Datasheet

11
LT1611
TYPICAL APPLICATIO S
U
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However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
Table 1. Inductor Vendors
VENDOR PHONE URL PART COMMENT
Sumida (847) 956-0666 www.sumida.com CLS62-22022 22µH Coupled
CD43-470 47µH
Murata (404) 436-1300 www.murata.com LQH3C-220 22µH, 2mm Height
Coiltronics (407) 241-7876 www.coiltronics.com CTX20-1 20µH Coupled, Low DCR
Table 2. Capacitor Vendors
VENDOR PHONE URL PART COMMENT
Taiyo Yuden (408) 573-4150 www.t-yuden.com Ceramic Caps X5R Dielectric
AVX (803) 448-9411 www.avxcorp.com Ceramic Caps
Tantalum Caps
Murata (404) 436-1300 www.murata.com Ceramic Caps
Capacitors
As described previously, ceramic capacitors can be used
with the LT1611 provided loop stability is considered. For
lower cost applications, small tantalum units can be used.
A value of 22µF is acceptable, although larger capacitance
values can be used. ESR is the most important parameter
in selecting an output capacitor. The “flying” capacitor (C2
in the schematic figures) should be a 1µF ceramic type. An
X5R or X7R dielectric should be used to avoid capacitance
decreasing severely with applied voltage. The input by-
pass capacitor is less critical, and either tantalum or
ceramic can be used with little trade-off in circuit perfor-
mance. Some capacitor types appropriate for use with the
LT1611 are listed in Table 2.
Diodes
A Schottky diode is recommended for use with the LT1611.
The Motorola MBR0520 is a very good choice. Where the
input to output voltage differential exceeds 20V, use the
MBR0530 ( a 30V diode). If cost is more important than
efficiency, a 1N4148 can be used, but only at low current
loads.
OPERATIO
U
V
IN
3.3V
–5V
70mA
1611 TA02
SW
L1
10µH
D1
D2
GND
LT1611
C1, C2: TAIYO YUDEN LMK212BJ105MG
C3: TAIYO YUDEN JMK325BJ226MM
D1, D2: MBR0520
L1: MURATA LQH3C-100
C1
1µF
C3
22µF
C2
1µF
10k
29.4k
NFB
SHDN
“Charge Pump” Inverting DC/DC Converter