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| quick start guide for demonstration circuit 616 4mhz, polyphase high efficiency synchronous boost converter 1 ltc3425euh description demonstration circuit 616 is a synchronous, 4-phase boost converter using the ltc3425. it is capable of op- erating below 1v input. DC616A is set for 3.3v output. dc616b is set for 5v output. on each demo board, the left circuit gives higher efficiency and current rating; while the right circuit has smaller size and lower cost. the switching frequency is set at 1mhz per phase, minimizing inductor and capacito r size. a single resistor at rt pin sets the frequency. if desired, the ltc3425 can be synchronized to an external clock. long wires run from input sources (such as wall adap- tors) can cause large voltage spikes during initial plug- in. c5 and c15 are installed on dc616 to damp the pos- sible voltage spikes. they are not required for applica- tions where input source is close to the regulator. please refer to application note 88 for details. design files for this circuit board are available. call the ltc factory. table 1. DC616A performance summary (t a = 25c unless otherwise noted) parameter condition value minimum input voltage (start-up) 1v output voltage v out1 (high efficiency circuit) v in = 2v to 3v, i out1 = 0a to 2.25a 3.3v 4% output voltage v out2 (low cost circuit) v in = 2v to 3v, i out2 = 0a to 1.8a 3.3v 4% maximum output current (h igh efficiency circuit) v in = 2v to 3v 2.25a maximum output current (low cost circuit) v in = 2v to 3v 1.8a typical output ripple v out v in = 2.4v, i out = 1.8a (20mhz bw) 28mv p?p typical switching frequency (each phase) 1mhz efficiency (high e fficiency circuit) v in = 2.4v, i out1 = 0.5a v in = 2.4v, i out1 = 2a 93.0% typical 88.6% typical logic low voltage-off, -40 c to 85 c 0.25v max logic high voltage-on (initial start-up), -40 c to 85 c 1v min on/off control logic high voltage-on (v out >2.4v), -40 c to 85 c 0.65v min
quick start guide for demonstration circuit 616 4mhz, polyphase high efficiency synchronous boost converter 2 demo circuit 616a = 3.3vout@2.25a or 1.8a demo circuit 616b = 5vout@2.0a or 1.5a quick start guide for demonstration circuit 616 4mhz, polyphase high efficiency synchronous boost converter 3 table 2. dc616b performance summary (t a = 25c unless otherwise noted) parameter condition value minimum input voltage (start-up) 1v output voltage v out1 (high efficiency circuit) v in = 2.5v to 4.5v, i out1 = 0a to 2a 5v 4% output voltage v out2 (low cost circuit) v in = 2.5v to 4.5v, i out2 = 0a to 1.5a 5v 4% maximum output current (h igh efficiency circuit) v in = 2.5v to 4.5v 2a maximum output current (low cost circuit) v in = 2.5v to 4.5v 1.5a typical output ripple v out v in = 3.3v, i out = 1.5a (20mhz bw) 33mv p?p typical switching frequency (each phase) 1mhz efficiency (high effi ciency circuit) v in = 3.3v, i out1 = 0.5a v in = 3.3v, i out1 = 2a 93.0% typical 92.3% typical logic low voltage-off, -40 c to 85 c 0.25v max logic high voltage-on (initial start-up), -40 c to 85 c 1v min on/off control logic high voltage-on (v out >2.4v), -40 c to 85 c 0.65v min quick start procedure demonstration circuit 616 is easy to set up to evaluate the performance of the ltc3425. refer to figure 1 for proper measurement equipment setup and follow the procedure below: note: when measuring the input or output voltage rip- ple, 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. 1. place jumpers in the following positions: jp1, jp5 run on jp4, jp6 dcm jp3, jp8 auto on. 2. with power off, connect the input power supply to vin1 and gnd or vin2 and gnd. 3. turn on the power at the input. note: make sure that the input voltage does not ex- ceed 4.5v. 4. check for the proper output voltage. 5. if there is no output, temporarily disconnect the load to make sure that the load is not set too high. 6. once the proper output voltage is established, adjust the load within the operating range and observe the output voltage regulation, ripple voltage, efficiency and other parameters. 7. different operating modes can be selected according to the following table: jp2, jp7 quick start guide for demonstration circuit 616 4mhz, polyphase high efficiency synchronous boost converter 4 8. the active clamping circuits are installed on dc616b to prevent the voltages at switch nodes from exceed- ing the maximum rating (refer to data sheet ?applica- tions where vout > 4.3v? section for details). if there is any momentary short-circuit condition, please add a 5 ? resistor in series with q1. table 3. ltc3425 operating modes operating mode jp3, jp8 position jp4, jp6 position forced burst burst mode dcm automatic burst (operating mode is load dependent) auto on dcm forced fixed frequency with pulse sk ipping at light load fixed freq dcm forced fixed frequency, low noise (no pulse skipping) fixed freq ccm graphic figure 1. proper measurement equipment setup quick start guide for demonstration circuit 616 4mhz, polyphase high efficiency synchronous boost converter 5 figure 2. measuring input or output ripple 0 0.5 1 1.5 2 2.5 3 3.5 1.8 1.9 2 2.1 2.2 2.3 2.4 2.5 input voltage (v) imax (a) low cost circuit (right-side) high efficiency circuit (left-side) figure 3. maximum output current vs input voltage for 3.3v output (DC616A) vin gnd quick start guide for demonstration circuit 616 4mhz, polyphase high efficiency synchronous boost converter 6 0 0.5 1 1.5 2 2.5 3 3.5 1.8 2 2.2 2.4 2.6 2.8 3 3.2 input voltage (v) imax (a) low cost circui t (right-side) high efficiency ci rcuit (left-side) figure 4. maximum output current vs input voltage for 5v output (dc616b) figure 5. DC616A load transient response (vin=2.4v;channel 1: vout1; channel 2: iout: load step from 0.2a to 2.25a) quick start guide for demonstration circuit 616 4mhz, polyphase high efficiency synchronous boost converter 7 figure 6. dc616b load transient response (vin=4.2v;channel 1: vout1; channel 2: iout1: load step from 0.2a to 2a) quick start guide for demonstration circuit 616 4mhz, polyphase high efficiency synchronous boost converter 8 quick start guide for demonstration circuit 616 4mhz, polyphase high efficiency synchronous boost converter 9 vin=1v to 3v vout=3.3v@2.25a quick start guide for demonstration circuit 616 4mhz, polyphase high efficiency synchronous boost converter 10 quick start guide for demonstration circuit 616 4mhz, polyphase high efficiency synchronous boost converter 11 vin=1v to 3v vout=3.3v@1.8a quick start guide for demonstration circuit 616 4mhz, polyphase high efficiency synchronous boost converter 12 quick start guide for demonstration circuit 616 4mhz, polyphase high efficiency synchronous boost converter 13 vin=2.5v to 4.5v vout=5v@2a quick start guide for demonstration circuit 616 4mhz, polyphase high efficiency synchronous boost converter 14 quick start guide for demonstration circuit 616 4mhz, polyphase high efficiency synchronous boost converter 15 vin=2.5v to 4.5v vout=5v@1.5a |
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