Datasheet

LT6110
16
6110fa
For more information www.linear.com/LT6110
applicaTions inForMaTion
To compensate for V
DROP
at I
LOAD(MAX)
set:
R
SET2
=
V
DROP
I
IMON
and
R
SET1
=
V
REG
I
SET
– R
SET2
As an example, to compensate this 3V regulator for a
500mV cable drop with a 1A load current set I
+IN
for 100µA
for best accuracy. Then:
R
SET1
= 301k and R
SET2
= 1.69k using nearest 1%
tolerance standard resistor values.
R
IN
=
1A • 20m
Ω
100µA
= 200
Ω
Compensating an Output Referred
Adjustable Voltage Regulator
Many
adjustable voltage regulators are biased from a
floating voltage reference that sets a voltage between the
output pin and an adjust pin. Three terminal fixed voltage
regulators can also be made adjustable by biasing up
the ground terminal. A feedback resistor string is used
to program the output voltage. The amount of current
through these resistors is scaled to a level to minimize
error caused by any bias current at the adjust pin.
As shown in Figure 6, an LT6110 can add cable drop
compensation by using the current sourced from the IMON
pin. To preserve accuracy the voltage at IMON should be
kept within 5V of V
–
, or ground in this example. By using
two resistors for the bottom resistor in the voltage regu-
lator programming
string, the cable drop compensation
voltage can be added to a voltage near ground appearing
at the IMON pin.
The following equations are used to design this circuit
using an LT1083, 7A adjustable voltage regulator:
V
REF
= 1.25V between OUT and ADJ pins, I
ADJ
= 75µA typ

I
SET
=
V
REF
R1
 I
ADJ
V
LOAD
(I
LOAD
= 0) = (I
SET
+ I
ADJ
) • (R2 + R
G
) + V
REF
V
SENSE
= I
LOAD
• R
SENSE
I
+IN
=
V
SENSE
R
IN
I
IMON
= 3 • I
+IN
As an example, Figure 6 is a 12V regulator for a 5A remotely
connected load with a wire resistance of 250mΩ. For the
higher load current an external 25mΩ sense resistor is
used. The cable drop voltage for such a high current ap
-
plication is significant:
V
DROP
= I
LOAD(MAX)
• (R
SENSE
+ R
WIRE
) = 5A • 275mΩ
= 1.375V
Figure 5. Wire Loss Compensation Using a Current Referenced LDO
IOUT
+IN –IN
R
IN
200Ω
LT6110
V
+
V
–
RS
IMON
I
MON
I
MON
= 3 I
IN
+
+
–
V
IN
R
WIRE
0.5Ω
V
LOAD
3V
1A
6110 F05
20mΩ
IN
LT3080
I
SET
SET
R
SET1
301k
R
SET2
1.69k
V
REG
LOAD
+
–