LM3429MHX National Semiconductor, LM3429MHX Datasheet - Page 20

• Manufacturer Part Number: LM3429MHX
• Description: LM3429 N-Channel Controller for Constant Current LED Drivers; Package: TSSOP EXP PAD; No of Pins: 14; Qty per Container: 2500/Reel
• Manufacturer: National Semiconductor

www.national.com
A high frequency compensation pole (ω
attenuate switching noise and provide better gain margin. As-
suming R
value of the pole and the RHP zero of the system (shown as
a maximizing function):
The total system loop gain (T) can then be written as:
Buck
Boost and Buck-boost
8. INPUT CAPACITANCE
Set the nominal input voltage ripple (Δv
the required capacitance (C
Buck
Boost
Buck-boost
Use D
solving for C
solving for C
The minimum allowable RMS input current rating (I
can be approximated:
Buck
Boost
MAX
FS
to set the worst case input voltage ripple, when
= 10Ω, C
IN
IN
in a buck-boost regulator and D
in a buck regulator.
FS
is calculated according to the higher
IN
):
IN-PP
P3
) can be used to
) by solving for
MID
= 0.5 when
CIN-RMS
)
20
Buck-boost
9. NFET
The NFET voltage rating should be at least 15% higher than
the maximum NFET drain-to-source voltage (V
Buck
Boost
Buck-boost
The current rating should be at least 10% higher than the
maximum average NFET current (I
Buck
Boost and Buck-boost
Approximate the nominal RMS transistor current (I
Buck
Boost and Buck-boost
Given an NFET with on-resistance (R
nominal power dissipation (P
10. DIODE
The Schottky diode voltage rating should be at least 15%
higher than the maximum blocking voltage (V
Buck
Boost
Buck-boost
T
):
T-MAX
DS-ON
):
), solve for the
RD-MAX
T-MAX
T-RMS
):
):
) :