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LTC3530 Datasheet(PDF) 11 Page - Linear Technology |
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LTC3530 Datasheet(HTML) 11 Page - Linear Technology |
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11 / 16 page  LTC3530 11 3530fb The output capacitance is usually many times larger than the minimum value in order to handle the transient response requirements of the converter. For a rule of thumb, the ratio of the operating frequency to the unity-gain bandwidth of the converter is the amount the output capacitance will have to increase from the above calculations in order to maintain the desired transient response. The other component of ripple is due to the ESR (equiva- lent series resistance) of the output capacitor. Low ESR capacitors should be used to minimize output voltage ripple. For surface mount applications, Taiyo Yuden or TDK ceramic capacitors, AVX TPS series tantalum capaci- tors or Sanyo POSCAP are recommended. See Table 2 for contact information. Input Capacitor Selection Since VIN is the supply voltage for the IC, as well as the input to the power stage of the converter, it is recommended to place at least a 10μF, low ESR ceramic bypass capaci- tor close to the VIN and GND pins. It is also important to minimize any stray resistance from the converter to the battery or other power source. Optional Schottky Diodes Schottky diodes across the synchronous switches B and D are not required (VOUT < 4.3V), but provide a lower drop during the break-before-make time (typically 15ns) improv- ing efficiency. Use a surface mount Schottky diode such as an MBRM120T3 or equivalent. Do not use ordinary rectifier diodes, since the slow recovery times will compromise efficiency. For applications with an output voltage above 4.3V, a Schottky diode is required from SW2 to VOUT. Output Voltage < 1.8V The LTC3530 can operate as a buck converter with output voltages as low as 0.4V. Synchronous switch D is powered from VOUT and the RDS(ON) will increase at low output volt- ages, therefore a Schottky diode is required from SW2 to VOUT to provide the conduction path to the output. Note that Burst Mode operation is inhibited at output voltages below 1V typical. Note also that if VOUT is less than 1V, the current limit will be 670mA (typ). Output Voltage > 4.3V A Schottky diode from SW2 to VOUT is required for output voltages over 4.3V. The diode must be located as close to the pins as possible in order to reduce the peak voltage on SW2 due to the parasitic lead and trace inductance. Input Voltage > 4.5V For applications with input voltages above 4.5V which could exhibit an overload or short-circuit condition, a 2Ω/1nF series snubber is required between SW1 and GND. A Schottky diode from SW1 to VIN should also be added as close to the pins as possible. For the higher input voltages, VIN bypassing becomes more critical; therefore, a ceramic bypass capacitor as close to the VIN and GND pins as possible is also required. Operating Frequency Selection Higher operating frequencies allow the use of a smaller inductor and smaller input and output filter capacitors, thus reducing board area and component height. How- ever, higher operating frequencies also increase the IC’s total quiescent current due to the gate charge of the four switches, as given by: Buck: Iq = (0.6 • VIN • f) mA Boost: Iq = [0.8 • (VIN + VOUT) • f] mA Buck/Boost: Iq = [f • (1.4 • VIN + 0.4 • VOUT)] mA Table 2. Capacitor Vendor Information SUPPLIER PHONE FAX WEB SITE AVX (803) 448-9411 (803) 448-1943 www.avxcorp.com Murata (814) 237-1431, (800) 831-9172 (814) 238-0409 www.murata.com Sanyo (619) 661-6322 (619) 661-1055 www.sanyovideo.com Taiyo Yuden (408) 573-4150 (408) 573-4159 www.t-yuden.com TDK (847) 803-6100 (847) 803-6296 www.component.tdk.com APPLICATIONS INFORMATION |
Similar Part No. - LTC3530_15 |
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