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 charge pump dc-dc converter. It comes with two assembly versions, DC903A-A and DC903A-B featuring the LTC3240-3.3 and LTC3240-2.5 respectively, each in a tiny 2mmx2mm DFN package. The DC903A-A and DC903A-B generate a fixed regulated output of 3.3V and 2.5V respectively over a wide input voltage range from 1.8V to 5.5V. The output current can reach up to 150mA when the input voltage is above 2.5V in DC903A-A. The maximum output current of DC903AB is designed at 60mA over the full input range. The DC903A optimizes the output efficiency by operating in the LDO step-down mode during most of the battery life time when the input is higher than the output voltage. When the battery voltage gets low enough it auto- matically switches into charge-pump doubling mode to maximize the battery usage. Additionally, DC903A features Automatic Burst Mode operation at light load to achieve low supply current (65µA, no load). Also, the built-in soft-start limits inrush current at turn-on, and short-circuit current limit/thermal protection help the part survive a continuous short-circuit. All these features make the circuit ideally suited for efficient DC-DC conversion in spaceconstrained applications such as battery-powered handheld electronics. Design files for this circuit board are available. Call the LTC factory. LTC is a trademark of Linear Technology Corporation Table 1. Performance Summary (TA = 25°C) PARAMETER CONDITION MINIMUM Input Voltage Range Maximum Output Current Output Voltage VOUT 150mA DC903A-B, 1.8V < VIN < 5.5V 60mA DC903A-A, Load Regulation (20MHz BW) VIN ≥ 2.5V, IOUT < 150mA 1.8V < VIN < 2.5V, IOUT <40mA VIN > 1.8V, IOUT < 60mA 3.168V 3.3V 3.432V 2.4V 2.5V 2.6V DC903A-A, IOUT = 150mA 32mVP–P DC903A-B, IOUT = 60mA 22mVP–P DC903A-A −1.7% −2.1% DC903A-B −0.6% −0.68% Nominal Switching Frequency Efficiency MAXIMUM 5.5V DC903A-A, VIN ≥ 2.5V DC903A-B, Output Ripple VOUT TYPICAL 1.8V 1.2MHz DC903A-A, VIN = 3.7V, IOUT = 150mA 85.8% DC903A-B, VIN = 1.8V, IOUT = 60mA 69.4% QUICK START PROCEDURE 1. Demonstration circuit 903A is easy to set up to evaluate the performance of the LTC3240-3.3 and LTC3240-2.5. Refer to Figure 1 for proper measurement equipment setup and follow the procedure below: 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 903A STEP-UP /STEP-DOWN DC-DC CHARGE PUMP CONVERTER NOTE: When measuring the input or output voltage ripple, care must be taken to avoid a long ground lead on the oscilloscope probe. Measure the input or output voltage ripple by touching the probe tip directly across the Vin or Vout and GND terminals. See Figure 2 for proper scope probe technique. 2. Place JP1 jumper in the ON position. 3. With power off, connect a 1.8V-5.5V, 500mA power supply to Vin and GND. 4. Connect a load (preset load current to 0A) to Vout and GND. 5. Turn on the power at the input. NOTE: Make sure that the input voltage does not exceed 5.5V. 6. Check for the proper output voltages. Vout should measure a typical 3.3V (could vary from 3.168V to 3.432V) for DC903A-A, and a typical 2.5V (could vary from 2.4V to 2.6V) for DC903A-B. 7. Once the proper output voltages are established, adjust the loads within the operating range and observe the output voltage regulation, ripple voltage, efficiency and other parameters. Figure 1. Proper Measurement Equipment Setup GND VIN Figure 2. Measuring Input or Output Ripple OPERATING PRINCIPLES The LTC3240 is a step-up/step-down charge pump DC/DC converter. For VIN greater than VOUT by about 100mV, the LTC3240 operates as a low dropout regulator. Once VIN drops to within 100mV of regulated VOUT, the 2 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 903A STEP-UP /STEP-DOWN DC-DC CHARGE PUMP CONVERTER part automatically switches into charge pump step-up mode to maintain the regulated output voltage. Regulation is achieved by sensing the output voltage through an internal resistor divider and modulating the charge pump output current based on the feedback error signal. In the charge pump mode, a 2-phase non-overlapping clock activates the charge pump switches. The flying capacitor is charged from VIN on the first phase of the clock. On the second phase of the clock it is stacked in series with VIN and connected to VOUT. Burst Mode operation, soft-start and short-circuit /thermal protection can be found on the LTC3240 datasheet at www.linear.com. 3 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 903A STEP-UP /STEP-DOWN DC-DC CHARGE PUMP CONVERTER 4