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LT3507EUHFTRPBF Datasheet(PDF) 7 Page - Linear Dimensions Semiconductor |
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LT3507EUHFTRPBF Datasheet(HTML) 7 Page - Linear Dimensions Semiconductor |
7 / 28 page LT3507 7 3507fa PIN FUNCTIONS BOOST1, BOOST2, BOOST3 (Pins 1, 27, 32): The BOOST pins are used to provide drive voltages, higher than the input voltage, to the internal bipolar NPN power switches. These pins must be tied through a diode from VOUT, VIN or another supply greater than 2.5V. VIN1 (Pins 2, 3): The VIN1 pins supply power to the internal switch of the 2.4A regulator and to the LT3507’s internal reference and start-up circuitry. These pins must be locally bypassed (Note 6). VINSW (Pin 4): The VINSW pin is a switched VIN1 for the user programmable undervoltage and overvoltage detec- tion. It is connected to VIN1 when any of the RUN pins are pulled high, and high impedance when all RUN pins are low or open. OVLO (Pin 5): The LT3507 goes into overvoltage shutdown when this pin goes above 1.2V. If unused, the OVLO pin should be tied to GND. UVLO(Pin6):TheLT3507goesintoundervoltageshutdown when this pin drops below 1.2V. If unused, the UVLO pin should be tied to VINSW. VC1, VC2, VC3 (Pins 7, 23, 19): The VC pins are the outputs of the internal error amps. The voltages on these pins control the peak switch currents. These pins are normally used to compensate the control loops. Each switching regulator can be shut down by pulling its respective VC pin to ground with an NMOS or NPN transistor. TRK/SS1, TRK/SS2, TRK/SS3, TRK/SS4 (Pins 8, 21, 18, 26): The TRK/SS pins allow a regulator to track the output of another regulator. When the TRK/SS pin is below 0.8V, the FB pin regulates to the TRK/SS voltage. This pin can also be used as a soft-start by connecting a capacitor from TRK/SS to ground. The TRK/SS pins should be left open if neither feature is used. FB1, FB2, FB3 (Pins 9, 22, 20): The FB pins are the nega- tive inputs of the error amplifiers. The LT3507 regulates each feedback pin to the lesser of 0.8V or the TRK/SS pin voltage. Connect the feedback resistor divider taps to these pins. Note 6: VINX pins that are connected together may share a bypass capacitor. PGOOD1, PGOOD2, PGOOD3 (Pins 10, 11, 12): The PGOOD pins are the open-collector outputs of an internal comparator. PGOOD remains low until the FB pin is within 10% of the final regulation voltage. As well as indicating output regulation, the PGOOD pins can sequence the switching regulators. These pins must be left unconnected if unused. The PGOOD outputs are valid when VIN is greater than 3.5V and any of the RUN pins are high. They are not valid when all RUN pins are low. RT/SYNC (Pin 13): The RT/SYNC pin requires a resistor to ground or a clock signal to set the operating frequency of the LT3507. RUN1, RUN2, RUN3 (Pins 14, 15, 16): The RUN pins are used to shut down the individual switching regulators. When all three RUN pins are low, the LT3507 shuts down and draws less than 1μA from VIN1. BIAS (Pin 17): The BIAS pin supplies the current to the LT3507’s internal regulator. This pin should be tied to the lowest available voltage source above 3V (either VIN, VOUT or any other available supply). The LDO pass transistor’s base current is supplied from the BIAS pin if it is at least 0.8V above the LDO DRIVE output. DRIVE (Pin 24): The DRIVE pin provides the base drive for an external NPN transistor used for the LDO regulator. FB4 (Pin 25): The FB4 pin is the negative input to the LDO error amplifier. It is regulated to 0.8V through the LDO feedback resistor divider. VIN2 (Pins 30, 31)/VIN3 (Pins 35, 36 ): The VIN2 and VIN3 pins supply power to the internal switches of the 1.5A con- verters. These pins must be locally bypassed (Note 6). SW1 (Pins 37, 38)/SW2 (Pins 28, 29)/SW3 (Pins 33, 34): The SW pins are the outputs of the internal power switches. Connect these pins to the inductors and switch- ing diodes. Exposed Pad (Pin 39): Ground. The underside Exposed Pad metal of the package provides both electrical contact to ground and good thermal contact to the printed circuit board. The Exposed Pad must be soldered to a grounded pad on the circuit board for proper operation. |
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