ZAMC4100 datasheet(84/156 Pages) RENESAS

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ZAMC4100 Datasheet

January 26, 2016

3.12.4. ADC Voltage References and Result Calculation

The ZAMC4100 ADC features different reference sources depending on the configured measurement mode. The

reference voltage is automatically selected depending on the INPSEL setting and the analog inputs configuration

(AINCONF register; Table 3.32). These settings also configure the result interpretation as described below.

Note: In the following descriptions of the measurement options, the coefficients CSR_X, IREF, VREF and Vt27 can

vary from chip to chip. If more precise calculations are needed their factory-trimmed values can be obtained from

the MCU FLASH memory (refer to section 4.2.3); otherwise the default values from Table 1.8, Table 1.11, and

Table 1.12 are used.

Ratiometric measurement

In the ratiometric measurement mode, the reference voltage for the ADC is the voltage between the S_P and S_N

sensor pins. The result of the ADC conversion is calculated as the RATIO of the voltage between the S_P, S_N

pins and the voltage at input AINx:

(

)

RATIO

RESCODE

100

210 −

∗

Depending on the application requirements, the result format can be configured as signed or unsigned. For

example, the signed ratiometric result can be used for position adjusting while the unsigned result format is

convenient for level measurement.

Absolute voltage measurement

The absolute voltage measurement mode is used for analog inputs measurement, for system supply measure-

ment (the voltage at VDDE pin), and for the EC_M pin diagnostic measurement (see Table 3.36). In this case, the

reference voltage for the ADC is provided by the internal reference source (VREF) with the value that is specified in

Table 1.12. The formula used for result calculation is

]

[

]

[

AINx

RESCODE

REF

∗

For VDDE measurements, the equation is:

[V]

VDDE[V]

RESCODE

REF

∗

210

Absolute current measurement

This measurement is for internal channels associated with half-bridge and high-side drivers. The equation below

represents a current measurement in RESCODE (unsigned) after internal translation using two constants:

CSR_X = Current Sense Ratio Coefficient (specified for each high-side and half bridge driver in Table 1.8)

IREF = Calibrated internal reference current as specified in Table 1.12 (typically 10µA)

]

[

]

[

CSR

RESCODE

REF

∗

Where IIN = Input current up to full-scale range equal to (CSR_X Û IREF)

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