QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 741 DUAL OUTPUT LOW NOISE LDO REGULATORS LTC3025 DESCRIPTION Demonstration circuit 741 is an ultra-low dropout voltage supply using the LTC3025 linear regulator, which comes in a small 2mm x 2mm 6-Pin DFN package. The DC741 has an input voltage range from 0.9V to 5.5V, an output voltage range between 0.4V and 2.6V, and is capable of delivering 300 mA max of output current. The 0.4V reference of the LTC3025 allows the DC741 to supply power to very low voltage applications. DC741 is also an excellent choice for post regulation of step-down switching regulators, creating a high efficiency low-noise supply. The DC741 comes assembled with small ceramic capacitors, showing the LTC3025 ability to maintain stability with ceramic output capacitors. Gerber files for this circuit are available. Call the LTC Factory. LTC is a trademark of Linear Technology Corporation. QUICK START PROCEDURE DC741 is easy to set up to evaluate the performance of the LTC3025. For proper measurement equipment configuration, set up the circuit according to the diagram in Figure 1. 4. Insert jumper JP5 into the OFF position and move the shunt from jumper JP2 into any of the remaining output voltage options: 0.8V, 1.5V, or 1.8V. Re-insert jumper JP5 into the ON position. Just as in the 1.2Vout test, the output voltage should read Vout +/- 2% tolerance under static line and load conditions, and +/- 2% tolerance under dynamic line and load conditions. 5. When finished evaluating, insert jumper JP5 into the OFF position. Please follow the procedure outlined below for proper operation. 1. 2. Before proceeding to test, insert jumper JP5 into the OFF position, and insert a shunt into jumper JP2 for 1.2V output. Apply 1.3V to Vin (100 mV above Vout), and 5V to Vbias. Caution: The bias voltage must be 1.4V, or greater, above the output voltage, and it must be 2.5V, or greater, for the circuit to regulate. Insert jumper JP5 into the ON position. Measure Vout; it should be 1.2V+/-2% (1.176V to 1.224V). 3. Vary the input voltage from 1.3V to 5.5V and the load current from no load to 300 mA. Vout should measure 1.2V +/- 2% (1.176V to 1.224V). Note - If the power for the demo board is carried in long leads, the input voltage at the part could “ring”, due to the inductance in the long leads. This ringing could affect the operation of the circuit or even exceed the maximum voltage rating of the IC. To eliminate the ringing, a small tantalum capacitor (for instance, an AVX part # TAJW106M025R) was inserted on the pads between the input power and return terminals on the bottom of the demo board. The (greater) ESR of the tantalum will dampen the (possible) ringing voltage due to the use of long input leads. On a normal, typical PCB, with short traces, the capacitor is not needed. 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 741 DUAL OUTPUT LOW NOISE LDO REGULATORS VBIAS must exceed Vout by 1.4V or greater Figure1. Proper Measurement Equipment Setup Figure 2. Measuring Input or Output Ripple 2 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 741 DUAL OUTPUT LOW NOISE LDO REGULATORS RMS Output Noise vs. Load Current (10 Hz to 100 kHz) 120 Vout - 1.8V 100 Output Noise (uVrms) Vout - 1.5V 80 Vout - 1.2V Vout - 0.8V 60 40 20 0 0 50 100 150 200 250 300 Load Current (mA) Output Noise Spectral Density Output Noise Spectral Density (uV/rootHz) 10 1 0.1 0.01 0.01 0.1 1 10 100 Frequency (kHz) 3 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 741 DUAL OUTPUT LOW NOISE LDO REGULATORS 10 Hz to 100 kHz Output Noise (X-Axis Scale: 1ms/div; Y-Axis Scale: 100uV/div) LTC3025 Load-Step Response 4 A B C D E 4 4 3 3 VIN 1 BIAS 6 ENABLE OUT 4 3 FB 5 GND 2 1 2 2 2 3 1 1 A B C D E Item Qty Reference 1 2 3 4 5 6 7 8 9 10 11 12 13 14 3 1 0 0 6 4 1 2 3 2 1 1 1 2 C1,COUT,CIN CIN1 COUT1 (Opt) COUT2 (Opt) E1,E2,E3,E4,E5,E6 JP1,JP2,JP3,JP4 JP5 XJP4,XJP5 R1,R2,R5 R3,R4 R6 U1 Part Description Cap., X5R 1uF 6.3V 20% Cap., Tant. 10uF 25V 20% Cap., X5R 1uF 6.3V 20% Cap., Tant. 100uF 10V 20% Testpoint, Turret Jumper, 2pins 2mm Ctrs. Headers, 3 Pins 2mm Ctrs. SHUNT, .079" CENTER Res., Chip 40.2K 1/16W 1% Res., Chip 30.1K 0.06W 1% Res., Chip 10M 1/16W 5% I.C., VLDO Linear Regulator PRINTED CIRCUIT BOARD STENCIL Page 1 - of - 1 Manufacture / Part # TDK C1005X5R0J105M AVX TAJW106M025R TDK C1005X5R0J105M AVX TPSD107M010R0100 Mill Max 2501-2 CommConn Con Inc. 2802S-02G2 CommConn Con Inc. 2802S-03G2 CommConn Con Inc. CCIJ2MM-138GW AAC CR05-4022FM AAC CR05-3012FM AAC CR05-106JM Linear Tech. Corp. LTC3025EDC DEMO CIRCUIT 741A STENCIL DC741A