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/GND 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/GND 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. 8)
Fig.6 Adjustable Output Voltage Application Circuit
Fig.7 Adjustable Output Voltage Application Circuit (FOR MLCC)
Fig.8 Adjustable Output Voltage Application with improved Ripple Rejection.
UNISONIC TECHNOLOGIES CO., LTD
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