R5973AD datasheet(23/38 Pages) STMICROELECTRONICS

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R5973AD

Application information



Inductor

The inductor value is very important as it fixes the ripple current flowing through the output

capacitor. The ripple current is usually fixed at 20 - 40% of Iomax, which is 0.3 - 0.6 A with

IOmax = 1.5 A. The approximate inductor value is obtained using the following formula:

Equation 20

where TON is the ON time of the internal switch, given by D · T. For example, with

VOUT = 3.3 V, VIN = 12 V and IO = 0.45 A, the inductor value is about 12 µH. The peak

current through the inductor is given by:

Equation 21

and it can be observed that if the inductor value decreases, the peak current (which must be

lower than the current limit of the device) increases. So, when the peak current is fixed,

a higher inductor value allows a higher value for the output current. In Table 8, some

inductor manufacturers are listed.

8.2

Layout considerations

The layout of switching DC-DC converters is very important to minimize noise and

interference. Power-generating portions of the layout are the main cause of noise and so

high switching current loop areas should be kept as small as possible and lead lengths as

short as possible.

Table 7. Output capacitor selection

Manufacturer

Series

Cap value (µF)

Rated voltage (V)

ESR (m

)

Sanyo POSCAP(1)

1. POSCAP capacitors have some characteristics which are very similar to tantalum.

TAE

100 to 470

4 to 16

25 to 35

THB/C/E

100 to 470

4 to 16

25 to 55

AVX

TPS

100 to 470

4 to 35

50 to 200

KEMET

T494/5

100 to 470

4 to 20

30 to 200

Sprague

595D

220 to 390

4 to 20

160 to 650

Table 8. Inductor selection

Manufacturer

Series

Inductor value (µH)

Saturation current (A)

Coilcraft

DO3316T

15 to 33

2.0 to 3.0

Coiltronics

UP1B

22 to 33

2.0 to 2.4

HM76-3

15 to 33

2.5 to 3.3

Epcos

B82476

15 to 33

2 to 3

Wurth Elektronik

74456115

15 to 33

2.5 to 3

VIN VOUT

–



I

---------------------------------- TON



IPK

I

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