DEMO CIRCUIT 1419A LT3663EDCB QUICK START GUIDE LT3663EDCB 1.2A, 1.5MHz Step-Down Switching Regulator with Output Current Limit DESCRIPTION Demonstration Circuit 1419 is a 1.5MHz current mode The LT3663EDCB is available in an 8-lead (2mm step-down switching regulator with programmable 3mm) DFN surface mount package with exposed pad. output current limit. The current limit accurately con- trols the system power dissipation and reduces the Design files for this circuit board are available. Call size of the power path components. the LTC factory. The wide operating input voltage range of 7.5V to 36V L, LTC, LTM, LT, Burst Mode, OPTI-LOOP, Over-The-Top and PolyPhase are registered (60V maximum) suits the LT3663 to a variety of input trademarks of Linear Technology Corporation. Adaptive Power, C-Load, DirectSense, Easy Drive, FilterCAD, Hot Swap, LinearView, Module, Micropower SwitcherCAD, Multimode sources, including unregulated 12V wall adapters, 24V Dimming, No Latency , No Latency Delta-Sigma, No R , Operational Filter, PanelProtect, SENSE industrial supplies, and automotive power. PowerPath, PowerSOT, SmartStart, SoftSpan, Stage Shedding, SwitcherCAD, ThinSOT, UltraFast and VLDO are trademarks of Linear Technology Corporation. Other product names The LT3663 includes a low current shutdown mode, may be trademarks of the companies that manufacture the products. input overvoltage lockout and thermal shutdown. PERFORMANCE SUMMARY Specifications are at T = 25C A SYMBOL PARAMETER CONDITIONS MIN MAX UNITS VIN Input Voltage Range 7.5 to 36.0 V VOUT Output Voltage Range Iou1 0mA to ILIM 3.3 or 5.0 V ILIM Current Limit 0.6 1.2 A OPERATING PRINCIPLE Refer to the block diagram within the LT3663 data node provides current limit. The LT3663 is internally sheet for its operating principle. compensated with a pole zero combination on the output of the gm amplifier. The LT3663 is a constant frequency, current mode step An external capacitor and internal diode are used to gen- down regulator. A switch cycle is initiated when the erate a voltage at the BOOST pin that is higher than the 1.5MHz oscillator enables the RS flip flop, turning on an input supply. This allows the driver to fully saturate the internal power switch, Q1. An amplifier and comparator internal bipolar NPN power switch for efficient operation. monitor the current flowing between the VIN and SW The switch driver operates from either VIN or BOOST to pins, turning the switch off when the current reaches a ensure startup. level determined by the voltage at node V . The error An internal regulator provides power to the control cir- C amplifier measures the output voltage through an exter- cuitry. This regulator includes an input under-voltage and nal resistor divider tied to the FB pin and servos the V overvoltage protection which disable switching action C node. If the error amplifiers output increases, more cur- when VIN is out of range. When switching is disabled, rent is delivered to the output if it decreases, less cur- the LT3663 can safely sustain input voltages up to 60V. rent is delivered. An active clamp (not shown) on the V C 1 LT3663EDCB Note that while switching is disabled the output will start pin. A capacitor averages the inductor ripple current. If to discharge. the averaged inductor current exceeds the programmed value then the V voltage is pulled low, reducing the cur- C Output current limiting is provided via the servo action of rent in the regulator. The output current limit circuit al- an amplifier. It compares the voltage across an inductor lows for a lower current rated inductor and diode and current sense resistor, RSENSE2, and compares it to a provides better control of system power dissipation. voltage programmed by external resistor R1 on the ILIM QUICK START PROCEDURE Using short twisted pair leads for any power con- 6. Set JP2 to 1 and JP3 to 0. Increase LOAD1 nections, with all loads and power supplies off, refer current until VOUT drops below 4.9V. Verify to Figure 1 for the proper measurement and equip- LOAD1 current is between 900mA and 1.1A. ment setup. Reduce LOAD1 current to 120mA. Follow the procedure below: 7. Set JP2 to 0 and JP3 to 1. Increase LOAD1 current until VOUT drops below 4.9V. Verify 1. Jumper, PS and LOAD 1ettings to start: LOAD1 current is between 700mA and JP1 = Run JP4 = 5.0V 900mA. Reduce LOAD1 current to 120mA. JP2 = 1 PS1 = OFF JP3 = 1 LOAD1 = OFF 8. Set JP2 to 0 and JP3 to 0. Increase LOAD1 current until VOUT drops below 4.9V. Verify 2. Turn on PS1 and slowly increase voltage to LOAD1 current is between 500mA and 5.5V while monitoring the input current. If the 700mA. Reduce LOAD1 current to 120mA. current remains less than 50mA, increase PS1 9. Set JP2 to 1, JP3 to 1 and JP4 to 3.3V. Verify until output turns on. Verify input voltage voltage on VOUT of 3.2V to 3.4V UVLO of 6.5V to 7.5V. 10. Set LOAD1 to 1.0A. Verify voltage on VOUT of 3. Increase PS1 to 12V and set LOAD1 to 3.2V to 3.4V and ripple voltage of <50mV. 120mA. Verify voltage on VOUT of 4.85V to 5.15V. 11. Increase PS1 to 36V and verify voltage on VOUT of 3.2V to 3.4V. 4. Set LOAD1 to 1.0A. Verify voltage on VOUT of 4.85V to 5.15V and ripple voltage of <50mV. 12. Increase PS1 to 40V and verify voltage on VOUT of 500mV. 5. Increase LOAD1 current until VOUT drops be- low 4.9V. Verify LOAD1 current is between 13. Decrease PS1 to 30V and verify voltage on 1.1A and 1.4A. Reduce LOAD1 current to VOUT of 3.2V to 3.4V. 120mA. 14. Turn off PS1 and Load 1. 2