MAX4295(2005) Ver la hoja de datos (PDF) - Maxim Integrated
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Fabricante
MAX4295 Datasheet PDF : 15 Pages
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Mono, 2W, Switch-Mode (Class D)
Audio Power Amplifier
VIN
VRAMP
+5V
VOUT
0V
Figure 2. PWM Waveforms
FS1 and FS2 program the oscillator to a frequency of
125kHz, 250kHz, 500kHz, and 1MHz. The sawtooth
oscillator swings between GND and 0.6 ✕ VCC. 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 ✕ VCC and is internally gen-
erated from the same resistive divider used to generate
the 0.6 ✕ VCC 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 VCC for normal operation.
Applications Information
Component Selection
Gain Setting
External feedback components set the gain of the
MAX4295. Resistors RF and RIN set the gain of the
input amplifier to -(RF/RIN). The amplifier’s noninverting
input is connected to the internally generated 0.3 ✕ VCC
(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 RF
increases.
The optimum impedance seen by the inverting input is
between 5kΩ and 20kΩ. The effective impedance is
given by (RF ✕ RIN)/(RF + RIN). For values of RF >
50kΩ, a small capacitor (≈3pF) connected across RF
compensates for the pole formed by the input capaci-
tance and the effective resistance at the inverting input.
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