ltm8033 Linear Technology Corporation, ltm8033 Datasheet - Page 15

• Manufacturer Part Number: ltm8033
• Description: Ultralow Noise Emc 36vin, 3a Dc/dc
• Manufacturer: Linear Technology Corporation

APPLICATIONS INFORMATION
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 LTM8033, select an R
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.
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
V
IN
T
resistor
V
RUN/SS
SHARE
RT
IN
SYNC GND
LTM8033
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
allowed to float and the RUN/SS pin is held high (either
by a logic signal or because it is tied to V
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
is held high, then parasitic diodes inside the LTM8033 can
pull large currents from the output through the V
Figure 3 shows a circuit that will run only when the input
voltage is present and that protects against a shorted or
reversed input.
V
BIAS
AUX
ADJ
OUT
8033 F03
V
OUT
IN
pin is grounded while the output
LTM8033
IN
), then the
IN
15
IN
pin is
pin.
8033f