8

LT3473/LT3473A

3473f

resulting sum is fed into the positive terminal of the PWM

comparator A2. When this voltage exceeds the level of the

switch Q1. The error amplifier sets the peak current level

to keep the output in regulation. If the error amplifier’s

output increases, more current is delivered to the output;

if it decreases, less current is delivered.

The LT3473 includes an internal power Schottky diode and

a PNP transistor, Q2, for output disconnect. Q2 discon-

nects the load from the input during shutdown. The part

also has a power good indication pin, PGOOD. When the

FB voltage reaches within 100mV of the reference voltage,

the comparator A4 turns on Q5, sinking current from

PGOOD pin.

The LT3473 has thermal shutdown feature with threshold

at about 145°C.

Inductor Selection

A 6.8µH inductor is recommended for the LT3473. The

minimum inductor size that may be used in a given appli-

cation depends on required efficiency and output current.

Inductors with low core losses and small DCR (copper

wire resistance) at 1.2MHz are good choices for LT3473

applications. Some inductors in this category with small

size are listed in Table 1. The efficiency comparison of

different inductors is shown in Figure 3.

Capacitor Selection

The small package of ceramic capacitors makes them

suitable for LT3473 applications. X5R and X7R types of

ceramic capacitors are recommended because they retain

their capacitance over wider voltage and temperature

ranges than other types such as Y5V or Z5U. A 4.7µF input

capacitor, a 0.47µF output capacitor and a 2.2µF capacitor

bypassing output disconnect PNP are sufficient for most

LT3473 applications.

Table 2. Recommended Ceramic Capacitor Manufacturers

MANUFACTURER

TELEPHONE

URL

Taiyo Yuden

408-573-4150

www.t-yuden.com

AVX

843-448-9411

www.avxcorp.com

Murata

814-237-1431

www.murata.com

Kemet

408-986-0424

www.kemet.com

APPLICATIO S I FOR ATIO

Table 1. Recommended Inductors

DCR

CURRENT

DIMENSION

PART

(mΩ)

RATING (A)

(mm)

MANUFACTURER

DO1605T-682

200

1.1

5.4 × 4.2 × 1.8

Coilcraft

ME3220-682

270

1.0

3.2 × 2.5 × 2.0

800-322-2645

MSS6122-682

100

1.45

6.1 × 6.1 × 2.2

www.coilcraft.com

MSS5131-682

60

1.05

5.1 × 5.1 × 3.1

LQH55DN6R8

74

2.0

5.7 × 5.0 × 4.7

Murata

814-237-1431

www.murata.com

CDRH5D18-6R2

71

1.4

5.7 × 5.7 × 2.0

Sumida

CDRH4D28-6R8

81

1.12

4.7 × 4.7 × 3.0

847-956-0666

CDRH5D28-6R2

33

1.8

5.7 × 5.7 × 3.0

www.sumida.com

CRD53-4R7

74

1.68

6.0 × 5.2 × 3.2

A918CY-6R2M

62

1.49

6.0 × 6.0 × 2.0

Toko

(TYPE D62LCB)

408-432-8281

A915AY-6R8M

68

1.51

5.0 × 5.0 × 3.0

www.tokoam.com

(TYPE D53LC)

0

70

75

80

80

3473 F03

65

60

55

20

40

60

100

TOKO A915AY-6R8M

SUMIDA CDRH4D28-6R8

SUMIDA CDRH5D18-6R2

COILCRAFT ME3220-682

COILCRAFT MSS5131-682

Figure 3. Efficiency Comparison of Different Inductors