参数资料
型号: MAX1577ZETA
厂商: MAXIM INTEGRATED PRODUCTS INC
元件分类: 稳压器
英文描述: 1.2A White LED Regulating Charge Pump for Camera Flashes and Movie Lights
中文描述: SWITCHED CAPACITOR REGULATOR, 1250 kHz SWITCHING FREQ-MAX, DSO8
封装: 3 X 3 MM, 0.8 MM HEIGHT, MO-229, TDFN-8
文件页数: 8/11页
文件大小: 664K
代理商: MAX1577ZETA
M
1.2A White LED Regulating Charge Pump for
Camera Flashes and Movie Lights
8
_______________________________________________________________________________________
Detailed Description
1x LDO to 2x Mode Switchover
When V
IN
is greater than V
OUT
, the MAX1577Y/
MAX1577Z are in 1x LDO mode and regulate the cur-
rent through R
CS
. As V
IN
decreases and the LDO
approaches dropout, the 2x charge pump starts boosting
the output to maintain the regulation current. When V
IN
rises enough above V
OUT
to maintain LDO regulation, the
charge pump stops and the MAX1577Y/MAX1577Z
switch back to the more efficient 1x LDO mode.
Soft-Start
The MAX1577Y/MAX1577Z include soft-start circuitry to
limit inrush current at turn-on. When starting up with an
output voltage that is not near the input voltage, the out-
put capacitor is charged directly from the input with a
ramped current source (with no charge-pump action)
until the output voltage approaches the input voltage. If
current-mode or voltage-mode regulation is met, soft-
start is terminated and normal operation begins in 1x
mode. Otherwise, after 500μs, the 2x charge-pump soft-
start operates until the voltage across the sense resistor
reaches the current regulation threshold, the output volt-
age is in regulation, or 500μs has elapsed, whichever
occurs first. If the output is shorted to ground, soft-start
is repeated until the output exceeds 2.3V.
Dimming and Shutdown
The MAX1577Y/MAX1577Z use two inputs (EN1 and
EN2) to select between three brightness levels and low-
power shutdown mode (see Table 1). By regulating the
voltage across the current-sense resistor (V
OUT
- V
CS
) to
one of three levels, the MAX1577Y/MAX1577Z control the
output current, thus providing the three-level dimming. In
shutdown mode, the IC is turned off, reducing the supply
current to 0.01μA (typ). When the MAX1577Y/MAX1577Z
are shut down, C1 is discharged and the output is pulled
to GND through an internal 5k
resistor.
Figure 4. Flash and Backlighting with the MAX1577Y
MAX1577Y
C1
2.2
μ
F*
UP TO 1.2A
5.1V, 4.6V, OR 3.4V
V
OUT
- (300 OR
100 OR 60mV)
CAMERA-FLASH
MOVIE LIGHT
MAIN DISPLAY
BACKLIGHT
5.3V OVP
2.7V TO 5.5V
C
IN
4.7
μ
F
C
IN
10
μ
F
R
CS
5.1V OR 100% CURRENT,
4.6V OR 33% CURRENT,
3.4V OR 20% CURRENT,
AND SHUTDOWN
CP
CN
EN1
IN
OUT
CS
GND
EN2
RGB DRIVER
ASIC
SUBDISPLAY
BACKLIGHT
*1
μ
F FOR LESS THAN 600mA OUTPUT.
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