LT1611 Linear Technology, LT1611 Datasheet - Page 10

• Manufacturer Part Number: LT1611
• Description: Constant-Current/ Constant-Voltage 1.4MHz Step-Up DC/DC Converter
• Manufacturer: Linear Technology

OPERATIO
LT1611
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
handle higher voltage (up to 36V). In Figure 17, the V
of the LT1611 is driven from a 5V supply, while input
inductor L
18’s graph shows maximum recommended output cur-
rent as the voltage on L
delivered when driving L
10
5V
Figure 17. Increase Output Current By Driving L1A from a Higher Voltage
C1, C2: TAIYO YUDEN LMK212BJ105MG
C3: TAIYO YUDEN JMK325BJ226MM
D1: MBR0520
L1A, L1B: SUMIDA CLS62-220
C1
1 F
1A
is driven from a separate 12V supply. Figure
V
SHDN
IN
LT1611
GND
U
(SEE TEXT)
NFB
SW
V
L
1A
1A
L1A
22 H
is varied. Up to 300mA can be
from a 12V supply.
29.4k
10k
IN
1 F
C2
is 10V, the SW pin can
1200pF
D1
22 H
L1B
IN
pin
C3
22 F
V
–5V
UP TO 300mA
OUT
1611 F17
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 0.5
suitable if using a coupled inductor such as Sumida
CLS62-220 or Coiltronics CTX20-1. If using two separate
inductors, increasing the value to 47 H 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.
Figure 18. Output Current Increases to
300mA When Driving V
350
300
250
200
150
100
3
4
or less. A value of 22 H is
5
6
7
V
L
(V)
L
from 12V Supply
8
9
10
11
1611 F18
12