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LTC1735 Datasheet(PDF) 7 Page - Linear Technology |
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LTC1735 Datasheet(HTML) 7 Page - Linear Technology |
7 / 24 page 7 LTC1778/LTC1778-1 1778fb PI FU CTIO S RUN/SS (Pin 1): Run Control and Soft-Start Input. A capacitor to ground at this pin sets the ramp time to full output current (approximately 3s/µF) and the time delay for overcurrent latchoff (see Applications Information). Forcing this pin below 0.8V shuts down the device. PGOOD (Pin 2, LTC1778): Power Good Output. Open drain logic output that is pulled to ground when the output voltage is not within ±7.5% of the regulation point. VON (Pin 2, LTC1778-1): On-Time Voltage Input. Voltage trip point for the on-time comparator. Tying this pin to the output voltage or an external resistive divider from the output makes the on-time proportional to VOUT. The comparator input defaults to 0.7V when the pin is grounded or unavailable (LTC1778) and defaults to 2.4V when the pin is tied to INTVCC. Tie this pin to INTVCC in high VOUT applications to use a lower RON value. VRNG (Pin 3): Sense Voltage Range Input. The voltage at this pin is ten times the nominal sense voltage at maxi- mum output current and can be set from 0.5V to 2V by a resistive divider from INTVCC. The nominal sense voltage defaults to 70mV when this pin is tied to ground, 140mV when tied to INTVCC. FCB (Pin 4): Forced Continuous Input. Tie this pin to ground to force continuous synchronous operation at low load, to INTVCC to enable discontinuous mode operation at low load or to a resistive divider from a secondary output when using a secondary winding. ITH (Pin 5): Current Control Threshold and Error Amplifier Compensation Point. The current comparator threshold increases with this control voltage. The voltage ranges from 0V to 2.4V with 0.8V corresponding to zero sense voltage (zero current). SGND (Pin 6): Signal Ground. All small-signal compo- nents and compensation components should connect to this ground, which in turn connects to PGND at one point. ION (Pin 7): On-Time Current Input. Tie a resistor from VIN to this pin to set the one-shot timer current and thereby set the switching frequency. VFB (Pin 8): Error Amplifier Feedback Input. This pin connects the error amplifier input to an external resistive divider from VOUT. EXTVCC (Pin 9): External VCC Input. When EXTVCC ex- ceeds 4.7V, an internal switch connects this pin to INTVCC and shuts down the internal regulator so that controller and gate drive power is drawn from EXTVCC. Do not exceed 7V at this pin and ensure that EXTVCC < VIN. VIN (Pin 10): Main Input Supply. Decouple this pin to PGND with an RC filter (1Ω, 0.1µF). INTVCC (Pin 11): Internal 5V Regulator Output. The driver and control circuits are powered from this voltage. De- couple this pin to power ground with a minimum of 4.7µF low ESR tantalum capacitor. BG (Pin 12): Bottom Gate Drive. Drives the gate of the bottom N-channel MOSFET between ground and INTVCC. PGND (Pin 13): Power Ground. Connect this pin closely to the source of the bottom N-channel MOSFET, the (–) terminal of CVCC and the (–) terminal of CIN. SW (Pin 14): Switch Node. The (–) terminal of the boot- strap capacitor CB connects here. This pin swings from a diode voltage drop below ground up to VIN. TG (Pin 15): Top Gate Drive. Drives the top N-channel MOSFET with a voltage swing equal to INTVCC superim- posed on the switch node voltage SW. BOOST (Pin 16): Boosted Floating Driver Supply. The (+) terminal of the bootstrap capacitor CB connects here. This pin swings from a diode voltage drop below INTVCC up to VIN + INTVCC. |
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Similar Description - LTC1735 |
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