LTC1174CS8 datasheet(10/16 Pages) LINER

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LTC1174

LTC1174-3.3/LTC1174-5

APPLICATI

I FOR ATIO

Figure 6. LTC1174 Layout Diagram (See Board Layout Checklist)

DESIGN EXAMPLE

As a design example, assume VIN = 9V (nominal), VOUT =

5V, and IOUT = 350mA maximum. The LTC1174-5 is used

for this application, with IPGM (pin 7) connected to VIN. The

minmum value of L is determined by assuming the

LTC1174-5 is operating in continuous mode.

Figure 7. Continuous Inductor Current

TIME

IPEAK

AVG CURRENT = IOUT

= 350mA

IPEAK + IV

1174 F07

With IOUT = 350mA and IPEAK = 0.6A (IPGM = VIN), IV =

0.1A.The peak-to-peak ripple inductor current, IRIPPLE, is

0.5A and is also equal to:

RIPPLE

OUT

=×







 ()

−

410

Solving for L in the above equation and with VD = 0.6V,

L = 44.8

µH. The next higher standard value of L is 50µH

(example: Coiltronics CTX50-4). The operating frequency,

neglecting voltage across diode VD is:

kHz

OUT

≈×

−









2 5 10 1

111

With the value of L determined, the requirements for CIN

and COUT are calculated. For CIN, its RMS current rating

should be at least:

RMS

OUT

RMS

−

()

[] ()

174

For COUT, the RMS current rating should be at least:

RMS

PEAK

RMS

≈

()

300

Now allow VIN to drop to 6V. At this minimum input voltage

the operating frequency will decrease. The new frequency

is 42kHz.

LTC1174

VOUT

1174 F06

OUTPUT DIVIDER

REQUIRED WITH

ADJUSTABLE

VERSION ONLY

0.1

µF

LBOUT

LBIN

GND

SHUTDOWN

IPGM

VIN

BOLD LINES INDICATE

HIGH CURRENT PATH

VIN

CIN

COUT

VOUT

(VFB)

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