QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 611 DUAL, SPREAD-SPECTRUM, LOW NOISE, INDUCTORLESS STEP DOWN DC/DC CONVERTER LTC3252 DESCRIPTION Demonstration circuit 611 is a dual, spread-spectrum, step down charge pump DC/DC converter featuring the LTC®3252EDE. It produces regulated 1.5V and 1.2V output voltages at up to 250mA of output current each from 2.7V to 5.5V input. The unique spread spectrum architecture of the LTC3252 provides highly efficient and low noise operation. The circuit has a low external parts count and requires only five small surface mount capacitors and four tiny surface mount resistors. DC611 demonstrates appropriate layout techniques for the LTC3252 inductorless DC-DC converter. This power supply circuit is ideally suited for space-constrained battery-powered applications that require small size and low operating current. Design files for this circuit board are available. Call the LTC factory. LTC is a registered trademark of Linear Technology Corporation. QUICK START PROCEDURE Demonstration circuit 611 is easy to set up and evaluate the performance of the LTC3252. Refer to Figure 1 for proper measurement equipment setup and follow the procedure below: 1. With power off, connect input power source to VIN and GND terminals. Input voltage range is limited to between 2.7V and 5.5V for the 1.2V output and between 3.21V and 5.5V for the 1.5V output. 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, VOUT1 or VOUT2 and GND terminals. See Figure 2 for proper scope probe technique. 2. Place selector jumper JP1 in the ON position to enable VOUT1 (1.5V), and jumper JP2 in the ON position to enable VOUT2. 3. If desired, loads may be connected from VOUT1 to GND and from VOUT2 to GND. The following VIN (min) vs. load chart must be followed to ensure correct regulation of VOUT1 and VOUT2: Table 1. VIN VS. LOAD CHART VIN (min) vs load VIN (MIN) IOUT1 IOUT2 3.5V 250mA 250mA 3.2V 100mA 250mA 3.1V 50mA 250mA 2.9V --- 250mA 2.7V --- 150mA 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 611 DUAL, SPREAD-SPECTRUM, LOW NOISE, INDUCTORLESS STEP DOWN DC/DC CONVERTER NOTE: VOUT1 is in dropout for VIN < 3.0V and will cause the LTC3252 to operate in continuous mode instead of the more efficient burst mode. To monitor the actual performance of VOUT2 for VIN <3.1V, VOUT1 should be disabled by placing jumper JP1 in the OFF position. 4. Turn on the power at the input. NOTE: Make sure that the input voltage does not exceed VOUT2 = 1.2V. If there is no output, temporarily disconnect the load to make sure that the load is not set too high. 6. Once the proper output voltages are established, adjust the loads up to 250mA and observe the output voltage regulation, input and output ripple voltage, efficiency and other parameters. Remember to follow the VIN (min) vs. load chart for correct regulation of VOUT1 and VOUT2. 5.5V. 5. Check for the proper output voltages. VOUT1 = 1.5V and Figure 1. Proper Measurement Equipment Setup Figure 2. Scope Probe Placement for Measuring Input or Output Ripple 2 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 611 DUAL, SPREAD-SPECTRUM, LOW NOISE, INDUCTORLESS STEP DOWN DC/DC CONVERTER 3