LM5088 datasheet(19/36 Pages) TI

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L =

0.4 x 7A x 250 kHz

1 -

55V

= 6.2 PH

I PP

T = 1/FSW

L =

VOUT

IPP x fSW

VOUT

1 -

VIN(max)

LM5088, LM5088-Q1

www.ti.com

SNVS600H – DECEMBER 2008 – REVISED MARCH 2013

OUTPUT INDUCTOR

The inductor value is determined based on the operating frequency, load current, ripple current and the input and

output voltages.

Knowing the switching frequency (fSW), maximum ripple current (IPP), maximum input voltage (VIN(max)) and the

nominal output voltage (VOUT), the inductor value can be calculated as follows:

(10)

Figure 23. Inductor Current

The maximum ripple current occurs at the maximum input voltage. Typically, IPP is selected between 20% and

40% of the full load current. Higher ripple current will result in a smaller inductor. However, it places more burden

on the output capacitor to smooth out the ripple current to achieve low output ripple voltage. For this example

40% ripple was chosen for a smaller sized inductor.

(11)

The nearest standard value of 6.8 µH will be used. To prevent saturation, the inductor must be rated for the peak

current. During normal operation, the peak current occurs at maximum load current (plus maximum ripple). With

properly scaled component values, the peak current is limited to VCS(TH)/RS During overload conditions. At the

maximum input voltage with a shorted output, the chosen inductor must be evaluated at elevated temperature. It

should be noted that the saturation current rating of inductors drops significantly at elevated temperatures.

CURRENT SENSE RESISTOR

The current limit value (ILIM) is set by the current sense resistor (RS).

RS can be calculated by

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LM5088 Datasheet(PDF) 19 Page - Texas Instruments