Datasheet

V
OUT
V
IN
I1
10 µF
V
REF
10 µF
R1
R2
I
ADJ
V
IN
V
OUT
ADJ
V
OUT
= V
REF
(1 +
R2) + I
ADJ
R2
R2
R1
LMS1585A , LMS1587
SNVS061G –MONTH 2003–REVISED JULY 2013 www.ti.com
APPLICATION NOTE
OUTPUT VOLTAGE
The adjustable version develops at 1.25V reference voltage, (VREF), between the output and the adjust terminal.
As shown in Figure 3, this voltage is applied across resistor R1 to generate a constant current I1. This constant
current then flows through R2. The resulting voltage drop across R2 adds to the reference voltage to sets the
desired output voltage.
The current I
ADJ
from the adjustment terminal introduces an output error. But since it is small (120μA max), it
becomes negligible when R1 is in the 100Ω range.
For fixed voltage devices, R1 and R2 are integrated inside the devices.
Figure 3. Basic Adjustable Regulator
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