QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 970A HIGH EFFICIENCY, 500MA BUCK PLUS 300MA VLDO REGULATOR LTC3541EDD/LTC3541EDD-1 DESCRIPTION DC970A-A/B featuring the LTC3541/LTC3541-1 provides a high efficiency, 500mA synchronous buck plus 300mA VLDO regulator. The DC970A has an input voltage range of 3.0V to 5.5V. The jumper selectable 2.5V/1.8V output is capable of delivering up to 500mA of output current; the jumper selectable 0.8V/1.2V/1.5V/1.8V output is capable of delivering up to 300mA of current. The synchronous buck converter provides a high efficiency output, typically 90% while switching at 2.25MHz, allowing the use of small surface mount inductor and capacitors. In Burst Mode operation, the LTC3541 /LTC3541-1’s low quiescent current results in high efficiency at light load currents. In Pulse Skip mode, the DC970A provides lower output ripple voltage at light load currents than in Burst Mode. In either mode, the DC970A can provide up to 95% efficiency and consumes less than 3uA in shutdown. The LTC3541 comes in a small 10Pin DFN package, which has an exposed pad on the bottom-side of the IC for good thermal performance. These features make the DC970 demo board an ideal reference circuit for battery-powered, hand-held applications. Design files for this circuit board are available. Call the LTC factory. LTC is a trademark of Linear Technology Corporation Table 1. Performance Summary (TA = 25°C) PARAMETER DC970A-A CONDITION Buck output Vout1 rise ahead of LDO Vout2 VALUE IC: LTC3541 DC970A-B LDO output Vout2 rise ahead of Buck Vout1 IC: LTC3541-1 Input Voltage range VIN • Vout2 + 1.4V 3V-5.5V Output Voltage VOUT1 VIN = 3V to 5.5V, IOUT1 = 0A to 500mA 1.8V / 2.5V ±2% Typical Output Ripple VOUT1 VIN = 4.5V, IOUT1= 500mA (20MHz BW) 20mVP–P 0.8V ±2% Output Voltage VOUT2 VIN = 3V to 5.5V, IOUT2 = 0A to 300mA 1.2V ±2% 1.5V ±2% 1.8V ±2% Typical Output Ripple VOUT2 Nominal Switching Frequency VIN = 4.5V, IOUT2 = 300mA (20MHz BW) 10mVP–P 2.25MHz 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 970A HIGH EFFICIENCY, 500MA BUCK PLUS 300MA VLDO REGULATOR QUICK START PROCEDURE Demonstration circuit 970A is easy to set up to evaluate the performance of the LTC3541. Refer to Figure 1 for proper measurement equipment setup and follow the procedure below. 4. Set JP9 in VOUT1 position. In some rare applications, if external input for VLDO is desired, set JP9 to LVIN_EXT. Check datasheet for more detailed usage of external input for VLDO. 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. See Figure 2 for proper scope probe technique. 5. Apply 3.3V at Vin. Measure both Vouts; they should read 0V. The supply current will be less than 3uA in shutdown condition. 6. Turn on Vout1 and Vout2 by changing jumpers JP5 and JP7 from the OFF position(s) to the ON position(s). Vary the input voltage from 3V to 5.5V and check output voltage. Both output voltages should be regulating. The regulated error should be less than 2% of rated voltage. In non load burst mode with both Buck (Vout1) and VLDO (Vout2) enabled the input current should be less than 70uA. 7. Set the load current of outputs between 25% to 100% load range, and measure both output ripple voltages; they should measure less than 20mV each. Please note, the maximum load on Vout1 is 500mA minus load on Vout2. The switching frequencies should be between 1.8MHz and 2.7MHz. 8. Jumper default position: (total of 6 jumpers needed) 1. 2. Connect the input power supply to the Vin and GND terminals on the left-side of the board. Do not hot-plug Vin or increase Vin over the rated maximum supply voltage of 5.5V. Connect the loads between the Vout and GND terminals on the right-side of the board. Refer to Figure 1 for the proper measurement equipment setup. Minimum operating VIN voltage required for VLDO regulator and linear regulator regulation is: VIN • Vout2 + 1.4V and VIN • 3.0V. 3. Before proceeding to operation, insert jumpers JP5 and JP7 into the OFF positions, jumper JP1-JP4 into the Vout2 voltage position of choice (0.8V, 1.2V, 1.5V, and 1.8V), jumper JP8 into the Vout1 voltage position of choice (1.8V and 2.5V) and jumper JP6 into the desired mode of operation: Pulse Skip or Burst Mode. JP9 JP8 JP7 JP6 JP5 JP1JP4 Vout1 1.8V ON BURST ON 1.2V 2 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 970A HIGH EFFICIENCY, 500MA BUCK PLUS 300MA VLDO REGULATOR - V Load + A V V + + - Power supply Load A Figure 1. Proper Measurement Equipment Setup Figure 2. Scope Probe Placement for Measuring Input or Output Ripple 3 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 970A HIGH EFFICIENCY, 500MA BUCK PLUS 300MA VLDO REGULATOR 4