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LTC3522

3522f

APPLICATIONS INFORMATION

of inductors that are well suited to many LTC3522 buck

converter applications.

Table 4. Representative Surface Mount Inductors

MANUFACTURER PART NUMBER

VALUE

MAX

CURRENT

DCR

HEIGHT

Taiyo Yuden

NP035B-4R7M

4.7μH

1.2A

0.047

Ω 1.8mm

NP035B-6R8M

6.8μH

1.0A

0.084

Ω 1.8mm

Coilcraft

MSS6132-472ML 4.7μH

1.8A

0.056

Ω 3.2mm

MSS6132-822ML 8.2μH

1.35A

0.070

Ω 3.2mm

Sumida

CDRH2D14NP-

4R7N

4.7μH

1.0A

0.135

Ω 1.55mm

CDRH2D18/

HPNP-4R7N

4.7μH

1.2A

0.110

Ω 2.0mm

CDRH3D16NP-

4R7N

4.7μH

0.9A

0.08

Ω 1.8mm

Cooper-

Bussmann

SD18-4R7

4.7μH

1.54A

0.082

Ω 1.8mm

SD10-4R7

4.7μH

1.08A

0.153

Ω 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.

tdk.com

C2012X5R0J475K 4.7μF, 6.3V

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 PVIN1 and

PVIN2 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.

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