LT4180IGN-PBF datasheet(9/16 Pages) LINER

9 / 16 page

LT4180

4180fp

APPLICATIONS INFORMATION

First determine the settling time (to 1% of ﬁnal value)

of the power supply. The settling time should be the

worst-case value (over the whole operating envelope: VIN,

ILOAD, etc.).

SETTLING

•

For example, if the power supply takes 1ms to settle

(worst-case) to within 1% of ﬁnal value:

500

•–

Next, determine the propagation time of the wiring. In

order to ignore transmission line effects, the dither period

should be approximately twenty times longer than this.

This will limit dither frequency to:

ns ft L

20 1 017

•.

/ •

Where VF is the velocity factor (or velocity of propagation),

and L is the length of the wiring (in feet).

For example, assume the load is connected to a power

supply with 1000ft of CAT5 cable. Nominal velocity of

propagation is approximately 70%.

kHz

20 1 017

9 1000

34 4

•.

•

–

The maximum dither frequency should not exceed F1 or

F2 (whichever is less):

fDITHER < min (F1, F2).

Continuing this example, the dither frequency should be

less than 500Hz (limited by the power supply).

With the dither frequency known, the division ratio can

be determined:

RATIO

OSC

DITHER

250 000

500

The nearest division ratio is 512 (set DIV0 = L, DIV1 =

DIV2 = H). Based on this division ratio, nominal dither

frequency will be:

DITHER

OSC

RATIO

250 000

512

488

After the dither frequency is determined, the minimum

load decoupling capacitor can be determined. This load

capacitor must be sufﬁciently large to ﬁlter out the dither

signal at the load.

LOAD

WIRE

DITHER

••

Where CLOADistheminimumloaddecouplingcapacitance,

RWIRE is the minimum wiring resistance of one conduc-

tor of the wiring pair, and fDITHER is the minimum dither

frequency.

Continuing the example, our CAT5 cable has a maximum

9.38Ω/100m conductor resistance.

Maximum wiring resistance is:

RWIRE = 2 • 1000ft • 0.305m/ft • 0.0938Ω/m

RWIRE = 57.2Ω

LT4180IGN-PBF Datasheet(PDF) 9 Page - Linear Technology

LT4180IGN-PBF Datasheet(HTML) 9 Page - Linear Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Datasheet Download

Link URL