LT3640EFE LINER [Linear Technology], LT3640EFE Datasheet - Page 8

• Manufacturer Part Number: LT3640EFE
• Description: Dual Monolithic Buck Regulator with Power-On Reset and Watchdog Timer
• Manufacturer: LINER [Linear Technology]

PIN FUNCTIONS
LT3640
FB2 (Pin 1/Pin 26): The low voltage converter regulates the
FB2 pin to 600mV. Connect the feedback resistor divider
tap to this pin to set output voltage.
PGOOD (Pin 2/Pin 27): Open-drain logic output that starts
to sink current when FB2 is in regulation.
EN/UVLO (Pin 3/Pin 28): Pull this pin below 0.3V to shut
down the LT3640. The 1.26V threshold can function as an
accurate undervoltage lockout, preventing the LT3640 from
operating until V
level.
SYNC (Pin 4/Pin 1): Driving the SYNC pin with an external
clock signal synchronizes both converters to the applied
frequency. The lowest external clock frequency should be
20% higher than the internal oscillator frequency.
SS1 (Pin 5/Pin 2): The SS1 pin sets the FB1 voltage ex-
ternally between 0V and 1.265V, providing soft-start and
tracking. Tie this pin 1.5V or higher to use the internal
1.265V reference. A capacitor to ground at this pin sets the
ramp time to regulated output voltage for the high voltage
converter. Use a resistor divider to track another supply.
FB1 (Pin 6/Pin 3): The high voltage converter regulates the
FB1 pin to 1.265V. Connect the feedback resistor divider
tap to this pin to set output voltage.
RT (Pin 7/Pin 4): Oscillator Resistor Input. Connecting a
resistor to ground from this pin sets the internal oscillator
frequency.
RST2 (Pin 8/Pin 5): Open-drain logic output that remains
asserted for the period set by the CPOR pin capacitor after
FB2 goes above 550mV.
RST1 (Pin 9/Pin 6): Open-drain logic output that remains
asserted for the period set by the CPOR pin capacitor after
FB1 goes above 1.165V.
WDO (Pin 10/Pin 7): Open-drain logic output that remains
asserted for the period set by the CPOR pin capacitor if
WDE is enabled and WDI pin is not driven by an appropri-
ate signal.
CWDT (Pin 11/Pin 8): Connect a capacitor to ground at
this pin to set watchdog timer.
CPOR (Pin 12/Pin 9): Connect a capacitor to ground at this
pin to set the power-on reset timer and WDO output timer.
8
IN
voltage has reached the programmed
(FE/QFN)
WDE (Pin 13/Pin 10): Watchdog Enable Pin.
WDI (Pin 14/Pin 11): The WDI pin receives watchdog
signals from a microprocessor.
GND (Pins 15, 16, 23, 26, Exposed Pad 29/Pins 12, 13,
20, 23, Exposed Pad 29): Ground. These pins must be
soldered to PCB ground.
NC (Pin 17/Pin 14): Not Connected.
DA (Pin 18/Pin 15): The DA pin is used to sense the catch
diode current for current limit and protection. Connect this
pin to catch diode anode.
SW1 (Pin 19/Pin 16): Output of the High Voltage Internal
Power Switch. Connect this pin to the inductor and catch
diode cathode.
SW (Pin 20/Pin 17): The SW pin is used to charge the
boost capacitor. Connect this pin to the boost capacitor.
BST (Pin 21/Pin 18): The BST pin is used to provide a drive
voltage, higher than V
channel internal power switch. Connect an external boost
diode to this pin.
V
the LT3640’s internal circuitry and to the high voltage
channel internal power switch. This pin must be locally
bypassed.
V
internal power MOSFET of the low voltage converter and
to the LT3640’s internal circuitry when V
SW2 (Pin 25/Pin 22): Switch Node of the Low Voltage
Converter. Connect this pin to an inductor.
EN2 (Pin 27/Pin 24): Low Voltage Converter Enable Pin.
Pull this pin below 0.3V to shut down the low voltage
converter. Pull this pin above 1.5V to enable the low volt-
age converter.
SS2 (Pin 28/Pin 25): The SS2 pin sets the FB2 voltage
externally between 0V and 0.6V, providing soft-start and
tracking. Tie this pin 0.8V or higher to use the internal
0.6V reference. A capacitor to ground at this pin sets the
ramp time to regulated output voltage for the low voltage
converter. Use a resistor divider to track another supply.
IN
IN2
(Pin 22/Pin 19): The V
(Pin 24/Pin 21): The V
IN
pin voltage, to the high voltage
IN2
IN
pin supplies current to the
pin supplies current to
IN2
is above 3V.
3640p