19-4266; Rev 0; 9/08
IT
EVALUATION K
AVAILABLE
Charge Pump for Backlight/Flash/RGB LEDs
with Safety Timer
General Description
The MAX8879 provides complete light management for
main display backlight, subdisplay backlight (or RGB
indicator), and white LED camera flash with regulated
constant current up to 610mA total. By utilizing adap-
tive 1x/1.5x/2x charge-pump modes and very-low-
dropout current regulators, it achieves high efficiency
over the full 1-cell Li+ battery input voltage range. The
1MHz fixed-frequency switching allows for tiny external
components while the regulation scheme is optimized
to ensure low EMI and low input ripple. An integrated
derating function protects the LEDs from overheating
during high ambient temperatures.
The MAX8879 features an internally trimmed reference
to set the maximum LED current. An I
2
C serial port is
used for on/off control and setting the LED currents in
32 linear steps for main, sub/RGB, and movie. When
using the RGB indicator, the I
2
C port provides 32k col-
ors and programmable ramp-up/down rates. The cam-
era flash for flash-mode operation is enabled by an
active-low signal on the
FSH
pin. A safety timer is acti-
vated on the falling edge of
FSH,
which has an I
2
C-
adjustable (programmable) period of no timer, 0.5s,
1.0s, or 2.0s (default). If the safety timer period expires,
both flash and movie modes are disabled.
Features
♦
Guaranteed 610mA Continuous Drive Capability
4 LEDs at 30mA Each for Main Display
3 LEDs at 30mA Each for Sub or RGB
400mA Total for Flash
♦
2-Wire I
2
C Serial Port
5-Bit (32-Step) Linear Dimming
32k Colors
Ramp-Up/Down Rates
♦
92% Peak/83% Avg Efficiency (P
LED
/P
BATT
)
♦
Adaptive 1x/1.5x/2x Mode Switchover
♦
0.3% (typ) LED Current Accuracy and Matching
♦
Low Input Ripple and EMI
♦
Low 0.1µA Shutdown Current
♦
Output Overvoltage Protection
♦
I
2
C Programmable Flash Safety Timer
♦
Thermal Derating Function Protects LEDs
♦
24-Pin, 4mm x 4mm Thin QFN Package
MAX8879
Ordering Information
PART
MAX8879ETG+
TEMP RANGE
-40°C to +85°C
PIN-
PACKAGE
24 Thin QFN
4mm x 4mm
Applications
Cell Phones and Smartphones
PDAs, Digital Cameras, Camcorders
Displays with Up to 11 LEDs
Pin Configuration appears at end of data sheet.
+Denotes
a lead-free/RoHS-compliant package.
Typical Operating Circuit
1μF
INPUT
2.7V TO 5.5V
4.7μF
1μF
OUTPUT
UP TO 610mA
10μF
MAIN
SUB OR RGB
FLASH
C1P
IN
PIN
GND
C1N
C2P
C2N
OUT
MAX8879
V
LOGIC
0.1μF
V
DD
I
2
C PORT
ON/OFF AND
BRIGHTNESS
FLASH
ON/OFF
SCK
SDA
FSH
PGND
M1
M2
M3
M4
S1
S2
S3
F1
F2
F3
F4
________________________________________________________________
Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
Charge Pump for Backlight/Flash/RGB LEDs
with Safety Timer
MAX8879
ABSOLUTE MAXIMUM RATINGS
V
DD
, IN, PIN, SCK, SDA,
FSH,
OUT to GND .........-0.3V to +6.0V
M_, S_, F_ to GND ....................................-0.3V to (V
OUT
+ 0.3V)
C1N, C2N to GND .......................................-0.3V to (V
IN
+ 0.3V)
C1P, C2P to GND...-0.3V to greater of (V
OUT
+ 0.3V) or (V
IN
+ 0.3V)
PGND to GND .......................................................-0.3V to +0.3V
OUT Short Circuit to GND ..........................................Continuous
Continuous Power Dissipation (T
A
= +70°C)
24-Pin Thin QFN (derate 20.8mW/°C above +70°C)...1666mW
Operating Temperature Range ...........................-40°C to +85°C
Junction Temperature ......................................................+150°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(V
IN
= V
PIN
= 3.6V, V
DD
= 1.8V, V
GND
= V
PGND
= 0V, temperature derating disabled, T
A
= -40°C to +85°C, typical values are at T
A
=
+25°C, unless otherwise noted.) (Note 1)
PARAMETER
IN Operating Voltage
V
DD
Operating Range
Undervoltage-Lockout Threshold
Undervoltage-Lockout Hysteresis
Output Overvoltage-Protection Threshold
IN + PIN No-Load Supply Current
IN + PIN Shutdown Supply Current
V
DD
Quiescent Current
V
OUT
rising
1.5x or 2x mode
10% setting, 1x mode, flash off
All LEDs off,
FSH
= SDA =
SCK = V
DD
, I
2
C ready
All LEDs off, SDA = SCK =
V
DD
, I
2
C ready
Startup into 1x mode
Soft-Start Time
LED Current Derating Function Start
Temperature
LED Current Derating Function Slope
LED Current SUB Output Accuracy
(Note 2)
LED Current FLASH and MAIN Output
Accuracy
Maximum M_, S_, F_ Sink Current
LED Dropout Voltage
1.5x and 2x Mode Regulation Voltage
1x to 1.5x and 1.5x to 2x Mode Transition
Threshold
V
M_
, V
S_
, V
F_
falling
Startup into 1.5x mode
Startup into 2x mode
Temperature derating enabled
T
A
= +40°C to +85°C, temperature derating
enabled
Default current setting, T
A
= +25°C
Default current setting, T
A
= -40°C to +85°C
Default current setting (Note 2)
M_, S_
F_
100% LED setting (Note 3)
M_, S_
F_
-2
-5
-5
28.5
95
±0.3
30.0
100
40
40
150
100
90
90
T
A
= +25°C
T
A
= +85°C
T
A
= +25°C
T
A
= +85°C
4.75
V
IN
rising or falling
CONDITIONS
MIN
2.7
1.6
2.25
50
5.00
4.0
0.35
0.7
0.8
0.1
0.1
0.5
1.0
1.5
+40
-1.7
±0.3
+2
+5
+5
°C
%/°C
%
%
mA
mV
mV
mV
ms
1
5
5.25
6.5
TYP
MAX
5.5
5.5
2.60
UNIT
V
V
V
mV
V
mA
µA
µA
2
_______________________________________________________________________________________
Charge Pump for Backlight/Flash/RGB LEDs
with Safety Timer
ELECTRICAL CHARACTERISTICS (continued)
(V
IN
= V
PIN
= 3.6V, V
DD
= 1.8V, V
GND
= V
PGND
= 0V, temperature derating disabled, T
A
= -40°C to +85°C, typical values are at T
A
=
+25°C, unless otherwise noted.) (Note 1)
PARAMETER
Input Voltage Mode Transition Hysteresis
M_, S_, F_ Leakage in Shutdown
OUT Pulldown Resistance in Shutdown
Maximum OUT Current
Open-Loop OUT Resistance
Switching Frequency
SDA = 111xxx00
S1, S2, S3 (RGB) Full-Scale Ramp Time
SDA = 111xxx01
SDA = 111xxx10
SDA = 111xxx11
Logic-Input High Voltage
Logic-Input Low Voltage
Logic-Input Current
SDA Output Low Voltage
I
2
C Clock Frequency
Bus-Free Time Between START and STOP
Hold Time Repeated START Condition
SCK Low Period
SCK High Period
Setup Time Repeated START Condition
SDA Hold Time
SDA Setup Time
Setup Time for STOP Condition
Thermal Shutdown
Thermal-Shutdown Hysteresis
t
BUF
t
HD_STA
t
LOW
t
HIGH
t
SU_STA
t
HD_DAT
t
SU_DAT
t
SU_STO
1.3
0.6
1.3
0.6
0.6
0
100
0.6
0.1
0.2
0.2
0.1
-0.01
50
0.1
+160
20
V
DD
= 1.6V to 5.5V
V
DD
= 1.6V to 5.5V
V
IL
= 0V or V
IH
=
5.5V
I
SDA
= 3mA
T
A
= +25°C
T
A
= +85°C
0.01
0.1
0.03
0.4
400
0.7 x V
DD
0.3 x V
DD
1
All LEDs off,
FSH
=
V
DD
T
A
= +25°C
T
A
= +85°C
610
0.5
1.5
2.0
1
2
9
2
18
2
19
2
20
V
V
µA
V
kHz
µs
µs
µs
µs
µs
µs
ns
µs
°C
°C
µs
2.5
3.5
4.1
MHz
Ω
CONDITIONS
MIN
TYP
150
0.01
0.1
5
1
MAX
UNIT
mV
µA
kΩ
mA
MAX8879
All LEDs off,
FSH
= V
DD
V
IN
≥
3.2V, V
OUT
= 3.9V
1x mode (V
IN
- V
OUT
) / I
OUT
1.5x mode (1.5 x V
IN
- V
OUT
) / I
OUT
2x mode (2 x V
IN
- V
OUT
) / I
OUT
Note 1:
All devices are 100% production tested at T
A
= +25°C. Limits over the operating temperature range are guaranteed
by design.
Note 2:
LED current specification includes both accuracy and matching tolerance.
Note 3:
Dropout voltage is defined as the M2 or F3 to GND voltage at which current into M2 or F3 drops 10% from the value at 0.2V.
All other current regulators are tested functionally by the accuracy test and guaranteed for low dropout by design.
_______________________________________________________________________________________
3
Charge Pump for Backlight/Flash/RGB LEDs
with Safety Timer
MAX8879
Typical Operating Characteristics
(T
A
= +25°C, unless otherwise noted.)
EFFICIENCY vs. SUPPLY VOLTAGE
DRIVING 4 MAIN LEDs
MAX8879 toc01
INPUT CURRENT vs. SUPPLY VOLTAGE
DRIVING LUMILEDS LXCL-PWF1 FLASH
MAX8879 toc02
INPUT CURRENT vs. SUPPLY VOLTAGE
DRIVING 4 MAIN LEDs AND RGB LEDs
SUPPLY VOLTAGE FALLING
30mA/LED
350
INPUT CURRENT (mA)
300
250
15mA/LED
200
150
100
1.9mA/LED
50
0
400
MAX8879 toc03
MAX8879 toc06
100
90
80
EFFICIENCY (%)
70
60
50
40
30
20
10
0
2.7
3.1
3.5
3.9
4.3
4.7
5.1
SUPPLY VOLTAGE FALLING
1.9mA/LED
30mA/LED
15mA/LED
900
800
700
INPUT CURRENT (mA)
600
500
400
300
200
100
0
200mA
100mA
400mA
450
5.5
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
SUPPLY VOLTAGE (V)
SUPPLY VOLTAGE (V)
SUPPLY VOLTAGE (V)
INPUT CURRENT vs. SUPPLY VOLTAGE
DRIVING 4 MAIN LEDs
MAX8879 toc04
INPUT CURRENT vs. SUPPLY VOLTAGE
DRIVING RGB LEDs
SUPPLY VOLTAGE FALLING
400
350
INPUT CURRENT (mA)
300
250
200
150
100
15mA/LED
1.9mA/LED
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
30mA/LED
MAX8879 toc05
LED CURRENT MATCHING
vs. SUPPLY VOLTAGE
(MAIN AND RGB AT FULL CURRENT)
31.2
30.9
30.6
LED CURRENT (mA)
30.3
30.0
29.7
29.4
29.1
28.8
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
SUPPLY VOLTAGE (V)
GREEN
V
F
= 2V
BLUE
V
F
= 4.2V
4 WHITE
V
F
= 3.4V
RED
V
F
= 1.9V
450
400
350
INPUT CURRENT (mA)
300
250
200
150
100
50
0
2.7
3.1
3.5
1.9mA/LED
15mA/LED
30mA/LED
SUPPLY VOLTAGE FALLING
450
50
0
3.9
4.3
4.7
5.1
5.5
SUPPLY VOLTAGE (V)
SUPPLY VOLTAGE (V)
LED CURRENT MATCHING
vs. SUPPLY VOLTAGE
(MAIN AND RGB AT 1.9mA/LED)
MAX8879 toc07
LED CURRENT vs. TEMPERATURE
THERMAL DERATING OFF
MAX8879 toc08
1.96
1.94
1.92
LED CURRENT (mA)
1.90
1.88
1.86
1.84
1.82
1.80
2.7
3.1
3.5
3.9
4.3
4.7
5.1
GREEN
V
F
= 1.9V
BLUE
V
F
= 3.4V
4 WHITE
V
F
= 2.9V
RED
V
F
= 1.7V
30
25
LED CURRENT (mA)
20
15
4 MAIN OR 4 FLASH LEDs
THERMAL DERATING ON
10
5
0
5.5
-40
-15
10
35
60
85
SUPPLY VOLTAGE (V)
TEMPERATURE (°C)
4
_______________________________________________________________________________________
Charge Pump for Backlight/Flash/RGB LEDs
with Safety Timer
Typical Operating Characteristics (continued)
(T
A
= +25°C, unless otherwise noted.)
OPERATING WAVEFORMS 1X MODE
MAX8879 toc09
MAX8879
OPERATING WAVEFORMS 1.5X MODE
MAX8879 toc10
V
OUT
50mV/div
(AC-COUPLED)
50mV/div
(AC-COUPLED)
100mA/div
0
1μs/div
V
OUT
50mV/div
(AC-COUPLED)
50mV/div
(AC-COUPLED)
100mA/div
0
1μs/div
V
IN
V
IN
I
IN
I
IN
OPERATING WAVEFORMS 2X MODE
MAX8879 toc11
MAIN BACKLIGHT STARTUP WAVEFORM
MAX8879 toc12
V
SDA
V
OUT
50mV/div
(AC-COUPLED)
V
OUT
V
IN
I
IN
50mV/div
(AC-COUPLED)
100mA/div
I
IN
0
1μs/div
1ms/div
5V/div
1V/div
0
200mA/div
0
MAIN STARTUP WITH RGB ALREADY ON
MAX8879 toc13
FLASH STARTUP WAVEFORM
MAX8879 toc14
V
SDA
V
OUT
5V/div
1V/div
V
SDA
5V/div
1V/div
V
OUT
0
I
IN
200mA/div
0
1ms/div
I
IN
0
200mA/div
0
1ms/div
_______________________________________________________________________________________
5
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