DC463A Analog Devices

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 463 STEP-DOWN REGULATOR WITH LDO LTC3700 DESCRIPTION Demonstration circuit 463 is a step-down (buck) regula- space. The demo circuit highlights the capabilities of the tor and a Low Drop Out (LDO) regulator using the LTC3700. A constant operating frequency of 550kHz LTC3700 in the 10-lead MSOP package. The buck regu- makes the LTC3700 attractive for noise-sensitive appli- lator is capable of providing 1A at an output voltage of cations while allowing for smaller external components 3.3V from an input supply of 5V to 9V. The LDO can be such as output filter inductor and capacitor. In addition, powered from either the buck regulator output or a high efficiency operation over a wide load current range separated DC input, and produces an output up to 2.5V makes the LTC3700 ideal for battery-powered applica- at 150mA. The combination of a buck regulator and a tions. LDO, and the use of surface mount components result in Design files for this circuit board are available. Call a highly efficient application circuit in a very small board the LTC factory. Table 1. Performance Summary PARAMETER CONDITION VALUE Input Voltage Range of Buck regulator 5V to 9V Input Voltage Range of LDO 3.3V to 5V V V = 5V to 9V, I = 0A to 1A 3.3V 3% OUT1 IN OUT1 V V = 3.3V to 5V, I = 0A to 150mA 2.5V 4% OUT2 IN OUT1 Typical Output Ripple V V = 5V, I = 1A 30mV OUT1 IN OUT1 PP Typical Output Ripple V V = 3.3V, I = 150mA 5mV OUT2 IN OUT2 PP Nominal Switching Frequency Buck Regulator 550kHz QUICK START PROCEDURE Demonstration circuit 463 is easy to set up to evaluate 2. To operate the LDO circuit with a separate, second the performance of the LTC3700. Refer to Figure 1 for input, set JP1 to the Vin2 position. Connect a second proper measurement equipment setup and follow the 3.3V to 5V power source to the Vin2 and GND termi- procedure below: nals. NOTE: When measuring the input or output voltage rip- 3. Connect the loads. ple, care must be taken to avoid a long ground lead on 4. For single source operation, set the input source se- the oscilloscope probe. Measure the input or output lector Jumper JP1 to Vout1 position. Remove the voltage ripple by touching the probe tip directly across connection of power source Vin2. The LDO will be the input or output and ground terminals. See Figure 2 powered from Vout1. for proper scope probe technique. 1. Connect a 5V to 9V power source to the Vin1 and GND terminals. 1 GND VIN QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 463 STEP-DOWN REGULATOR WITH LDO + LOAD + + + + LOAD + Figure 1. Proper Measurement Equipment Setup Figure 2. Measuring Input or Output Ripple 20mV/DIV 10mV/DIV 1s/DIV 1s/DIV Figure 3. 3.3V Buck Output Ripple Figure 4. 2.5V LDO Output Ripple (V = 5V, I = 1A) (V = 3.3V, I = 150mA) IN OUT IN OUT 2 + + + + + +