LM3409HVEVAL National Semiconductor, LM3409HVEVAL Datasheet - Page 5

• Manufacturer Part Number: LM3409HVEVAL
• Description: BOARD EVALUATION FOR LM3409HV
• Manufacturer: National Semiconductor
• Series: PowerWise®r

Specifications of LM3409HVEVAL

• Current - Output / Channel: 1.5A
• Outputs And Type: 1, Non-Isolated
• Voltage - Output: 42V
• Features: Dimmable
• Voltage - Input: 6 ~ 75 V
• Utilized Ic / Part: LM3409HV
• Kit Contents: Board, Datasheet
• Svhc: No SVHC (15-Dec-2010)
• Kit Features: Drives 12 LEDs At Maximum Average LED Current 1.5A From DC Input Voltage 48V
• Mcu Supported Families: LM3409HV
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

6. P-CHANNEL MOSFET
Determine minimum Q1 voltage rating and current rating:
A 100V 3.8A PFET is chosen with R
20nC. Determine I
The chosen component from step 6 is:
7. RE-CIRCULATING DIODE
Determine minimum D1 voltage rating and current rating:
A 100V 3A diode is chosen with V
The chosen component from step 7 is:
8. INPUT UNDER-VOLTAGE LOCKOUT (UVLO)
Solve for R8:
The closest 1% tolerance resistor is 49.9 kΩ so V
T-RMS
and P
T
:
D
= 750mV. Determine P
DS-ON
= 190mΩ and Q
HYS
is:
g
D
=
:
5
Solve for R7:
The closest 1% tolerance resistor is 6.98 kΩ so V
The chosen components from step 8 are:
9. IADJ CONNECTION METHOD
The IADJ pin controls the high-side current sense threshold
in three ways outlined in the datasheet. The LM3409HV eval-
uation board allows for all three methods to be evaluated
using C6, R10, and the VADJ terminal.
Method #1: If the VADJ terminal is not connected to the pow-
er supply, then the internal Zener diode biases the pin to
1.24V and the current sense threshold is nominally 248mV.
Method #2: Applying an external voltage to the VADJ termi-
nal between 0 and 1.24V linearly scales the current sense
threshold between 0 and 248mV nominally. It can be neces-
sary to have an RC filter when using an external power supply
in order to remove any high frequency noise or oscillations
created by the power supply and the connecting cables. The
filter is chosen by assuming a standard value of C6 = 0.1µF
and solving for a cut-off frequency f
Since an exact f
used. The Typical Waveforms section shows a typical LED
current waveform when analog dimming using an external
voltage source.
Method #3: (This method requires modification of the re-
ceived evaluation board). The internal 5µA current source can
be used to bias the voltage across an external resistor to
ground (R
is sized knowing the desired average LED current I
be < 1.5A which is default using method #1):
The chosen components from step 9 are:
EXT
) across C6 on the evaluation board. The resistor
C
is not critical, a standard value of 1kΩ is
C
< 2kHz:
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TURN-ON
LED
(must
is: