DEMO CIRCUIT 952 LTC3810 QUICK START GUIDE LTC3810 Current Mode Synchronous Switching Regulator Controller DESCRIPTION Demonstration circuit 952 is a current mode syn- A Power Good output is provided. The PGOOD chronous switching regulator featuring the output is normally high, with a pull up resistor to LTC3810. The circuit is configured as a synchro- VLOGIC. If the output voltage is not within 10% nous step-down regulator operating at 230kHz of nominal value the PGOOD signal will go low. switching frequency. Output voltage is 12V at 6A The circuit can be synchronized to an external maximum load. The input voltage range is 13V clock signal. 80V. Design files for this circuit board are available. The operating mode can be selected with jumper Call the LTC factory. JP1. Depending on the position of this jumper, at L, LTC, LTM, LT, Burst Mode, OPTI-LOOP, Over-The-Top and PolyPhase are low load the circuit will operate in forced continu- registered trademarks of Linear Technology Corporation. Adaptive Power, C-Load, DirectSense, Easy Drive, FilterCAD, Hot Swap, LinearView, Module, Micropower ous mode (for best load transient response at low SwitcherCAD, Multimode Dimming, No Latency , No Latency Delta-Sigma, No R , Operational Filter, PanelProtect, PowerPath, PowerSOT, SmartStart, current) or in pulse skip mode (for best efficiency SENSE SoftSpan, Stage Shedding, SwitcherCAD, ThinSOT, UltraFast and VLDO are at low current). With jumper JP1 in the mid position trademarks of Linear Technology Corporation. Other product names may be trade- marks of the companies that manufacture the products. the circuit can synchronize to an external clock signal on the Mode/Sync pin. PERFORMANCE SUMMARY Specifications are at TA = 25C SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS V Input Supply Range 13 80 V IN V Output Voltage V = 24V, I = 100mA 11.8 12 12.2 V OUT IN LOAD I Output Current V = 24V 0 6 A OUT IN I Input Current In Shutdown V = 24V, RUN/SS = 0V 288 648 A Q IN I V Current In Pulse Skip Mode V = 24V, V = INTVCC, No Load 3.5 mA IN IN IN FCB (No Load) I V Current In Forced Continuous Mode V = 24V, V = 0V, No Load 26 mA IN IN IN FCB (No Load) Efficiency Efficiency V = 24V, I = 6A 96.4 % IN OUT OPERATING PRINCIPLES The LTC3810 is a synchronous step-down switch- cycles with accurate cycle-by-cycle current limit ing regulator controller that can directly step down without requiring a current sense resistor. The cur- voltages from up to 100V input, making it ideal for rent limit is adjustable and the operating frequency telecom and automotive applications. is selected by an external resistor. The LTC3810 uses a constant on-time valley cur- The LTC3810 has a precise (0.5%) internal refer- rent control architecture to deliver very low duty ence, a 25MHz error amplifier, large gate drivers, 1 LTC3810 programmable softstart, a shutdown pin, a Sync An internal low dropout regulator can be used to input and a Power Good output. provide the bias voltage if a 6.7V15V voltage source is available. For example, in Demonstration The LTC3810 has a flexible bias regulator circuit Circuit 952 the bias voltage is generated from the that can be configured in many different ways to fit input voltage during startup and from the output the application. The 10V bias regulator can control voltage during normal operation. an external series transistor that allows the bias voltage to be generated from the input voltage. The demonstration circuit can be configured to use The demo board provides different footprints for current sense resistor by moving a couple of zero this external series transistor. ohm resistors to different locations. EQUIPMENT 4 DMMs 1 DC Supply 0-80V capable of delivering at least 85W 1 Adjustable load 0-6A QUICK START PROCEDURE Demonstration circuit 952 is easy to set up to evaluate the performance of the LTC3810. Refer to Figure 1 for proper measurement equipment setup and follow the procedure below: 1. Place jumpers in the following positions: JP1 Forced continuous mode operation JP2 ON 2. With power off, connect the input power supply to Vin and GND. 3. Set the power supply to 24V and turn on the power at the input. NOTE. Make sure that the input voltage does not exceed 80V. 4. Check for the proper output voltage. Vout = 11.8V to 12.2V. NOTE. If there is no output, temporarily disconnect the load to make sure that the load is not set too high. 5. Once the proper output voltages are established, adjust input voltage and load within the operating range and observe the output voltage regulation, ripple voltage, efficiency and other parameters. 2