LM3409MYX National Semiconductor Corporation, LM3409MYX Datasheet - Page 17
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LM3409MYX
Manufacturer Part Number
LM3409MYX
Description
Pfet Buck Controller For High Power Led Drives
Manufacturer
National Semiconductor Corporation
Datasheet
1.LM3409MYX.pdf
(30 pages)
Available stocks
Company
Part Number
Manufacturer
Quantity
Price
Part Number:
LM3409MYX
Manufacturer:
NS/国半
Quantity:
20 000
4. OUTPUT CAPACITANCE
A minimum output capacitance (C
reduce Δi
the known dynamic resistance (r
the required impedance (Z
Solve for C
5. INPUT CAPACITANCE
Set the input voltage ripple (Δv
quired minimum capacitance (C
The necessary RMS input current rating (I
6. PFET
The PFET voltage rating should be at least 15% higher than
the maximum input voltage (V
be at least 10% higher than the average PFET current (I
Given a PFET with on-resistance (R
transistor current (I
7. DIODE
The Schottky diode needs a voltage rating similar to the
PFET. Higher current diodes with a lower forward voltage are
suggested. Given a diode with forward voltage (V
the average diode current (I
LED-PP
O-MIN
:
below Δi
T-RMS
) and power dissipation (P
L-PP
C
) for C
D
. With the specified Δi
) and power dissipation (P
IN-MAX
IN-MIN
D
IN-PP
) of the LED string, solve for
O-MIN
O-MIN
) and current rating should
DS-ON
) by solving for the re-
):
) may be necessary to
:
), solve for the RMS
IN-RMS
) is:
D
), solve for
LED-PP
T
):
D
T
):
and
):
17
8. INPUT UVLO
Input UVLO is set with the turn-on threshold voltage (V
ON
R
To set V
9. IADJ CONNECTION METHOD
The IADJ pin controls the high-side current sense threshold
in three ways outlined in the Theory of Operation section.
Method #1: Leave IADJ pin open and I
the Average LED Current section of the Design Guide.
Method #2: Apply an external voltage (V
between 0 and 1.24V to analog dim or to reduce I
lows:
Keep in mind that analog dimming will eventually push the
converter in to DCM and the inductor current ripple will no
longer be constant causing a divergence from linear dimming
at low levels.
A 0.1µF capacitor connected from the IADJ pin to GND is
recommended when using this method. It may also be nec-
essary to have a 1kΩ series resistor with the capacitor to
create an RC filter. The filter will help remove high frequency
noise created by other connected circuitry.
Method #3: Connect an external resistor or potentiometer to
GND (R
voltage. Again, a 0.1µF capacitor connected from the IADJ
pin to GND is recommended. To set I
10. PWM DIMMING METHOD
There are two methods to PWM dim using the LM3409/09HV:
Method #1: Apply an external PWM signal to the EN terminal.
Method #2: Perform external parallel FET shunt dimming as
detailed in the External Parallel FET PWM Dimming section.
UV2
) and the desired hysteresis (V
:
EXT
TURN-ON
) and the internal 5µA current source will set the
, solve for R
UV1
:
HYS
). To set V
LED
LED
, solve for R
ADJ
is calculated as in
) to the IADJ pin
HYS
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LED
, solve for
EXT
as fol-
TURN-
: