LM3429BKBSTEVAL National Semiconductor, LM3429BKBSTEVAL Datasheet - Page 21
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LM3429BKBSTEVAL
Manufacturer Part Number
LM3429BKBSTEVAL
Description
BOARD, EVALUATION, FOR LM3429
Manufacturer
National Semiconductor
Datasheet
1.LM3429MHNOPB.pdf
(34 pages)
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,
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
11. 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.
FD
), solve for the nominal power dissipation (P
TURN-OFF
MAX
with D in the I
, solve for R
D
). Given a diode with forward voltage
HYSO
OVP
OV1
= 47 pF) should be added from
D-MAX
). To set V
:
D-MAX
equation to solve for the
):
HYSO
, solve for R
TURN-OFF
D
):
) and
OV2
:
21
12. 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
13. PWM DIMMING METHOD
PWM dimming can be performed several ways:
Method #1: Connect the dimming MosFET (Q
to the nDIM pin and the source to GND. Apply an external
PWM signal to the gate of Q
necessary to properly turn off Q
Method #2: Connect the anode of a Schottky diode to the
nDIM pin. Apply an external inverted PWM signal to the cath-
ode of the same diode.
14. ANALOG DIMMING METHOD
Analog dimming can be performed several ways:
Method #1: Place a potentiometer in series with the R
resistor to dim the LED current from the nominal I
zero.
Method #2: Connect a controlled current source as detailed
in the Analog Dimming section to the CSH pin. Increasing the
current sourced into the CSH node will decrease the LEDs
from the nominal I
UVH
HYS
:
).
TURN-ON
UV1
, solve for R
LED
as in Method #1. To set V
to zero current.
TURN-ON
UV1
DIM
TURN-ON
HYS
:
. A pull down resistor may be
) and the desired hysteresis
3
.
, solve for R
, assume R
3
UV2
) with the drain
HYS
UV2
www.national.com
:
LED
, solve for
= 10 kΩ
to near
CSH