LTC3637_15 Datasheet, PDF (7/26 Pages) Linear Technology – 76V, 1A Step-Down Regulator

LTC3637
PIN FUNCTIONS
SW (Pin 1): Switch Node Connection to Inductor. This
pin connects to the drains of the internal power MOSFET
switches.
NC (Pins 2, 4, 13, 15 DHC Package Only): No Internal
Connection. Leave these pins open.
V_IN (Pin 3): Main Input Supply Pin. A ceramic bypass
capacitor should be tied between this pin and GND.
FBO (Pin 5): Feedback Comparator Output. The typical
pull-up current is 20µA. The typical pull- down imped-
ance is 70Ω.
V_PRG2, V_PRG1 (Pins 6, 7): Output Voltage Selection. Short
both pins to ground for an external resistive divider pro-
grammable output voltage. Short V_PRG1 to SS and short
V_PRG2 to ground for a 5V output voltage. Short V_PRG1 to
ground and short V_PRG2 to SS for a 3.3V output voltage.
Short both pins to SS for a 1.8V output voltage.
GND (Pins 8, 16, Exposed Pad Pin 17): Ground. The ex-
posed backside pad must be soldered to the PCB ground
plane for optimal thermal performance.
V_FB (Pin 9): Output Voltage Feedback. When configured
for an adjustable output voltage, connect to an external
resistive divider to divide the output voltage down for
comparison to the 0.8V reference. For the fixed output
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.
I_SET (Pin 11): Peak Current Set Input and Voltage Output
Ripple Filter. A resistor from this pin to ground sets the
peak current comparator threshold. Leave floating for the
maximum peak current (2.4A typical) or short to ground
for minimum peak current (0.24A typical). The maximum
output current is one-half the peak current. The 5µA current
that is sourced out of this pin when switching, is reduced
to 1µA in sleep. Optionally, a capacitor can be placed from
this pin to GND to trade off efficiency for light load output
voltage ripple. See Applications Information.
OVLO (Pin 12): Overvoltage Lockout Input. Connect to
the input supply through a resistor divider to set the over-
voltage lockout level. A voltage on this pin above 1.21V
disables the internal MOSFET switch. Normal operation
resumes when the voltage on this pin decreases below
1.10V. A transient exceeding the OVLO threshold triggers
a soft-start reset, resulting in a graceful recovery from
an input supply transient. Connect this pin to ground to
disable the overvoltage lockout.
RUN (Pin 14): Run Control Input. A voltage on this pin
above 1.21V enables normal operation. Forcing this pin
below 0.7V shuts down the LTC3637, reducing quiescent
current to approximately 3µA. Optionally, connect to the
input supply through a resistor divider to set the under-
voltage lockout.
For more information www.linear.com/LTC3637
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