LM98640CVAL datasheet(29/55 Pages) TI2

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LM98640QML-SP

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SNAS461G – MAY 2010 – REVISED NOVEMBER 2018

Product Folder Links: LM98640QML-SP

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Feature Description (continued)

(1)

Referred to Input

7.3.4 Programmable Analog Offset Correction

The LM98640QML-SP provides two analog DACs per channel to provide flexibility in offset control. Each channel

has a Coarse DAC and Fine DAC which have ±8-bit resolutions (8 bit + Sign). The two DACs can be used

independently or as Coarse/Fine configuration. The Coarse DAC provides a sufficient range with moderate step

sizes, while the Fine DAC is for designs which need a finely tuned offset. The correction voltage is applied to the

"Video" level for both Sample & Hold and CDS input modes. Because of the DACs location in the signal path, the

correction range lowers as CDS gain increases, and the output referred correction steps and ranges increase

with PGA gain. Table 1 provides the range and step size of each DAC.

Table 1. Analog Offset DAC Specifications

CDS/SH GAIN

RANGE(1)

STEP SIZE(1)

OUTPUT ADC CODES

Coarse DAC

±250 mV

1 mV

±2048

±125 mV

500 µV

±2048

Fine DAC

±5 mV

20 µV

±41

±2.5 mV

10 µV

±41

To use the Offset Correction DACs, the Coarse DAC and Fine DAC must be enabled using bits[6:5] of the Main

Configuration Register (0x00). Then the desired correction value should be entered into the CDAC or FDAC

in Table 2.

Table 2. Analog Offset Correction DAC Format

CDAC / FDAC INPUT VALUE

CDAC CORRECTION (CODES)

FDAC CORRECTION (CODES)

1 1111 1111

+2048

+41

1 0111 1111

+1024

+20

0 1111 1111

0 0111 1111

–1024

–20

0 0000 0000

–2048

–41

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