Datasheet MAX4295 (Maxim) - 8

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