified func-
tional block diagram of the MAXQ7665/MAXQ7666 temperature sensor.
The MAXQ7665/MAXQ7666 perform temperature measurement by measuring the voltage across a diode-connected transistor (inter-
nal or remote) at two different current levels. The following equation illustrates the algorithm used for temperature calculations:
Temperature = (V
HIGH
- V
LOW
) x (q/k) / (n x ln[I
HIGH
/ I
LOW
])
Where:
V
HIGH
= sensor-diode voltage with high current flowing (I
HIGH
)
V
LOW
= sensor-diode voltage with low current flowing (I
LOW
)
q = charge of electron = 1.602 x 10
-19
coulombs
k = Boltzman constant = 1.38 x 10
-23
J/K
n = ideality factor (slightly greater than 1)
The temperature measurement process is fully automated in the MAXQ7665/MAXQ7666 ROM utility routine "tempConv." All the required
setup and temperature measurement algorithm steps for both internal and external temperature measurements are handled in the utili-
ty routine and it returns the local or remote temperature result. See the utility ROM section (
Sections 15 and 16) for details of the routine.
Figure 3-14. MAXQ7665/MAXQ7666 Temperature Sensor Block Diagram
AIN15
AIN4
DEMUX
ADCMX2
ADCMX2
2N3904
RESISTORS
OPTIONAL
ADCMX3
ADCMX1
ADCMX1
ADCMX4
AGND
0
1
2
3
4
ADCMX
12-BIT ADC
500ksps
AGND
AIN3
AIN1
AIN0
AIN2
ADCDIF
MAXQ7665/
MAXQ7666
Maxim Integrated