LM3532TMX-40ASLASHNOPB datasheet(13/47 Pages) TI1

13 / 47 page

0.1

100

BRIGHTNESS CODE (D)

16 32

64 80 96 112 128 144 160 176 192 208 224 240 256

FULLSCALE

LED

40 ¨

Code

PWM

x D

LM3532

www.ti.com

SNVS653D – JULY 2011 – REVISED JUNE 2013

3. Ramp up from one brightness level to the next

4. Ramp down from one brightness level to the next

See Table 4 and Table 5.

Startup and Shutdown Current Ramping

The startup and shutdown ramp rates are independently programmable in the startup/Shutdown Ramp Rate

are independently programmable from the shutdown ramp rates, but not independently programmable for each

Control Bank. For example, programming a startup or shutdown ramp rate, programs the same ramp rate for

each Control Bank.

Run Time Ramp Rates

Current ramping from one brightness level to the next is programmed via the Run Time Ramp Rate Register (see

Table 5). There are 8 different ramp-up and 8 different ramp-down rates. The ramp-up rate is independently

programmable from the ramp-down rate, but not independently programmable for each Control Bank. For

example, programming a ramp-up or a ramp-down rate programs the same rate for each Control Bank.

LED Current Mapping Modes

All LED current brightness codes are 8 bits (256 different levels), where each bit represents a percentage of the

programmed full-scale current setting for that particular Control Bank. The percentage of the full-scale current is

different depending on which mapping mode is selected. The mapping mode can be either exponential or linear.

Mapping mode is selected via bit [1] of the Control A, B, or C Brightness Configuration Registers.

Exponential Current Mapping Mode

In exponential mapping mode, the backlight code to LED current approximates the following equation:

(1)

where Code is the 8-bit code in the programmed brightness register and DPWM is the duty cycle of the PWM input

that is assigned to the particular control bank. For the exponential mapped mode (Figure 29) shows the typical

response of % full-scale current setting vs 8-bit brightness code.

Figure 29. Exponential Mapping Response

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LM3532TMX-40A/NOPB Datasheet(PDF) 13 Page - Texas Instruments