QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 658 MULTI-OUTPUT DC/DC CONVERTER POWERED BY 2-CELL, USB OR WALL ADAPTER LTC3456 DESCRIPTION Demonstration Circuit 658 is a complete power man- When using a long wire connection to the input source agement system using the LTC3456 for portable applica- (a wall adapter or a USB port), there can be large voltage tions powered by a wall adapter, a USB port or a 2-cell transients during initial plug-in due to the stray wiring alkaline battery, in that order of priority. DC658 provides inductance. This voltage spike can be large enough to three outputs: a 1.8V, 200mA core supply, a 3.3V, damage the LTC3456. C7, R16, C8, and R20 are used to 150mA main supply, and a 3.3V, 50mA Hot Swap supply. damp the possible voltage transients. Please refer to All outputs are discharged to ground during shutdown. Application Note 88 for details. Since the battery is usu- ally assembled close to the circuit and its series resis- The 1.8V output switcher is a high efficiency, 1MHz fixed tance also provides damping for the resonant tank, C11 frequency synchronous buck regulator. The 3.3V output at the battery input is mainly intended for demo board switcher is a high efficiency, 1MHz fixed frequency syn- evaluations when a bench power supply is used to simu- chronous buck regulator (when powered from a wall late the battery voltage. adapter or a USB port), or a synchronous boost regula- tor (when powered from a 2-cell alkaline battery). Design files for this circuit board are available. Call the LTC factory. Table 1. Performance Summary (T = 25C unless otherwise noted) A PARAMETER CONDITION VALUE Battery Input Voltage Range 2V to 3.2V USB Input Voltage Range 4.35V to 5.5V Wall Adapter Input Voltage Range 4.5V to 5.5V Core Output Voltage V =2.4V, I = 0mA to 200mA 1.8V 4% BAT OUT1 Typical Output Ripple (Core) V = 2.4V, I = 200mA (20MHz BW) 5mV BAT OUT1 PP Main Output Voltage V =2.4V, I = 0mA to 150mA 3.27V 4% BAT OUT2 Typical Output Ripple (Main) V = 2.4V, I = 150mA (20MHz BW) 25mV BAT OUT2 PP Hot Swap Output Voltage V =2.4V, I = 0mA to 50mA 3.27V 4% BAT OUT3 Typical Output Ripple (Main) V = 2.4V, I = 50mA (20MHz BW) 8mV BAT OUT3 PP Typical Switching Frequency (All Switchers) 1MHz 88% Typical Efficiency (Fixed Frequency Mode) V = 2.4V, I = 200mA, I = 150mA, I = 50mA BAT OUT1 OUT2 OUT3 USB maximum current in 500mA mode USB voltage is 5V, USB Active and 500mA mode 500mA (max) USB maximum current in 100mA mode USB voltage is 5V, USB Active and 100mA mode 100mA (max) 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 658 MULTI-OUTPUT DC/DC CONVERTER POWERED BY 2-CELL, USB OR WALL ADAPTER QUICK START PROCEDURE Demonstration circuit 658 is easy to set up to evaluate 5. Once the proper output voltages are established, ad- the performance of the LTC3456. Refer to Figure 1 for just the load currents within the operating range and proper measurement equipment setup and follow the observe the output voltage regulation, ripple voltage, procedure below: efficiency and other parameters. NOTE: When measuring the input or output voltage rip- 6. Pushing the OFF button turns off the converter. ple, care must be taken to avoid a long ground lead on USB POWERED OPERATION the oscilloscope probe. Measure the input or output voltage ripple by touching the probe tip directly across 7. Place the USB SUSPEND jumper in the USB active the Vin or Vout and GND terminals. See Figure 2 for position. Place the USB CURRENT jumper in the proper scope probe technique. 500mA position. Keep the wall adapter input voltage at zero. Set the USB input voltage above 4.35V. (The BATTERY POWERED OPERATION EXT PWR LED goes on when the USB pin voltage is 1. Set both the wall adapter input voltage and USB input greater than 4.1V) voltage to zero. The circuit is now powered from the NOTE: Make sure that the USB input voltage does not battery input. If a bench power supply is used, set exceed 5.5V. the voltage between 2V and 3.2V. 8. Repeat 4 and 5 to evaluate the circuit operation. 2. Push ON button to start the converter. Note that the When powered by the USB input, the converter al- Reset LED goes on for 262msec. This simulates the ways operates in forced PWM mode regardless of the reset signal that the LTC3456 provides to the micro- status of the MODE pin. processor during initial power up. AC WALL ADAPTER POWERED OPERATION 3. When powered by the battery, the Burst Mode can be selected to improve light load efficiency by use of the 9. Ramp up the wall adapter voltage. When the wall Mode jumper (JP1). Once selected, each switcher adapter voltage exceeds 4.5V, the converter will will automatically enter into Burst Mode operation switch over from USB input to be powered by the wall when its load current falls below a predetermined adapter. value. NOTE: Make sure that the wall adapter input voltage 4. Check for the proper output voltages. does not exceed 5.5V. NOTE: If any output is not in regulation, temporarily 10. Repeat 4 and 5 to evaluate the circuit operation. disconnect the load at the output to make sure that When powered by the wall adapter, the converter al- the load current is not set too high. The MAIN ways operates in forced PWM mode regardless of the (Vout2) and HOT SWAP (Vout3) outputs will be status of the MODE pin. turned off when the CORE output (Vout1) goes out of regulation. 2