ZAMC4100 datasheet(79/155 Pages) IDT

79 / 155 page

ZAMC4100 Datasheet

January 26, 2016

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

S_P

AINx

S_N

ADC

SPSWEN

VREFP

VREFN

VSSA

VDD5V0

SNSWEN

Signal

Source

AINx

VSSA

Int.Ref

VREF

ADC

VREFP

VREFN

A) External Sensor Supply

C) Absolute Measurement

S_P

AINx

S_N

VSSA

VDD5V0

-VE

+VE

Ratiometric Inputs Configuration

B) Internal Sensor Supply

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

the sensor absolute voltage is measured at the corresponding AINx pin.

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