LM3401-MR16DEMO/NOPB National Semiconductor, LM3401-MR16DEMO/NOPB Datasheet - Page 2

• Manufacturer Part Number: LM3401-MR16DEMO/NOPB
• Description: BOARD DEMO LM3401
• Manufacturer: National Semiconductor
• Series: PowerWise®r

Specifications of LM3401-MR16DEMO/NOPB

• Current - Output / Channel: 1.5A
• Outputs And Type: 1, Non-Isolated
• Voltage - Output: -
• Features: -
• Voltage - Input: 4.5 ~ 35 V
• Utilized Ic / Part: LM3401
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

www.national.com
Connecting the LED Array
The LM3401 demo board includes a female 6-pin SIP con-
nector as well as two turret posts for the cathode and anode
connections of the LED array. These are labeled “LED+” and
“LED-“. Either connection can be used. Figure 2 shows the
pinout of the SIP connector.
Ripple Reduction Capacitor C3
The component C3 is optional and not installed on the stan-
dard demo board. This capacitor is used to reduce LED ripple
current without changing average LED current or inductor
current. Without C3, the LED ripple current is equal to the
inductor ripple current. The peak-to-peak ripple current val-
ues shown in Table 3 are without C3 installed. A typical C3
value of 1 µF is recommended for most applications. Any type
of low ESR capacitor can be used. However, the working
Ref. #
C3*
IC1
Q1
D1
C1
C2
R1
R2
R3
L1
FIGURE 2. LED Connection
40V, 1.8A, 100 mΩ, PFET
50V, 33 µF, electrolytic
68 uH, 1.7A, Inductor
50V, 2.2 µF, ceramic
40V, 2A, Schottky
0.59Ω, 1%, 1/4W
LED Controller
Description
Not installed
5.76 kΩ, 1%
24.9 kΩ1%
30025402
TABLE 2. Bill of Materials
SR732BLTER590F
MSS1260T-683ML
C3225X5R1H225K
CRCW08055761F
CRCW08052492F
EEEHA1H330XP
Part Number
Si2319DS
LM3401
SSA24
2
-
voltage must be rated higher than the maximum input voltage.
C3 can also be used to reduce switching noise which could
affect the SNS and DIM pins, especially at higher LED current.
For noise reduction purposes, a C3 value of 220 pF is rec-
ommended.
PWM Dimming
The DIM terminal on the PCB provides an input for a pulse
width modulated (PWM) signal to control dimming of the LED
string. The PWM signal should have a minimum logic high
level of 2.25V, and minimum low and high periods of 100 ns.
For the default demo board circuit, a dimming frequency less
than 1kHz is recommended to maintain an adequate contrast
ratio. The maximum contrast ratio is shown in Figure 10, and
assumes a minimum of 2 switching cycles. The maximum
contrast ratio depends largely on the rise time of the inductor
current, and therefore is dependant on input voltage, inductor
size, and LED string forward voltage. Additionally, if C3 is in-
stalled, the maximum contrast ratio or DIM frequency will be
further reduced.
Open Circuit/Short Circuit
If the LED array is disconnected or fails open, the LM3401 will
operate at 100% duty cycle. The output voltage (at LED+) and
CS node will rise to equal the input voltage; the circuit is rated
to 40V and will not suffer damage. However, care should be
taken not to connect an LED string when the demo board is
powered up and the output is high as excessive surge current
may damage the LEDs.
The default current limit threshold is typically 1.5A, set by R3.
The current limit will protect the circuit from a short at the LED
anode or cathode. Current limit is sensed across the R
the PFET and will therefore vary with temperature. R3 can be
adjusted if a different current limit threshold is required. Refer
to the LM3401 datasheet for current limit details.
MSOP-8
6.6 x 6.6
SOT-23
12x12
SMA
1210
1206
1206
0805
0805
Size
Panasonic
Coilcraft
Vendor
Vishay
Vishay
Vishay
Vishay
NSC
KOA
TDK
-
DSon
of