MAX1582 Datasheet, PDF (6/10 Pages) Maxim Integrated Products – High-Efficiency, 26V Step-Up Converter for White LED Main and Subdisplay Backlighting

High-Efficiency, 26V Step-Up Converter
for White LED Main and Subdisplay Backlighting
2.6V TO 5.5V
V+ VP
PWM
CONTROL
C_IN
2.2µF
LX
PGND
L1
22µF
D1
C_OUT1
0.1µF
f_OSC
1.0MHz
SLOPE COMP.
OVERVOLTAGE
CURRENT SENSE ^PROTECTION
OUT1
UP TO 27V
DAC OR
CTRL ^114kΩ
336kΩ
PWM
g_m
1.25V CLAMP
50kΩ
EN1
ENABLE
INPUTS
EN2
MAX1582
SHUTDOWN
GND
COMP
2 TO 4 LEDS
C_COMP
0.022µF
MAIN DISPLAY
OUT2
CS
UP TO 13V
2 TO 3 LEDS
SUBDISPLAY
R_SENSE
7.5Ω
Figure 1. Functional Diagram
Detailed Description
The MAX1582’s high efficiency and small size make it
ideally suited to drive up to six series-connected LEDs.
Separate enable inputs are provided to control the main
and subdisplay backlighting. The MAX1582 operates as
a boost DC-to-DC converter that regulates output current
rather than voltage. It provides even illumination by sourc-
ing the same output current through each LED, eliminat-
ing the need for expensive factory calibration. The fast
1MHz internal oscillator allows for a small inductor and
small input and output capacitors while minimizing input
and output ripple.
Shutdown for Main and Subdisplay
The MAX1582 has two enable inputs (EN1 and EN2)
used to enable or shutdown the main and subdisplay
LEDs. When EN1 and EN2 are both high, all LEDs are
lit. With EN1 high and EN2 low, the main-display LEDs
are lit, and the subdisplay LEDs are shorted by the
MAX1582. With EN1 low and EN2 high, the main-display
LEDs are shorted and the subdisplay LEDs are lit.
When both EN1 and EN2 are low, the MAX1582 enters
shutdown, reducing supply current to 0.01µA (typ).
Although the internal N-channel MOSFET does not
switch in shutdown, there is still a DC-current path
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