MAX8678 Maxim Integrated Products, MAX8678 Datasheet - Page 7

• Manufacturer Part Number: MAX8678
• Description: White LED Charge Pump
• Manufacturer: Maxim Integrated Products

www.DataSheet4U.com
Figure 1. Functional Diagram
The MAX8678 integrates a charge pump for white LEDs
with an audio loudspeaker amplifier. The high-efficiency,
adaptive charge pump drives up to four LEDs with con-
stant current for uniform brightness for display back-
lighting or camera flash. 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. Figure 1 is the
MAX8678 functional diagram.
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.
DIFFERENTIAL
AUDIO INPUT
INPUT SUPPLY
AND DIMMING
2.7V TO 5.5V
AMP ON/OFF
4.7μF
LED ON/OFF
AND GAIN
C1
_______________________________________________________________________________________
_______________________________________________________________________________________
OPTIONAL FILTER
CAPACITORS
Detailed Description
ENAMP
ENLED
GND
A+
A-
IN
C+
White LED Charge Pump with
CIRCUITRY
CIRCUITRY
CONTROL
CONTROL
INVERTING
CHARGE
PUMP
1μF
C3
C-
To reduce power consumption when not in use, the
charge-pump LED driver and the audio amplifier have
separate shutdown controls. To disable the LED driver,
drive ENLED low for at least 3.2ms. To disable the
audio amplifier, drive ENAMP low for at least 3.2ms.
When both ENLED and ENAMP are held low, the IC
supply current is reduced to about 0.1µA.
The thermal-overload protection circuitry monitors the
temperature of the IC. When the die temperature reach-
es +160°C, the IC is shut down. The IC turns on after it
has cooled by approximately 20°C. During continuous
overload conditions, this results in a pulsed output.
1.1W Audio Amplifier
LED CURRENT
REGULATORS
AUDIO AMP
CLASS AB
SUPPLY
HALF
MAX8678
MONO
BIAS
Thermal-Overload Protection
NEG
LED3
LED4
BIAS
OUT+
OUT-
LED1
LED2
0.1μF
1μF
C2
C4
EARPIECE/
LOUDSPEAKER
Shutdown
7
7