Preliminary
APPLICATIONS INFORMATION
1.25V to 10.7V Adjustable Regulator
EP1117
Fixed Voltage Model—Basic Connections.
* Needed if device is far from filter capacitors
V
out
=
1.250
V
×
R
1
+
R
2
R
1
Output Voltage
The EP1117 develops a 1.25V reference voltage between the output and the adjust terminal. By placing a
resistor between these two terminals, a constant Current is caused to flow through R1 and down through R2 to
set the overall output voltage. Normally this current is chosen to be the specified minimum load current of 10mA.
For fixed voltage devices R1 and R2 are included in the device.
⎛
R
2
⎞
V
out
=
V
REF
⎜
1
+
⎟ +
I
ADJ
R
2
⎝
R
1
⎠
Figure 1. Basic Adjustable Regulator
Load Regulation
When the adjustable regulator is used, load regulation will be limited by the resistance of the wire
connecting the regulator to the load. The datasheet specification for load regulation is measured at
the output pin of the EP1117. Best load regulation is obtained when the top of the resistor divider
(R1) is tied directly to the output pin of the device, not to the load. For fixed voltage devices, the top
of R1 is internally connected to the output, and the ground pin can be connected to low side of the
load. If R1 were connected to the load, RP is multiplied by the divider ratio, the effective resistance
between the regulator and the load would be: Rp X (1+ R2/R1 ), where Rp is Parasitic Line
Resistance.
Rev.01
5/8
ETC [ ETC ]
