LTC3521 Datasheet, PDF (16/20 Pages) Linear Technology – Wide VIN, 1A Buck-Boost DC/DC and Dual 600mA Buck DC/DC Converters

LTC3521
applications information
Capacitor Vendor Information
Both the input and output capacitors used with the LTC3521
must be low ESR and designed to handle the large AC cur-
rents generated by switching converters. The vendors in
Table 5 provide capacitors that are well suited to LTC3521
application circuits.
Table 5. Capacitor Vendor Information
MANUFACTURER WEB SITE
REPRESENTATIVE PART
NUMBERS
Taiyo Yuden
www.t-yuden.com JMK212BJ106K 10μF, 6.3V
JMK212BJ226K 22μF, 6.3V
TDK
www.component. C2012X5R0J106K 10μF, 6.3V
tdk.com
Murata
www.murata.com GRM21BR60J106K 10μF, 6.3V
GRM32ER61C226K 22μF, 16V
AVX
www.avxcorp.com SM055C106KHN480 10μF
Minimizing solution size is usually a priority. Please be
aware that ceramic capacitors can exhibit a significant
reduction in effective capacitance when a bias is applied.
The capacitors exhibiting the highest reduction are those
packaged in the smallest case size.
PCB Layout Considerations
The LTC3521 switches large currents at high frequencies.
Special care should be given to the PCB layout to ensure
stable, noise-free operation. Figure 5 depicts the recom-
mended PCB layout to be utilized for the LTC3521. A few
key guidelines follow:
1. All circulating high current paths should be kept as short
as possible. This can be accomplished by keeping the
routes to all bold components in Figure 5 as short and
as wide as possible. Capacitor ground connections
should via down to the ground plane in the shortest
route possible. The bypass capacitors on PV_IN1 and
PV_IN2 should be placed as close to the IC as possible and
should have the shortest possible paths to ground.
2. The small-signal ground pad (GND) should have a single
point connection to the power ground. A convenient
way to achieve this is to short the pin directly to the
Exposed Pad as shown in Figure 5.
3. The components shown in bold, and their connections,
should all be placed over a complete ground plane.
4. To prevent large circulating currents from disrupting
the output voltage sensing, the ground for each resistor
divider should be returned directly to the small signal
ground pin (GND).
5. Use of vias in the die attach pad will enhance the ther-
mal environment of the converter, especially if the vias
extend to a ground plane region on the exposed bottom
surface of the PCB.
3521f
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