LTC3769
9
3769fa
For more information www.linear.com/LTC3769
PIN FUNCTIONS
(QFN/TSSOP)
input determines how the LTC3769 operates at light loads.
Pulling this pin to ground selects Burst Mode operation.
An internal 100k resistor to ground also invokes Burst
Mode operation when the pin is floated. Tying this pin
to INTV
CC
forces continuous inductor current operation.
Tying this pin to a voltage greater than 1.2V and less than
INTV
CC
– 1.3V selects pulse-skipping operation. This can
be done by adding a 100k resistor between the PLLIN/
MODE pin and INTV
CC
.
RUN (Pin 11/Pin 6): Run Control Input. Forcing this pin
below 1.28V shuts down the controller. Forcing this pin
below 0.7V shuts down the entire LTC3769, reducing
quiescent current to approximately 4µA. An external
resistor divider connected to V
IN
can set the threshold
for converter operation. Once running, a 4.5µA current is
sourced from the RUN pin allowing the user to program
hysteresis using the resistor values.
SS (Pin 12/Pin 7): Output Soft-Start Input. A capacitor to
ground at this pin sets the ramp rate of the output voltage
during start-up.
SENSE
–
(Pin 13/Pin 8): Negative 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.
SENSE
+
(Pin 14/Pin 9): Positive Current Sense Comparator
Input. The (+) input to the current comparator is normally
connected to the positive terminal of a current sense resis
-
tor. The current sense resistor is normally placed at the
input of the boost controller in series with the inductor.
This pin also supplies power to the current comparator.
The common mode voltage range on SENSE
+
and SENSE
–
pins is 2.3V to 60V (65V abs max).
VFB (Pin 15/Pin 10): Error Amplifier Feedback Input. This
pin receives the remotely sensed feedback voltage from
an external resistive divider connected across the output.
ITH (Pin 16/Pin 11): Current Control Threshold and Error
Amplifier Compensation Point. The voltage on this pin sets
the current trip threshold.
OVMODE (Pin 17/Pin 12): Overvoltage Mode Selection
Input. This pin is used to select how the LTC3769 operates
when the output feedback voltage (V
FB
) 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 LTC3769 is synchronized to an external clock through
the PLLIN/MODE pin.
When OVMODE is tied to ground, overvoltage protection
is enabled and the top MOSFET gate (TG) is turned on
continuously until the overvoltage condition is cleared.
When OVMODE is grounded, the LTC3769 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.
When OVMODE is tied to INTV
CC
, overvoltage protection
is disabled and TG is not forced on during an overvolt-
age event. Instead, the state of TG is determined by the
mode of operation selected by the PLLIN/MODE pin and
the inductor current. See the Operation
section
for more
details. When OVMODE is tied to INTV
CC
, the LTC3769
operates in pulse-skipping mode when synchronized.
SW (Pin 18/Pin 13): Switch Node. Connect to the source
of the synchronous N-channel MOSFET, the drain of the
main N-channel MOSFET and the inductor.
TG (Pin 19/Pin 14): Top Gate. Connect to the gate of the
synchronous N-channel MOSFET.
BOOST (Pin 20/Pin 15): Floating power supply for the
synchronous N-channel MOSFET. Bypass to SW with a
capacitor and supply with a Schottky diode connected
to INTV
CC
.
BG (Pin 21/Pin 16): Bottom Gate. Connect to the gate of
the main N-channel MOSFET.
EXTV
CC
(Pin 23/Pin 18): External Power Input to an internal
LDO Connected to INTV
CC
. This LDO supplies INTV
CC
power,
bypassing the internal LDO powered from V
BIAS
whenever
EXTV
CC
is higher than 4.7V. See EXTV
CC
Connection in the
Applications Information section. Do not float or exceed
14V on this pin. Connect to ground if not used.
