Datasheet LTC3637 (Analog Devices) - 7

LTC3637
PIN FUNCTIONS SW (Pin 1):
Switch Node Connection to Inductor. This
ISET (Pin 11):
Peak Current Set Input and Voltage Output pin connects to the drains of the internal power MOSFET Ripple Filter. A resistor from this pin to ground sets the switches. peak current comparator threshold. Leave floating for the
NC (Pins 2, 4, 13, 15 DHC Package Only)
: No Internal maximum peak current (2.4A typical) or short to ground Connection. Leave these pins open. for minimum peak current (0.24A typical). The maximum output current is one-half the peak current. The 5µA current
VIN (Pin 3):
Main Input Supply Pin. A ceramic bypass that is sourced out of this pin when switching, is reduced capacitor should be tied between this pin and GND. to 1µA in sleep. Optionally, a capacitor can be placed from
FBO (Pin 5):
Feedback Comparator Output. The typical this pin to GND to trade off efficiency for light load output pull-up current is 20µA. The typical pull- down imped- voltage ripple. See Applications Information. ance is 70Ω.
OVLO (Pin 12):
Overvoltage Lockout Input. Connect to
V
the input supply through a resistor divider to set the over-
PRG2, VPRG1 (Pins 6, 7):
Output Voltage Selection. Short both pins to ground for an external resistive divider pro- voltage lockout level. A voltage on this pin above 1.21V grammable output voltage. Short V disables the internal MOSFET switch. Normal operation PRG1 to SS and short V resumes when the voltage on this pin decreases below PRG2 to ground for a 5V output voltage. Short VPRG1 to ground and short V 1.10V. A transient exceeding the OVLO threshold triggers PRG2 to SS for a 3.3V output voltage. Short both pins to SS for a 1.8V output voltage. a soft-start reset, resulting in a graceful recovery from an input supply transient. Connect this pin to ground to
GND (Pins 8, 16, Exposed Pad Pin 17):
Ground. The ex- disable the overvoltage lockout. posed backside pad must be soldered to the PCB ground plane for optimal thermal performance.
RUN (Pin 14):
Run Control Input. A voltage on this pin above 1.21V enables normal operation. Forcing this pin
VFB (Pin 9):
Output Voltage Feedback. When configured below 0.7V shuts down the LTC3637, reducing quiescent for an adjustable output voltage, connect to an external current to approximately 3µA. Optionally, connect to the resistive divider to divide the output voltage down for input supply through a resistor divider to set the under- comparison to the 0.8V reference. For the fixed output voltage lockout. configuration, directly connect this pin to the output supply.
SS (Pin 10):
Soft-Start Control Input. A capacitor to ground at this pin sets the output voltage ramp time. A 50µA current initially charges the soft-start capacitor until switching begins, at which time the current is reduced to its nominal value of 5µA. The output voltage ramp time from zero to its regulated value is 1ms for every 16.5nF of capacitance from SS to GND. If left floating, the ramp time defaults to an internal 0.8ms soft-start. 3637fa For more information www.linear.com/LTC3637 7 Document Outline Features Applications Description Typical Application Absolute Maximum Ratings Pin Configuration Order Information Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Operation Applications Information Typical Applications Package Description Typical Application Related Parts