Wide Brightness Range

CCFL Backlight Controllers

10

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Detailed Description

The MAX1739/MAX1839 regulate the brightness of a

CCFL in three ways:

1) Linearly controlling the lamp current.

2) Digitally pulse-width modulating (or chopping) the

lamp current (DPWM).

3) Using both methods simultaneously for widest dim-

ming range.

DPWM is implemented by pulse-width modulating the

lamp current at a rate faster than the human eye can

detect. Figure 1 shows the current and voltage wave-

forms for the three operating modes with the brightness

control set to 50% of full scale.

The MAX1739/MAX1839 include a 5.3V linear regulator

to power most of the internal circuitry, drivers for the

buck and Royer switches, and the synchronizable

DPWM oscillator. The MAX1739/MAX1839 are very flex-

ible and include a variety of operating modes, an ana-

log interface, an SMBus interface (MAX1739 only), a

shutdown mode, lamp-out detection, and buck-switch

short detection.

Figure 1. Brightness Control Methods

(DAC SET TO MIDSCALE)

EFFECTIVE BRIGHTNESS IS:

50% IN CONTINUOUS AND DPWM CONTROL

25% IN COMBINED CONTROL

CURRENT + DPWM CONTROL

CONTINUOUS CURRENT CONTROL

DPWM CONTROL

TRANSFORMER

VOLTAGE

LAMP CURRENT