LT3460(2003) Ver la hoja de datos (PDF) - Linear Technology

Número de pieza

componentes Descripción

Fabricante

LT3460
(Rev.:2003)

1.3MHz Step-Up DC/DC Converter in SC70 and ThinSOT

Linear Technology 

LT3460

U

OPERATIO

margin, CF should be chosen so that the midpoint fre-

quency between the zero and the pole is at the cross over

frequency.

With CF = 20pF, the feedback loop Bode plot is reshaped

as shown in Figure 4. The phase margin is about 60°.

60

50 GAIN

40

30

20

10 PHASE

0

–10

–20

–30

–40

1

10

100

FREQUENCY (kHz)

Figure 4.

90

45

0

–45

–90

–135

–180

–225

–270

–315

–360

1000

3460 F04

The feed-forward capacitor increases the gain at high

frequency. The feedback loop therefore needs to have

enough attenuation at the switching frequency to reject the

switching noise. Additional internal compensation com-

ponents have taken this into consideration.

For most of the applications of LT3460, the output capaci-

tor ESR zero is at very high frequency and can be ignored.

If a low frequency ESR zero exists, for example, when a

high-ESR Tantalum capacitor is used at the output, the

phase margin may be enough even without a feed-forward

capacitor. In these cases, the feed-forward capacitor should

not be added because it may cause the feedback loop to

not have enough attenuation at the switching frequency.

Layout Hints

The high speed operation of the LT3460 demands careful

attention to board layout. You will not get advertised

performance with careless layout. Figure 5 shows the

recommended component placement.

L1

D1

C1

VOUT

+

C2

R2

GND

R1

CF

(SOT-23 PACKAGE)

VIN

SHUTDOWN

L1

D1

C1

VOUT

+

C2

R2

GND

Figure 5. Suggested Layout

R1

CF

(SC70 PACKAGE)

VIN

SHUTDOWN

3460 F05

3460f

6

Share Link: