APPLICATION BULLETIN ® Mailing Address: PO Box 11400 • Tucson, AZ 85734 • Street Address: 6730 S. Tucson Blvd. • Tucson, AZ 85706 Tel: (602) 746-1111 • Twx: 910-952-111 • Telex: 066-6491 • FAX (602) 889-1510 • Immediate Product Info: (800) 548-6132 DOUBLE THE OUTPUT CURRENT TO A LOAD WITH THE DUAL OPA2604 AUDIO OP AMP By Morgan Monks supplied by A1 is matched by the current I2, the output current of A2. The load will receive a total current of I1 + I2. The ratio between the output currents, I1 and I2, is equal to: Headphones typically have an impedance of 40Ω to 300Ω. By using the dual OPA2604 and four resistors one can economically drive a 2.8V peak signal into the 40Ω headphones. I2 = I1 (R3/R4) Figure 1 illustrates a circuit that can be used to drive loads that exceed the output current capabilities of an operational amplifier, but not enough to require the use of a power operational amplifier. The OPA2604 used in this application is a dual, FET-input operational amplifier that can typically sink or source 35mA on the output. By taking advantage of the fact that the OPA2604 is a dual, this circuit will sink or source 70mA. In addition, each operational amplifier has its own short circuit protection of ±40mA (typ), which makes the overall typical short circuit current of this application ±80mA. Resistors R3 and R4 are set equal for equal output currents. Resistors R1 and R2 set the overall gain of the circuit. The transfer function is: VOUT = VIN (1 + R2/R1) The OPA2604 is a dual, FET-input operational amplifier designed for enhanced AC performance. Very low distortion, low noise and wide bandwidth provide superior performance in high quality audio applications. The OPA2604 is available is plastic 8-pin DIP and plastic 8-pin SOIC. One side of the dual OPA2604, A2, is in the feedback loop of the other side of the dual, A1. The current, I1, which is 1/2 OPA2604 A2 I2 1/2 OPA2604 R3 51Ω R4 51Ω A1 VIN IL = I1 + I2 R2 I1 VOUT Load R1 FIGURE 1. Using the Dual OPA2604 Op Amp to Double the Output Current to a Load. © 1993 Burr-Brown Corporation AB-051 Printed in U.S.A. March, 1993