Datasheet

'i
L1
=
V
IN
x D x T
S
2 x L
1
I
L1
=
D
1-D
D
1-D
I
L2
=
I
OUT
'i
L2
=
V
IN
x D x T
S
2 x L
2
C
IN
: VISHAY/SPRAGUE 595D226X0020C2T
C
CUK
: TAIYO YUDEN X5R LMK212BJ105MG
C
OUT
: TAIYO YUDEN X5R JMK325BJ226MM
D: ON SEMICONDUCTOR MBR0520
L1: SUMIDA CLS62-220 or MURATA LZH3C220 (UNCOUPLED)
L1A
22PH
C
CUK
2.2PF
C
OUT
22PF
L1B
22PH
V
IN
12V
V
OUT
-5V
375mA
V
DD
5V
D
C
FF
1000pF
R
FB1
29.4k
R
FB2
10k
V
IN
SW
NFB
GND
SHDN
LM2611A
1
2
34
5
C
IN
22PF
I
L1
v
L1
(V)
i
L1
(A)
'I
L1
V
IN
V
OUT
t
t
LM2611
www.ti.com SNOS965I –JUNE 2001–REVISED APRIL 2013
Figure 14. Voltage and Current Waveforms in Inductor L1 of a Cuk Converter
The voltage and current waveforms of inductor L2 are shown in Figure 15. During the first cycle of operation,
when the switch is closed, V
IN
is applied across L2. When the switch opens, V
OUT
is applied across L2.
Figure 15. Voltage and Current Waveforms in Inductor L2 of a Cuk Converter
The following equations define values given in Figure 14 and Figure 15:
I
L2
= I
OUT
(2)
(3)
(4)
(5)
Use these equations to choose correct core sizes for the inductors. The design of the LM2611's internal
compensation assumes L1 and L2 are equal to 10 - 22 µH, thus it is recommended to stay within this range.
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