SPX1585
Basic Adjustable Regulator
Output Voltage
Consider Figure 2. The resistance R
1
generates a constant
current flow, normally the specified load current of 10mA. This
current will go through the resistance R
2
to set the overall output
voltage. The current I
ADJ
is very small and constant. Therefore
its contribution to the overall output voltage is very small and
can generally be ignored
.
Load Regulation
Parasitic line resistance can degrade load regulation. In order
not to affect the behavior of the regulator, it is best to connect
directly the R
1
resistance from the resistor divider to the case,
and not to the load. For the sa
me reason, it is best to connect
the resistor R
2
to the Negative side of the load.
Output Voltage
The fixed voltage LDO voltage regulators are simple to use
regulators since the V
OUT
is preset to the specifications. It is
important,
however, to provide the proper output capacitance
for stability and improvement. For most operating conditions a
capacitance of 22uF tantalum or 100uF electrolytic will ensure
stability and prevent oscillation.
SPX1585
Fig.2 Basic Adjustable Regulator
V
REF
R
1
R
2
V
OUT
= V
REF
* ( 1 + R
2
/R
1
) + I
ADJ
* R
2
I
ADJ
ADJ
V
IN
V
OUT
50uA
SPX1585
Fig.3 Basic Adjustable Regulator
V
IN
R
2
R
1
Connect R
2
to Load
R
L
Connect R
1
to
Case of Regulator
R
P
Parasitic Line
Resistance
V
OUT
ADJ
SPX1585
Basic Fixed Regulator
V
IN
V
OUT
5V
C1
10uF
C2
10uF
3.3V
4/7
