LM3424MH/NOPB National Semiconductor, LM3424MH/NOPB Datasheet - Page 28

• 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

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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
12. DIODE
The Schottky diode voltage rating should be at least 15%
higher than the maximum blocking voltage (V
Buck
Boost
Buck-boost
The current rating should be at least 10% higher than the
maximum average diode current (I
Buck
Boost and Buck-boost
Replace D
average diode current (I
(V
FD
), solve for the nominal power dissipation (P
MAX
with D in the I
D
). Given a diode with forward voltage
T
D-MAX
):
D-MAX
T-MAX
equation to solve for the
DS-ON
):
):
), solve for the
RD-MAX
D
):
T-RMS
):
) :
28
13. OUTPUT OVLO
For boost and buck-boost regulators, output OVLO is pro-
grammed with the turn-off threshold voltage (V
the desired hysteresis (V
To set V
Boost
Buck-boost
A small filter capacitor (C
the OVP pin to ground to reduce coupled switching noise.
14. INPUT UVLO
For all topologies, input UVLO is programmed with the turn-
on threshold voltage (V
(V
Method #1: If no PWM dimming is required, a two resistor
network can be used. To set V
To set V
Method #2: If PWM dimming is required, a three resistor net-
work is suggested. To set V
and solve for R
R
UVH
HYS
:
).
TURN-OFF
TURN-ON
UV1
, solve for R
, solve for R
as in Method #1. To set V
TURN-ON
HYSO
OVP
UV1
OV1
TURN-ON
= 47 pF) should be added from
). To set V
HYS
:
) and the desired hysteresis
:
, solve for R
, assume R
HYSO
, solve for R
UV2
TURN-OFF
HYS
UV2
:
, solve for
= 10 kΩ
) and
OV2
: