LTC3215 Linear Technology, LTC3215 Datasheet - Page 9

• Manufacturer Part Number: LTC3215
• Description: 700mA Low Noise High Current LED Charge Pump
• Manufacturer: Linear Technology

APPLICATIO S I FOR ATIO
compare the amount of achievable capacitance for a given
case size rather than comparing the specified capacitance
value. For example, over rated voltage and temperature
conditions, a 1µF, 10V, Y5V ceramic capacitor in a 0603 case
may not provide any more capacitance than a 0.22µF, 10V,
X7R available in the same case. The capacitor
manufacturer’s data sheet should be consulted to determine
what value of capacitor is needed to ensure minimum
capacitances at all temperatures and voltages.
Table 2 shows a list of ceramic capacitor manufacturers
and how to contact them.
Table 2. Recommended Capacitor Vendors
AVX
Kemet
Murata
Taiyo Yuden
Vishay
TDK
Layout Considerations and Noise
Due to its high switching frequency and the transient
currents produced by the LTC3215, careful board layout is
necessary. A true ground plane and short connections to
all capacitors will improve performance and ensure proper
regulation under all conditions.
The flying capacitor pins C1
very high edge rate waveforms. The large dv/dt on these
U
www.avxcorp.com
www.kemet.com
www.murata.com
www.t-yuden.com
www.vishay.com
www.tdk.com
U
+
, C2
+
, C1
C
W
CPO
–
and C2
Figure 4. Example Board Layout
U
–
PIN 1
will have
C1
pins can couple energy capacitively to adjacent PCB runs.
Magnetic fields can also be generated if the flying capaci-
tors are not close to the LTC3215 (i.e., the loop area is
large). To decouple capacitive energy transfer, a Faraday
shield may be used. This is a grounded PCB trace between
the sensitive node and the LTC3215 pins. For a high quality
AC ground, it should be returned to a solid ground plane
that extends all the way to the LTC3215.
The following guidelines should be followed when design-
ing a PCB layout for the LTC3215.
• The Exposed Pad should be soldered to a large copper
• Input and output capacitors (C
• The flying capacitors must also be placed as close to the
• V
• LED pads must be large and should be connected to as
plane that is connected to a solid, low impedance
ground plane using plated, through-hole vias for proper
heat sinking and noise protection.
be placed as close to the part as possible.
part as possible. The traces running from the pins to the
capacitor pads should be as wide as possible.
possible. This is necessary to minimize inductance,
as well as provide sufficient area for high current
applications.
much solid metal as possible to ensure proper heat
sinking.
IN
, CPO and I
C2
LED
C
IN
3215 F04
traces must be made as wide as
IN
and C
LTC3215
CPO
) must also
9
3215f