DEMO CIRCUIT 453B LT1970A QUICK START GUIDE LT1970A Power Amplifier with Adjustable Current Limiting DESCRIPTION Demonstration circuit 453B is useful for evaluating the LEDs provide an indication of faults detected by the LT1970A, a power amplifier with adjustable current limit- LT1970A. Separate indicators illuminate when the am- ing. The demo circuit is available in two versions plifier enters sourcing or sinking current limit and if the DC453B-A with up to 500mA of output current and LT1970A overheats and enters thermal shutdown protec- DC453B-B for applications with up to 5 Amps of output tion. current. For the 5 Amp version a Class B MOSFET based Several jumpers enable flexible amplifier operation. Con- current boost stage has been added to the output section figurations include: with current limit control still provided by the LT1970A. Single or dual power supplies The maximum output current of the board is set by two Separate or common input stage and power output on-board potentiometers to permit independent control stage supplies of the sinking and sourcing current limit. The current AC or DC coupled inputs limit adjustment can also be provided by external voltage Non-Inverting gains of 1 or 2, Inverting gain of 1 sources. Symmetrical sourcing and sinking current limit Separate or common current limit control with a single control is also possible. Design files for this circuit board are available. Call the LTC factory. , LTC and LT are registered trademarks of Linear Technology Corporation. ThinSOT and PowerPath are trademarks of Linear Technology Corporation. TYPICAL PERFORMANCE SUMMARY T = 25C, Common 12V Supplies A SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS V Power Supply Range Single Supply 8 36 V SUPPLY Dual Supply 8 18 V I Adjustable Output Current Limit Range DC453B-A (LT1970A basic amplifier), Vcc 8V 4 500 mA OUT DC453B-B (Boosted) 0.04 5 A BW Small Signal 3dB Bandwidth DC453B-A (LT1970A basic amplifier) S A = +1, Vout=200mV , R =100, 1.6 MHz V P-P LOAD DC453B-B (Boosted) A = +1, Vout=200mV , R =10 7.2 KHz V P-P LOAD BW Large Signal 3dB Bandwidth DC453B-A (LT1970A basic amplifier) L A = +1, Vout=20V , R =100 58 KHz V P-P LOAD DC453B-B (Boosted) A = +1, Vout=10V , R =10, 7 KHz V P-P LOAD SR Slew Rate 1.6 V/S V Output Sat Voltage High DC453B-A (LT1970A basic amplifier), V =V+- SATH SAT V 1.4 V OUT Common 12V Supplies, R =250 2.1 V LOAD Common 12V Supplies, R =25 0.1 V LOAD Vcc/Vee=12V and V+/V-=5V, R =100 0.8 V LOAD Vcc/Vee=12V and V+/V-=5V, R =10 LOAD 1 LT1970A TYPICAL PERFORMANCE SUMMARY T = 25C, Common 12V Supplies A SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS DC453B-B (Boosted), See Operational Notes V Output Sat Voltage Low DC453B-A (LT1970A basic amplifier), V = V SATL SAT OUT- V- 2.1 V Common 12V Supplies, R =250 2.8 V LOAD Common 12V Supplies, R =25 0.3 V LOAD Vcc/Vee=12V and V+/V-=5V, R =100 1.3 V LOAD Vcc/Vee=12V and V+/V-=5V, R =10 LOAD DC453B-B (Boosted), See Operational Notes I Total Quiescent Supply Current No Load S DC453B-A (LT1970A basic amplifier) 9 mA DC453B-B (Boosted) 12 mA QUICK START PROCEDURE Demonstration circuit 453B is easy to set up to evaluate DUAL sets the DC bias of the inputs and output to the performance of the LT1970A. Before applying power ground when symmetrical dual + and - power supplies to the amplifier, configure all on-board jumpers for the are used. desired operation. Figure 1 provides an overview of how SINGLE sets the DC bias of the inputs and output to Vcc when a single power supply is used. This setting also biases the inputs and output to the midpoint of asymme- JP1: Input Signal Coupling, AC or DC trical dual supplies. the placement of each of the jumpers adjusts the confi- Removing the shunt from this jumper can allow the pow- guration. Position each jumper for the following results: er amplifier to bias at the same dc potential as the input signal for DC coupled single supply uses. DC coupling, non-inverting, applies the input signal di- rectly to the amplifier + input with a 5K input imped- ance, inverting, directly connects to a 10K resistor to JP4: Gain Configuration Setting the amplifier input. AC coupling connects the input signal through a series The four positions of this jumper configure the amplifier 10F capacitor. Depending on the amplifier topology the to one of three gain values. The inset diagram on the lower 3dB corner frequency is in the range of 1.6Hz to schematic, Figure 4, shows how the amplifier feedback is 6.2Hz. arranged for each jumper position. A small table is also included on the printed circuit board to serve as a ready reference for the jumper settings. JP2: Inverting (INV) or Non-Inverting (NI) The jumper position shorting pins 2 and 3 provides the Directs the input signal for an Inverting or Non-Inverting same configuration as shorting pins 3 and 4. amplifier. JP5: Separate (S) or Common (C) Current Limit Control JP3: Input biasing for SINGLE or DUAL Power Supplies Separate (S) position allows for the independent setting of the amplifier sourcing current limit and sinking current 2