LM3429BKBSTEVAL National Semiconductor, LM3429BKBSTEVAL Datasheet - Page 19

• Manufacturer Part Number: LM3429BKBSTEVAL
• Description: BOARD, EVALUATION, FOR LM3429
• Manufacturer: National Semiconductor

Specifications of LM3429BKBSTEVAL

• Kit Contents: LM3429 Assembled Evaluation Board, Application Note, LM3429 Datasheet
• Svhc: No SVHC (15-Dec-2010)
• Kit Features: Drives 4 To 8 LED At Max Average LED Current 1A, Overvoltage Protection,

5. 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
The minimum allowable RMS output capacitor current rating
(I
Buck
Boost and Buck-boost
6. PEAK CURRENT LIMIT
Set the peak current limit (I
path sense resistor (R
7. 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
CO-RMS
) can be approximated:
O
.
LIM
):
O
):
LIM
) by solving for the transistor
U
LED-PP
) of the regulator can
), by solving for
MAX
when
19
Where the pole (ω
Buck
Boost
Buck-boost
And the RHP zero (ω
Boost
Buck-boost
And the uncompensated DC loop gain (T
Buck
Boost
Buck-boost
For all topologies, the primary method of compensation is to
place a low frequency dominant pole (ω
that there is ample phase margin at the crossover frequency.
This is accomplished by placing a capacitor (C
COMP pin to GND, which is calculated according to the lower
value of the pole and the RHP zero of the system (shown as
a minimizing function):
If analog dimming is used, C
larger to maintain stability as the LEDs are dimmed to zero.
P1
) is approximated:
Z1
) is approximated:
CMP
should be approximately 4x
P2
U0
) which will ensure
) is approximated:
CMP
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) from the