Datasheet

MAX4295
Mono, 2W, Switch-Mode (Class D)
Audio Power Amplifier
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FS1 and FS2 program the oscillator to a frequency of
125kHz, 250kHz, 500kHz, and 1MHz. The sawtooth
oscillator swings between GND and 0.6
✕
V
CC
. The
input signal is typically AC-coupled to the internal input
op amp, whose gain can be controlled through exter-
nal feedback components. The common-mode voltage
of the input amplifier is 0.3
✕
V
CC
and is internally gen-
erated from the same resistive divider used to generate
the 0.6
✕
V
CC
reference for the PWM oscillator.
Current Limit
A current-limiting circuit in the H-bridge monitors the
current in the H-bridge transistors and disables the H-
bridge if the current in any of the H-bridge transistors
exceeds 1A. The H-bridge is enabled after a period of
100µs. A continuous short circuit at the output results
in a pulsating output.
Thermal Overload Protection
Thermal overload protection limits total power dissipa-
tion in the MAX4295. When the junction temperature
exceeds +145°C, the thermal detection disables the H-
bridge transistors. The H-bridge transistors are
enabled after the IC’s junction temperature cools by
10°C. This results in a pulsating output under continu-
ous thermal overload conditions. Junction temperature
does not exceed the thermal overload trip point in nor-
mal operation, but only in the event of fault conditions,
such as when the H-bridge outputs are short circuited.
Undervoltage Lockout
At low supply voltages, the MOSFETs in the H-bridge
may have inadequate gate drive thus dissipating
excessive power. The undervoltage lockout circuit pre-
vents the device from operating at supply voltages
below +2.2V.
Low-Power Shutdown Mode
The MAX4295 has a shutdown mode that reduces
power consumption and extends battery life. Driving
SHDN low disables the H-bridge, turns off the circuit,
and places the MAX4295 in a low-power shutdown
mode. Connect SHDN to V
CC
for normal operation.
Applications Information
Component Selection
Gain Setting
External feedback components set the gain of the
MAX4295. Resistors R
F
and R
IN
set the gain of the
input amplifier to -(R
F
/R
IN
). The amplifier’s noninverting
input is connected to the internally generated 0.3
✕
V
CC
(VCM) that sets the amplifier’s common-mode voltage.
The amplifier’s input bias current is low, ±50pA, and
does not affect the choice of feedback resistors. The
noise in the circuit increases as the value of R
F
increases.
The optimum impedance seen by the inverting input is
between 5kΩ and 20kΩ. The effective impedance is
given by (R
F
✕
R
IN
)/(R
F
+ R
IN
). For values of R
F
>
50kΩ, a small capacitor (≈3pF) connected across R
F
compensates for the pole formed by the input capaci-
tance and the effective resistance at the inverting input.
V
IN
V
RAMP
+5V
V
OUT
0V
Figure 2. PWM Waveforms