TC2575 Datasheet, PDF(7/25 Page) TelCom Semiconductor, Inc

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TC2575 Datasheet, PDF (7/25 Pages) TelCom Semiconductor, Inc – 1.0A Step-Down Switching Regulator

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1.0A Step-Down Switching Regulator

TC2575

Procedure (Fixed Output Voltage Version)

In order to simplify the switching regulator design, a step-by-step design procedure and some examples are provided.

Procedure

Given Parameters:

VOUT = Regulated Output Voltage (3.3V, 5.0V or 12V)

VIN(max) = Maximum DC Input Voltage

ILOAD(max) = Maximum Load Current

1. Controller IC Selection

According to the required input voltage, output voltage and

current select the appropriate type of the controller IC output

voltage version.

2. Input Capacitor Selection (CIN )

To prevent large voltage transients from appearing at the input

and for stable operation of the converter, an aluminum or tantalum

electrolytic bypass capacitor is needed between the input pin +VIN

and ground pin GND. This capacitor should be located close to the

IC using short leads. This capacitor should have a low ESR

(Equivalent Series Resistance) value.

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 withstand 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. According to the required working conditions, select the

correct inductor value using the selection guide from

Figures 32 to 36.

B. From the appropriate inductor selection guide, identify the

inductance region intersected by the Maximum Input Voltage

line and the Maximum Load Current line. Each region is

identified by an inductance value and an inductor code.

C. Select an appropriate inductor from the several different

manufacturers part numbers listed in Table 1 or Table 2

When using Table 2 for selecting the right inductor, the

designer must realize that the inductor current rating must

be higher than the maximum peak current flowing through the

inductor. This maximum peak current can be calculated as

follows:

IP(max)

ILOAD

(max)+

(VIN

VOUT

)

tON

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

Example

Given Parameters:

VOUT = 5.0V

VIN (max) = 20V

ILOAD (max) = 0.8A

1. Controller IC Selection

According to the required input voltage, output voltage,

current polarity and current value, use the TC2575 (5V)

controller IC.

2. Input Capacitor Selection (CIN )

A 47ÂµF, 25V aluminium electrolytic capacitor

located near to the input and ground pins provides

sufficient bypassing.

3. Catch Diode Selection (D1)

A. For this example the current rating of the diode is 1.0A

B. Use a 30V 1N5818 Schottky diode, or any of the

suggested fast recovery diodes shown in Table 4.

4. Inductor Selection (L1)

A. Use the inductor selection guide shown in Figure 32

to 36.

B. From the selection guide, the inductance area

intersected by the 20V line and 0.8A line is L300.

C. Inductor value required is 300ÂµH. From Table 1, or

Table 2, choose an inductor from any of the listed

manufacturers.

tON

VOUT

VIN

1.0

fOSC

For additional information about the inductor, see the inductor

section in the âEXTERNAL COMPONENTSâ section of this

data sheet.

TC2575-1 3/13/00

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