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LTC3521

3521f

applicaTions inForMaTion

Capacitor Vendor Information

BoththeinputandoutputcapacitorsusedwiththeLTC3521

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.

tdk.com

C2012X5R0J106K 10μF, 6.3V

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. Allcirculatinghighcurrentpathsshouldbekeptasshort

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

PVIN2shouldbeplacedasclosetotheICaspossibleand

should have the shortest possible paths to ground.

2. Thesmall-signalgroundpad(GND)shouldhaveasingle

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.

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