LT1110 Datasheet, PDF (13/16 Pages) Linear Technology – Micropower DC-DC Converter Adjustable and Fixed 5V, 12V

LT1110
APPLICATI S I FOR ATIO
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. 33kΩ 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-10M range are
optimal. The addition of R3 will change the trip point,
however.
+5V
V_IN
47k
R1
LT1110
V_BAT
220mV
REF
–
AO
TO
SET
+
PROCESSOR
GND
R2
R3
( ) R1 =
V_LB – 220mV
4.33µA
V_LB = BATTERY TRIP POINT
R2 = 33kΩ
R3 = 2MΩ
LT1110 • TA07
Figure 12. Setting Low Battery Detector Trip Point
Output ripple of the LT1110, normally 90mV at 5V_OUT can
be reduced significantly by placing the gain block in front
of the FB input as shown in Figure 13. This effectively
reduces the comparator hysteresis by the gain of the gain
block. Output ripple can be reduced to just a few millivolts
using this technique. Ripple reduction works with step-
down or inverting modes as well. For this technique to be
effective, output capacitor C1 must be large, so that each
switching cycle increases V_OUT by only a few millivolts.
1000µF is a good starting value.
V_BAT
L1
R3
270k
I_LIM
AO
V _IN
SW1
LT1110
FB
GND
SET
SW2
D1
V_OUT
R2
+
C1
R1
( )( ) ^VOUT ⁼
R2
R1
+
1
220mV
LT1110 • TA08
Figure 13. Output Ripple Reduction Using Gain Block
Table 1. Inductor Manufacturers
MANUFACTURER
Coiltronics International
984 S.W. 13th Court
Pompano Beach, FL 33069
305-781-8900
Sumida Electric Co. USA
708-956-0666
PART NUMBERS
CTX100-4 Series
Surface Mount
CD54
CDR74
CDR105
Surface Mount
Table 2. Capacitor Manufacturers
MANUFACTURER
Sanyo Video Components
2001 Sanyo Avenue
San Diego, CA 92173
619-661-6835
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
Table 3. Transistor Manufacturers
MANUFACTURER
Zetex
Commack, NY
516-543-7100
PART NUMBERS
OS-CON Series
PL Series
150D Solid Tantalums
550D Tantalex
267 Series
Surface Mount
PART NUMBERS
ZTX Series
FZT Series
Surface Mount
13