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LD1117A

LOW DROP FIXED AND ADJUSTABLE POSITIVE VOLTAGE REGULATORS

Unisonic Technologies 

LD1117/A

LINEAR INTEGRATED CIRCUIT

„ APPLICATION NOTE of LD1117/A ADJUSTABLE

The LD1117/A ADJUSTABLE has a reference voltage of between the OUT and ADJ pins. IADJ is 60μA typ.

(120μA max.) and ΔIADJ is 1μA typ. (5μA max.).

R1 is normally fixed to 120Ω.

From figure 4 we obtain:

VOUT=VREF+R2(IADJ + IR1)=VREF + R2(IADJ + VREF / R1)=VREF(1+R2/R1) + R2 x IADJ.

Usually R2 value is in the range of few KΩ, so the R2 X IADJ product could be neglected; then the above

expression becomes: VOUT=VREF(1+R2/R1)

For better load regulation, realize a good Kelvin connection of R1 and R2 is important. Particularly R1

connection must be realized very close to OUT and ADJ pin, while R2 ground connection must be placed as

near as possible to the negative Load pin. Ripple rejection can be improved by introducing a 10μF electrolytic

capacitor placed in parallel to the R2 resistor (See Fig. 5)

VIN

+

10μF

UTC LD1117/A

IN

OUT

ADJ

R1

120Ω

+

VREF

VOUT

10μF

R2

FIG.4 Adjustable Output Voltage Application Circuit

FIG.5 Adjustable Output Voltage Application with improved Ripple Rejection.

UNISONIC TECHNOLOGIES CO., LTD

www.unisonic.com.tw

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