QUICK START GUIDE FOR DC989B-A TINY NO RSENSE BOOST CONVERTER LTC3872 DESCRIPTION Demonstration circuit 989B-A is a single-output boost converter, it features tiny, boost controller LTC3872. The input voltage is from 3.0V to 4.5V without output de-rating. The supply has one output: 5V/2AMAX. Minimum input voltage is 2.75V. When input voltage is lower than 3V, output current should be de-rated. The design employs the LTC3872, the small footprint NO RSENSE boost regulator. The switching frequency is fixed at 550 kHz. With current mode control and OPTI-LOOP compensation, DC989B-A can be optimized to provide fast transient response. NO RSENSE technique reduces both: size of the converter and power dissipation. However, care should be taken to MOSFET selection, it’s not only switching element, but also its RDS(ON) represents the current sensing element for the control loop, see LTC3872 datasheet for details. LTC3872 allows design small size and high efficiency step-up DC/DC solutions. Design files for this circuit board are available. Call the LTC factory. TM-NO RSENSE is trademark of Linear Technology Corporation Table 1. Performance Summary (TA = 25°C) 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 VOUT 5V +/- 2% Maximum Continuous output Current Vin = 3V to 4.5V 2A Typical Operating Frequency Fixed 550kHz Typical Output Ripple (VOUT) 20MHz BW, 2A load, VIN = 3V, frequency = 550kHz 30mVP-P Efficiency VIN=3V, VOUT=5V IOUT=2A 90% QUICK START PROCEDURE Demonstration circuit 989B-A is easy to set up to evaluate the performance of the LTC3872. Please refer to Figure 1 for proper measurement equipment setup and follow the procedure below: 2. Connect the input power supply to the VIN and GND terminals on the right, center of the board. NOTE: Do not increase VIN over 5V. 1. Place RUN in ON position for normal operation. Connect the desired loads between 5V output terminal and the GND terminal on the board. 3. Vary the input voltage from 3.0V to 4.5V and adjust the load current from 0 to 2A. Measure the output voltages. VOUT should read between 5.0V 0.1V within specified maximum load current. 4. Measure the output ripple voltage at maximum output current level and minimum in- NOTE: The maximum load is 2A. 1 QUICK START GUIDE FOR DC989B-A TINY NO RSENSE BOOST CONVERTER 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 QUICK START GUIDE FOR DC989B-A TINY NO RSENSE BOOST CONVERTER Figure 3. Typical Switch Node and Output Ripple Waveform VIN=3.0V, VOUT=5V, IOUT=2A Vout 200mV/DiV Iout 1A/DiV Figure 4. Load Step Response VIN = 3.3V, VOUT = 5V & 1.6A Load Step 2 3 OFF J1 2 ON 1 RUN/SS R6 OPT VIN RUN/SS 47pF C7 C6 1800pF R3 17.4K 1% R5 OPT C4 (opt) R1 11K 1% 3 2 1 R4 5.11 K 1% VFB ITH IPRG U1 [1] 6 RUN SW 5 C5 OPT C9 0.1uF RUN/SS 7 8 R2 34.8K 1% NGATE V IN G ND 4 4 Q3 Si4116DY OPT Q1 Si3460DDV 3 2 L1 1.0uH FDV0630-1R0 1 2 5 6 4 C10 10uF 10V D1 B320 5 6 7 8 1 2 3 1 C1 100uF 10V [1] C2 100uF 10V Vout IC LTC3872ETS8 LTC3872-1ETS8 -B C13 OPT -A C3 OPT + VERSION C11 OPT C8 470uF Sanyo TPE For Demo Board Test Only Vin E4 E3 E2 E1 GND 5V@2A VOUT GND 3V-4.5V VIN QUICK START GUIDE FOR DC989B-A TINY NO RSENSE BOOST CONVERTER 3 QUICK START GUIDE FOR DC989B-A TINY NO RSENSE BOOST CONVERTER 4