Datasheet

10
LT1611
OPERATIO
U
Output Current
The LT1611 will deliver 150mA at –5V from a 5V ±10%
input supply. If a higher voltage supply is available, more
output current can be obtained. Figure 17’s schematic
shows how to get more current. Although the LT1611’s
maximum voltage allowed at V
IN
is 10V, the SW pin can
handle higher voltage (up to 36V). In Figure 17, the V
IN
pin
of the LT1611 is driven from a 5V supply, while input
inductor L
1A
is driven from a separate 12V supply. Figure
18’s graph shows maximum recommended output cur-
rent as the voltage on L
1A
is varied. Up to 300mA can be
delivered when driving L
1A
from a 12V supply.
COMPONENT SELECTION
Inductors
Each of the two inductors used with the LT1611 should
have a saturation current rating (where inductance is
approximately 70% of zero current inductance) of ap-
proximately 0.25A or greater. If the device is used in
“charge pump” mode, where there is only one inductor,
then its rating should be 0.5A or greater. DCR of the
inductors should be 0.5Ω or less. A value of 22µH is
suitable if using a coupled inductor such as Sumida
CLS62-220 or Coiltronics CTX20-1. If using two separate
inductors, increasing the value to 47µH will result in the
same ripple current. Inductance can be reduced if operat-
ing from a supply voltage below 3V. Table 1 lists several
inductors that will work with the LT1611, although this is
not an exhaustive list. There are many magnetics vendors
whose components are suitable.
V
IN
5V
V
OUT
–5V
UP TO 300mA
1611 F17
SW
L1A
22µH
L1B
22µH
D1
GND
LT1611
C1, C2: TAIYO YUDEN LMK212BJ105MG
C3: TAIYO YUDEN JMK325BJ226MM
D1: MBR0520
L1A, L1B: SUMIDA CLS62-220
C1
1µF
C3
22µF
C2
1µF
V
L
(SEE TEXT)
10k
29.4k
1200pF
NFB
SHDN
V
L
(V)
34
5 6 7 8 9 10 11 12
MAXIMUM RECOMMENDED
OUTPUT CURRENT (mA)
1611 F18
350
300
250
200
150
100
Figure 17. Increase Output Current By Driving L1A from a Higher Voltage Figure 18. Output Current Increases to
300mA When Driving V
L
from 12V Supply