LT1110
13
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.
U
S
A
O
PP
L
IC
AT
I
WU
U
I FOR ATIO
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.
Figure 13. Output Ripple Reduction Using Gain Block
Figure 12. Setting Low Battery Detector Trip Point
LT1110 • TA07
V
BAT
R1
R2
220mV
REF
SET
GND
V
IN
LT1110
47k
+5V
TO
PROCESSOR
R1 =
V
LB
– 220mV
( )
4.33µA
V
LB
= BATTERY TRIP POINT
+
–
AO
R3
R2 = 33kΩ
R3 = 2MΩ
L1
LT1110 • TA08
GND SW2
SET
SW1
LIM
I
IN
V
D1
R3
270k
FB
+
V
OUT
R2
R1
C1
V = +1 220mV
OUT
R2
R1
( ) ( )
LT1110
AO
V
BAT
Table 2. Capacitor Manufacturers
MANUFACTURER PART NUMBERS
Sanyo Video Components OS-CON Series
2001 Sanyo Avenue
San Diego, CA 92173
619-661-6835
Nichicon America Corporation PL Series
927 East State Parkway
Schaumberg, IL 60173
708-843-7500
Sprague Electric Company 150D Solid Tantalums
Lower Main Street 550D Tantalex
Sanford, ME 04073
207-324-4140
Matsuo 267 Series
714-969-2491 Surface Mount
Table 3. Transistor Manufacturers
MANUFACTURER PART NUMBERS
Zetex ZTX Series
Commack, NY FZT Series
516-543-7100 Surface Mount
Table 1. Inductor Manufacturers
MANUFACTURER PART NUMBERS
Coiltronics International CTX100-4 Series
984 S.W. 13th Court Surface Mount
Pompano Beach, FL 33069
305-781-8900
Sumida Electric Co. USA CD54
708-956-0666 CDR74
CDR105
Surface Mount
