LT1110CS8 datasheet(13/16 Pages) LINER

13 / 16 page

LT1110

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

Ω 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.

APPLICATI

I FOR ATIO

Output ripple of the LT1110, normally 90mV at 5VOUT 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 VOUT by only a few millivolts.

1000

µF is a good starting value.

Figure 13. Output Ripple Reduction Using Gain Block

Figure 12. Setting Low Battery Detector Trip Point

LT1110 • TA07

VBAT

220mV

REF

SET

GND

VIN

LT1110

47k

+5V

PROCESSOR

R1 =

VLB – 220mV

(

)

4.33

µA

VLB = BATTERY TRIP POINT

–

R2 = 33k

Ω

R3 = 2M

Ω

LT1110 • TA08

GND

SW2

SET

SW1

LIM

270k

VOUT

+ 1 220mV

OUT

(

)(

)

LT1110

VBAT

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

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