LT8705 datasheet(9/38 Pages) LINER

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LTC3784

3784fb

For more information www.linear.com/LTC3784

pin FuncTions (QFN/SSOP)

OVMODE (Pin 12/Pin 15): Overvoltage Mode Selection

Input. This pin is used to select how the LTC3784 operates

when the output feedback voltage (VFB) is overvoltage

(>110% of its normal regulated point of 1.2V). It is also

used to determine the light-load mode of operation when

the LTC3784 is synchronized to an external clock through

the PLLIN/MODE pin.

WhenOVMODEistiedtoground,overvoltageprotectionis

enabled and the top MOSFET gates (TG1, TG2) are turned

on continuously until the overvoltage condition is cleared.

When OVMODE is grounded, the LTC3784 operates in

forced continuous mode when synchronized. There is an

internal weak pull-down resistor that pulls the OVMODE

pin to ground when it is left floating.

WhenOVMODEistiedtoINTVCC,overvoltageprotectionis

disabledandTG1/TG2arenotforcedonduringanovervolt-

age event. Instead, the state of TG1/TG2 is determined by

themodeofoperationselectedbythePLLIN/MODEpinand

the inductor current. See the Operation section for more

details. When OVMODE is tied to INTVCC, the LTC3784

operates in pulse-skipping mode when synchronized.

SW2, SW1 (Pin 13, Pin 24/Pin 16, Pin 27): Switch Node.

Connect to the source of the synchronous N-channel

MOSFET, the drain of the main N-channel MOSFET and

the inductor.

TG2, TG1 (Pin 14, Pin 23/Pin 17, Pin 26): Top Gate. Con-

nect to the gate of the synchronous N-channel MOSFET.

BOOST2, BOOST1 (Pin 15, Pin 22/Pin 18, Pin 25): Float-

ing power supply for the synchronous N-channel MOSFET.

Bypass to SW with a capacitor and supply with a Schottky

diode connected to INTVCC.

PGND (Pin 19/Pin 22): Driver Power Ground. Connects

to the sources of bottom (main) N-channel MOSFETs and

the (–) terminal(s) of CIN and COUT.

BG2, BG1 (Pin 16, Pin 21/Pin 19, Pin 24): Bottom Gate.

Connect to the gate of the main N-channel MOSFET.

INTVCC (Pin 17/Pin 20): Output of Internal 5.4V LDO.

Power supply for control circuits and gate drivers. De-

couple this pin to GND with a minimum 4.7μF low ESR

ceramic capacitor.

EXTVCC(Pin18/Pin21):ExternalPowerInputtoaninternal

LDOConnectedtoINTVCC.ThisLDOsuppliesINTVCCpower,

bypassing the internal LDO powered from VBIASwhenever

EXTVCC is higher than 4.8V. See EXTVCC Connection in the

Applications Information section. Do not float or exceed

14V on this pin. Connect to ground if not used.

VBIAS (Pin 20/Pin 23): Main Supply Pin. It is normally

tied to the input supply VIN or to the output of the boost

converter. A bypass capacitor should be tied between this

pin and the signal ground pin. The operating voltage range

on this pin is 4.5V to 60V (65V abs max).

PGOOD(Pin25/Pin28):PowerGoodIndicator.Open-drain

logic output that is pulled to ground when the output volt-

age is more than ±10 % away from the regulated output

voltage. To avoid false trips the output voltage must be

outside the range for 45μs before this output is activated.

ILIM (Pin 26/Pin 1): Current Comparator Sense Voltage

Range Input. This pin is used to set the peak current sense

voltageinthecurrentcomparator.ConnectthispintoSGND,

leave floating or connect to INTVCC to set the peak current

sense voltage to 50mV, 75mV or 100mV, respectively.

GND (Exposed Pad Pin 29) UFD Package: Ground. Must

be soldered to PCB ground for rated thermal performance.

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