DEMO CIRCUIT 964A LT3501 QUICK START GUIDE LT3501 3A Dual Monolithic Step-Down DC/DC Converter DESCRIPTION Demo circuit 964A is a dual monolithic step-dow n DC/DC converter featuring LT3501. The demo circuit is designed for 3.3V and 1.8V outputs from a 4.5V to 24V input. The current capability of each channel is up to 3A. Independent input voltage, feedback, soft-start and pow er good pins for each channel simplify complex pow er supply tracking/sequencing requirements. Both converters are synchronized to either a common external clock input or a resistor programmable 250kH z to 1.5M H z internal oscillator. At all frequencies, a 180° phase shift betw een channels is maintained, reducing voltage ripple and component size. Programmable frequency allow s for optimization betw een efficiency and external component size. cles, only sw itching off w hen the boost capacitor needs recharging,resulting in ~95% maximum duty cycle. Each output can be independently disabled using its ow n soft-start pin, or by using the SH DN pin the entire part can be placed in a low quiescent current shutdow n mode. The LT3501 datasheet gives a complete description of the part,operation and application information. The datasheet must be read in conjunction w ith this quick start guide for demo circuit 964A. Design files for this circuit board are available. Call the LTC factory. ,LTC and LT are registered trademarks ofLinear Technology Corporation. M inimum input-to-output voltage ratios are improved by allow ing the sw itch to stay on through multiple clock cy- Performance Summary ( TA = 25oC ) PAR AM ETER M inimum Input Voltage M aximum Input Voltage O utput Voltage VOUT1 O utput Voltage VOUT2 Sw itching Frequency M aximum O utput Current Iout1 and Iout2 Voltage R ipple VOUT1 Voltage R ipple VOUT2 CO N DITIO N VIN=4.5~16V VIN=16~24V VIN=12V,Iout1=3A VIN=12V,Iout2=3A VALU E 4.5V 24V 3.3V ±4% 1.8V ±4% 500kH z ±20% 3.0A 2.8A <10mV <10mV 1 LT3501 QUICK START PROCEDURE Demo circuit 964A is easy to set up to evaluate the performance of the LT3501. R efer to Figure 1 for proper measurement equipment setup and follow the procedure below : NOTE. W hen measuring the input or output voltage ripple,care must be taken to avoid a long ground lead on the oscilloscope probe. M easure the input or output voltage ripple by touching the probe tip directly across the VIN or VO U T and GND terminals. See Figure 2 for proper scope probe technique. 1. Place JP1 on the CO M BINED position. 2. W ith pow er off, connect the input pow er supply to VIN1 and G ND. (Connect another input pow er supply to VIN2 and G ND ifINDEPENDENT is selected.) 3. Turn on the pow er at the input. NOTE. M ake sure that the input voltage does not exceed 24V. 4. Check for the proper output voltages. NOTE. Ifthere is no output,temporarily disconnect the load to make sure that the load is not set too high. 5. O nce the proper output voltage is established, adjust the load w ithin the operating range and observe the output voltage regulation,ripple voltage,efficiency and other parameters. Figure 1. Proper M easurem ent Equipm ent Setup 2 LT3501 GND VIN Figure 2. M easuring Input or Output Ripple ADDITIONAL NOTES 1. Install a 10k resistor at R 22 if the board is synchronized from an external signal generator. 2. Different tracking and sequencing schemes can be exercised. H ow ever, the Vout1 should stay on for proper operation ofVout2. 3 LT3501 4