MAX8822 Maxim Integrated Products, MAX8822 Datasheet - Page 8

• Manufacturer Part Number: MAX8822
• Description: Ultra-Efficient Negative Charge-Pump LED Driver
• Manufacturer: Maxim Integrated Products

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The MAX8822 drives up to four white LEDs (WLEDs) with
regulated constant current for display backlighting in cell
phones, cameras, PDAs, and other handheld devices.
The IC also includes two low-noise, high-PSRR, 200mA
LDOs for powering camera modules or other devices.
Figure 3 depicts the MAX8822 block diagram.
The MAX8822 IC utilizes a 0.5x inverting charge pump
and extremely low-dropout current regulators to
achieve high efficiency over the full 1-cell Li+ battery
Ultra-Efficient Negative Charge-Pump LED
Driver with Dual LDOs in 3mm x 3mm Thin QFN
Figure 1. Timing Characteristics for LED Serial-Pulse Control Interface
Figure 2. Timing Characteristics for LDO Serial-Pulse Control Interface
8
INTERNAL
INTERNAL
SETTING
SETTING
ENLED
INTERNAL
CURRENT
SETTING
ENLDO
LDO1
LDO2
_______________________________________________________________________________________
V
V
I
LED_
LDO1
LDO2
SHDN
SHDN
SHDN
SHDN
SHDN
SHDN
1
0
24.0mA
0V
0V
t
INIT
t INIT
2
1
2.8V
22.4mA
1.2V
Detailed Description
3
2
20.8mA
3.3V
1.2V
4
3
2.8V
1.5V
19.2mA
2.5ms
t
HOLD
t HOLD
2.5ms
19.2mA
2.8V
1.5V
1
1
t
24.0mA
HI
2.8V
1.2V
t
HI
2
22.4mA
2
3.3V
1.2V
voltage range. The charge pump remains inactive
unless the LED current regulators require additional
voltage to prevent them from entering dropout. To max-
imize efficiency, the current regulators operate with as
little as 150mV voltage drop. Additionally, each LED
current regulator is independently monitored and
switched, ensuring the least possible power consump-
tion to extend battery life (see the Adaptive Current
Regulator Switchover section for details).
t
LO
t
LO
3
20.8mA
3
2.8V
1.5V
13
5.6mA
12
0V
2.8V
14
4.8mA
13
1.8V
0V
2.5ms
t
HOLD
2.5ms
t
HOLD
4.8mA
t
2.5ms
SHDN
t
t
t
t
2.5ms
t
t
t
INIT
HI
LO
SHDN
INIT
HI
LO
= 500ns TO 500μs
1.8V
= 500ns TO 500μs
= 500ns TO 500μs
= 500ns TO 500μs
0V
= 120μs
= 120μs
SHDN
SHDN
SHDN
SHDN
SHDN