Datasheet

LD1117 SERIES
17/27
Figure 10: Post-Regulated Dual Supply
LD1117 ADJUSTABLE: APPLICATION NOTE
The LD1117 ADJUSTABLE has a thermal
stabilized 1.25±0.012V reference voltage between
the OUT and ADJ pins. I
ADJ
is 60µA typ. (120µA
max.) and ∆I
ADJ
is 1µA typ. (5µA max.).
R1 is normally fixed to 120Ω. From figure 11 we
obtain:
V
OUT
= V
REF
+ R2 (I
ADJ
+I
R1
) = V
REF
+ R2 (I
ADJ
+V
REF
/R1) = V
REF
(1 + R2 / R1) + R2 x I
ADJ
.
In normal application R2 value is in the range of
few kohm, so the R2 x I
DJ
product could not be
considered in the V
OUT
calculation; then the
above expression becomes:
V
OUT
= V
REF
(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. 12).