LTC3522_15 Datasheet, PDF (16/20 Pages) Linear Technology – Synchronous 400mA Buck-Boost and 200mA Buck Converters

LTC3522
APPLICATIONS INFORMATION
of inductors that are well suited to many LTC3522 buck
converter applications.
Table 4. Representative Surface Mount Inductors
MAX
MANUFACTURER PART NUMBER VALUE CURRENT DCR HEIGHT
Taiyo Yuden
NP035B-4R7M 4.7μH 1.2A 0.047Ω 1.8mm
NP035B-6R8M 6.8μH 1.0A 0.084Ω 1.8mm
Coilcraft
MSS6132-472ML 4.7μH 1.8A 0.056Ω 3.2mm
MSS6132-822ML 8.2μH 1.35A 0.070Ω 3.2mm
Sumida
CDRH2D14NP- 4.7μH 1.0A 0.135Ω 1.55mm
4R7N
CDRH2D18/ 4.7μH 1.2A 0.110Ω 2.0mm
HPNP-4R7N
CDRH3D16NP- 4.7μH 0.9A 0.08Ω 1.8mm
4R7N
Cooper-
Bussmann
SD18-4R7
SD10-4R7
4.7μH 1.54A 0.082Ω 1.8mm
4.7μH 1.08A 0.153Ω 1.0mm
Capacitor Vendor Information
Both the input and output capacitors used with the LTC3522
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 LTC3522
application circuits.
Table 5. Capacitor Vendor Information
MANUFACTURER WEB SITE
REPRESENTATIVE PART
NUMBERS
Taiyo Yuden
www.t-yuden.com JMK107BJ105MA 4.7μF, 6.3V
TDK
www.component. C2012X5R0J475K 4.7μF, 6.3V
tdk.com
Murata
www.murata.com GRM219R61A475K 4.7μF
AVX
www.avxcorp.com SM055C475KHN480 4.7μF
PCB Layout Considerations
The LTC3522 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 LTC3522. 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.
6. Keep the connection from the resistor dividers to the
feedback pins FB1 and FB2 as short as possible and
away from the switch pin connections.
3522fa
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