SC283 datasheet(15/20 Pages) SEMTECH

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SC283

Applications Information (continued)

minimum gap possible to limit the distance that magnetic

fields can radiate from the inductor. However shielded

inductors typically have a higher DCR and are thus less

efficient than a similarly sized non-shielded inductor.

Final inductor selection depends on various design

considerations such as efficiency, EMI, size, and cost.

Table 2 lists the manufacturers of recommended inductor

options. The saturation characteristics and DC current

ratings are also shown.

Manufacturer

Part Number

(μH)

DCR

Max

(Ω)

Rated

Current

(A)

L at

Rated

Current

(μH)

Dimen-

sions

LxWxH

(mm)

TOKO

1071AS-2R2M

2.20±20% 0.060

1.80

1.54

2.8x3.0x1.5

TOKO

1071AS-1R0N

1.00±30% 0.040

2.70

0.70

2.8x3.0x1.5

TOKO

1127AS-2R2M

2.20±20% 0.048

2.50

1.54

3.5x3.7x1.8

Panasonic

ELLVGG1R0N

1.00±23% 0.062

2.20

0.70

3.2x3.2x1.5

Table 2 – Recommended Inductors

OUT Selection

The internal voltage loop compensation in the SC283

limits the minimum output capacitor value to 22µF if

using a 2.2µH inductor or 44µF if using a 1µH inductor.

This is due to its influence on the the loop crossover

frequency, phase margin, and gain margin. Increasing

the output capacitor above this minimum value will

reduce the crossover frequency and provide greater

phase margin. The total output capacitance should not

exceed 50µF to avoid any start-up problems. For most

typical applications it is recommended to use an output

capacitance of 22µF to 44µF. When choosing the output

capacitor’s capacitance, verify the voltage derating effect

from the capacitor vendor’s data sheet.

Capacitors with X7R or X5R ceramic dielectric are

recommended for their low ESR and superior temperature

and voltage characteristics. Y5V capacitors should not

be used as their temperature coefficients make them

unsuitable for this application.

The output voltage droop due to a load transient is deter-

mined by the capacitance of the ceramic output capacitor.

The ceramic capacitor supplies the load current initially

until the loop responds. Within a few switching cycles the

loop will respond and the inductor current will increase to

match the required load. The output voltage droop during

the period prior to the loop responding can be related to

the choice of output capacitor by the relationship from

Equation 4.

OSC

DROOP

LOAD

OUT

⋅

∆

⋅

(4)

The outputcapacitorRMSripplecurrentmaybecalculated

from Equation 5.

(

)













⋅

−

⋅

OSC

OUT

MAX

OUT

RMS

COUT

)

(

)

(

(5)

Table 3 lists the manufacturers of recommended output

capacitor options.

Manufacturer

Part Nunber

Value

(μF)

Type

Rated

Voltage

(VDC)

Value

3.3V

(μF)

Dimensions

LxWxH

(mm)

Murata

GRM21BR60J106K

10±10%

X5R

6.3

4.74

2.0x1.25x1.25

(EIA:0805)

Murata

GRM219R60J106K

10±10%

X5R

6.3

4.05

2.0x1.25x0.85

(EIA:0805)

Murata

GRM21BR60J226M

22±20%

X5R

6.3

6.57

2.0x1.25x1.25

(EIA:0805)

Murata

GRM31CR60J476M

47±20%

X5R

6.3

20.3

3.2x1.6x1.6

(EIA:1206)

Table 3 – Recommended Capacitors

IN Selection

The SC283 source input current is a DC supply current

with a triangular ripple imposed on it. To prevent large

input voltage ripple, a low ESR ceramic capacitor is

required. A minimum value of 10μF should be used. It is

important to consider the DC voltage coefficient charac-

teristics when determining the actual required value. It

should be noted a 10µF, 6.3V, X5R ceramic capacitor with

5V DC applied may exhibit a capacitance as low as 4.5µF.

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