LM3424BSTEVAL National Semiconductor, LM3424BSTEVAL Datasheet - Page 26

• Manufacturer Part Number: LM3424BSTEVAL
• Description: LM3424 Constant Current N-Channel Controller with Thermal Foldback for Driving LEDs; Qty per Container: 1/
• Manufacturer: National Semiconductor

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The minimum allowable inductor RMS current rating (I
can be calculated as:
Buck
Boost and Buck-boost
6. LED RIPPLE CURRENT
Set the nominal LED ripple current (Δi
the output capacitance (C
Buck
Boost and Buck-boost
To set the worst case LED ripple current, use D
solving for C
mended to use a minimum of 40 µF of output capacitance to
improve performance.
The minimum allowable RMS output capacitor current rating
(I
Buck
Boost and Buck-boost
7. PEAK CURRENT LIMIT
Set the peak current limit (I
path sense resistor (R
CO-RMS
) can be approximated:
O
. Remember, when PWM dimming it is recom-
LIM
):
O
):
LIM
) by solving for the transistor
LED-PP
), by solving for
MAX
L-RMS
when
)
26
8. SLOPE COMPENSATION
For all topologies, the preferred method to set slope compen-
sation is to ensure any duty cycle is attainable for the nominal
V
9. LOOP COMPENSATION
Using a simple first order peak current mode control model,
neglecting any output capacitor ESR dynamics, the neces-
sary loop compensation can be determined.
First, the uncompensated loop gain (T
be approximated:
Buck
Boost and Buck-boost
Where the pole (ω
Buck
Boost
Buck-boost
And the RHP zero (ω
Boost
Buck-boost
O
and chosen L by solving for R
P1
) is approximated:
Z1
) is approximated:
SLP
:
U
) of the regulator can