LD1117ADT28TR(2004) Просмотр технического описания (PDF) - STMicroelectronics

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LD1117ADT28TR
(Rev.:2004)

LOW DROP FIXED AND ADJUSTABLE POSITIVE VOLTAGE REGULATORS

STMicroelectronics 

Figure 9: Post-Regulated Dual Supply

LD1117A SERIES

LD1117A ADJUSTABLE: APPLICATION NOTE

The LD1117A 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

electrolytic capacitor placed in parallel to the R2

resistor (see Fig. 10).

9/17

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