Datasheet LT3640 (Analog Devices) - 8

LT3640 pin FuncTions
(FE/QFN) FB2 (Pin 1/Pin 26):
The low voltage converter regulates the
WDE (Pin 13/Pin 10):
Watchdog Enable Pin. FB2 pin to 600mV. Connect the feedback resistor divider
WDI (Pin 14/Pin 11):
The WDI pin receives watchdog tap to this pin to set output voltage. signals from a microprocessor.
PGOOD (Pin 2/Pin 27):
Open-drain logic output that starts
GND (Pins 15, 16, 23, 26, Exposed Pad Pin 29/Pins 12,
to sink current when FB2 is in regulation.
13, 20, 23, Exposed Pad Pin 29):
Ground. These pins
EN/UVLO (Pin 3/Pin 28):
Pull this pin below 0.3V to shut must be soldered to PCB ground. down the LT3640. The 1.26V threshold can function as an
NC (Pin 17/Pin 14):
Not Connected. This pin can be con- accurate undervoltage lockout, preventing the LT3640 from nected to ground. operating until VIN voltage has reached the programmed level.
DA (Pin 18/Pin 15):
The DA pin is used to sense the catch diode current for current limit and protection. Connect this
SYNC (Pin 4/Pin 1):
Driving the SYNC pin with an external pin to catch diode anode. clock signal synchronizes both converters to the applied frequency. The lowest external clock frequency should be
SW1 (Pin 19/Pin 16):
Output of the High Voltage Internal 20% higher than the internal oscillator frequency. Power Switch. Connect this pin to the inductor and catch diode cathode.
SS1 (Pin 5/Pin 2):
The SS1 pin sets the FB1 voltage ex- ternally between 0V and 1.265V, providing soft-start and
SW (Pin 20/Pin 17):
The SW pin is used to charge the tracking. Tie this pin 1.5V or higher to use the internal boost capacitor. Connect this pin to the boost capacitor. 1.265V reference. A capacitor to ground at this pin sets the
BST (Pin 21/Pin 18):
The BST pin is used to provide a drive ramp time to regulated output voltage for the high voltage voltage, higher than V converter. Use a resistor divider to track another supply. IN pin voltage, to the high voltage channel internal power switch. Connect an external boost
FB1 (Pin 6/Pin 3):
The high voltage converter regulates the diode to this pin. FB1 pin to 1.265V. Connect the feedback resistor divider
V
tap to this pin to set output voltage.
IN (Pin 22/Pin 19):
The VIN pin supplies current to the LT3640’s internal circuitry and to the high voltage
RT (Pin 7/Pin 4):
Oscillator Resistor Input. Connecting a channel internal power switch. This pin must be locally resistor to ground from this pin sets the internal oscillator bypassed. frequency.
VIN2 (Pin 24/Pin 21):
The VIN2 pin supplies current to the
RST2 (Pin 8/Pin 5):
Open-drain logic output that remains internal power MOSFET of the low voltage converter and asserted for the period set by the CPOR pin capacitor after to the LT3640’s internal circuitry when VIN2 is above 3V. FB2 goes above 550mV.
SW2 (Pin 25/Pin 22):
Switch Node of the Low Voltage
RST1 (Pin 9/Pin 6):
Open-drain logic output that remains Converter. Connect this pin to an inductor. asserted for the period set by the CPOR pin capacitor after
EN2 (Pin 27/Pin 24):
Low Voltage Converter Enable Pin. FB1 goes above 1.165V. Pull this pin below 0.3V to shut down the low voltage
WDO (Pin 10/Pin 7):
Open-drain logic output that remains converter. Pull this pin above 1.5V to enable the low volt- asserted for the period set by the CPOR pin capacitor if age converter. WDE is enabled and WDI pin is not driven by an appropri-
SS2 (Pin 28/Pin 25):
The SS2 pin sets the FB2 voltage ate signal. externally between 0V and 0.6V, providing soft-start and
CWDT (Pin 11/Pin 8):
Connect a capacitor to ground at tracking. Tie this pin 0.8V or higher to use the internal this pin to set watchdog timer. 0.6V reference. A capacitor to ground at this pin sets the ramp time to regulated output voltage for the low voltage
CPOR (Pin 12/Pin 9):
Connect a capacitor to ground at this converter. Use a resistor divider to track another supply. pin to set the power-on reset timer and WDO output timer. 3640f Document Outline Features Applications Description Typical Application Absolute Maximum Ratings Pin Configuration Order Information Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Timing Diagrams Operation Applications Information Typical Applications Package Description Typical Application Related Parts