LT3481EMSE#TRPBF Integrated Circuits (ICs)

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1. Describe

The LT®3481 is an adjustable frequency (300kHz to 2.8MHz) Input-Accepting Monolithic Buck Switching Regulators Voltage up to 34V (36V max). high efficiency 0.18Ω switch is included on chip with boost Schottky diodes and necessary oscillators, controls and logic circuit. current mode topology for fast transient response and good loop stability. Low ripple Burst Mode operation maintains high efficiency at low output current while keeping output ripple below 15mV in typical applications. Additionally, the LT3481 can further improve low output current efficiency by drawing Bias current from the output when VOUT is above 3V. Shutdown reduces input supply current to less than 1µA while the resistor and capacitor on the RUN/SS pin provide a Controlled output voltage ramp (soft start). good power Flag signal when VOUT reaches 90% of programmed The output voltage. LT3481 in 10-Pin MSOP and 3mm x 3mm DFN package with exposed pad for Low thermal resistance.

2. Feature

    1. Wide input range: 3.6V to 34V operating voltage, 36V maximum

    2. 2A maximum output current

    3. Low Ripple Burst Mode® Operation 50µA IQ at 12VIN to 3.3VOUT Output ripple < 15mV

    4. Adjustable switching frequency: 300kHz to 2.8MHz

    5. Low shutdown current: IQ < 1μA

    6. Integrated boost diode

    7. Power good sign

    8. Saturated switching design: 0.18Ω on-resistance

    9. 1.265V feedback reference voltage

  10. Output Voltage: 1.265V to 20V

  11. Soft start capability

  12. Syncable from 275kHz to 475kHz

  13. Small 10-Pin Thermally Enhanced MSOP and (3mm × 3mm) DFN Packages

3. Application

    1. Vehicle battery regulation

    2. Portable product power supply

    3. Distributed Supply Supervision

    4. Industrial Supplies

    5. Wall transformer regulation

4. Pin configuration

5. PIN FUNCTIONS

    1. BD (Pin 1): This pin connects to the anode of the boost Schottky diode.

    2. BOOST (Pin 2): This pin is used to provide a drive voltage, higher than the input voltage, to the internal bipolar NPN power switch.

    3. SW (Pin 3): The SW pin is the output of the internal power switch. Connect this pin to the inductor, catch diode and boost capacitor.

    4. VIN (Pin 4): The VIN pin supplies current to the LT3481’s internal regulator and to the internal power switch. This pin must be locally bypassed.

    5. RUN/SS (Pin 5): The RUN/SS pin is used to put the LT3481 in shutdown mode. Tie to ground to shut down the LT3481. Tie to 2.3V or more for normal operation. If the shutdown feature is not used, tie this pin to the VIN pin. RUN/SS also provides a soft-start function; see the Applications Information section.

    6. PG (Pin 6): The PG pin is the open-collector output of an internal comparator. PG remains low until the FB pin is within 10% of the fi nal regulation voltage. PG output is valid when VIN is above 3.5V and RUN/SS is high.

    7. BIAS (Pin 7): The BIAS pin supplies the current to the LT3481’s internal regulator. Tie this pin to the lowest available voltage source above 3V (typically VOUT). This architecture increases effi ciency especially when the input voltage is much higher than the output.

    8. FB (Pin 8): The LT3481 regulates the FB pin to 1.265V. Connect the feedback resistor divider tap to this pin.

    9. VC (Pin 9): The VC pin is the output of the internal error amplifi er. The voltage on this pin controls the peak switch current. Tie an RC network from this pin to ground to compensate the control loop.

  10. RT (Pin 10): Oscillator Resistor Input. Connecting a resistor to ground from this pin sets the switching frequency.

6. APPLICATIONS INFORMATION

Of course, such a simple design guide will not always result in the optimum inductor for your application. A larger value inductor provides a slightly higher maximum load current and will reduce the output voltage ripple. If your load is lower than 2A, then you can decrease the value of the inductor and operate with higher ripple current. This allows you to use a physically smaller inductor, or one with a lower DCR resulting in higher effi ciency. There are several graphs in the Typical Performance Characteristics section of this data sheet that show the maximum load current as a function of input voltage and inductor value for several popular output voltages. Low inductance may result in discontinuous mode operation, which is okay but further reduces maximum load current. For details of maximum output current and discontinuous mode operation, see Linear Technology Application Note 44. Finally, for duty cycles greater than 50% (VOUT/VIN > 0.5), there is a minimum inductance required to avoid subharmonic oscillations. See AN19.