APPLICATION BULLETIN ® Mailing Address: PO Box 11400, Tucson, AZ 85734 • Street Address: 6730 S. Tucson Blvd., Tucson, AZ 85706 • Tel: (520) 746-1111 Telex: 066-6491 • FAX (520) 889-1510 • Product Info: (800) 548-6132 • Internet: www.burr-brown.com/ • FAXLine: (800) 548-6133 IMPROVE OPA541 CURRENT-LIMIT STABILITY By Hubert Biagi (602) 746-7422 and R. Mark Stitt OPA541 is the industry’s highest performance monolithic power amplifier. It can operate on ±40V power supplies and put out 5A continuously (10A peak). Internal current-limit circuitry can be user-programmed with a single external resistor to protect the amplifier and load from fault conditions. CALCULATING CURRENT LIMIT RESISTOR VALUE OPA541M R 0.08 to 0.16 0.17 to 0.77 0.78 to 10.0 R1 (Ω) C1 (µF) 10 to 5 5 to 1 1 to 0 0.68(1) 1.3(1) 2.7 0.68 0.33 0.068 0. 809 − 0. 057 I CL R CL = 0. 813 − 0. 020 I CL Where: RCL = Current limit resistor (Ω) ICL = Current limit (|A|) The compensation circuit consists of an R, C network connected to the amplifier drive output as shown. Component values for the network depend on the output current limit desired. Table I below shows recommended values. RCL (Ω) = OPA541P Under some conditions, the OPA541 may oscillate during current limit. In some applications, this is acceptable. However, you can improve stability during current limit by adding external compensation as shown in Figure 1. CURRENT LIMIT (A) CL NOTE: (1) You can use two or four parallel connected 2.7Ω resistors to make 1.3Ω or 0.68Ω. TABLE I. R 1, C 1 Network Values for OPA541— see Figure 1. V+ +In –In Current Sense R CL Output Drive VO R1 C1 OPA541 Power Amp V– FIGURE 1. An R1, C1 network can be added to the OPA541 output to improve stability during current limit. The information provided herein is believed to be reliable; however, BURR-BROWN assumes no responsibility for inaccuracies or omissions. BURR-BROWN assumes no responsibility for the use of this information, and all use of such information shall be entirely at the user’s own risk. Prices and specifications are subject to change without notice. No patent rights or licenses to any of the circuits described herein are implied or granted to any third party. BURR-BROWN does not authorize or warrant any BURR-BROWN product for use in life support devices and/or systems. 1993 Burr-Brown Corporation AB-055 Printed in U.S.A. May, 1993