LT3681
APPLICATIONS INFORMATION
a battery or some other supply is diode ORed with the
Caution should be used when synchronizing more than
50% above the initial switching frequency (as set by the
RT resistor) because at higher clock frequencies the
amplitude of the internal slope compensation used to
prevent subharmonic switching is reduced. This type of
subharmonic switching only occurs at input voltages less
than twice output voltage. Higher inductor values will tend
to reduce this problem.
LT3681’s output. If the V pin is allowed to float and the
IN
RUN/SSpinisheldhigh(eitherbyalogicsignalorbecause
it is tied to V ), then the LT3681’s internal circuitry will
IN
pull its quiescent current through its SW pin. This is fine
if your system can tolerate a few mA in this state. If you
ground the RUN/SS pin, the SW pin current will drop to
essentially zero. However, if the V pin is grounded while
IN
the output is held high, then parasitic diodes inside the
LT3681 can pull large currents from the output through
Reversed Input Protection
the SW pin and the V pin. Figure 8 shows a circuit that
will run only when the input voltage is present and that
protects against a shorted or reversed input.
In some systems, the output may be held high when the
input to the LT3681 is absent. This may occur in battery
charging applications or in battery backup systems where
IN
D4
MBRS140
V
IN
V
BD BOOST
LT3681
IN
V
RUN/SS
SW
OUT
V
C
DC
GND DA FB
BACKUP
3681 F08
Figure 8. Diode D4 Prevents a Shorted Input from Discharging a Backup Battery Tied
to the Output. It Also Protects the Circuit from a Reversed Input. The LT3681 Runs Only
When the Input is Present
3681f
16
Linear [ Linear ]
