Audio ICs Low-current audio headphone driver BA3574BFS The BA3574BFS is a headphone driver with a fixed-gain bass boost circuit and an AVC circuit that keeps the output below a fixed level. It features low current dissipation, and low output noise, and is ideal for use in portable digital audio equipment. Applications Portable CD and MD players Features 1) Low current dissipation (when VCC = 2.4V, the quiescent current is 4.9mA). 2) Suitable for use in digital audio equipment (voltage gain: GV = 11.8dB, output noise voltage: VNO = 102dBm typ.). 3) Bass boost circuit. 4) AVC (Auto Volume Control) circuit, for output limiting. 5) Standby switch. 6) Mute switch. 7) Ripple filter. 8) No output coupling capacitor required. 9) Beep circuit. 10) SSOP-A20 package. 583 Audio ICs FBlock diagram FAbsolute maximum ratings (Ta = 25_C) FRecommended operating conditions (Ta = 25_C) 584 BA3574BFS Audio ICs BA3574BFS FElectrical characteristics (unless otherwise noted, Ta = 25_C, VCC = 2.4V, RL = 16Ω, f = 1kHz, and BB = OFF) 585 Audio ICs Measurement circuit 586 BA3574BFS Audio ICs BA3574BFS Measurement circuit switch table 587 Audio ICs Application example 1 588 BA3574BFS Audio ICs BA3574BFS Application example 2 589 Audio ICs Application example 3 590 BA3574BFS Audio ICs Operation notes (1) Application circuits Provided the recommended circuit constants are used, the application circuits should function correctly. However, we recommend that you confirm the characteristics of the circuits in actual use. If you change the circuit constants, check both the static and transient characteristics of the circuit, and allow sufficient margin to accommodate variations between both ICs and external components. In particular, the capacitors connected to the OUT 1, OUT 2, and Vref pins must have low impedance at high frequency. (2) Wiring of PCB The PCB pattern for the external components should be designed carefully to prevent oscillation and degradation of the circuit characteristics. Keep the wiring tracks as short as possible, and ensure that there is no impedance between the common connections. (3) Recommended power supply voltage range The curves in Fig. 5 below show the maximum allowable power output (PO (Max.) / ch) plotted against the supply voltage (VCC) for different values of ambient temperature (Ta). When VCC y 3.6V, operate the IC in the region below the dotted line, and do not exceed it. If the maximum allowable power output for each channel (PO (Max.) / ch) is exceed, the internal power consumption will exceed the power dissipation capacity of the package, and destroy the IC. BA3574BFS (4) Switching noise prevention Operate the BA3574BFS according to the timing diagram given in Fig. 6 below to prevent a “pop” sound from being output to the headphones. (5) BIAS OUT (pin 15) The internal operating point voltage of the BA3574BFS is supplied from BIAS OUT (pin 15). The current capacity is limited, so do not use this as the operating point for external circuits. 591 Audio ICs Electrical characteristics curves 592 BA3574BFS Audio ICs BA3574BFS External dimensions (Units: mm) 593