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MAX8678ETE+T

P1-P3P4-P6P7-P9P10-P12P13-P13
MAX8678
Serial-Pulse Gain Adjustment (ENAMP)
The audio amplifier has an internal gain adjustment,
controlled by a serial-pulse interface. The gain setting
of the input amplifier is adjustable from -9dB to +18dB
in 3dB steps. This allows the amplifier to be used for
both hands-free and for receiver mode, without any
external components.
Driving ENAMP high turns on the amplifier and sets the
internal register to -9dB. Adjust the gain by pulsing
ENAMP low (500ns to 500µs pulse width). Each rising
edge sets the gain as shown in Table 3. Once the
desired setting is reached, hold ENAMP high for at
least 3.2ms to set the internal register and change the
gain. To set a new current level, repeat the previous
sequence from the beginning. To shut down the ampli-
fier, hold ENAMP low for at least 3.2ms. Figure 3 is a
timing diagram for ENAMP.
Applications Information
BTL Amplifier
The MAX8678 is designed to drive a load differentially,
a configuration referred to as bridge-tied load (BTL).
The BTL configuration offers advantages over the sin-
gle-ended configuration, where one side of the load is
connected to ground. Driving the load differentially
doubles the output voltage, thus quadrupling output
power compared to a single-ended amplifier under
similar configurations.
Since the differential outputs are biased at midsupply,
there is no net DC voltage across the load. This elimi-
nates the need for DC-blocking capacitors required for
single-ended amplifiers. These capacitors can be
large, expensive, consume board space, and degrade
low-frequency performance.
White LED Charge Pump with
1.1W Audio Amplifier
10 ______________________________________________________________________________________
OPTIONAL FILTER
CAPACITORS
DIFFERENTIAL
AUDIO INPUT
MONO
CLASS AB
AUDIO AMP
EARPIECE /
LOUDSPEAKER
R
IN
R
IN
A+
A-
OUT+
OUT-
MAX8678
Figure 4. Differential Audio Input with Optional Filter Capacitors
SINGLE-ENDED
AUDIO INPUT
MONO
CLASS AB
AUDIO AMP
EARPIECE /
LOUDSPEAKER
R
IN
R
IN
A+
A-
OUT+
OUT-
MAX8678
NOTE: FILTER CAPACITORS REQUIRED FOR SINGLE-ENDED AUDIO OUTPUT.
Figure 5. Single-Ended Audio Input
R
IN
(kΩ)
ENAMP
RISING
EDGES
GAIN
SETTING
(dB)
MIN TYP MAX
1 -9 69.1 99.0 140.0
2 -6 62.4 89.2 116.0
3 -3 54.9 78.4 102.0
4 0 46.8 66.9 87.0
5 3 38.8 55.5 72.1
6 6 31.3 44.7 58.1
7 9 24.6 35.1 45.6
8 12 18.8 26.9 35.0
9 15 14.1 20.2 26.2
10 18 10.5 15.0 19.5
Table 3. Audio Amplifier-Input Impedance
Input Filter
The fully differential amplifier inputs can be biased at
voltages other than midsupply. The common-mode
feedback circuit adjusts for input bias, ensuring the
outputs are still biased at midsupply. Input capacitors
are not required as long as the common-mode input
voltage is within the specified range listed in the
Electrical Characteristics
.
If input capacitors are used (see Figure 4), the input
capacitor in conjunction with the amplifier input imped-
ance (R
IN
) form a highpass filter that removes the DC
bias from an incoming signal. The AC-coupling capacitor
allows the amplifier to bias the signal to an optimum DC
level. Assuming zero-source impedance, the -3dB point
of the highpass filter is given by:
where R
IN
is the input impedance given in Table 2.
Figure 5 shows a single-ended audio input.
Setting f
-3dB
too high affects the low-frequency
response of the amplifier. Use capacitors with
dielectrics that have low-voltage coefficients, such as
tantalum or aluminum electrolytic. Capacitors with high
voltage coefficients, such as ceramics, can increase
distortion at low frequencies.
PCB Layout
Good PC board (PCB) layout is essential for optimizing
performance. Use large traces for the power-supply
inputs and amplifier outputs to minimize losses due to
parasitic trace resistance and to route heat away from
the device. Good grounding improves audio perfor-
mance and prevents any digital switching noise from
coupling into the audio signal. The exposed paddle low-
ers the thermal resistance of the package by providing a
direct-heat conduction path from the die to the PCB.
Connect the exposed paddle to NEG directly under the
IC. Refer to the MAX8678 Evaluation Kit for a good PCB
layout example.
f
RC
dB
IN IN
−
=
××
3
1
2π
MAX8678
White LED Charge Pump with
1.1W Audio Amplifier
______________________________________________________________________________________ 11
Chip Information
PROCESS: BiCMOS
MAX8678
White LED Charge Pump with
1.1W Audio Amplifier
12 ______________________________________________________________________________________
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information
go to www.maxim-ic.com/packages
.)
12x16L QFN THIN.EPS
0.10 C 0.08 C
0.10 M C A B
D
D/2
E/2
E
A1
A2
A
E2
E2/2
L
k
e
(ND - 1) X e
(NE - 1) X e
D2
D2/2
b
L
e
L
C
L
e
C
L
L
C
L
C
PACKAGE OUTLINE
21-0136
2
1
I
8, 12, 16L THIN QFN, 3x3x0.8mm
MARKING
AAAA
P1-P3P4-P6P7-P9P10-P12P13-P13

MAX8678ETE+T

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Buy MAX8678ETE+T
Manufacturer:
Maxim Integrated
Description:
LED Lighting Drivers White LED Charge Pump w/1.1W Aud Amp
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