Datasheet

SW
LM3404
GND
CS
8V
V
TRANSIENT
~ 0.675
Module
Connector
Module
Connector
LM3404, LM3404HV
www.ti.com SNVS465F –OCTOBER 2006–REVISED MAY 2013
CS PIN PROTECTION
When hot swapping in a load (e.g. test points, load boards, LED stack), any residual charge on the load will be
immediately transferred through the output capacitor to the CS pin, which is then damaged as shown in
Figure 24 below. The EOS event due to the residual charge from the load is represented as V
TRANSIENT
.
From measurements, we know that the 8V ESD structure on the CS pin can typically withstand 25mA of direct
current (DC). Adding a 1kΩ resistor in series with the CS pin, shown in Figure 25, results in the majority of the
transient energy to pass through the discrete sense resistor rather than the device. The series resistor limits the
peak current that can flow during a transient event, thus protecting the CS pin. With the 1kΩ resistor shown, a
33V, 49A transient on the LED return connector terminal could be absorbed as calculated by:
V = 25mA * 1kΩ + 8V = 33V (15)
I = 33V / 0.67Ω = 49A (16)
This is an extremely high energy event, so the protection measures previously described should be adequate to
solve this issue.
Figure 24. CS Pin, Transient Path
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