DC1687B Analog Devices

DEMO MANUAL DC1687B LTC3115-1 40V, 2A Synchronous Buck-Boost DC/DC Converter DESCRIPTION Demonstration circuit 1687B features the LTC 3115-1, a The demo board also has optional provisions to back high voltage monolithic synchronous buck-boost converter. feed V in order to increase efficiency in some 5V out- CC put applications. There is also a provision for an optional The DC1687B demo board has two user-selectable operat- Schottky diode from SW2 to V for applications where OUT ing modes: Burst Mode operation and forced continuous V is greater than 20V and short circuit protection is OUT operation (fixed frequency PWM) (JP1). There is also an desired. Consult the data sheet for more information on accurate programmable RUN pin which is used to enable these options. the converter (JP2). Figures 1 and 2 show typical demo board efficiency. The DC1687B operates with a 2.7V to 40V input volt- age range. The demo board has been designed with the The LTC3115-1 data sheet has detailed information about output voltage set to 5V. The LTC3115-1 incorporates a the operation, specifications, and applications of the part. proprietary low noise switching algorithm which optimizes The data sheet should be read in conjunction with this efficiency with input voltages above, below or equal to the quick start guide. output voltage and ensures seamless transitions between Design files for this circuit board are available. operating modes. All registered trademarks and trademarks are the property of their respective owners. The demo board has been programmed to operate at 1MHz in PWM mode to optimize small size with high efficiency operation. PERFORMANCE SUMMARY PARAMETER VALUE Input Voltage Range 2.7V to 40V V 5.0V OUT I (See Note 1) 1A For V 3.6V, OUT IN 2A For V > 6V IN Efficiency See Figures 1 and 2 Note 1: The Demo Board output current is a function of V . Please refer to the data sheet for more information IN Note: This manual is intended to be used with an updated version of the demo board titled, Demo Circuit 1687B. See Figure3. Rev. 0 1DEMO MANUAL DC1687B QUICK START PROCEDURE Using short twisted pair leads for any power connections 3. Connect a 500mA load to V as shown in Figure3 OUT and with all loads and power supplies off, refer to Figure3 (10 for V = 5V). Connect an ammeter if accurate OUT for the proper measurement and equipment setup. The current measurement or monitoring is desired. battery/power supply (PS1) should not be connected to 4. Turn on PS1 and slowly increase voltage until the volt- the circuit until told to do so in the procedure below. age at V is 4.0V. IN When measuring the input or output voltage ripple, care 5. Verify V is ~5.0V. OUT must be taken to avoid a long ground lead on the oscil- 6. V can now be varied between 2.7V and 40V. I may loscope probe. Measure the input or output voltage ripple IN OUT need to be reduced for V < 4V. V should remain in by touching the probe tip directly across the V or V IN OUT IN OUT regulation. and GND terminals (see Figure4), or by using an oscil- loscope probe tip jack. 7. Load current (I ) can also be varied. The maximum OUT I is a function of V and the current limit. Consult 1. Jumper and PS1 settings to start: OUT IN the data sheet for more information on I vs V . In OUT IN PS1 = OFF general for V > 3.6V I can be increased to 1A. For IN OUT JP1 (PWM) = fixed frequency V > 6V I can be increased to 2A. IN OUT JP2 (RUN) = ON 8. For Burst Mode operation, move Jumper JP1 to burst. I is limited in Burst Mode operation. See the data OUT 2. With power OFF connect the power supply (PS1) as sheet for more information. shown in Figure3 . If accurate current measurements are desired (for efficiency calculation for example) then 9. NOTE: If V drops out of regulation, check to be sure OUT connect an ammeter in series with the supply as shown. the maximum load has not been exceeded, or that V IN The ammeter is not required however. is not below the minimum value for regulation (see data sheet) 100 100 90 90 80 80 70 70 60 60 LOAD = 100mA LOAD = 500mA LOAD = 200mA LOAD = 1A LOAD = 300mA 50 50 0 5 10 15 20 25 30 35 40 0 5 10 15 20 25 30 35 40 V (V) V (V) IN IN Figure1. DC1687B Efficiency in PWM Mode Figure2. DC1687B Efficiency in Burst Mode Operation Rev. 0 2 EFFICIENCY (%) EFFICIENCY (%)