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LD1117 series

LD1117 Adjustable: Application note

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LD1117 Adjustable: Application note

The LD1117 Adjustable has a thermal stabilized 1.25±0.012V reference voltage between

the OUT and ADJ pins. IADJ is 60µA typ. (120µA max.) and ∆IADJ is 1µA typ. (5µA max.).

R1 is normally fixed to 120W. From figure 10 we obtain:

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

IADJ.

In normal application R2 value is in the range of few kohm, so the R2 x IADJ product could

not be considered in the VOUT calculation; then the above expression becomes:

VOUT = VREF (1 + R2 / R1).

In order to have the better load regulation it is important to realize a good Kelvin connection

of R1 and R2 resistors. In particular 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. 11).

Figure 10.

Adjustable output voltage application

Figure 11.

Adjustable output voltage application with improved ripple rejection

LD1117SC-R 데이터시트(PDF) 23 Page - STMicroelectronics