Datasheet

C
IN
: VISHAY/SPRAGUE 595D226X0020C2T
C
CUK
: TAIYO YUDEN X5R EMK316BJ225ML
C
OUT
: TAIYO YUDEN X5R JMK325BJ226MM
D: ON SEMICONDUCTOR MBR0520
L1: SUMIDA CR32-220
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
C
BYP
0.1PF
LM2611
SNOS965I –JUNE 2001–REVISED APRIL 2013 www.ti.com
Figure 28. LM2611 Operating with Separate Power and Biasing Supplies
Split Supply Operation
The LM2611 may be operated with separate power and bias supplies. In the circuit shown in Figure 28. V
IN
is the
power supply that the regulated voltage is derived from, and V
DD
is a low current supply used to bias the
LM2611. Conditions for the supplies are:
2.7V ≤ V
DD
≤ 14V (12)
0V ≤ V
IN
≤ (36 - IV
OUT
I) V (13)
As the input voltage increases, the maximum output current capacbility increases. Using a separate, higher
voltage supply for power conversion enables the LM2611 to provide higher output currents than it would with a
single supply that is limited in voltage by V
IN(MAX)
.
Shutdown/Soft Start
A soft start circuit is used in switching power supplies to limit the input inrush current upon start-up. Without a
soft-start circuit, the inrush current can be several times the steady-state load current, and thus apply
unnecessary stress to the input source. The LM2611 does not have soft-start circuitry, but implementing the
circuit in Figure 29 will lower the peak inrush current. The SHDN pin is coupled to the output through C
SS
. The
LM2611 is toggled between shutdown and run states while the output slowly decreases to its steady-state value.
The energy required to reach steady-state is spread over a longer time and the input current spikes decrease
(see Figure 30 and Figure 31).
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