480mA White LED 1x/1.5x/2x Charge Pump for
Backlighting and Camera Flash
INPUT
1 μ F
1 μ F
OUTPUT
where K = 23, 70, or 233 (depending upon the state of
ENM1 and ENM2, see Table 1 ), and R SETM is the resis-
tor connected between SETM and ground (see the
2.7V TO 5.5V
C1P
INP
C1N C2P
C2N
OUT
UP TO 480mA
Typical Operating Circuit ).
4.7 μ F
1 μ F
IN
PGND
GND1
MAX1576
LED1
LED2
LED3
4.7 μ F
LUXEON
DS25
Setting the Flash Output Current
SETF controls the LED5–LED8 bias current. Current
flowing into LED5, LED6, LED7, and LED8 is a multiple
of the current flowing out of SETF.
ON/OFF AND
CURRENT
SETTING
ENM1
ENM2
ENF1
LED4
LED5
LED6
LED7
I LED5 = I LED6 = I LED7 = I LED8 = N x (0.604V / R SETF )
where N = 142, 283, or 708 (depending upon ENF1
and ENF2, see Table 2 ), and R SETF is the resistor con-
ENF2
SETM
SETF
LED8
GND2
nected between SETF and ground (see the Typical
Operating Circuit ).
Single-Wire Pulse Dimming
For more dimming flexibility or to reduce the number of
control traces, the MAX1576 supports serial pulse dim-
Figure 2. Typical Application Circuit for Driving a Single High-
Brightness LED
Table 1. ENM1/ENM2 States
ming. Connect ENM1 and ENM2 (or ENF1 and ENF2)
together to enable single-wire pulse dimming of the
main (or flash) LEDs. When ENM1 and ENM2 (or ENF1
and ENF2) go high simultaneously, the main (or flash)
ENM1/ENM2 STATES
ENM1 = low, ENM2 = low
ENM1 = low, ENM2 = high
ENM1 = high, ENM2 = low
ENM1 = high, ENM2 = high
BRIGHTNESS
Shutdown
1/10 Brightness
3/10 Brightness
Full Brightness
LED1–LED4
CURRENT
0
23 x I SETM
70 x I SETM
233 x I SETM
LEDs are enabled at full brightness. Each subsequent
low-going pulse (500ns to 250μs pulse width) reduces
the LED current by 10%, so after one pulse the LED
current is 0.9 x I LED_ . The 10th pulse reduces the cur-
rent by 5% so the LED current reduces from 0.1 x I LED_
to 0.05 x I LED_ . The 11th pulse sets the LED current
back to I LED_ . Figure 3 shows a timing diagram for sin-
Table 2. ENF1/ENF2 States
gle-wire pulse dimming. Because soft-start is longer
than the initial t HI , apply dimming pulses quickly upon
ENF1/ENF2 STATES
ENF1 = low, ENF2 = low
ENF1 = low, ENF2 = high
ENF1 = high, ENF2 = low
ENF1 = high, ENF2 = high
BRIGHTNESS
Shutdown
1/5 Brightness
2/5 Brightness
Full Brightness
LED5–LED8
CURRENT
0
142 x I SETM
283 x I SETM
708 x I SETM
startup (after initial t HI ) to avoid LED_ current transition-
ing through full brightness.
Simple On/Off Control
If dimming control is not required, connect ENM1 to
ENM2 (or ENF1 to ENF2) for simple on/off control. In
this case, LED current is set by the values of R SETM
(or R SETF ).
INITIAL t HI
0
≥ 50 μ s
1
2
3
4
5
6
7
8
9
10
11
ENM1 AND ENM2
OR ENF1 AND ENF2
I LED_
SHDN
t SOFT-START
100%
90%
80%
70%
60%
t LO
500ns TO 250 μ s
50%
t HI
≥ 500ns
40%
30%
20%
10%
5%
100% 90%
t SHDN
0.5ms (typ)
SHDN
Figure 3. EN_ Timing Diagram
_______________________________________________________________________________________
9
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