PGA400-Q1
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SLDS186 –MARCH 2012
NOTE
For capacitive sensors, one common set of configurations registers are implemented. If
different settings are needed for the two capacitive sensors, then the software must
dynamically update the register values.
I
X
I
C
t
-I
C
V
x
3.3
dV
T
x
dt
V
1.65
H
0
t
Figure 6-3. Capacitive Sensor Drive Waveforms
6.5 Internal Temperature Block and External Temperature Sensing
The device has the ability to perform temperature compensation via an internal or external temperature
sensor. The user can select the source of the sensor with the TEMP_SEN bit in the Sensor Control
Register (SENCTRL). When the TEMP_SEN bit is set to "0" the internal temperature sensor is used, and
when the TEMP_SEN bit is set to "1" the external temperature sensor is used. For more information on
programming this device please refer to the PGA400-Q1 Programming Application Note (SLDA015)
6.5.1 Internal Temperature Sensor
The device contains an internal temperature sensor which is converted by an ADC and made available to
the 8051 microprocessor so that appropriate temperature compensation algorithms can be implemented in
software. The nominal relationship between the device temperature and the ADC Code is shown in
Equation 3.
ADC Code = 2.8* TEMP -80, TEMP is temperature in °C.
(3)
6.5.2 External Temperature Sensor
The device accepts a temperature from an external temperature sensor via the VIN3 pin. The input
temperature needs to be in the form of a voltage.
NOTE
The Offset TC block has been configured to operate with the internal temperature sensor
transfer function. If an external temperature sensor is used and the user needs to use Offset
TC compensation, then the temperature-to-voltage transfer function of the external
temperature sensor has to match the transfer function of the internal temperature sensor.
6.6 Using the Analog Front End
The PGA400 can be used to interface with Resistive Bridge Sensors as well as Capacitive Sensors. To
enable multiple sensors of either type a series of muxes are used. These muxes are controlled by the
Sensor Control Register (SENCTRL) and Capacitve Sensor Setting Register (CAPSEN).
Copyright © 2012, Texas Instruments Incorporated
FUNCTIONAL DESCRIPTIONS
15
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