LM3404FSTDIMEV National Semiconductor, LM3404FSTDIMEV Datasheet - Page 12

• Manufacturer Part Number: LM3404FSTDIMEV
• Description: BOARD, EVAL, FAST DIMMING, LM3404
• Manufacturer: National Semiconductor

Specifications of LM3404FSTDIMEV

• Kit Contents: LM3404FSTDIM Assembled Evaluation Board, LM3404 Datasheet, Application Note
• Svhc: No SVHC (15-Dec-2010)
• Kit Features: Designed To Drive A Series String Of High Power, High Brightness

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V
for the output current. Output current overshoot is limited to
300 mV / R
The OVP/OCP comparator can also be used to prevent the
output voltage from rising to V
open-circuit. This is the most common failure mode for LEDs,
due to breaking of the bond wires. In a current regulator an
output open circuit causes V
maximum duty cycle.
diode, Z1, and zener limiting resistor, R
age to the reverse breakdown voltage of Z1 plus 200 mV. The
zener diode reverse breakdown voltage, V
than the maximum combined V
maximum recommended value for R
LOW POWER SHUTDOWN
The LM3404/04HV can be placed into a low power state (I
SD
MOSFET as shown in
2N7000, 2N3904, or equivalent are recommended devices
for putting the LM3404/04HV into low power shutdown. Logic
gates can also be used to shut down the LM3404/04HV as
SNS
= 90 µA) by grounding the RON pin with a signal-level
exceeds 300 mV. This threshold provides a hard limit
SNS
by this comparator during transients.
Figure 2
Figure
3. Low power MOSFETs like the
SNS
O(MAX)
shows a method using a zener
F
of all LEDs in the array. The
to fall to zero, commanding
in the event of an output
Z
is 1 kΩ.
Z
, to limit output volt-
FIGURE 2. Output Open Circuit Protection
Z
, must be greater
FIGURE 3. Low Power Shutdown
IN-
12
As discussed in the Maximum Output Voltage section, there
is a limit to how high V
that is always less than V
output stage of the LM3404/04HV is capable of withstanding
V
the inductor will oscillate and can go above V
A small (typically 10 nF) capacitor across the LED array
dampens this oscillation. For circuits that use an output ca-
pacitor, the system can still withstand V
long as C
blocked in output open-circuit and the risk of thermal stress is
minimal, hence the user may opt to allow the output voltage
to rise in the case of an open-circuit LED failure.
long as the logic low voltage is below the over temperature
minimum threshold of 0.3V. Noise filter circuitry on the RON
pin can cause a few pulses with longer on-times than normal
after RON is grounded or released. In these cases the OVP/
OCP comparator will ensure that the peak inductor or LED
current does not exceed 300 mV / R
O(MAX)
indefinitely, however the voltage at the output end of
O
is rated to handle V
O
can rise during an output open-circuit
IN
. If no output capacitor is used, the
20205412
IN
. The high current paths are
20205413
SNS
.
O(MAX)
IN
indefinitely as
or below 0V.