LM3501TL-16 National Semiconductor Corporation, LM3501TL-16 Datasheet - Page 12

• Manufacturer Part Number: LM3501TL-16
• Description: Synchronous Step-up DC/DC Converter For White Led Applications
• Manufacturer: National Semiconductor Corporation

www.national.com
Application Information
CAPACITOR SELECTION
Choose low ESR ceramic capacitors for the output to mini-
mize output voltage ripple. Multilayer X7R or X5R type ce-
ramic capacitors are the best choice. For most applications,
a 1µF ceramic output capacitor is sufficient.
Local bypassing for the input is needed on the LM3501.
Multilayer X7R or X5R ceramic capacitors with low ESR are
a good choice for this as well. A 1µF ceramic capacitor is
sufficient for most applications. However, for some applica-
tions at least a 4.7µF ceramic capacitor may be required for
proper startup of the LM3501. Using capacitors with low
ESR decreases input voltage ripple. For additional bypass-
ing, a 100nF ceramic capacitor can be used to shunt high
frequency ripple on the input. Some recommended capaci-
tors include but are not limited to:
TDK C2012X7R1C105K
Taiyo-Yuden EMK212BJ105 G
Vishay Vitramon VJ1206S105KXJ
LAYOUT CONSIDERATIONS
The input bypass capacitor C
be placed close to the device and connect between the V
and GND pins. This will reduce copper trace resistance
IN
, as shown in Figure 2, must
FIGURE 3. Evaluation Board Layout (2X Magnification)
(Continued)
IN
Top Layer
12
which effects the input voltage ripple of the IC. For additional
input voltage filtering, a 100nF bypass capacitor can be
placed in parallel with C
to ground. The output capacitor, C
close to the LM3501 and connected directly between the
V
C
directly effects output voltage ripple and efficiency. The cur-
rent setting resistor, R
to minimize copper trace connections that can inject noise
into the system. The ground connection for the current set-
ting resistor should connect directly to the GND pin. The
AGND pin should connect directly to the GND pin. Not
connecting the AGND pin directly, as close to the chip as
possible, may affect the performance of the LM3501 and
limit its current driving capability. Trace connections made to
the inductor should be minimized to reduce power dissipa-
tion, EMI radiation and increase overall efficiency. It is good
practice to keep the V
such as the FB pin. Failure to do so may inject noise into the
FB pin and affect the regulation of the device. See Figure 3
and Figure 4 for an example of a good layout as used for the
LM3501 evaluation board.
OUT
OUT
and GND pins. Any copper trace connections for the
capacitor can increase the series resistance, which
LED
20065384
SW
IN
, should be kept close to the FB pin
to shunt any high frequency noise
routing away from sensitive pins
OUT
, should also be placed