ltm8033 Linear Technology Corporation, ltm8033 Datasheet - Page 17

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

APPLICATIONS INFORMATION
Hot-Plugging Safely
The small size, robustness and low impedance of ceramic
capacitors make them an attractive option for the input
bypass capacitor of LTM8033. However, these capacitors
can cause problems if the LTM8033 is plugged into a live
supply (see Application Note 88 for a complete discus-
sion). The low loss ceramic capacitor combined with
stray inductance in series with the power source forms an
underdamped tank circuit, and the voltage at the V
of the LTM8033 can ring to more than twice the nominal
input voltage, possibly exceeding the LTM8033’s rating and
damaging the part. A similar phenomenon can occur inside
the LTM8032 module, at the output of the integrated EMI
filter (FIN), with the same potential of damaging the part.
If the input supply is poorly controlled or the user will be
plugging the LTM8033 into an energized supply, the input
network should be designed to prevent this overshoot.
This can be accomplished by installing a small resistor
in series to V
ling input voltage overshoot is adding an electrolytic bulk
capacitor to the V
high equivalent series resistance damps the circuit and
eliminates the voltage overshoot. The extra capacitor
improves low frequency ripple filtering and can slightly
improve the efficiency of the circuit, though it can be a
large component in the circuit.
Electromagnetic Compliance
The LTM8033 was evaluated by an independent nation-
ally recognized test lab and found to be compliant with
EN 55022 class B: 2006 by a wide margin. Sample graphs
of the LTM8033’s radiated EMC performance are given in the
Typical Performance Characteristics section, while further
data, operating conditions and test set-up are detailed in
the electromagnetic compatibility test report, available
on the Linear Technology website. Conducted emissions
requirements may be met by adding an appropriate input
power line filter. The proper implementation of this filter
depends upon the system operating and performance
IN
, but the most popular method of control-
IN
or FIN net. This capacitor’s relatively
IN
pin
conditions as a whole, of which the LTM8033 is typically
only a component, so conducted emissions are not ad-
dressed at this level.
Thermal Considerations
The LTM8033 output current may need to be derated if it
is required to operate in a high ambient temperature or
deliver a large amount of continuous power. The amount
of current derating is dependent upon the input voltage,
output power and ambient temperature. The temperature
rise curves given in the Typical Performance Charac-
teristics section can be used as a guide. These curves
were generated by an LTM8033 mounted to a 40cm
4-layer FR4 printed circuit board. Boards of other sizes
and layer count can exhibit different thermal behavior, so
it is incumbent upon the user to verify proper operation
over the intended system’s line, load and environmental
operating conditions.
The thermal resistance numbers listed in the Pin Con-
figuration are based on modeling the μModule package
mounted on a test board specified per JESD51-9 “Test
Boards for Area Array Surface Mount Package Thermal
Measurements.” The thermal coefficients provided in this
page are based on JESD 51-12 “Guidelines for Reporting
and Using Electronic Package Thermal Information.”
For increased accuracy and fidelity to the actual application,
many designers use FEA to predict thermal performance.
To that end, the Pin Configuration typically gives four
thermal coefficients:
• θ
• θ
• θ
• θ
bottom of the product case.
the product case.
circuit board.
JA
JCBOTTOM
JCTOP
JB
– Thermal resistance from junction to ambient.
– Thermal resistance from junction to the printed
– Thermal resistance from junction to top of
– Thermal resistance from junction to the
LTM8033
17
8033f
2