LM3424MH/NOPB National Semiconductor, LM3424MH/NOPB Datasheet - Page 29

• 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

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
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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