LTC3428

8

3428fb

APPLICATIONS INFORMATION

Table 2. Capacitor Vendor Information

SUPPLIER

PHONE

FAX

WEBSITE

AVX

(803) 448-9411 (803) 448-1943 www.avxcorp.com

Sanyo

(619) 661-9322 (619) 661-1055 www.sanyovideo.com

TDK

(847) 803-6100 (847) 803-6296 www.component.tdk.com

Murata

(814) 237-1431 (814) 238-0490 www.murata.com

Taiyo Yuden (408) 573-4150 (408) 573-4159 www.t-yuden.com

Output Diode Selection

For high efficiency, a fast switching diode with low reverse

leakage and a low forward drop is required. Schottky diodes

are recommended for their low forward drop and fast

switching times. When selecting a diode, it is important to

remember that the average diode current in a boost

When selecting a diode, make sure that the peak forward

current and average power dissipation ratings meet

the application requirements. See Table 3 for a list of

Schottky diode manufacturers. Example diodes are Philips

PMEG1020, PMEG2010, On-Semi MBRA210, IR 10BQ015,

Microsemi UPS120E, UPS315.

Table 3. Diode Vendor Information

SUPPLIER

PHONE

FAX

WEBSITE

Philips

+31 40 27 24825

www.philips.com

Microsemi

(949) 221-7100

(949)756-0308

www.microsemi.com

On-Semi

(602) 244-6600

www.microsemi.com

International

Rectifier

(310) 469-2161

(310) 322-3332 www.irf.com

Thermal Considerations

To deliver maximum power, it is necessary to provide a

good thermal path to dissipate the heat generated within

the LTC3428’s package. The large thermal pad on the IC

underside can accomplish this requirement. Use multiple

PC board vias to conduct heat from the IC and to a copper

plane that has as much area as possible.

If the junction temperature gets too high, the LTC3428 will

stop all switching until the junction temperature drops

to safe levels. The typical over temperature threshold is

150°C.

Closing the Feedback Loop

The LTC3428 uses current mode control with internal,

adaptive slope compensation. Current mode control

eliminates the 2nd order pole in the loop response of voltage

mode converters due to the inductor and output capacitor,

simplifying it to a single pole response. The product of the

modulator control to output DC gain and the error amp

open-loop gain equals the DC gain of the system.

GG

G

V

V

G

V

I

G

DC

CONTROL

EA

REF

OUT

CONTROL

IN

OUT

EA

=

=

≈

••

•

2

100

The output filter pole is given by:

f

I

VC

Hz

POLE

OUT

OUT

OUT

=

π ••

filter zero is given by:

f

RC

Hz

ZERO

ESR

OUT

=

1

2• •

•

π

resistance.

A complication of the boost converter topology is the right

half plane (RHP) zero and is given by:

f

VR

LV

Hz

RHP

IN

O

O

=

2

2

2

•

•• •

π