TC2575 datasheet(9/25 Pages) TELCOM

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TC2575

TC2575-1 3/13/00

1.0A Step-Down Switching Regulator

Procedure (Adjustable Output Version: TC2575-ADJ) (Continued)

Procedure

Example

3. Catch Diode Selection (D1)

A. Since the diode maximum peak current exceeds the

regulator maximum load current the catch diode current

rating must be at least 1.2 times greater than the

maximum load current. For a robust design, the diode

should have a current rating equal to the maximum

current limit of the TC2575 to be able to with stand a

continuous output short.

B. The reverse voltage rating of the diode should be at least

1.25 times the maximum input voltage.

4. Inductor Selection (L1)

A. Use the following formula to calculate the inductor

Volt x microsecond [V x

µs] constant:

E x T = ( VIN – VOUT)

VOUT

[V x

µsec]

VIN

F[Hz]

B. Match the calculated E x T value with the corresponding

number on the vertical axis of the Inductor Value

Selection Guide shown in Figure 37. This E x T constant

is a measure of the energy handling capability of an

inductor and is dependent upon the type of core, the core

area, the number of turns, and the duty cycle.

C. Next step is to identify the inductance region intersected

by the E x T value and the maximum load current value

on the horizontal axis shown in Figure 35.

D. From the inductor code, identify the inductor value. Then

select an appropriate inductor from Table 1 or Table 2.

The inductor chosen must be rated for a switching

frequency of 52kHz and for a current rating of 1.15 x

ILOAD . The inductor current rating can also be deter-

mined by calculating the inductor peak current:

IP (max) = ILOAD(max) +

(VIN – VOUT) tON

where tON is the "on" time of the power switch and

tON =

(VOUT

1.0 )

VIN

fOSC

For additional information about the inductor, see

the inductor section in the “External Components”

section of this data sheet.

3. Catch Diode Selection (D1)

A. For this example, a 3.0A current rating is adequate.

B. Use a 20V IN5820 or MBR320 Schottky diode or any

suggested fast recovery diodes in Table 4.

4. Inductor Selection (L1)

A. Calculate E x T [V x

µsec] constant:

E x T = ( 12 – 8.0) x

8.0

1000

= 51[V x

µsec]

B. E x T = 51 [V x

µsec]

C. ILOAD(max) = 1.0A

Inductance Region = L220

D. Proper inductor value = 220

µH

Choose the inductor from Table 1 or Table 2

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