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LTC1629-6 Datasheet(PDF) 11 Page - Linear Technology |
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LTC1629-6 Datasheet(HTML) 11 Page - Linear Technology |
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11 / 28 page  11 LTC1629-6 16296f OPERATIO (Refer to Functional Diagram) INTVCC/EXTVCC Power Power for the top and bottom MOSFET drivers and most of the IC circuitry is derived from INTVCC. When the EXTVCC pin is left open, an internal 5V low dropout regulator supplies INTVCC power. If the EXTVCC pin is taken above 4.7V, the 5V regulator is turned off and an internal switch is turned on connecting EXTVCC to INTVCC. This allows the INTVCC power to be derived from a high efficiency external source such as the output of the regu- lator itself or a secondary winding, as described in the Applications Information section. An external Schottky diode can be used to minimize the voltage drop from EXTVCC to INTVCC in applications requiring greater than the specified INTVCC current. Voltages up to 7V can be applied to EXTVCC for additional gate drive capability. Differential Amplifier This amplifier provides true differential output voltage sensing. Sensing both VOUT+ and VOUT– benefits regula- tion in high current applications and/or applications hav- ing electrical interconnection losses. The amplifier has an output slew rate of 5V/ µs and is capable of driving capaci- tive loads with an output RMS current typically up to 25mA. The amplifier is not capable of sinking current and therefore must be resistively loaded to do so. The differen- tial amplifier is configured as a unity-gain differencing amplifier. Power Good (PGOOD) The PGOOD pin is connected to the drain of an internal MOSFET. The MOSFET turns on when the output is not within ±10% of its nominal output level as determined by the feedback divider. When the output is within ±10% of its nominal value, the MOSFET is turned off within 10 µs and the PGOOD pin should be pulled up by an external resistor to a source of up to 7V. Short-Circuit Detection The RUN/SS capacitor is used initially to limit the inrush current from the input power source. Once the controllers have been given time, as determined by the capacitor on the RUN/SS pin, to charge up the output capacitors and provide full load current, the RUN/SS capacitor is then used as a short-circuit timeout circuit. If the output voltage falls to less than 70% of its nominal output voltage the RUN/SS capacitor begins discharging assuming that the output is in a severe overcurrent and/or short-circuit condition. If the condition lasts for a long enough period as determined by the size of the RUN/SS capacitor, the controller will be shut down until the RUN/SS pin voltage is recycled. This built-in latchoff can be overidden by providing a >5 µA pull-up current at a compliance of 5V to the RUN/SS pin. This current shortens the soft-start period but also prevents net discharge of the RUN/SS capacitor during a severe overcurrent and/or short-circuit condition. Foldback current limiting is activated when the output voltage falls below 70% of its nominal level whether or not the short-circuit latchoff circuit is enabled. APPLICATIO S I FOR ATIO The basic LTC1629-6 application circuit is shown in Fig- ure 1 on the first page. External component selection is driven by the load requirement, and begins with the selection of RSENSE1, 2. Once RSENSE1, 2 are known, L1 and L2 can be chosen. Next, the power MOSFETs and D1 and D2 are selected. The operating frequency and the inductor are chosen based mainly on the amount of ripple current. Finally, CIN is selected for its ability to handle the input ripple current (that PolyPhase operation minimizes) and COUT is chosen with low enough ESR to meet the output ripple voltage and load step specifications (also minimized with PolyPhase). The circuit shown in Figure 1 can be configured for operation up to an input voltage of 28V (limited by the external MOSFETs). |
Similar Part No. - LTC1629-6_15 |
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Similar Description - LTC1629-6_15 |
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