Datasheet

L =
5V
0.4 x 7A x 250 kHz
5V
1 -
55V
x
= 6.2 PH
0
I
PP
T = 1/F
SW
I
O
L =
V
OUT
I
PP
x f
SW
V
OUT
1 -
V
IN(max)
x
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 (f
SW
), maximum ripple current (I
PP
), maximum input voltage (VIN
(max)
) and the
nominal output voltage (V
OUT
), the inductor value can be calculated as follows:
(10)
Figure 23. Inductor Current
The maximum ripple current occurs at the maximum input voltage. Typically, I
PP
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 V
CS(TH)
/R
S
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 (I
LIM
) is set by the current sense resistor (R
S
).
R
S
can be calculated by
Copyright © 2008–2013, Texas Instruments Incorporated Submit Documentation Feedback 19
Product Folder Links: LM5088 LM5088-Q1