The IS32BL3556 is a step-up controller with an
integrated switching FET for driving white LED arrays
in LCD panel backlight applications. The boost
controller is a current mode, fixed frequency
architecture with the switching frequency set by an
external resistor. The integrated boost controller
generates the minimum output voltage to keep all
LEDs illuminated at the set current. The current in
each of the 4 channels is programmed to a specific
value with an external current set resistor and
matched to within 1%.
LED dimming is achieved using an external digital
PWM signal to either adjust the internal ISET current
or pulse-width-modulate the LED intensity. The LED
sinks have a fast response to a PWM input making it
possible to achieve a high contrast ratio of 10,000:1.
A synchronization pin can be used to synchronize
multiple IS32BL3556 devices or to synchronize with
the external PWM source in the range of 580 kHz to
2.3MHz. The high switching frequency allows the
IS32BL3556 to operate above the AM radio band.
The IS32BL3556 integrates a control block to drive an
external P-Channel FET to disconnect the input
supply from the system whenever a fault is detected.
It has safety protection features to prevent damage
during fault conditions. Protection features include
output short and overvoltage, open or shorted diode,
open or shorted LED pin, shorted boost switch,
shorted FSET or ISET resistor, and IC over
temperature. A dual level cycle-by-cycle current limit
function provides soft start and protects the internal
current switch against high current overloads.
The IS32BL3556 is available in a thermally enhanced