LT3460

6

3460f

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

frequency.

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

°.

OPERATIO

60

50

40

30

20

10

0

–10

–20

–30

–40

90

45

0

–45

–90

–135

–180

–225

–270

–315

–360

FREQUENCY (kHz)

PHASE

GAIN

1

10

100

1000

3460 F04

R1

R2

GND

C2

L1

D1

C1

SHUTDOWN

+

R1

R2

GND

C2

L1

D1

C1

SHUTDOWN

3460 F05

+

(SOT-23 PACKAGE)

(SC70 PACKAGE)

Figure 5. Suggested Layout

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.

Figure 4.