19-0786; Rev 0; 4/07
KIT
ATION
EVALU
BLE
AVAILA
White LED Charge Pump with
1.1W Audio Amplifier
Features
♦
High-Efficiency White LED Charge Pump
Individual Adaptive Supply for Each LED
4 Low-Dropout LED Current Regulators
24mA to 0.1mA Dimming Range
Single-Wire, Serial-Pulse Dimming Interface
1% (typ) Accuracy
Low 140µA Quiescent Current
♦
Mono Class AB Audio Amplifier
1.1W RMS Mono BTL Output (8Ω, V
IN
= 5V)
Low 0.004% THD+N at 1kHz
High 90dB PSRR at 1kHz
Fully Differential Inputs
-9dB to +18dB Gain Settings in 3dB Steps
Integrated Click/Pop Suppression
Low Quiescent Current
♦
Soft-Start Limits Inrush Current
♦
Thermal Shutdown, Open- and Short-Circuit
Protection
♦
16-Pin, 3mm x 3mm Thin QFN Package
General Description
The MAX8678 integrates a charge pump for white light-
emitting diodes (LEDs) with an audio loudspeaker
amplifier. The high-efficiency, adaptive charge pump
drives up to four LEDs with constant current for uniform
brightness. The LED current is adjustable from
0.1mA/LED to 24mA/LED in 31 pseudo-logarithmic
steps through a single-wire serial-pulse interface. High
accuracy and LED-to-LED current matching are main-
tained throughout the adjustment range. Individual
adaptive mode switching for each LED provides high
efficiency with a wide range of LED forward voltages.
The mono class AB audio amplifier directly drives an 8Ω
loudspeaker with 1.1W RMS continuous power from a 5V
supply with less than 1% THD+N. The gain is adjustable
from -9dB to +18dB in ten 3dB steps through a single-
wire serial-pulse interface. Clicks and pops are sup-
pressed during on/off and all gain adjustments.
Differential inputs improve common-mode noise rejection.
The MAX8678 includes soft-start, thermal shutdown,
open-circuit and short-circuit protection, and is avail-
able in the 16-pin, 3mm x 3mm Thin QFN package
(0.8mm max height).
MAX8678
Ordering Information
PART
MAX8678ETE+
PIN-PACKAGE
16 Thin QFN
3mm x 3mm
TOP MARK
AFF
PKG CODE
T1633-5
Applications
Cell Phones and Smartphones
Camera Phones
PDAs, Digital Cameras, Camcorders
+Denotes
a lead-free package.
Typical Operating Circuit
INPUT
2.7V TO 5.5V
1μF
Note:
The device is specified over the -40°C to +85°C extend-
ed temperature range.
Pin Configuration
LED4
LED3
LED2
10
C-
LED1
9
TOP VIEW
C+
IN
4.7μF
GND
LED1
LED2
LED3
LED4
LED ON/OFF
AND DIMMING
AMP ON/OFF
AND GAIN
DIFFERENTIAL
AUDIO
INPUT
0.1μF
ENLED
MAX8678
ENAMP
ENLED 16
A+
A-
EP
NEG
OUT+
OUT-
LOUDSPEAKER
8Ω
BIAS
BACKLIGHT
OR FLASH
0.1mA TO
24mA
NEG 13
C- 14
C+ 15
12
11
8
7
BIAS
OUT-
OUT+
ENAMP
MAX8678
6
5
+
1
IN
2
GND
3
A+
4
A-
1μF
THIN QFN
3mm
×
3mm
________________________________________________________________
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.
White LED Charge Pump with
1.1W Audio Amplifier
MAX8678
ABSOLUTE MAXIMUM RATINGS
IN to GND ..............................................................-0.3V to +6.0V
IN to NEG ..............................................................-0.3V to +6.0V
ENLED, ENAMP, LED_, C+, A+, A-, OUT+, OUT-,
BIAS to GND…….....................................-0.3V to (V
IN
+ 0.3V)
ENLED, ENAMP, LED_, C+, A+, A-, OUT+, OUT-,
BIAS, C- to NEG ...................................…-0.3V to (V
IN
+ 0.3V)
GND to NEG ......................................................…-0.3V to +6.0V
GND to C-..............................................................-0.3V to +6.0V
OUT+, OUT- Short Circuit to GND or IN ....................Continuous
Continuous Power Dissipation (T
A
= +70°C)
16-Pin Thin QFN 3mm x 3mm
(derate 17.5mW/°C above +70°C) ............................1398mW
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
= 3.6V, V
GND
= 0V, T
A
= -40°C to +85°C, unless otherwise noted. Typical values are at T
A
= +25°C.) (Note 1)
PARAMETER
IN Operating Voltage
Undervoltage-Lockout (UVLO) Threshold
UVLO Hysteresis
Shutdown Supply Current
(All Outputs Off)
ENLED = ENAMP =
GND
T
A
= +25°C
T
A
= +85°C
V
IN
rising
CONDITIONS
MIN
2.7
2.25
2.45
100
0.1
0.1
140
0.45
3
+160
20
V
IN
= 2.7V to 4.2V
V
IN
= 4.2V to 5.5V
V
IN
= 2.7V to 5.5V
V
IL
= 0V or
V
IH
= 5.5V
See Figures 2 and 3
See Figures 2 and 3
See Figures 2 and 3
See Figures 2 and 3
0.5
0.5
1
0.1
5
10
LED V
F
= 3.9V, V
IN
= 3.2V
All LEDs off, ENLED = GND
96
10
23
T
A
= +25°C
T
A
= +85°C
0.01
0.1
3.2
3.2
500
500
1.4
1.5
0.4
1
°C
°C
200
1.5
TYP
MAX
5.5
2.65
UNITS
V
V
mV
µA
µA
Charge pump inactive, LED_ = 1.6mA
ENAMP = GND, T
A
= +25°C
No-Load Supply Current
Charge pump active, 1MHz switching, LEDs at
24mA setting, ENAMP = GND
ENAMP = IN, ENLED = GND
Thermal Shutdown
Thermal-Shutdown Hysteresis
SERIAL-PULSE INTERFACE (EN_)
Logic Input-High Voltage
Logic Input-Low Voltage
Logic Input Current
t
SHDN
t
HOLD
t
LO
t
HI
CHARGE PUMP
Switching Frequency
Soft-Start Time
Regulation Voltage (OVP) (V
IN
- V
NEG
)
Open-Loop NEG Output Resistance
((V
NEG
-V
IN
)/I
NEG
)
Guaranteed Output Current
NEG Discharge Resistance in Shutdown
mA
V
V
µA
ms
ms
µs
µs
MHz
ms
V
Ω
mA
kΩ
2
_______________________________________________________________________________________
White LED Charge Pump with
1.1W Audio Amplifier
ELECTRICAL CHARACTERISTICS (continued)
(V
IN
= 3.6V, V
GND
= 0V, T
A
= -40°C to +85°C, unless otherwise noted. Typical values are at T
A
= +25°C.) (Note 1)
PARAMETER
LED DRIVER
Current-Setting Range
24mA setting, T
A
= +25°C
Current Accuracy
24mA setting, T
A
= -40°C to +85°C
1.6mA setting, T
A
= +25°C
LED_ Dropout
LED_ Voltage-Mode Transition Threshold
(1x to 2x)
LED_ Voltage-Mode Transition
Hysteresis
LED_ Leakage in Shutdown
AUDIO AMPLIFIER
Common-Mode Bias Voltage
Output Offset Voltage
Common-Mode Input Voltage
Input Impedance (R
IN
)
Common-Mode Rejection Ratio
Power-Supply Rejection Ratio
Table 2
V
IN
= 3.2V
f = 1kHz, V
IN
= 3.2V
V
A+
= V
A-
= V
BIAS
,
200mV
P-P
at IN
THD+N = 1%,
f = 1kHz (Note 3)
f = 217Hz
f = 1kHz
R
L
= 8Ω, V
IN
= 3.2V
R
L
= 4Ω, V
IN
= 3.2V
R
L
= 8Ω, V
IN
= 5V
Output Current Limit
Gain Accuracy
Total Harmonic Distortion + Noise
Signal-to-Noise Ratio
Maximum Capacitive Drive
Power-Up from Shutdown Time, t
UP
Shutdown Time, t
PD
See Figure 3
See Figure 3
-9dB
≤
Gain
≤
15dB
Gain = 18dB
R
L
= 8Ω, f = 1kHz, P
OUT
= 0.25W, V
IN
= 3.2V
R
L
= 8Ω, f = 1kHz, P
OUT
= 0.25W, V
IN
= 3.2V
0.004
104
500
10
3.5
0.8
0.6
0.36
V
A+
= V
A-
= V
BIAS
, gain
≤
12dB
-5%
-25
0.5
10
50
67
60
70
93
90
0.5
0.65
1.1
1
1.6
±0.13
±0.17
A
dB
%
dB
pF
ms
µs
W
V
IN
/ 2
±1
+5%
+25
(V
IN
-
1.2)
140
mV
V
kΩ
dB
dB
All LEDs off
T
A
= +25°C
T
A
= +85°C
24mA setting (Note 2)
V
LED_
falling
Charge pump inactive
Charge pump active
125
0.1
-2
-5
±5
72
132
150
100
0.01
0.1
1
120
360
175
mV
mV
mV
µA
±1
24.0
+2
+5
%
mA
CONDITIONS
MIN
TYP
MAX
UNITS
MAX8678
Output Power
Note 1:
Limits are 100% production tested at T
A
= +25°C. Limits over the operating temperature range are guaranteed by design.
Note 2:
Dropout voltage is defined as the LED_ to GND (charge pump inactive) or LED_ to NEG (charge pump active) voltage at
which current into LED_ drops 10% from the value at V
LED_
= 0.5V.
Note 3:
Output power is specified by a combination of a functional output current test and characterization analysis.
_______________________________________________________________________________________
3
White LED Charge Pump with
1.1W Audio Amplifier
MAX8678
Typical Operating Characteristics
(V
IN
= 3.2V, R
L
= 8Ω, T
A
= +25°C, unless otherwise noted.)
TOTAL HARMONIC DISTORTION +
NOISE vs. FREQUENCY
MAX8678 toc01
TOTAL HARMONIC DISTORTION +
NOISE vs. OUTPUT POWER
MAX8678 toc02
OUTPUT POWER vs. SUPPLY VOLTAGE
MAX8678 toc03
0.1
100
2000
10
OUTPUT POWER = 150mW
THD+N (%)
OUTPUT POWER = 50mW
0.01
THD+N (%)
1
f
IN
= 10kHz
OUTPUT POWER (mW)
f
IN
= 1kHz
THD+N = 10%
1000
THD+N = 1%
0.1
OUTPUT POWER = 300mW
0.001
10
GAIN = 3dB
100
1000
FREQUENCY (Hz)
10,000
100,000
0.01
GAIN = 3dB
0
0.2
0.4
f
IN
= 100kHz
0
0.6
0.8
1.0
2.5
3.5
4.5
5.5
OUTPUT POWER (W)
SUPPLY VOLTAGE (V)
0.001
POWER DISSIPATION vs. OUTPUT POWER
MAX8678 toc04
OUTPUT POWER vs. LOAD RESISTANCE
MAX8678 toc05
AMPLIFIER GAIN AND PHASE
vs. FREQUENCY
25dB
20dB
AMPLIFIER GAIN AND PHASE
15dB
10dB
5dB
0dB
0°
-30°
-60°
-90°
GAIN = 18dB
MAX8678 toc06
500
POWER DISSIPATION POWER (mW)
1.2
1.0
OUTPUT POWER (W)
0.8
0.6
0.4
0.2
0
THD+N = 1%
THD+N = 10%
400
300
200
100
0
0
100
200
300 400
500
600
700
OUTPUT POWER (mW)
4
6
8
10
12
14
16
10
100
1k
FREQUENCY (Hz)
10k
100k
LOAD RESISTANCE (Ω)
COMMON-MODE REJECTION RATIO
vs. FREQUENCY
-25dB
-35dB
-45dB
REJECTION RATIO
REJECTION RATIO
-55dB
-65dB
-75dB
-85dB
-95dB
GAIN = 18dB
V
RIPPLE
100mV
P-P
100
1k
FREQUENCY (Hz)
10k
MAX8678 toc07
POWER-SUPPLY REJECTION RATIO
vs. FREQUENCY
-25dB
-35dB
-45dB
-55dB
-65dB
-75dB
-85dB
-95dB
-105dB
-125dB
100
1k
FREQUENCY (Hz)
10k
V
ENAMP
V
OUT-
V
OUT+
- V
OUT-
GAIN = 18dB
V
RIPPLE
18mV
P-P
V
OUT+
MAX8678 toc08
AMPLIFIER STARTUP
AND SHUTDOWN
MAX8678 toc09
1V/div
1V/div
100mV/div
2V/div
4ms/div
4
_______________________________________________________________________________________
White LED Charge Pump with
1.1W Audio Amplifier
Typical Operating Characteristics (continued)
(V
IN
= 3.2V, R
L
= 8Ω, T
A
= +25°C, unless otherwise noted.)
LED EFFICIENCY vs. SUPPLY VOLTAGE
(MISMATCHED LEDs)
MAX8678 toc10
MAX8678
SUPPLY CURRENT vs. SUPPLY VOLTAGE
(MISMATCHED LEDs)
180
160
SUPPLY CURRENT (mA)
140
120
100
80
60
40
20
0
4 x 1.6mA
4 x 6.4mA
4 x 20.8mA
4 x 16mA
MAX8678 toc11
100
90
80
EFFICIENCY (%)
70
60
50
40
30
20
10
0
2.7
3.0
3.3
3.6
3.9
4 x 6.4mA
4 x 20.8mA
4 x 1.6mA
200
4.2
4.2
3.9
3.6
3.3
3.0
2.7
SUPPLY VOLTAGE (V)
SUPPLY VOLTAGE (V)
LED EFFICIENCY vs. SUPPLY VOLTAGE
(MATCHED LEDs)
MAX8678 toc12
MAX8678 EFFICIENCY vs. SUPPLY VOLTAGE
(MATCHED LEDs)
20.4mA/LED
1.6mA/LED
MAX8678 toc13
100
90
80
EFFICIENCY (%)
70
60
50
40
30
20
10
0
2.7
3.0
3.3
3.6
3.9
1.6mA/LED
16.4mA/LED
6.4mA/LED
20.4mA/LED
100
90
80
70
EFFICIENCY
6.4mA/LED
16.4mA/LED
60
50
40
4.2
4.20
3.90
SUPPLY VOLTAGE (V)
3.85 3.75 3.65 3.55 3.40
3.00
3.50
3.80 3.70 3.60
SUPPLY VOLTAGE, TIME WEIGHTED (V)
LED CURRENT MATCHING
vs. SUPPLY VOLTAGE
16.8
16.6
LED CURRENT (mA)
16.4
16.2
16.0
15.8
15.6
15.4
15.2
15.0
2.7
3.0
3.3
3.6
3.9
4.2
4 OF 16mA/LED
I
IN
V
LED1
MAX8678 toc14
LED STARTUP/
SHUTDOWN WAVEFORMS
MAX8678 toc15
17.0
V
ENLED
2V/div
1V/div
500mA/div
1ms/div
SUPPLY VOLTAGE (V)
_______________________________________________________________________________________
5
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