QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 903A STEP-UP /STEP-DOWN DC-DC CHARGE PUMP CONVERTER LTC3240-3.3 and LTC3240-2.5 DESCRIPTION Demonstration circuit 903A is a step-up/step-down matically switches into charge-pump doubling mode to charge pump dc-dc converter. It comes with two assem- maximize the battery usage. bly versions, DC903A-A and DC903A-B featuring the Additionally, DC903A features Automatic Burst Mode LTC3240-3.3 and LTC3240-2.5 respectively, each in a operation at light load to achieve low supply current tiny 2mmx2mm DFN package. (65mA, no load). Also, the built-in soft-start limits in- The DC903A-A and DC903A-B generate a fixed regulated rush current at turn-on, and short-circuit current output of 3.3V and 2.5V respectively over a wide input limit/thermal protection help the part survive a continu- voltage range from 1.8V to 5.5V. The output current can ous short-circuit. All these features make the circuit ide- reach up to 150mA when the input voltage is above 2.5V ally suited for efficient DC-DC conversion in space- in DC903A-A. The maximum output current of DC903A- constrained applications such as battery-powered hand- B is designed at 60mA over the full input range. held electronics. The DC903A optimizes the output efficiency by operating Design files for this circuit board are available. Call in the LDO step-down mode during most of the battery the LTC factory. life time when the input is higher than the output volt- LTC is a trademark of Linear Technology Corporation age. When the battery voltage gets low enough it auto- Table 1. Performance Summary (T = 25C) A PARAMETER CONDITION MINIMUM TYPICAL MAXIMUM Input Voltage Range 1.8V 5.5V DC903A-A, V 2.5V 150mA IN Maximum Output Current DC903A-B, 1.8V < V < 5.5V 60mA IN V 2.5V, I < 150mA IN OUT DC903A-A, 3.168V 3.3V 3.432V Output Voltage V 1.8V < V < 2.5V, I <40mA OUT IN OUT DC903A-B, V > 1.8V, I < 60mA 2.4V 2.5V 2.6V IN OUT DC903A-A, I = 150mA 32mV PP OUT Output Ripple V (20MHz BW) OUT DC903A-B, I = 60mA 22mV PP OUT DC903A-A -1.7% -2.1% Load Regulation DC903A-B -0.6% -0.68% Nominal Switching Frequency 1.2MHz DC903A-A, V = 3.7V, I = 150mA 85.8% IN OUT Efficiency DC903A-B, V = 1.8V, I = 60mA 69.4% IN OUT QUICK START PROCEDURE 1. Demonstration circuit 903A is easy to set up to evalu- Refer to Figure 1 for proper measurement equipment ate the performance of the LTC3240-3.3 and setup and follow the procedure below: LTC3240-2.5. 1 GND VIN QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 903A STEP-UP /STEP-DOWN DC-DC CHARGE PUMP CONVERTER NOTE: When measuring the input or output voltage rip- 5. Turn on the power at the input. ple, care must be taken to avoid a long ground lead on NOTE: Make sure that the input voltage does not ex- the oscilloscope probe. Measure the input or output ceed 5.5V. voltage ripple by touching the probe tip directly across 6. Check for the proper output voltages. Vout should the Vin or Vout and GND terminals. See Figure 2 for measure a typical 3.3V (could vary from 3.168V to proper scope probe technique. 3.432V) for DC903A-A, and a typical 2.5V (could vary 2. Place JP1 jumper in the ON position. from 2.4V to 2.6V) for DC903A-B. 3. With power off, connect a 1.8V-5.5V, 500mA power 7. Once the proper output voltages are established, ad- supply to Vin and GND. just the loads within the operating range and observe 4. Connect a load (preset load current to 0A) to Vout and the output voltage regulation, ripple voltage, efficiency GND. and other parameters. Figure 1. Proper Measurement Equipment Setup Figure 2. Measuring Input or Output Ripple OPERATING PRINCIPLES The LTC3240 is a step-up/step-down charge pump 100mV, the LTC3240 operates as a low dropout regula- DC/DC converter. For V greater than V by about tor. Once V drops to within 100mV of regulated V , the IN OUT IN OUT 2