Datasheet
LTM8033
15
8033fa
For more information www.linear.com/LTM8033
Synchronization
The internal oscillator of the LTM8033 can be synchro-
nized by applying an external 250kHz to 2MHz clock to
the SYNC pin. Do not leave this pin floating. Ground the
SYNC pin if the synchronization function is not used.
When synchronizing the L
TM8033, select an R
T
resistor
value that corresponds to an operating frequency 20%
lower than the intended synchronization frequency (see
the Frequency Selection section).
In addition to synchronization, the SYNC pin controls Burst
Mode behavior. If the SYNC pin is driven by an external
clock, or pulled up above 0.7V, the LTM8033 will not en
-
ter Burst Mode operation, but will instead skip pulses to
maintain regulation instead.
APPLICATIONS INFORMATION
Figure 3. The Input Diode Prevents a Shorted Input from Discharging
a Backup Battery Tied to the Output. It Also Protects the Circuit from a
Reversed Input. The LTM8033 Runs Only When the Input is Present
8033 F03
V
IN
RUN/SS
SHARE
V
IN
V
OUT
V
OUT
AUX
BIAS
ADJ
RT
LTM8033
SYNC GND
Shorted Input Protection
Care needs to be taken in systems where the output will be
held high when the input to the LTM8033 is absent. This
may occur in battery charging applications or in battery
backup systems where a battery or some other supply is
diode OR-ed with the LTM8033’s output. If the V
IN
pin is
allowed to float and the RUN/SS pin is held high (either
by a logic signal or because it is tied to V
IN
), then the
LTM8033’s internal circuitry will pull its quiescent current
through its internal power switch. This is fine if your system
can tolerate a few milliamps in this state. If you ground the
RUN/SS pin, the SW pin current will drop to essentially
zero. However, if the V
IN
pin is grounded while the output
is held high, then parasitic diodes inside the LTM8033 can
pull large currents from the output through the V
IN
pin.
Figure 3 shows a circuit that will run only when the input
voltage is present and that protects against a shorted or
reversed input.