MAX8678 Maxim Integrated Products, MAX8678 Datasheet - Page 11

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

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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
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
Figure 5 shows a single-ended audio input.
IN
IN
) form a highpass filter that removes the DC
is the input impedance given in Table 2.
f
−
______________________________________________________________________________________
3
dB
=
2π
×
R
IN
1
×
C
IN
Input Filter
White LED Charge Pump with
Setting f
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.
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.
PROCESS: BiCMOS
1.1W Audio Amplifier
-3dB
too high affects the low-frequency
Chip Information
PCB Layout
11