LT3667
40V 400mA Step-Down
Switching Regulator with
Dual Fault Protected LDOs
DESCRIPTION FEATURES Triple Output Supply from a Single Input Requires
Only One Inductor
n I = 50μA at 12V to 5V, 3.3V and 2.5V with No Load
Q
IN
n Buck Regulator: Low Ripple ( VOVLO (overvoltage lockout, 42V typical), allowing the output to fall out of regulation. During start-up, short-circuit, or other overload conditions
the inductor peak current might reach and even exceed the
maximum current limit of the LT3667, especially in those
cases where the switch already operates at minimum ontime. The catch diode current limit circuitry prevents the
switch from turning on again if the inductor valley current
is above 500mA nominal.
Inductor Selection and Maximum Output Current
For a given input and output voltage, the inductor value
and switching frequency will determine the ripple current,
which increases with higher VIN1 or VOUT1 and decreases
with higher inductance and higher switching frequency.
A good first choice for the inductor value is: L = ( VOUT1 + VD ) • 2.4
fSW where fSW is the switching frequency in MHz, VOUT1 is the
output voltage, VD is the catch diode drop (~0.5V) and L is …