LM98722CCMTSLASHNOPB datasheet(39/150 Pages) TI1

39 / 150 page

LM98722

www.ti.com

SNAS487B – SEPTEMBER 2009 – REVISED MARCH 2015

7.4.12.3 Calibration Initiation

Once these settings have been made, the Register Lock Control bit (Page 0, Register 0, Bit 0) should be set to

begin converting pixels. Once the sensor data from the test image is stable the calibration process can be started

by either setting the CAL register bit at Page 0, Register 0x01h, Bit 5, or by applying a logic high to the CAL input

pin. (Both of these inputs are active when the Register Lock Control is set.) The CAL input pin is particularly

useful for implementing page gap calibration.

7.4.12.4 Key Calibration Settings

Table 8. Key Calibration Settings

General Settings

Calibration Mode

Page 2, Register 0, Bits[1:0]

Black Calibration Only

Black and White Full Calibration

Black and White Fine Tuning:

Number of Lines

Page 2, Register 1

Black Loop Specific Settings

# Black Pixels Averaged

Page 2, Register 2, Bits[1:0]

Black Target

Page 2, Register 3

Black Pixels Start

Page 2, Register 8

ADAC Scaling

Page 2, Register 2, Bits[3:2]

DDAC Scaling

Page 2, Register 2, Bits[5:4]

DDAC enable/disable

Page 2, Register 0, Bit 2

White Loop Specific Settings

White Target

Page 2, Register 5

White Loop Tolerance

Page 2, Register 4, Bits[6:3]

White Pixel Averaging Window Size

Page 2, Register 4, Bits[2:0]

Active/White Pixels Start

Page 2, Registers 0x09h, 0x0Ah

Active/White Pixels End

Page 2, Registers 0x0Bh, 0x0Ch

The calibration loops are intended to be used prior to scanning the page or between pages being scanned. The

black loop calibrates the channel offset such that the ADC outputs the desired code for Optical Black Pixels. The

white loop calibrates the channel gain such that the ADC outputs the desired maximum white value when

scanning a white target image.

The Black Loop and White loop will both update until the # Lines setting is met. Settings of 1 to 254 lines will

cause the loops to run for that many lines, and then stop. A setting of 255 will cause the calibration loops to run

indefinitely.

While using the Auto Black Level Correction Loop, the DAC registers are re-written as required every line the

loop is running.

While using the Auto White Level Correction Loop, the PGA registers are re-written as required every line the

loop is running.

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