ltm8033 Linear Technology Corporation, ltm8033 Datasheet - Page 11

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

APPLICATIONS INFORMATION
For most applications, the design process is straight for-
ward, summarized as follows:
• Look at Table 1 and find the row that has the desired
• Apply the recommended C
• Connect BIAS as indicated.
As the integrated input EMI filter may ring in response to
an application of a step input voltage, a bulk capacitance
may be applied between FIN and GND. See the Hot-Plug-
ging Safely section for details.
While these component combinations have been tested
for proper operation, it is incumbent upon the user to
verify proper operation over the intended system’s line,
load and environmental conditions. Bear in mind that the
maximum output current is limited by junction tempera-
ture, the relationship between the input and output voltage
magnitude and polarity and other factors. Please refer to
the graphs in the Typical Performance Characteristics
section for guidance.
The maximum frequency (and attendant R
which the LTM8033 should be allowed to switch is given
in Table 1 in the f
frequency (and R
given input condition is given in the f
There are additional conditions that must be satisfied if
the synchronization function is used. Please refer to the
Synchronization section for details.
Note: An input bulk capacitance is required at either V
or FIN. Refer to the Typical Performance Characteristics
section for load conditions.
input range and output voltage.
values.
T
MAX
value) for optimal efficiency over the
column, while the recommended
IN
, C
FIN
, C
OUT
OPTIMAL
, R
T
ADJ
value) at
column.
and R
IN
T
Capacitor Selection Considerations
The C
minimum recommended values for the associated oper-
ating conditions. Applying capacitor values below those
indicated in Table 1 is not recommended, and may result
in undesirable operation. Using larger values is generally
acceptable, and can yield improved dynamic response, if
it is necessary. Again, it is incumbent upon the user to
verify proper operation over the intended system’s line,
load and environmental conditions.
Ceramic capacitors are small, robust and have very low
ESR. However, not all ceramic capacitors are suitable.
X5R and X7R types are stable over temperature and ap-
plied voltage and give dependable service. Other types,
including Y5V and Z5U have very large temperature and
voltage coefficients of capacitance. In an application cir-
cuit they may have only a small fraction of their nominal
capacitance resulting in much higher output voltage ripple
than expected.
Ceramic capacitors are also piezoelectric. In Burst Mode
operation, the LTM8033’s switching frequency depends
on the load current, and can excite a ceramic capacitor
at audio frequencies, generating audible noise. Since the
LTM8033 operates at a lower current limit during Burst
Mode operation, the noise is typically very quiet to a
casual ear.
If this audible noise is unacceptable, use a high perfor-
mance electrolytic capacitor at the output. It may also be
a parallel combination of a ceramic capacitor and a low
cost electrolytic capacitor.
A final precaution regarding ceramic capacitors concerns
the maximum input voltage rating of the LTM8033. A
ceramic input capacitor combined with trace or cable
inductance forms a high Q (under damped) tank circuit.
If the LTM8033 circuit is plugged into a live supply, the
input voltage can ring to twice its nominal value, possibly
exceeding the device’s rating. This situation can be easily
avoided; see the Hot-Plugging Safely section.
IN
, C
FIN
and C
OUT
capacitor values in Table 1 are the
LTM8033
11
8033f