ZAMC4100 Datasheet, PDF (79/155 Pages) Integrated Device Technology – Actuator and Motor Controller

ZAMC4100 Datasheet
3.12.2. ADC External Inputs Configuration
The external analog inputs AIN1-AIN4 of the ADC can be configured for measurement in ratiometric or absolute
mode or for temperature measurement using internal current sources. All AINx inputs are configured via settings
in the AINCONF register (see Table 3.32 and Table 3.33).
Figure 3.21 Ratiometric versus Absolute Measurement Inputs Configuration
Ratiometric Inputs Configuration
A) External Sensor Supply
B) Internal Sensor Supply
VDD5V0
VDD5V0
+VE
S_P
SPSWEN
S_P
C) Absolute Measurement
Int.Ref
VREF
AINx
S_N
-VE
VSSA
AINx
S_N
VREFP
ADC
VREFN
SNSWEN
VSSA
AINx
Signal
Source
VSSA
VREFP
ADC
VREFN
Ratiometric Measurement on AIN1-AIN4
By default, the analog input pins are configured for ratiometric measurements with the external supply source as
shown in the Figure 3.21-A. The ADC reference inputs are connected to the S_P or S_N pins, which “sense” the
sensor supply voltage and ensure accurate ratiometric conversion results.
The supply switches SPSWEN and SNSWEN are controlled by the AINCONF register. This register will
determine the usage of the external or internal supply source for the sensor and the ADC reference as shown in
Figure 3.21-A and Figure 3.21-B. In general, when the external sensor supply source is used, the measurement
can provide more accurate results because the voltage drop across the connections to the S_P and S_N pins is
negligible due to the very low current through them.
If the signed ADC result mode is used, the sign is determined as positive if the measured voltage is in the upper
half of the voltage difference between S_P and S_N pins and negative if in the lower half.
Absolute Measurement on AIN1-AIN4
Absolute measurement as shown in Figure 3.21-C can be achieved by setting the AINxMD bits in the AINCONF
register (where x = channel 1 to 4). During the absolute measurement, the ADC uses its internal reference and
the sensor absolute voltage is measured at the corresponding AINx pin.
© 2016 Integrated Device Technology, Inc.
79
January 26, 2016