DEMO C IR C U IT 14 8 9 A LTC3619EDD/LTC3619BEDD Q U IC K S TAR T G U IDE L T C 3 6 19 EDD/ L T C 3 6 19 B EDD S Y N C H R ON OU S B U C K DU AL R EG U L AT OR W IT H ADJ U S TAB L E IN P U T C U R R EN T L IMIT DESCRIPTION Demonstration circuit 1489A is a synchronous buck dual regulator w ith adjustable input current limit featuring the LTC3619EDD/ LTC3619BEDD and is ideally suited for pulsed load applications w here the input current needs to be limited. The LTC3619EDD operates in burst mode for higher light load efficiency, w hile the LTC3619BEDD operates in pulse-skip mode for low er output ripple. The package style for the LTC3619EDD/ LTC3619BEDD is a 10 lead 3mm x 3mm plastic DFN. Demonstration circuit 1489A is configured for 500mA maximum input current limit. The outputs are configured for a 3.3V / 400mA continuous current output and a 3.4V output that can handle pulsed load currents of up to 2A, w ith duty cycles of up to 15% . The input voltage range is 5V ±10% . The fixed input current limit can be adjusted by replacing one resistor. Please see the datasheets for more information. The LTC3619/LTC3619B datasheets gives complete descriptions of these parts, operation and application information and must be read in conjunction w ith this quick start guide for demo circuit 1489A. Design files for this circuit board are available. Call the LTC factory. Table 1. Perform ance Sum m ary (TA = 25°C) PAR AM ETER CON DITIO N S /N O TES Input Voltage Range VIN Input Current Limit Output Voltage VOUT1 Output Voltage VOUT2 Efficiency (Figures 4 and 5) VIN VIN VIN VIN VIN VIN VALUE = 4.5V to 5.5V,IOUT1 = 0A to 400mA = 4.5V to 5.5V,IIN = 0A to 500mA = 4.5V,IOUT1 = 400mA = 5.5V,IOUT1 = 400mA = 4.5V,IOUT2 = 500mA = 5.5V,IOUT2 = 500mA 4.5V – 5.5V 500mA ± 5% 3.3V ± 3% 3.4V ± 3% 92.6% typical 92.3% typical 93.4% typical 92.6% typical Q U ICK STA RT PROCEDU RE Demonstration circuit 1489A is easy to set up to evaluate the performance of the LTC3619EDD/ LTC3619BEDD. Refer to Figure 1 for proper measurement equipment setup and follow the procedure below : NOTE: When measuring the input or output voltage ripple, care must be taken to avoid a long ground lead on the oscilloscope probe. Measure the input or output voltage ripple by touching the probe tip directly across the VIN or VOUT and GND terminals or directly across the capacitor. See Figure 2 for proper scope probe technique. 1. Place the jumper in the following position: JP1 On JP2 On 2. With power off, connect the input power supply to VIN and GND. 3. Turn on the power at the input. NOTE: Make sure that the input voltage does not exceed 5.5V. 4. Check for the proper output voltage. VOUT1 = 3.200 to 3.400V, V OUT2 = 3.298 to 3.502V If there is no output, temporarily disconnect the load to make sure that the load is not set too high. 5. Once the proper output voltages are established, adjust the loads within the operating range and ob- 1 LTC3619EDD/LTC3619BEDD serve the output voltage regulation, ripple voltage, efficiency and other parameters. + Optional Circuit for Pulsed Loads BNC cable to scope 10mV/A 6. The method for evaluating pulsed loads will be discussed in the next section. VIN supply VIN IIN A + V - - Pulse Generator 0-5V + I OUT2 I OUT1 A + VOUT2 Load - V OUT2 A + VOUT1 + V V - - + VOUT1 Load - Figure 1. Proper M easurem ent Equipm ent Setup Figure 2. M easuring Input or Output R ipple Directly Across Bulk Capacitor PU L SED L OA D TESTING Demonstration circuit 1489A can be setup for simple evaluation of pulse loads – please see optional circuit in 2 Figure 1 for proper setup. The circuit is capable of pulsed load of up to 2A w ith duty cycles up to 15% on VO U T2. LTC3619EDD/LTC3619BEDD Starting from step 5 in the quick start procedure above, follow the procedure below : 1. Disconnect all loads from VO U T2 as the pulse load circuitry is on board. 2. The pulsed load current is measured by connecting J1 to the scope using a BNC cable and setting the oscilloscope to 10mV/div 3. Input current and output voltage can be measured on an oscilloscope for evaluation. 4. A pulse generator w ith adjustable amplitude is connected betw een IOSTEP CLK and GND as indicated in Figure 1. The pulse generator should be capable of generating up to 5V pulses. Adjust the period and duty cycle of this signal to match that of the required load prior to attaching the pulse generator. 5. Adjust pulse generator amplitude until the required load current is achieved as measured on J1 (10mV/A). 6. An example result show ing VO U T2, IIN and a pulse load IO UT2 is given in Figure 3. Vout2 (100mV/div AC coupled) Iin (200mA/div) Iout2 (1A/div) (IOSTEP at 10mV/div) Figure 3. Pulse Load W aveform s for 2A pulsed load, 1/8th duty cycle, 4.6m s period A DJ U STING INPU T CU RRENT L IM IT It is possible to modify the demonstration circuit for either higher or low er input current limits. This is accomplished by changing resistor R9 to the required value as suggested in the LTC3619EDD/ LTC3619BEDD data- sheets. Note that for these different current values, the inductor may not be optimum and may have to be changed as w ell. Please refer to the datasheet for more information. 3 LTC3619EDD/LTC3619BEDD Figure 4. Typical Efficiency vs. Load Current, CH1, 3.3Vout for A-A and A-B boards 4 LTC3619EDD/LTC3619BEDD M aximum output current is input current limited M aximum output current is input current limited Figure 5. Typical Efficiency vs. Load Current, CH2, 3.4Vout for A-A and A-B boards 5 GND VOUT2 3.4V / 2A Pulsed Load PGOOD2 RUN2 GND E9 E7 E5 E3 1000K R3 E2 COUT3 2200uF 6.3V R12 0.01 1 CIN2 10uF 6.3V COUT4 2200uF 6.3V R2 200K R13 (OPT) R11 51 R10 10K 1 E11 OFF E12 GND J1 10mV / A IOSTEP CLK C1 (OPT) 10 7 8 9 ** R7 215K 1% L2 1.5uH JP2 RUN2 ON 2 R5 COUT7 1000K (OPT) 1% DYNAMIC LOAD CIRCUIT COUT2 4.7uF 6.3V CIN1* 68uF 6.3V Q1 SUD50N03-10CP-E3 VOUT2 VOUT2 COUT1 (OPT) 3 2 1 3 -B LTC3619BEDD LTC3619EDD -A L1 R8 221K 1% 3.3uH C3 2200pF 1 5 4 2 U1 R9 110K 1% Vfb1 SW1 PGOOD1 Run1 ASSY Vfb2 SW2 PGOOD2 Run2 U1* * 6 Vin 11 G ND VIN E1 4.5V - 5.5V Up to 500mA 2 3 4 5 R lim 3 6 R6 1000K 1% OFF ON JP1 RUN1 C2 10pF 2 1 3 * FOR DEMO BOARD USE ONLY COUT6 (OPT) R1 200K COUT5 4.7uF 6.3V E10 E8 E6 E4 1000K R4 GND VOUT1 3.3V / 400mA PGOOD1 RUN1 LTC3619EDD/LTC3619BEDD