QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 519 1.1MHZ DUAL STEP-DOWN DC/DC CONVERTER LT1940 DESCRIPTION Demonstration circuit 519 is a 1.1MHz dual step-down smallest size generates 3.3V at up to 1A and 1.8V at DC/DC switching converter using the LT1940. The up to 1A output from a 4.8V14V input. The larger, LT1940 features fast switching speed, two 1.6A inter- more versatile circuit generates 5V at up to 1.4A and nal power switches, and a wide input voltage range, 3.3V at up to 1.4A output from a separate 6.8V to 25V making it a versatile and powerful IC that fits easily input. The two circuits are completely isolated from into space-constrained applications and removes the each other and can be run simultaneously or inde- need for two separate dc/dc converters in dual output pendently. The versatile circuit has options for chang- step-down applications. The constant 1.1MHz switch- ing the boost diodes for highest efficiency under dif- ing frequency allows for the use of tiny, surface mount ferent output voltage conditions. The feedforward ca- external components. The current-mode control topol- pacitors and noise-reduction capacitors on the Vc pins ogy yields fast transient response and good loop sta- further increase the parts count on the versatile board, bility, requiring a minimum number of external com- yet they improve the transient response and give the pensation components and allowing the use of ce- ability to optimize loop compensation under various ramic input and output capacitors. The anti-phase conditions. switching and single-IC solution require the use of This board is designed for applications that require only a single input capacitor. The low resistance inter- two step-down supplies with up to 1.4A load current in nal 2A power switches (0.21 ) maintain high efficien- a small board space with low cost and low parts count cies (as high as 90%) over a wide range of input volt- as well as simple circuit design. The high current, on- ages and loads. Its 30A shutdown current (activated board, dual monolithic switches eliminate the need for via the Run/SS pins) extends battery life. The wide V IN external switches. The use of ceramic capacitors in range of the LT1940 allows step-down configurations this circuit not only demonstrates small size and low with up to 25V input. cost, but the advantage of current-mode control in The demonstration board has two circuits to demon- step-down applications with a simple compensation strate both the small space that the monolithic dual network and a feedforward capacitor for more rugged step-down converter can achieve with high currents stability and excellent transient response. and a single IC as well as the versatility and maximum Design files for this circuit board are available. Call power output of the IC. The circuit demonstrating the LTC factory. Table 1. Typical Performance (T = 25C) for Small Dual Step-Down Converter (VOUT1=3.3V and VOUT2=1.8V) A PARAMETER VALUE V 4.8V to 14V IN VOUT1 3.3V V 1.8V OUT2 V Load Current 1A(max) OUT1 V Load Current 1A(max) OUT2 Efficiency 80% at 1A load current (V and V ) OUT1 OUT2 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 519 1.1MHZ DUAL STEP-DOWN DC/DC CONVERTER Table 2. Typical Performance (T = 25C) for Customizable Dual Step-Down Converter (VOUT1=5.0V and VOUT2=3.3V) A Parameter Value V 6.8V to 25V IN VOUT1 5.0V VOUT2 3.3V VOUT1 Load Current 1.4A(max) VOUT2 Load Current 1.4A(max) Efficiency 84% at 1A load current (VOUT1 and VOUT2) 100% 100% 90% 90% 80% 80% 70% 70% 60% 60% VIN = 5V VIN = 8V 50% 50% VIN = 8V VIN = 12V 40% 40% VIN = 12V VIN = 18V 30% 30% 20% 20% 10% 10% 0% 0% 0 200 400 600 800 1.0k 0 200 400 600 800 1.0k 1.2k 1.4k V OUT1 LOAD CURRENT (mA) V OUT1 LOAD CURRENT (mA) VOUT2 LOAD CURRENT = 1A VOUT2 LOAD CURRENT = 1A Figure 1. Typical Efficiency of Demo Circuit 519 LT1940, Small Figure 3. Typical Efficiency of Demo Circuit 519 LT1940, Custom- Dual Step-Down VOUT1=3.3V, VOUT2=1.8V izable Dual Step-Down VOUT1=5.0V, VOUT2=3.3V 100% 100% 90% 90% 80% 80% 70% 70% 60% 60% VIN = 5V VIN = 8V 50% 50% VIN = 8V VIN = 12V 40% 40% VIN = 12V VIN = 18V 30% 30% 20% 20% 10% 10% 0% 0% 0 200 400 600 800 1.0k 0 200 400 600 800 1.0k 1.2k 1.4k V OUT2 LOAD CURRENT (mA) V OUT2 LOAD CURRENT (mA) VOUT1 LOAD CURRENT = 1A VOUT1 LOAD CURRENT = 1A Figure 2. Typical Efficiency of Demo Circuit 519 LT1940, Small Figure 4. Typical Efficiency of Demo Circuit 519 LT1940, Custom- Dual Step-Down VOUT1=3.3V, VOUT2=1.8V izable Dual Step-Down VOUT1=5.0V, VOUT2=3.3V 2 EFFICIENCY EFFICIENCY EFFICIENCY EFFICIENCY