Datasheet LTC3778 (Analog Devices) - 7

LTC3778
U U U PI FU CTIO S RUN/SS (Pin 1):
Run Control and Soft-Start Input. A and shuts down the internal regulator so that controller capacitor to ground at this pin sets the ramp time to full power is drawn from EXTVCC. Do not exceed 7V at this pin output current (approximately 3s/µF) and the time delay and ensure that EXTVCC < VIN. for overcurrent latchoff (see Applications Information).
V
Forcing this pin below 0.8V shuts down the device.
IN (Pin 11):
Main Input Supply. Decouple this pin to SGND with an RC filter (1Ω, 0.1µF).
VON (Pin 2):
On-Time Voltage Input. Voltage trip point for
INTV
the on-time comparator. Tying this pin to the output
CC (Pin 12):
Internal 5V Regulator Output. The inter- nal control circuits are powered from this voltage. De- voltage makes the on-time proportional to VOUT. The couple this pin to power ground with a minimum of 1µF comparator input defaults to 0.7V when the pin is grounded, low ESR tantalum or ceramic capacitor. 2.4V when the pin is tied to INTVCC.
DRV PGOOD (Pin 3):
Power Good Output. Open drain logic
CC (Pin 13):
Voltage Supply to Bottom Gate Driver. Normally connected to the INTV output that is pulled to ground when the output voltage is CC pin through a decoupling RC filter (1Ω, 0.1µF). Decouple this pin to power ground not within ±10% of the regulation point. with a minimum of 4.7µF low ESR tantalum or ceramic
VRNG (Pin 4):
Sense Voltage Range Input. The voltage at capacitor. Do not exceed 7V at this pin. this pin is ten times the nominal sense voltage at maximum
BG (Pin 14):
Bottom Gate Drive. Drives the gate of the output current and can be set from 0.5V to 2V by a resistive bottom N-channel MOSFET between ground and DRV divider from INTV CC. CC. The nominal sense voltage defaults to 70mV when this pin is tied to ground, 140mV when tied
PGND (Pin 15):
Power Ground. Connect this pin closely to to INTV the source of the bottom N-channel MOSFET or to the CC. bottom of the sense resistor when used, the (–) terminal
ITH (Pin 5):
Current Control Threshold and Error Amplifier of C Compensation Point. The current comparator threshold VCC and the (–) terminal of CIN. increases with this control voltage. The voltage ranges
SENSE– (Pin 16):
Current Sense Comparator Input. The from 0V to 2.4V with 0.8V corresponding to zero sense (–) input to the current comparator is used to accurately voltage (zero current). Kelvin sense the bottom side of the sense resistor or MOSFET.
FCB (Pin 6):
Forced Continuous Input. Tie this pin to ground to force continuous synchronous operation at low
SENSE+ (Pin 17):
Current Sense Comparator Input. The load, to INTV (+) input to the current comparator is normally connected CC to enable discontinuous mode operation at low load or to a resistive divider from a secondary output to the SW node unless using a sense resistor (See Appli- when using a secondary winding. cations Information).
SGND (Pin 7):
Signal Ground. All small-signal compo-
SW (Pin 18):
Switch Node. The (–) terminal of the boot- nents and compensation components should connect to strap capacitor CB connects here. This pin swings from a this ground, which in turn connects to PGND at one point. diode voltage drop below ground up to VIN.
I TG (Pin 19):
Top Gate Drive. Drives the top N-channel
ON (Pin 8):
On-Time Current Input. Tie a resistor from VIN to this pin to set the one-shot timer current and thereby set MOSFET with a voltage swing equal to DRVCC superim- the switching frequency. posed on the switch node voltage SW.
V BOOST (Pin 20):
Boosted Floating Driver Supply. The (+)
FB (Pin 9):
Error Amplifier Feedback Input. This pin connects the error amplifier input to an external resistive terminal of the bootstrap capacitor CB connects here. This divider from V pin swings from a diode voltage drop below DRV OUT. CC up to V
EXTV
IN + DRVCC.
CC (Pin 10):
External VCC Input. When EXTVCC ex- ceeds 4.7V, an internal switch connects this pin to INTVCC 3778f 7