lx1734 evaluation board user?s guide lx1734 1mhz inverting dc-dc converter integrated products
lx1734 e valuation b oard u ser g uide copyright ? 2002 microsemi page 2 rev. 1.0 8/15/03 integrated products 11861 western avenue, garden grove , ca. 92841, 714-898-8121, fax: 714-893-2570 t able o f c ontents overview ............................................................................................................................... ......................................3 lx1734 overview evaluation board operation t ables header d escript ions ........................................................................................................... ..................... 3 lx1734 evaluation boar d component list ........................................................................................ ... 4 f igures lx1734 evaluation boar d silk screen............................................................................................ ........ 4 lx1734 evaluation bo ard sche matic .............................................................................................. ....... 5
lx1734 e valuation b oard u ser g uide copyright ? 2002 microsemi page 3 rev. 1.0 8/15/03 integrated products 11861 western avenue, garden grove , ca. 92841, 714-898-8121, fax: 714-893-2570 o verview the lx1734 is a fixed frequency (1mhz) current mode controller designed to develop a negative output voltage from a positive input voltage. the switching transistor and current sense resistor are integrated into the part. the pwm functions in a peak regulation mode using the amplified error signal to determine the peak switch current each cycle. slope compensation is added to provide stable operation at high duty cycles. a current limit detector overrides the regulation loop and prevents the switch current from exceeding the over current threshold level. the bandgap control circuit keeps q1 biased on and produces a reference current (i ref ) that produces a voltage drop across the internal resistance that has a positive temperature coefficient. when this resistor voltage drop is added to the negative temperature coefficient of the base- emitter voltage drop of q1, the result is a temperature compensated reference voltage (v ref ) at the nfb pin. the summing node from the external feedback network is connected directly to nfb pin, which is relatively high impedance (typically 150k). the feedback loop minimizes the error current, (i error ) which effectively regulates the voltage at the nfb pin. as with a conventional er ror amplifier, the error signal is proportional to the difference between the temperature compensated reference voltage v ref ) and the summing node voltage. a slight correction factor is necessary to account for the added summing node voltage due to the reference current (i ref , typically 4adc) flowing through the thevenin equivalent summing node external resistance. e valuation b oard o peration the lx1734 evaluation board contains two application circuits. application circuit #1 is configured to provide a -5v output, and application circuit #2 is configured to provide both +5v and -5v outputs. each application circuit has separate header connections associated with the input, output and shutdown pins for independent control of each circuit along with providing the user flexibility in applying a load to either circuit . the header pin descriptions for application circuit #1 and application circuit #2 are summarized in table 1 and table 2 respectively. please refer to these tables for evaluation board setup. the factory installed active and passive components list can be found in table 3. following the two tables you will find the pcb silkscreen figure 1 and the circuit schematic in figure 2. all necessary pcb traces and components are on the topside of the board. header pin description ? application circuit #1 vin input power (4.5v to 5.5v); p1-1 references the positive terminal, p1-2 references gnd. vout output voltage (-5v); p2-1 references the output terminal; p2-2 references gnd. user can either monitor the output voltage direct or apply an external load. shdn shutdown pin; p3-1 references the positive termina l; p3-2 references gnd. the lx1734 is active when shdn > 2.0v. it is recommended to tie this pin to the vin. table 1 ? header explanation; application circuit #1 header pin description ? application circuit #2 vin input power (4.5v to 5.5v); p1a-1 references the positive terminal, p1a-2 references gnd. vout1 output voltage (+5v); p2a-1 re ferences the output terminal; p2 a-2 references gnd. user can either monitor the output voltage direct or apply an external load. vout2 output voltage (-5v); p4-1 references the output terminal; p4-2 references gnd. user can either monitor the output voltage direct or apply an external load. shdn shutdown pin; p3a-1 references the positive terminal; p3a-2 references gnd. the lx1734 is active when shdn > 2.0v. it is recommended to tie this pin to the vin. table 2 ? header explanation; application circuit #2
lx1734 e valuation b oard u ser g uide copyright ? 2002 microsemi page 4 rev. 1.0 8/15/03 integrated products 11861 western avenue, garden grove , ca. 92841, 714-898-8121, fax: 714-893-2570 lx1734 evaluation board component list bill of materials part description manufacturer & part # reference designators qty ic, converter microsemi lx1734clm u1, u1a 2 capacitor, x5r, 10uf, 6.3v, 10%, 1210 murata grm32dr60j226mad1l c1, c1a, c5, c5a, c6, c6a, c7, c8 8 capacitor, x7r, 100nf, 50v, 10%, 0805 novacap 0805b104k500nt c2, c2a 2 capacitor, x7r, 1uf, 50v, 10%, 1210 murata grm42-2x7r105k050al c3, c3a 2 capacitor, x7r, 1.2nf, 16v, 10%, 0805 novacap 0805b122k160nt c4, c4a 2 diode, schottky, 1a, 20v, smt microsemi ups5817 d1, d2, d3, d4 4 inductor, 20uh, smt sumida cls62-220nc l1 1 inductor, 47uh, 480ma, smt toko a920cy-470m l1a 1 connector, vertical, 2-pin, .1 spacing amp 87220-2 p1, p1a, p2, p2a, p3, p3a, p4 7 resistor, 29.4k, 1%, 1/10w, 0805 asj cr21f2942t r1, r1a 2 resistor, 10.0k, 5%, 1/8w, 0805 asj cr21j103t r2, r2a, r3, r3a 4 table 3 ? lx1734 bom lx1734 evaluation board silkscreen figure 1 ? silkscreen top rr
lx1734 e valuation b oard u ser g uide copyright ? 2002 microsemi page 5 rev. 1.0 8/15/03 integrated products 11861 western avenue, garden grove , ca. 92841, 714-898-8121, fax: 714-893-2570 lx1734 evaluation board schematic application circuit #1 application circuit #2 figure 2 ? lx1734 evaluation board schematic -5v output (application circuit #1) and +5v and -5v output (application circ uit #2) configurations
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