QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 832 DUAL OUTPUT LOW NOISE LDO REGULATORS LT3028 DESCRIPTION Demonstration circuit 832 is a dual output and dual in- have an exposed pad on the bottom-side of the IC for put regulator consisting of two identical LDO linear regu- better thermal performance. The DC832 comes installed lators, based on the LT3028 monolithic linear regulator. with ceramic capacitors, because of the LT3028 ability of Each independent input has a voltage range of 2.3V to maintaining stability with ceramic output capacitors. 20V, with one output (Vout1) capable of delivering up to There are ceramic bypass capacitors on each output for 500mA of output current, and the other output (Vout2) extra low noise performance. These features make the capable of delivering up to 100mA of output current. DC832 demo board an ideal circuit for use in battery- The DC supply current is typically only 50uA (for the powered, hand-held applications or noise sensitive ap- entire IC) at no load. The LT3028 comes in either a 16- plications. Gerber files for this circuit are avail- lead DFN package or TSSOP package, both of which able. Call the LTC Factory. QUICK START PROCEDURE The DC832 is easy to set up to evaluate the perform- 6. Vary Vout1 load current from 0 to 500mA. Its ance of the LT3028. For a proper measurement output voltages should be within a tolerance equipment configuration, set up the circuit according of +/- 4%. to the diagram in Figure 1. 7. Vary Vout2 load current from 0 to 100mA. Its Please follow the procedure outlined below for proper output voltages should be within a tolerance of +/- 4%. operation. 8. Observe both output voltages AC-coupled 1. Connect the input power supply to the Vin and they should measure noise voltages of less GND terminals. Connect the loads between than 5mVAC each. Refer to Figure 2 for the Vout and GND terminals. Refer to figure 1 proper measurement technique. for the proper measurement equipment setup. 9. When finished, insert jumpers JP1 and JP2 to 2. Before proceeding to operation, insert jump- the OFF position(s) and disconnect the power. ers JP1 and JP2 into the OFF positions, jump- ers JP3 and JP4 into the voltage options of Warning - If the power for the demo board is carried in choice (2.5V, 3.3V, and 5V). long leads, the input voltage at the part could ring, which could affect the operation of the circuit or even 3. Apply 6.5V at Vin. Measure both Vouts they exceed the maximum voltage rating of the IC. To elimi- should read 0V. nate the ringing, insert a small tantalum capacitor (for 4. Turn on Vout1 and Vout2 by changing jump- instance, AVX part TAJW106M025R) on the pads be- ers JP3 and JP4 from the OFF positions to the tween the input power and return terminals on the bot- ON positions. Both output voltages should be tom of the demo board. The (greater) ESR of the tanta- within a tolerance of +/- 2%. lum will dampen the (possible) ringing voltage due to 5. Vary the input voltage from 6.5V to 20V. Both the use of long input leads. On a normal, typical PCB, output voltages should be within +/- 3.3% tol- with short traces, the capacitor is not needed. erance. 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 832 DUAL OUTPUT LOW NOISE LDO REGULATORS Figure1. Proper Measurement Equipment Setup Figure 2. Measuring Input or Output Ripple 2