I
OR
L
1
C
u
rr
e
n
t
I
O
I
PK+
I
PK-
0 mA
1/Fs
I
PK+(CL)
=
R
5
1.5A x (150 m
:
+ R
5
)
+ I
OR(max)
I
OR(max)
=
L1
min
x F
S(min)
x V
IN(max)
V
OUT1
x (V
IN(max)
±
V
OUT1
)
I
PK+
= I
O(max)
+
2
I
OR(max)
I
AVE
=
(R5 + 0.11
:
) x V
IN(max)
I
O(max)
x R
5
x (V
IN(max)
±
V
OUT
)
Increasing the Current Limit
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where, 0.11
Ω
is the minimum value of the internal resistance from SGND to ISEN. The next smaller
standard value resistor should be used for R5. With the addition of R5 it is necessary to check the
average and peak current values to ensure they do not exceed the LM2695 limits. At maximum load
current the average current through the internal sense resistor is shown in
Equation 9
:
(9)
If I
AVE
is less than 1.5A no changes are necessary. If it exceeds 1.5A, R5 must be reduced. The upper
peak of the inductor current (I
PK+
), at maximum load current, is calculated using
Equation 10
:
(10)
where I
OR(max)
is calculated using
Equation 11
.
(11)
where, L1
min
is the minimum inductor value based on the manufacturer’s tolerance, and F
S(min)
is the
minimum switching frequency (380 kHz - 25% = 285 kHz for this evaluation board). If I
PK+
exceeds 2A , the
inductor value must be increased to reduce the ripple amplitude. This necessitates recalculation of I
OR(min)
,
I
PK-
, and R5. When the circuit is in current limit, the upper peak current out of the SW pin can be as high
as:
(12)
The inductor L1 and diode D1 must be rated for this current.
Figure 5. Inductor Current
6
AN-1444 LM2695 Evaluation Board
SNVA147A – February 2006 – Revised April 2013
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