LM3424MH/NOPB National Semiconductor, LM3424MH/NOPB Datasheet - Page 27

• Manufacturer Part Number: LM3424MH/NOPB
• Description: IC LED DVR BUCK/BOOST 20-TSSOP
• Manufacturer: National Semiconductor
• Series: PowerWise®r
• Type: High Power, Constant Currentr

Specifications of LM3424MH/NOPB

• Constant Current: Yes
• Topology: Flyback, PWM, SEPIC, Step-Down (Buck), Step-Up (Boost)
• Number Of Outputs: 1
• Internal Driver: No
• Type - Primary: Automotive
• Type - Secondary: High Brightness LED (HBLED)
• Frequency: 2MHz
• Voltage - Supply: 4.5 V ~ 75 V
• Mounting Type: Surface Mount
• Package / Case: 20-TSSOP Exposed Pad, 20-eTSSOP, 20-HTSSOP
• Operating Temperature: -40°C ~ 125°C
• Current - Output / Channel: 1A
• Internal Switch(s): Yes
• Efficiency: 96%
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Voltage - Output: -
• Other names: LM3424MH

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.
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
FS
= 10Ω, C
FS
is calculated according to the higher
CMP
should be approximately 4x
P2
U0
P3
) which will ensure
) is approximated:
) can be used to
CMP
) from the
27
10. 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
Buck-boost
11. NFET
The NFET voltage rating should be at least 15% higher than
the maximum NFET drain-to-source voltage (V
Buck
Boost
Buck-boost
MAX
to set the worst case input voltage ripple, when
IN
IN
in a buck-boost regulator and D
in a buck regulator.
IN
):
IN-PP
) by solving for
MID
T-MAX
www.national.com
= 0.5 when
):
CIN-RMS
)