Datasheet LTC1778, LTC1778-1 (Analog Devices) - 7

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