ILED = ILED_FULLSCALE x

1

2047

x Code x DPWM

ILED = ILED_FULLSCALE x

1

255

x Code x DPWM

(44 -

)

ILED = ILED_FULLSCALE x 0.85

Code

5.8181818

x DPWM

+ 1

8

(44 -

)

ILED = ILED_FULLSCALE x 0.85

Code + 1

5.8181818

x DPWM

13

LM3697

www.ti.com

SNOSCS2D – NOVEMBER 2013 – REVISED MARCH 2019

Product Folder Links: LM3697

Submit Documentation Feedback

Copyright © 2013–2019, Texas Instruments Incorporated

7.3.8 High-Voltage Control A and B Ramp Select

The LM3697 provides three options for Control A and B ramp times (see Table 8). When the Run-time Ramp

Select bits are set to 00, the control bank uses both the Start-up/Shutdown and Run-time ramp times. When the

Run-time Ramp Select bits are set to 01, the control bank uses the Start-up/Shutdown ramp times for both start-

up/shutdown and run-time. When the Run-time Ramp Select bits are set to 1x the control bank uses a zero µsec

run-time ramp.

7.4 Device Functional Modes

7.4.1 LED Current Mapping Modes

All control banks can be programmed for either exponential or linear mapping modes (see Figure 10 and

Figure 11). These modes determine the transfer characteristic of backlight code to LED current. Independent

mapping of Control Banks A and B is not allowed: both banks uses the same mapping mode.

7.4.1.1 Exponential Mapping

In Exponential Mapping Mode the current ramp (either up or down) appears to the human eye as a more uniform

transition then the linear ramp. This is due to the logarithmic response of the eye.

7.4.1.1.1

8-Bit Code Calculation

In Exponential Mapping Mode the brightness code to backlight current transfer function is given by the equation:

(1)

Where ILED_FULLSCALE is the full-scale LED current setting (see Table 10), Code is the 8-bit backlight code in the

Control Brightness MSB register and DPWM is the PWM Duty Cycle.

7.4.1.1.2

11-Bit Code Calculation

In Exponential Mapping Mode the brightness code to backlight current transfer function is given by the equation:

(2)

Where ILED_FULLSCALE is the full-scale LED current setting (see Table 10), Code is the 11-bit backlight code in the

Control Brightness MSB and LSB registers and DPWM is the PWM Duty Cycle.

7.4.1.2 Linear Mapping

In Linear Mapping Mode the brightness code to backlight current has a linear relationship.

7.4.1.2.1

8-Bit Code Calculation

The 8-bit linear mapping follows the equation:

(3)

Where ILED_FULLSCALE is the full-scale LED current setting, Code is the 8-bit backlight code in the Control

Brightness MSB register and DPWM is the PWM Duty Cycle.

7.4.1.2.2

11-Bit Code Calculation

The 11-bit linear mapping follows the equation:

(4)

Where ILED_FULLSCALE is the full-scale LED current setting, Code is the 11-bit backlight code in the Control

Brightness MSB and LSB registers and DPWM is the PWM Duty Cycle.