MAX158 Maxim, MAX158 Datasheet - Page 6

• Manufacturer Part Number: MAX158
• Description: High-Efficiency / 26V Step-Up Converter for White LED Main and Subdisplay Backlighting
• Manufacturer: Maxim

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.
High-Efficiency, 26V Step-Up Converter
for White LED Main and Subdisplay Backlighting
Figure 1. Functional Diagram
6
_______________________________________________________________________________________
ENABLE
DAC OR
INPUTS
PWM
CTRL
EN1
EN2
Detailed Description
MAX1582
114kΩ
1.0MHz
f
OSC
1.25V CLAMP
336kΩ
CONTROL
PWM
2.6V TO 5.5V
50kΩ
SLOPE COMP.
CURRENT SENSE
GND
V+
g
m
VP
SHUTDOWN
OVERVOLTAGE
PROTECTION
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
C
2.2µF
IN
Shutdown for Main and Subdisplay
COMP
PGND
OUT1
OUT2
CS
LX
C
L1
22µF
0.1µF
C
0.022µF
OUT1
COMP
D1
UP TO 27V
UP TO 13V
R
7.5Ω
SENSE