Datasheet

LT6110
18
6110fa
For more information www.linear.com/LT6110
applicaTions inForMaTion
ERROR SOURCES
The LT6110 output current allows for reliable compensa-
tion for
small or large connection wiring voltage drops.
The
voltage regulation at the remote load can be improved
dramatically using the LT6110. With properly designed
cable drop compensation the load voltage variation will
be reduced to only the error in the compensation voltage
created. This error voltage is a combination of several
circuit characteristics.
The first step in determining the error is to determine the
amount of compensation voltage required. Figure 7 is an
example circuit that indicates the various error terms to be
considered. For this example a 5V regulator will provide
2A maximum to a remote load connected through 6 feet
(~2 meters) of 28AWG (7/36) stranded hook-up wire. Us
-
ing 28AWG provides
the thinnest, low cost wire suitable
for this application. Using wire resistance Table 4, the DC
resistance of 6 ft of 28AWG (7/36) can be determined:
R
WIRE
= 6ft • 63.3mΩ/ft = 380mΩ. At 2A full load current
this will create a V
DROP
of 760mV. Without the LT6110
compensator the regulation of the 5V supply at the load
would be 15%.
This example design will use the internal 20mΩ sense
resistor of the LT6110 and will assume
that the feedback
r
esistor network in the voltage regulator cannot be modified
or optimized for compensation. The R
F
used to develop the
compensation voltage is fixed at 10k and the reference volt-
age at
the feedback node where the compensator connects
is
0.8V. From these parameters the basic compensation
circuit can be easily designed:
V
SENSE
at full load is 20mΩ • 2A or 40mV
The compensation voltage, V
COMP
, required is:
V
WIRE
+ V
SENSE
, 760mV + 40mV, or 800mV
To create this compensation voltage will require a current
through feedback resistor R
F
of V
COMP
/R
F
, 800mV/10k
for an I
IOUT
of 80µA. This is well within the most accurate
range of current (30µA to 300µA) flowing into the IOUT pin.
1k
IOUT
V
IOUT
V
–
–IN
IMON
V
IMON
NC
LT6110
+IN
±V
OS
*
R
IN
V
COMP
≥0.1µF
0.8V
I
+IN
I
+IN
V
LOAD
6 FT, AWG 28
7/36 STRANDED
WIRE
6110 F07
RSV
+
R
SENSE
0.020Ω
R
WIRE
+ V
WIRE
–
I
LOAD
I
IOUT
±IOUT
ERROR
±IMON
ERROR
+ V
SENSE
–
+
V
DROP
–
+
–
OUT
R
F
10k
V
IN
V
FB
REGULATOR
GND
IN
V
REG
LOAD
BIAS
+
–
+
–
I
IMON
*± V
OS
= V
OS
+
Δ
V
OS
ΔI
+IN
+
Δ
V
OS
ΔV
IOUT
+
Δ
V
OS
ΔV
IMON
+ T
C
V
OS
• ΔT
Figure 7. Cable Drop Compensation Error Sources