19-0786; Rev 0; 4/07
White LED Charge Pump with
1.1W Audio Amplifier
MAX678
General Description
Features
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.
♦ 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, VIN = 5V)
Low 0.004% THD+N at 1kHz
High 90dB PSRR at 1kHz
Fully Differential Inputs
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.
-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
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).
♦ 16-Pin, 3mm x 3mm Thin QFN Package
Ordering Information
Applications
PART
PIN-PACKAGE TOP MARK PKG CODE
Cell Phones and Smartphones
16 Thin QFN
3mm x 3mm
MAX8678ETE+
AFF
T1633-5
Camera Phones
+Denotes a lead-free package.
PDAs, Digital Cameras, Camcorders
Note: The device is specified over the -40°C to +85°C extend-
ed temperature range.
Typical Operating Circuit
INPUT
2.7V TO 5.5V
Pin Configuration
1μF
TOP VIEW
C+
C-
LED1
LED2
LED3
LED4
IN
BACKLIGHT
OR FLASH
12
11
10
9
4.7μF
GND
BIAS
8
7
6
5
NEG 13
C- 14
0.1mA TO
24mA
OUT-
0.1μF
LED ON/OFF
AND DIMMING
ENLED
MAX8678
MAX8678
BIAS
C+
OUT+
15
16
AMP ON/OFF
AND GAIN
ENAMP
A+
ENAMP
ENLED
+
OUT+
OUT-
DIFFERENTIAL
AUDIO
LOUDSPEAKER
8Ω
A-
INPUT
1
2
3
4
EP
NEG
THIN QFN
3mm × 3mm
1μF
________________________________________________________________ Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.