LTC3787
PIN FUNCTIONS (QFN/SSOP)
SS (Pin 7/Pin ±0): Output Soft-Start Input. A capacitor to
ground at this pin sets the ramp rate of the output voltage
during start-up.
PGND (Pin ±9/Pin 22): Driver Power Ground. Connects
to the sources of bottom (main) N-channel MOSFETs and
the (–) terminal(s) of C and C
.
IN
OUT
–
–
SENSE2 , SENSE± (Pin 8, Pin 28/Pin ±±, Pin 3): Nega-
tive Current Sense Comparator Input. The (–) input to the
current comparator is normally connected to the negative
terminal of a current sense resistor connected in series
with the inductor.
BG2, BG± (Pin ±6, Pin 2±/Pin ±9, Pin 24): Bottom Gate.
Connect to the gate of the main N-channel MOSFET.
INTV (Pin ±7/Pin 20): Output of Internal 5.4V LDO.
CC
Power supply for control circuits and gate drivers. De-
couple this pin to GND with a minimum 4.7μF low ESR
ceramic capacitor.
+
+
SENSE2 , SENSE± (Pin 9, Pin 27/Pin ±2, Pin 2): Posi-
tive Current Sense Comparator Input. The (+) input to the
current comparator is normally connected to the positive
terminalofacurrentsenseresistor.Thecurrentsenseresis-
tor is normally placed at the input of the boost controller in
serieswiththeinductor.Thispinalsosuppliespowertothe
current comparator. The common mode voltage range on
EXTV (Pin ±8/Pin 2±): External Power Input. When this
CC
pin is between 4.8V and 6V, an internal switch bypasses
the internal regulator and supply power to INTV directly
CC
from EXTV . Do not float this pin. It can be connected to
CC
ground when not used.
+
–
VBIAS (Pin 20/Pin 23): Main Supply Pin. It is normally
SENSE and SENSE pins is 2.5V to 38V (40V abs max).
tied to the input supply V or to the output of the boost
IN
VFB (Pin ±0/Pin ±3): Error Amplifier Feedback Input. This
pin receives the remotely sensed feedback voltage from
an external resistive divider connected across the output.
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 38V (40V abs max).
ITH (Pin ±±/Pin ±4): Current Control Threshold and Error
AmplifierCompensationPoint.Thevoltageonthispinsets
the current trip threshold.
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 25μs before this output is activated.
NC (Pin ±2/Pin ±5): No Connect.
SW2, SW± (Pin ±3, Pin 24/Pin ±6, 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.
ILIM (Pin 26/Pin ±): Current Comparator Sense Voltage
Range Input. This pin is used to set the peak current
sense voltage in the current comparator. Connect this pin
to SGND, open, and INTV to set the peak current sense
CC
TG2, TG± (Pin ±4, Pin 23/Pin ±7, Pin 26): Top Gate. Con-
nect to the gate of the synchronous N-channel MOSFET.
voltage to 50mV, 75mV and 100mV, respectively.
GND (Exposed Pad Pin 29) UFD Package: Ground. Must
be soldered to the PCB for rated thermal performance.
BOOST2, BOOST± (Pin ±5, Pin 22/Pin ±8, Pin 25): Float-
ingpowersupplyforthesynchronousN-channelMOSFET.
Bypass to SW with a capacitor and supply with a Schottky
diode connected to INTV .
CC
3787fc
10
Linear Systems [ Linear Systems ]
