MAX4295(2005) View Datasheet(PDF) - Maxim Integrated
Part Name
Description
Manufacturer
MAX4295 Datasheet PDF : 15 Pages
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Mono, 2W, Switch-Mode (Class D)
Audio Power Amplifier
AOUT
IN
MAX4295
0.3 ✕ VCC
(VCM)
FS1
PWM
FS2
OSC
VCC
SS
POWER MANAGEMENT
AND PROTECTION
CSS
GND
PVCC
GATE
DRIVE
OUT+
PGND
PVCC
GATE
OUT-
DRIVE
PGND
Figure 1. Functional Diagram
Detailed Description
The MAX4295 switch-mode, Class D audio power
amplifier is intended for portable multimedia and gener-
al-purpose audio applications. Linear amplifiers in the
1W to 2W output range are inefficient; they overheat
when operated near rated output power levels. The effi-
ciency of linear amplifiers is <50% when the output
voltage is equal to 1/2 the supply. The MAX4295 Class
D amplifier achieves efficiencies of 87% or greater and
is capable of delivering up to 2W of continuous maxi-
mum power to a 4Ω load. The lost power is due mainly
to the on-resistance of the power switches and ripple
current in the output.
In a Class D amplifier, a PWM controller converts the
analog input to a variable pulse-width signal. The pulse
width is proportional to the input voltage, ideally 0% for
a 0V input signal and 100% for full-scale input voltages.
A passive lowpass LC network filters the PWM output
waveform to reconstruct the analog signal. The switch-
ing frequency is selected much higher than the maxi-
mum input frequencies so that intermodulation products
are outside the input signal bandwidth. Higher switching
frequencies also simplify the filtering requirements.
The MAX4295 consists of an inverting input operational
amplifier, a PWM ramp oscillator, a controller that con-
verts the analog input to a variable pulse-width signal,
and a MOSFET H-bridge power stage (Figure 1). The
control signal is generated by the PWM comparator; its
pulse width is proportional to the input voltage. Ideally
the pulse width varies linearly between 0% for a 0V
input signal and 100% for full-scale input voltages
(Figure 2). This signal controls the H-bridge. The
switches work in pairs to reverse the polarity of the sig-
nal in the load. Break-before-make switching of the H-
bridge MOSFETs by the driver circuit keeps supply
current glitches and crowbar current in the MOSFETs at
a low level. The output swing of the H-bridge is a direct
function of the supply voltage. Varying the oscillator
swing in proportion to the supply voltage maintains
constant gain with varying supply voltage.
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