LM3424BKBSTEVAL/NOPB National Semiconductor, LM3424BKBSTEVAL/NOPB Datasheet - Page 29
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LM3424BKBSTEVAL/NOPB
Manufacturer Part Number
LM3424BKBSTEVAL/NOPB
Description
BOARD EVAL BUCK BOOST LM3424
Manufacturer
National Semiconductor
Series
PowerWise®r
Specifications of LM3424BKBSTEVAL/NOPB
Current - Output / Channel
1A
Outputs And Type
1, Non-Isolated
Features
Dimmable
Voltage - Input
10 ~ 70 V
Utilized Ic / Part
LM3424
Core Chip
LM3424
Topology
Buck-Boost
No. Of Outputs
1
Dimming Control Type
PWM / Analog
Development Tool Type
Hardware - Eval/Demo Board
Mcu Supported Families
LM3424 Family
Lead Free Status / RoHS Status
Lead free / RoHS Compliant
Voltage - Output
-
Other names
LM3424BKBSTEVAL
15. SOFT-START
For all topologies, if soft-start is desired, find the start-up time
without C
Then, if the desired total start-up time (t
t
that a C
Then solve for C
SU
, solve for the base start-up time (t
SS
SS
greater than 40% of C
(t
SU
):
SS
:
CMP
will be used:
SU-SS-BASE
TSU
) is larger than
), assuming
29
16. 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.
The DDRV pin should be connected to the gate of the dimFET
with or without level-shifting circuitry as described in the PWM
Dimming section. The dimFET should be rated to handle the
average LED current and the nominal output voltage.
17. ANALOG DIMMING METHOD
Analog dimming can be performed several ways:
Method #1: Place a potentiometer in place of the thermistor
in the thermal foldback circuit shown in the Thermal Folback /
Analog Dimming section.
Method #2: Place a potentiometer in series with the R
resistor to dim the LED current from the nominal I
zero.
Method #3: Connect a controlled current source as detailed
in the Thermal Folback / Analog Dimming section to the CSH
pin. Increasing the current sourced into the CSH node will
decrease the LEDs from the nominal I
the same manner as the thermal foldback circuit.
DIM
. A pull down resistor may be
3
.
LED
to zero current in
3
) with the drain
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LED
to near
CSH