QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1283 500mA VERY LOW DROPOUT LINEAR REGULATOR LTC3025-1 DESCRIPTION Demonstration circuit 1283 is an ultra-low dropout volt- regulation of step-down switching regulators, combining age supply using the LTC3025-1 linear regulator, which to create a high efficiency low-noise supply. The comes in a small 2mm x 2mm 6-Pin DFN package. The DC1283 comes installed with small ceramic capacitors, DC1283A has an input voltage range from 0.9V to 5.5V, showing the LTC3025-1 ability to maintain stability with an output voltage range between 0.4V and 2.6V, and is ceramic output capacitors. capable of delivering 500 mA max of output current. The 0.4V reference of the LTC3025-1 allows the Design files for this circuit board are available. Call DC1283A to supply power to very low voltage applica- the LTC factory. tions. The DC1283A is also an excellent choice for post Table 1. Performance Summary (T = 25C) A PARAMETER CONDITIONS VALUE Input Voltage Range 0.9V to 5.5V Bias Voltage Range V V + 1.5V 2.5V to 5.5V BIAS OUT 0.8V2%(1.152V to 1.248V) V = 2.25V to 5.5V, I = 0A to 500 mA, 1.2V2%(1.152V to 1.248V) IN OUT Output Voltage Regulation V = 5V 1.5V 2%(1.44V to 1.56V) BIAS 1.8V2%(1.728V to 1.872V) Typical Dropout Voltage V = 1.5V, V = 2.8V, I = 500mA 75mV IN BIAS OUT Typical Output Voltage Ripple & Noise < 10mV PP QUICK START PROCEDURE The DC1283 demonstration board is easy to set directly across the Vin or Vout and GND termi- up to evaluate the performance of the LTC3025- nals. See Figure 1 for proper scope probe tech- 1. For proper measurement equipment configu- nique. The DC1283 is easy to set up to evalu- ration, set up the circuit according to the dia- ate the performance of the LTC3025-1. For a gram in Figure 2. Before proceeding to test, in- proper measurement equipment configuration, sert the Vout Enable jumper into the OFF (up- set up the circuit according to the diagram in per) position, connecting the RUN pin to ground Figure 2. (GND), which shuts down the circuit. When measuring the input or output ripple or Please follow the procedure outlined below for noise voltage, care must be taken to avoid a proper operation. long ground lead on the oscilloscope probe. Measure the voltages by touching the probe tip 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1283 500mA VERY LOW DROPOUT LINEAR REGULATOR 1. Before proceeding to test, insert the Vout Re-insert the Vout Enable jumper into the Enable jumper into the OFF position, and ON position. Just as in the 1.2V Vout test, insert a shunt into jumper of the 1.2V out- the output voltage should read Vout +/- 2% put voltage option. tolerance under static line and load condi- tions, and +/- 2% tolerance under dynamic 2. Apply 1.4V to Vin (100 mV above Vout), line and load conditions. and 5V to Vbias. 5. When finished evaluating, insert the Vout Caution: The bias voltage must be 1.5V, or Enable jumper into the OFF position. greater, above the output voltage, and it must be 2.5V, or greater, for the circuit to Note - If the power for the demo board is carried in regulate. long leads, the input voltage at the part could ring, due to the inductance in the long leads. Insert Vout Enable jumper into the ON po- This ringing could affect the operation of the circuit sition. Measure Vout it should be 1.2V+/- or even exceed the maximum voltage rating of the 2% (1.176V to 1.224V). IC. To eliminate the ringing, a small tantalum ca- 3. Vary the input voltage from 1.4V to 5.5V pacitor (for instance, an AVX part and the load current from no load to 500 TAJW226M010R) was inserted on the pads be- mA. Vout should measure 1.2V +/- 2% tween the input power and return terminals on the (1.176V to 1.224V). bottom of the demo board. The (greater) ESR of the tantalum will dampen the (possible) ringing 4. Insert the Vout Enable jumper into the OFF voltage due to the use of long input leads. On a position and move the Vout shunt from the normal, typical PCB, with short traces, the capaci- 1.2V option into any of the remaining out- tor is not needed. put voltage options: 0.8V, 1.5V, or 1.8V. Figure 1. Measuring Input or Output Ripple 2