Mono, 2W, Switch-Mode (Class D)Audio Power AmplifierMAX4295 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 VIN may have inadequate gate drive thus dissipating excessive power. The undervoltage lockout circuit pre- VRAMP vents the device from operating at supply voltages below +2.2V. +5V Low-Power Shutdown Mode VOUT The MAX4295 has a shutdown mode that reduces power consumption and extends battery life. Driving 0V SHDN low disables the H-bridge, turns off the circuit, and places the MAX4295 in a low-power shutdown Figure 2. PWM Waveforms mode. Connect SHDN to VCC for normal operation. Applications Information FS1 and FS2 program the oscillator to a frequency of 125kHz, 250kHz, 500kHz, and 1MHz. The sawtooth Component Selection oscillator swings between GND and 0.6 ✕ VCC. The Gain Setting input signal is typically AC-coupled to the internal input External feedback components set the gain of the op amp, whose gain can be controlled through exter- MAX4295. Resistors R nal feedback components. The common-mode voltage F and RIN set the gain of the input amplifier to -(R of the input amplifier is 0.3 ✕ V F/RIN). The amplifier’s noninverting CC and is internally gen- input is connected to the internally generated 0.3 ✕ V erated from the same resistive divider used to generate CC (VCM) that sets the amplifier’s common-mode voltage. the 0.6 ✕ VCC reference for the PWM oscillator. The amplifier’s input bias current is low, ±50pA, and Current Limit does not affect the choice of feedback resistors. The A current-limiting circuit in the H-bridge monitors the noise in the circuit increases as the value of RF current in the H-bridge transistors and disables the H- increases. bridge if the current in any of the H-bridge transistors The optimum impedance seen by the inverting input is exceeds 1A. The H-bridge is enabled after a period of between 5kΩ and 20kΩ. The effective impedance is 100µs. A continuous short circuit at the output results given by (R in a pulsating output. F ✕ RIN)/(RF + RIN). For values of RF > 50kΩ, a small capacitor (≈3pF) connected across RF Thermal Overload Protection compensates for the pole formed by the input capaci- Thermal overload protection limits total power dissipa- tance and the effective resistance at the inverting input. tion in the MAX4295. When the junction temperature exceeds +145°C, the thermal detection disables the H- _______________________________________________________________________________________9
