LTC1265I Ver la hoja de datos (PDF) - Linear Technology

Número de pieza

componentes Descripción

Fabricante

LTC1265I

1.2A, High Efficiency Step-Down DC/DC Converter

Linear Technology 

LTC1265/LTC1265-3.3/LTC1265-5

APPLICATIONS INFORMATION

Design Example

As a design example, assume VIN = 5V, VOUT = 3.3V, IMAX

= 0.8A and f = 250kHz. With this information we can easily

calculate all the important components.

From (1),

RSENSE = 100mV/0.8 = 0.125Ω

From (2) and assuming VD = 0.4V,

CT ≅ 100pF

Using (3), the value of the inductor is:

L ≥ 5.2(105)(0.125)(100pF)3.3V = 22µH

For the catch diode, a MBRS130LT3 or 1N5818 will be

sufficient in this application.

CIN will require an RMS current rating of at least 0.4A at

temperature, and COUT will require an ESR of (from 5):

ESRCOUT < 0.25Ω

The inductor ripple current is given by:

) IRIPPLE =

VOUT + VD

L

tOFF = 0.22A

At light loads the peak inductor current is at:

IPEAK = 25mV/0.125 = 0.2A

Therefore, at load current less than 0.1A the LTC1265 will

be in Burst Mode operation. Figure 8 shows the complete

circuit and Figure 9 shows the efficiency curve with the

above calculated component values.

VIN

5V

+

CIN

0.1µF PWR VIN

SHDN

VIN

SW

1k

3900pF 100pF

LTC1265-3.3

ITH

PGND

SENSE+

CT

SENSE–

SGND

22µH

D1

0.125Ω

+

VOUT

3.3V

0.8A

COUT

1000pF

LTC1265 F08

Figure 8. Design Example Circuit

100

L = DALE LPT4545-220 (22µH)

VOUT = 3.3V

95 CT = 100pF

90

85

80

75

70

0.01

0.1

LOAD CURRENT (mA)

1.0

1265 G11

Figure 9. Design Example Efficiency Curve

12

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