QUICK START GUIDE FOR DC989B-A TINY NO R BOOST CONVERTER SENSE LTC3872 DESCRIPTION Demonstration circuit 989B-A is a single-output to MOSFET selection, its not only switching ele- boost converter, it features tiny, boost controller ment, but also its R represents the current DS(ON) LTC3872. The input voltage is from 3.0V to 4.5V sensing element for the control loop, see LTC3872 without output de-rating. The supply has one out- datasheet for details. LTC3872 allows design put: 5V/2A . Minimum input voltage is 2.75V. small size and high efficiency step-up DC/DC solu- MAX When input voltage is lower than 3V, output cur- tions. rent should be de-rated. The design employs the Design files for this circuit board are available. LTC3872, the small footprint NO R boost SENSE Call the LTC factory. regulator. The switching frequency is fixed at 550 kHz. With current mode control and OPTI-LOOP TM-NO R is trademark of Linear Technology Corporation SENSE compensation, DC989B-A can be optimized to provide fast transient response. NO R tech- SENSE nique reduces both: size of the converter and power dissipation. However, care should be taken Table 1. Performance Summary (T = 25C) A PARAMETER CONDITION VALUE Minimum Input Voltage If the input voltage must be lower than 3V, degrade output load current. 2.75V Maximum Input Voltage 4.5V Output Voltage V 5V +/- 2% OUT Maximum Continuous output Vin = 3V to 4.5V 2A Current Typical Operating Frequency Fixed 550kHz Typical Output Ripple (V ) 20MHz BW, 2A load, V = 3V, frequency = 550kHz 30mV OUT IN P-P Efficiency V =3V, V =5V I=2A 90% IN OUT OUT QUICK START PROCEDURE Demonstration circuit 989B-A is easy to set up to 2. Connect the input power supply to the VIN evaluate the performance of the LTC3872. Please and GND terminals on the right, center of refer to Figure 1 for proper measurement equip- the board. ment setup and follow the procedure below: NOTE: Do not increase V over 5V. IN 1. Place RUN in ON position for normal oper- 3. Vary the input voltage from 3.0V to 4.5V ation. and adjust the load current from 0 to 2A. Connect the desired loads between 5V output Measure the output voltages. V should OUT terminal and the GND terminal on the board. read between 5.0V 0.1V within specified maximum load current. NOTE: The maximum load is 2A. 4. Measure the output ripple voltage at maxi- mum output current level and minimum in- 1 QUICK START GUIDE FOR DC989B-A TINY NO R BOOST CONVERTER SENSE put voltage it usually will measure less than 30mV. A Figure 1. Proper Measurement Equipment Setup Figure 2. Scope Probe Placements for Measuring Input or Output Ripple. 2