MCP3465RT-ESLASHSFX datasheet(55/110 Pages) MICROCHIP

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DS20006414C-page 55

MCP3465R

FIGURE 5-12:

ADC Output and Data Ready Event Behavior with Digital Offset Calibration Enabled.

5.13.2

DIGITAL GAIN ERROR

CALIBRATION

The Gain Error Calibration register (GAINCAL,

address: 0xA) is an unsigned 16-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 MCP3465R device, the gain error calibration is

done by multiplying the GAINCAL value to the ADC

output code. The last byte of the GAINCAL register

(GAINCAL[7:0]) is ignored and internally reset to 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 16-bit

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 Data Ready Event.

FIGURE 5-13:

ADC Output and Data Ready Event Behavior with Digital Gain Error Calibration Enabled.

SPI

Write

EN_OFFCAL =

Data Ready Event

ADC STATUS

Data 2 Conversion

Data 1 Conversion

Data 3 Conversion

ADCDATA

DATA1

DATA0

DATA2 + OFFSETCAL1

Write

OFFSETCAL[23:8] = OFFSETCAL1

Write

OFFSETCAL[23:8] = OFFSETCAL2

Data 4 Conversion

DATA3 + OFFSETCAL2

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

code)/32768

SPI

Write

EN_GAINCAL =

Data Ready Event

ADC STATUS

Data 3 Conversion

DATA1

DATA0

DATA2 x GAINCAL2

Write

GAINCAL[23:8] = GAINCAL1

Write

GAINCAL[23:8] = GAINCAL2

Data 4 Conversion

DATA3 x GAINCAL2

TGCAL

ADCDATA

Data 2 Conversion

Data 1 Conversion

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