LT1111
O U
W
U
PPLICATI
S I FOR ATIO
A
Using the Gain Block
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.
The gain block (GB) on the LT1111 can be used as an error
amplifier, low-battery detector or linear post regulator.
ThegainblockitselfisaverysimplePNPinputopampwith
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.
5V
LT1111
V
IN
47k
R1
R2
1.25V
REF
–
+
A0
TO
PROCESSOR
SET
V
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
isadequate.R3canbeaddedtointroduceasmallamount
of hysteresis. This will cause the gain block to “snap”
BAT
V
– 1.25V
LB
R1 =
GND
35.1µA
V
= BATTERY TRIP POINT
R2 = 33k
LB
R3
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
INDUCTOR
VALUE
INDUCTOR
PART NUMBER
CAPACITOR
VALUE
NOTES
2 to 3.1
2 to 3.1
2 to 3.1
2 to 3.1
5
5
5
90mA
10mA
30mA
10mA
90mA
30mA
50mA
300mA
300mA
75mA
250mA
4
4
4
4
4
4
5
5
5
6
6
15µH
47µH
15µH
47µH
33µH
47µH
15µH
56µH
120µH
56µH
120µH
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
33µF
10µF
22µF
10µF
22µF
15µF
47µF
47µF
47µF
47µF
100µF
*
12
12
12
12
5
5
5
–5
–5
5
6.5 to 11
12 to 20
20 to 30
5
**
**
**
12
**
S = Sumida
C = Coiltronics
* Add 47Ω from I to V
LIM
IN
** Add 220Ω from I to V
LIM
IN
Table 2. Inductor Manufacturers
MANUFACTURER
Table 3. Capacitor Manufacturers
MANUFACTURER
PART NUMBERS
PART NUMBERS
Coiltronics Incorporated
6000 Park of Commerce Blvd.
Boca Raton, FL 33487
407-241-7876
CTX100-4 Series
Surface Mount
Sanyo Video Components
1201 Sanyo Avenue
San Diego, CA 92073
619-661-6322
OS-CON Series
Toko America Incorporated
1250 Feehanville Drive
Mount Prospect, IL 60056
312-297-0070
Type 8RBS
Nichicon America Corporation
927 East State Parkway
Schaumberg, IL 60173
708-843-7500
PL Series
Sumida Electric Co. USA
708-956-0666
CD54
CDR74
CDR105
Surface Mount
Sprague Electric Company
Lower Main Street
Sanford, ME 04073
207-324-4140
150D Solid Tantalums
550D Tantalex
Matsuo
714-969-2491
267 Series
Surface Mount
1111fd
13
Linear [ Linear ]
