LM3404EVAL National Semiconductor, LM3404EVAL Datasheet - Page 18

• Manufacturer Part Number: LM3404EVAL
• Description: BOARD, EVALUATION, FOR LM3404
• Manufacturer: National Semiconductor

Specifications of LM3404EVAL

• Kit Contents: Board, Datasheet
• Svhc: No SVHC (15-Dec-2010)
• Features: Thermal Shutdown Protection, Separate PWM Dimming And Low Power Shutdown
• Kit Features: Cycle-by-Cycle Current Limit, Separate PWM

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VIN PIN PROTECTION
The VIN pin also has an ESD structure from the pin to GND
with a breakdown voltage of approximately 80V. Any transient
that exceeds this voltage may damage the device. Although
transient absorption is usually present at the front end of a
switching converter circuit, damage to the VIN pin can still
occur.
When V
charge C
circuit board trace inductance as shown in
cited trace inductance then resonates with the input capaci-
tance (similar to an under-damped LC tank circuit) and
causes voltages at the VIN pin to rise well in excess of both
V
IN
and the voltage at the module input connector as clamped
IN
IN
is hot swapped in, the current that rushes in to
up to the V
IN
value also charges (energizes) the
FIGURE 10. VIN Pin with Typical Input Protection
Figure
10. The ex-
18
by the input TVS. If the resonating voltage at the VIN pin ex-
ceeds the 80V breakdown voltage of the ESD structure, the
ESD structure will activate and then “snap-back” to a lower
voltage due to its inherent design. If this lower snap-back
voltage is less than the applied nominal V
nificant current will flow through the ESD structure resulting
in the IC being damaged.
An additional TVS or small zener diode should be placed as
close as possible to the VIN pins of each IC on the board, in
parallel with the input capacitor as shown in
nor amount of series resistance in the input line would also
help, but would lower overall conversion efficiency. For this
reason, NTC resistors are often used as inrush limiters in-
stead.
20205461
IN
voltage, then sig-
Figure
11. A mi-