LT8331 datasheet(15/24 Pages) AD

15 / 24 page

LT8334

Rev. 0

For more information www.analog.com

For the bulk C component, which also contributes 1% to

the total ripple is given by Equation 15.

COUT ≥

IO(MAX)

0.01 • VOUT • fOSC

(15)

The output capacitor in a boost regulator experiences high

RMS ripple currents, as shown in Figure 4. The RMS rip-

ple current rating of the output capacitor can be deter-

mined with Equation 16.

IRMS(COUT) ≥ ID(MAX) •

DMAX

− DMAX

(16)

Multiple capacitors are often paralleled to meet ESR

requirements. Typically, once the ESR requirement is sat-

isfied, the capacitance is adequate for filtering and has the

required RMS current rating. Additional ceramic capaci-

tors in parallel are commonly used to reduce the effect of

parasitic inductance in the output capacitor, which reduces

high frequency switching noise on the converter output.

CERAMIC CAPACITORS

Ceramic capacitors are small, robust and have very low

ESR. However, ceramic capacitors can cause problems

when used with the LT8334 due to their piezoelectric

nature. When in Burst Mode operation, the LT8334’s

switching frequency depends on the load current, and

at very light loads the LT8334 can excite the ceramic

capacitor at audio frequencies, generating audible noise.

Since the LT8334 operates at a lower current limit during

Burst Mode operation, the noise is typically very quiet to a

casual ear. If this is unacceptable, use a high performance

tantalum or electrolytic capacitor at the output. Low noise

ceramic capacitors are also available.

Table 3. Ceramic Capacitor Manufacturers

Taiyo Yuden

www.ty-top.com

AVX

www.avx.com

Murata

www.murata.com

BOOST CONVERTER: DIODE SELECTION

A Schottky diode is recommended for use with the

LT8334. Low leakage Schottky diodes are necessary when

low quiescent current is desired at low loads. The diode

leakage appears as an equivalent load at the output and

should be minimized. Choose Schottky diodes with suf-

ficient reverse voltage ratings for the target applications.

Table 4. Recommended Schottky Diodes

PART NUMBER

AVERAGE

FORWARD

CURRENT

(A)

REVERSE

VOLTAGE

(V)

REVERSE

CURRENT

(µA)

MANUFACTURER

DFLS240

Diodes, Inc.

PMEG4050EP

Nexperia

PMEG3020DEP

Nexperia

PMEG4020EPA

Nexperia

BOOST CONVERTER: LAYOUT HINTS

The high speed operation of the LT8334 demands careful

attention to board layout. Careless layout will result in per-

formance degradation. Figure 5 shows the recommended

component placement for a boost converter. Note the vias

under the exposed pad. These should connect to a local

ground plane for better thermal performance.

VOUT

8334 F05

SW1

BIAS

GND

VIN

INTVCC

SYNC

FBX

VIN

SW2

VOUT

VIN

Figure 5. Suggested Boost Converter Layout

APPLICATIONS INFORMATION

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