DEMO CIRCUIT 1359 LT3640 QUICK START GUIDE LT3640 Dual Monolithic Buck Regulator with Power- On Reset and Watchdog Timer DESCRIPTION Demonstration circuit 1359 is a Dual Monolithic Buck The circuit can be synchronized to an external clock con- Regulator with Power-On Reset and Watchdog Timer nected to the SYNC terminal. If the SYNC function is featuring the LT3640. The board operates from inputs up used, the Rt resistor (R9) should be chosen to set the to 35V and withstands transients up to 55V. The outputs LT3640 internal switching frequency at least 20% below are 3.3V, 0.8A and 1.2V, 1A. At light loads, both regula- the lowest synchronization input frequency. tors operate in low ripple Burst Mode to maintain high The LT3640 datasheet gives complete descriptions of the efficiency and low output ripple. Users can populate R13 part, operation and application information. The data- on the EN/UVLO pin to provide a programmable under sheet must be read in conjunction with this quick start voltage lockout. Both channels have cycle-by-cycle cur- guide for working on or modifying the demo circuit rent limit, providing protection against shorted outputs. 1359. The power-on reset and watchdog timer periods are in- dependently adjustable using external capacitors. Tight Design files for this circuit board are available. Call accuracy specifications and glitch immunity ensure reli- the LTC factory. able operation of the circuit. Watchdog can be enabled or disabled by JP1. L, LTC, LTM, LT are trademarks of Linear Technology Corporation. Other product names may be trademarks of the companies that manufacture the products. PERFORMANCE SUMMARY Specifications are at TA = 25C SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS V = 3.3V, I = 0.8A OUT1 OUT1 V Input Supply Range 5 35 V IN V = 1.2V, I = 1A OUT2 OUT2 V Output Voltage 1 V = 12V, I = 0.8A 3.20 3.30 3.40 V OUT1 IN OUT1 V Output Voltage 2 V = 12V, I = 1A 1.16 1.20 1.24 V OUT2 IN OUT2 I Output Current 1 0 0.8 A OUT1 I Output Current 2 0 1 A OUT2 I No Load Quiescent Current V = 12V, V = 3.3V, V = 1.2V, No 0.33 mA Q IN OUT1 OUT2 Load F Switching Frequency 1.75 2 2.35 MHz SW T Watchdog Upper Boundary Period C7 = 1500pF 55.5 ms WDU T Watchdog Lower Boundary Period C7 = 1500pF 3.5 ms WDL T Programmed Reset Period C8 = 1500pF 55.5 ms RST 1 LT3640 QUICK START PROCEDURE Demonstration circuit 1359 is easy to set up to evaluate 5. Check for the proper output voltages: the performance of the LT3640. Refer to Figure 1 for VOUT1 = 3.3V, VOUT2 = 1.2V proper measurement equipment setup and follow the NOTE. If there is no output, temporarily disconnect the load to make sure procedure below: that the load is not set too high or is shorted. 1. Place Jumper JP1 in the following position: 6. Once the proper output voltages are established, ad- OFF: Watchdog Disabled just the loads within the operating range and observe the output voltage regulation, ripple voltage, efficiency ON: Watchdog Enabled and other parameters. 2. With power off, connect the input power supply to VIN 7. To test the watchdog timer, connect a clock input to and GND. the WDI terminal. Observe the output at the WDO ter- 3. With power off, connect loads from VOUT1 to GND minal while the clock parameters are adjusted. and VOUT2 to GND. 8. To test Power-On Reset, observe output at the RESET 4. Turn on the power at the input. terminals: RST1 and RST2. NOTE. Make sure that the input voltage does not exceed 35V. 2