LT1111_15 Datasheet, PDF (13/16 Pages) Linear Technology – Micropower DC/DC Converter Adjustable and Fixed 5V, 12V

LT1111
APPLICATI S I FOR ATIO
Using the Gain Block
The gain block (GB) on the LT1111 can be used as an error
amplifier, low-battery detector or linear post regulator.
The gain block itself is a very simple PNP input op amp with
an open collector NPN output. The negative input of the
gain block is tied internally to the 1.25V reference. The
positive input comes out on the SET pin.
Arrangement of the gain block as a low-battery detector
is straightforward. Figure 12 shows hookup. R1 and R2
need only be low enough in value so that the bias current
of the SET input does not cause large errors. 33k for R2
is adequate. R3 can be added to introduce a small amount
of hysteresis. This will cause the gain block to “snap”
when the trip point is reached. Values in the 1M to 10M
range are optimal. However, the addition of R3 will
change the trip point.
5V
LT1111
V _IN
47k
R1
1.25V
REF
–
V_BAT
SET
+
A0
TO
PROCESSOR
R2
GND
R3
R1 = ^{VLB – 1.25V}
35.1µA
V_LB = BATTERY TRIP POINT
R2 = 33k
R3 = 1.6M
LT1111 • F12
Figure 12. Setting Low-Battery Detector Trip Point
Table 1. Component Selection for Common Converters
INPUT
VOLTAGE
OUTPUT
VOLTAGE
OUTPUT
CURRENT (MIN)
CIRCUIT
FIGURE
2 to 3.1
5
90mA
4
2 to 3.1
5
10mA
4
2 to 3.1
12
30mA
4
2 to 3.1
12
10mA
4
5
12
90mA
4
5
12
30mA
4
6.5 to 11
5
50mA
5
12 to 20
5
300mA
5
20 to 30
5
300mA
5
5
–5
75mA
6
12
–5
250mA
6
S = Sumida
* Add 47Ω from I_LIM to V_IN
C = Coiltronics ** Add 220Ω from I_LIM to V_IN
INDUCTOR
VALUE
15µH
47µH
15µH
47µH
33µH
47µH
15µH
56µH
120µH
56µH
120µH
INDUCTOR
PART NUMBER
S CD75-750K
S CD54-470K, C CTX50-1
S CD75-150K
S CD54-470K, C CTX50-1
S CD75-330K
S CD75-470K, C CTX50-1
S CD54-150K
S CD105-560K, C CTX50-4
S CD105-121K, C CTX100-4
S CD75-560K, C CTX50-4
S CD105-121K, C CTX100-4
CAPACITOR
VALUE
33µF
10µF
22µF
10µF
22µF
15µF
47µF
47µF
47µF
47µF
100µF
NOTES
*
**
**
**
**
Table 2. Inductor Manufacturers
MANUFACTURER
Coiltronics Incorporated
6000 Park of Commerce Blvd.
Boca Raton, FL 33487
407-241-7876
Toko America Incorporated
1250 Feehanville Drive
Mount Prospect, IL 60056
312-297-0070
Sumida Electric Co. USA
708-956-0666
PART NUMBERS
CTX100-4 Series
Surface Mount
Type 8RBS
CD54
CDR74
CDR105
Surface Mount
Table 3. Capacitor Manufacturers
MANUFACTURER
Sanyo Video Components
1201 Sanyo Avenue
San Diego, CA 92073
619-661-6322
Nichicon America Corporation
927 East State Parkway
Schaumberg, IL 60173
708-843-7500
Sprague Electric Company
Lower Main Street
Sanford, ME 04073
207-324-4140
Matsuo
714-969-2491
PART NUMBERS
OS-CON Series
PL Series
150D Solid Tantalums
550D Tantalex
267 Series
Surface Mount
1111fd
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