LD1117A データシートの表示（PDF） - STMicroelectronics

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LD1117A

LOW DROP FIXED AND ADJUSTABLE POSITIVE VOLTAGE REGULATORS

STMicroelectronics 

LD1117A/B SERIES

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 120Ω. From figure 7 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 IDJ 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 electrolitic capacitor placed in parallel to the R2 resistor (see

Fig.8)

FIGURE 7: Adjustable Output Voltage Application Circuit

FIGURE 8: Adjustable Output Voltage Application with improved Ripple Rejection

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