Datasheet LT3507A (Analog Devices) - 7

LT3507A
pin Functions BIAS:
The BIAS pin supplies the current to the LT3507A’s
RT/SYNC:
The RT/SYNC pin requires a resistor to ground internal regulator. This pin should be tied to the lowest or a clock signal to set the operating frequency of the available voltage source above 3V (either VIN, VOUT or any LT3507A. other available supply). The LDO pass transistor’s base
RUN1, RUN2, RUN3:
The RUN pins are used to shut current is supplied from the BIAS pin if it is at least 0.8V down the individual switching regulators. When all three above the LDO DRIVE output. RUN pins are low, the LT3507A shuts down and draws
BOOST1, BOOST2, BOOST3:
The BOOST pins are used less than 1µA from VIN1. to provide drive voltages, higher than the input voltage,
SW1, SW2, SW3:
The SW pins are the outputs of the to the internal bipolar NPN power switches. These pins internal power switches. Connect these pins to the induc- must be tied through a diode from VOUT, VIN or another tors and switching diodes. supply greater than 2.5V.
TRK/SS1, TRK/SS2, TRK/SS3, TRK/SS4:
The TRK/SS pins
DRIVE:
The DRIVE pin provides the base drive for an allow a regulator to track the output of another regulator. external NPN transistor used for the LDO regulator. When the TRK/SS pin is below 0.8V, the FB pin regulates
FB1, FB2, FB3:
The FB pins are the negative inputs of the to the TRK/SS voltage. This pin souces 1.25µA and can error amplifiers. The LT3507A regulates each feedback pin be used as a soft-start by connecting a capacitor from to the lesser of 0.8V or the TRK/SS pin voltage. Connect TRK/SS to ground. The TRK/SS pins should be left open the feedback resistor divider taps to these pins. if neither feature is used.
FB4:
The FB4 pin is the negative input to the LDO error
UVLO:
The LT3507A goes into undervoltage shutdown amplifier. It is regulated to 0.8V through the LDO feedback when this pin drops below 1.2V. If unused, the UVLO pin resistor divider. should be tied to VINSW.
GND:
Ground. The underside exposed pad metal of the
VC1, VC2, VC3:
The VC pins are the outputs of the internal package provides both electrical contact to ground and error amps. The voltages on these pins control the peak good thermal contact to the printed circuit board. The switch currents. These pins are normally used to com- exposed pad must be soldered to a grounded pad on the pensate the control loops. Each switching regulator can circuit board for proper operation. be shut down by pulling its respective VC pin to ground
OVLO:
The LT3507A goes into overvoltage shutdown with an NMOS or NPN transistor. when this pin goes above 1.2V. If unused, the OVLO pin
VIN1:
The VIN1 pins supply power to the internal switch of should be tied to GND. the 2.7A regulator and to the LT3507A’s internal reference
PGOOD1, PGOOD2, PGOOD3:
The PGOOD pins are the and start-up circuitry. VIN1 must be above the internal UVLO open-collector outputs of an internal comparator. PGOOD threshold of 3.8V (typical) for any of the four channels to remains low until the FB pin is within 10% of the final operate. These pins must be locally bypassed. regulation voltage. As well as indicating output regulation,
VIN2/VIN3:
The VIN2 and VIN3 pins supply power to the the PGOOD pins can sequence the switching regulators. internal switches of the 1.8A converters. These pins must These pins must be left unconnected if unused. The PGOOD be locally bypassed. outputs are valid when VIN is greater than 3.8V and any of
V
the RUN pins are high. They are not valid when all RUN
INSW:
The VINSW pin is a switched VIN1 for the user pro- grammable undervoltage and overvoltage detection. It is pins are low. connected to VIN1 when any of the RUN pins are pulled high, and high impedance when all RUN pins are low or open. 3507afa For more information www.linear.com/LT3507A 7 Document Outline Features Applications Description Typical Application Absolute Maximum Ratings Pin Configuration Order Information Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Operation Applications Information Typical Applications Package Description Package Description Typical Applications Related Parts