MCP3461RT-ESLASHST datasheet(58/118 Pages) MICROCHIP

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MCP3461/2/4R

DS20006404C-page 58

 2020-2021 Microchip Technology Inc.

FIGURE 5-12:

ADC Output and IRQ Behavior with Digital Offset Calibration Enabled.

5.13.2

DIGITAL GAIN ERROR

CALIBRATION

The Gain Error Calibration register (GAINCAL,

address: 0xA) is an unsigned 24-bit register that holds

the digital gain error calibration value, GAINCAL.

Equation 5-8 calculates the GAINCAL multiplier.

EQUATION 5-8:

GAINCAL CALIBRATION

VALUE (MULTIPLIER

VALUE)

For the MCP3461/2/4R devices, the gain error

calibration is done by multiplying the GAINCAL value to

the ADC output code. The last byte of the GAINCAL

0x00 during the calibration; therefore, the multiplication

just takes into account the GAINCAL[23:8] bits.

The gain error calibration value range in equivalent

voltage is [0; 2-2-15], which can cancel any possible

gain error in the ADC and in the system. The gain

error calibration is made with a simple add-and-shift

circuit clocked on DMCLK and induces a pipeline

delay of TGCAL = 15 DMCLK periods. This pipeline

delay acts as a delay on the data ready interrupt

position that is shifted by TGCAL = 15 DMCLK periods.

During this delay, the converter can process the next

conversion, the delay does not shift the next conver-

sion and does not change the Conversion Time,

TCONV. Enabling the gain error calibration will affect

the next conversion result. The conversion result

already held in the ADCDATA register (0x0) is not

modified when the EN_GAINCAL is set to ‘1’, but the

next one will take the offset calibration into account.

Changing the GAINCAL register to a new value will

not affect the current ADCDATA value, but the next

one (after a data ready interrupt) will take the new

GAINCAL value into account. Figure 5-13 shows the

different cases and their associated effects on the

ADCDATA register and the IRQ output.

FIGURE 5-13:

ADC Output and IRQ Behavior with Digital Gain Error Calibration Enabled.

ADC DATA

VALUE

SPI

Wri te

EN _OFFC AL = 1

IRQ

ADC

STATUS

Data 2 Conversion

Data 1 Conversion

Data 3 Conversion

DATA1

DATA0

DATA2 + OFFSETCAL1

Wri te

OFFSE TCA L[2 3 : ] = OFFSE TCA L1

Wri te

OFFSE TCA L[2 3 : ] = OFFSE TCA L2

Data 4 Conversion

DATA3 + OFFSETCAL2

GAINCAL (V/V) = (GAINCAL[23:8] unsigned decimal

code)/32768

SPI

Wri te

EN _GAINCAL = 1

IRQ

ADC

STATUS

Data 3 Conversion

DATA1

DATA0

DATA2 x GAINCAL1

Wri te

GAINCAL[2 3 : ] = GAINCAL1

Wri te

GAINCAL[2 3 : ] = GAINCAL2

Data 4 Conversion

DATA3 x GAINCAL2

TGCAL

ADCDATA

Data 2 Conversion

Data 1 Conversion

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