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LT3513 Datasheet(PDF) 8 Page - Linear Technology |
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LT3513 Datasheet(HTML) 8 Page - Linear Technology |
8 / 20 page LT3513 8 3513fa PGOOD (Pin 11): Power Good Comparator Output. This is the open collector output of the power good comparator and can be used in conjunction with an external P-chan- nel MOSFET to provide output disconnect for AVDD as shown in Figure 2. When switcher 2’s output reaches approximately 90% of its programmed voltage, PGOOD will be pulled to ground. This will pull down on the gate of the MOSFET, connecting AVDD. A 100k pull-up resistor between the source and the gate of the P-channel MOSFET keeps it off when switcher 2’s output is low. VC3 (Pin 12): Control Voltage and Compensation Pin for Internal Error Amplifier. Connect a series RC from this pin to ground to compensate switching regulator 3. CT (Pin 13): Timing Capacitor Pin. This is the input to the VON timer and programs the time delay from all four feedback pins reaching 1.125V to VON turning on. The CT capacitor value can be set using the equation C = (20μA • tDELAY)/1.1V. GND (Pins 14, 17, 33): Ground. SW2 (Pins 15, 16): Switch Node. The SW2 pin is the col- lector of the internal NPN bipolar transistor for switching regulator 2. Minimize trace area at this pin to keep EMI down. BIAS (Pins 18, 29): The BIAS pin is used to improve ef- ficiency when operating at higher input voltages. Connect- ing this pin to the output of switching regulator 1 forces most of the internal circuitry to draw its operating current from VLOGIC rather than VIN. The drivers of switches 2, 3, 4 and 5 are supplied by BIAS. Switches 2, 3, 4 and 5 will not switch until the BIAS pin reaches approximately 2.7V. Both BIAS pins must be tied to VLOGIC. FB2 (Pin 19): Feedback Pin. Tie the resistor divider tap to this pin and set AVDD according to AVDD = 1.23V • (1 + R5/R6). Reference designators refer to Figure 2. VC2 (Pin 20): Control Voltage and Compensation Pin for Internal Error Amplifier. Connect a series RC from this pin to ground to compensate switching regulator 2. VC4 (Pin 21): Control Voltage and Compensation Pin for Internal Error Amplifier. Connect a series RC from this pin to ground to compensate switching regulator 4. RUN-SS1 (Pin 22): Run/Soft-Start Pin. This is the soft-start pin for switching regulator 1. Place a soft-start capacitor here to limit start-up inrush current and output voltage ramp rate. When power is applied to the VIN pin, a 2μA current source charges the capacitor. When the voltage at this pin reaches 0.8V, switch 1 turns on and begins switching. For slower start-up use a larger capacitor. For complete shutdown tie RUN-SS1 to ground. NFB4 (Pin 23): Negative Feedback Pin. Tie the resistor di- vider tap to this pin and set VOFF according to VOFF = –1.18 • (1 + R3/R4). Reference designators refer to Figure 2. D4 (Pin 24): Internal Schottky Diode Pin. This pin is the anode of an internal Schottky diode with the other end connected to ground. This Schottky diode is used in generating the VOFF output. SW4 (Pin 25): Switch Node. The SW4 pin is the collector of the internal NPN bipolar transistor for switching regulator 4. Minimize trace area at this pin to keep EMI down. BD (Note 26): NPN LDO Base Drive. This pin controls the base of the external NPN LDO transistor. LDOPWR (Pin 27): Input Voltage for LDO Driver. This pin supplies the current for the NPN LDO base. This pin can be connected to VIN. To save power at high VIN voltages, the pin can alternatively be connected to the AVDD supply. BOOST (Pin 28): The BOOST pin is used to provide a drive voltage higher than VIN to the switch 1 drive circuit. An internal Schottky diode is connected between BIAS and BOOST. A capacitor needs to be connected between BOOST and SW1. SENSE– (Pin 30) Negative Current Sense Input. This pin (along with the SENSE+ pin) is used to sense the inductor current for the buck switching regulator. PIN FUNCTIONS |
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