Datasheet

LT6110
15
6110fa
For more information www.linear.com/LT6110
applicaTions inForMaTion
In Figure 3 R
F
is split into R
FA
and R
FB
. V
REG
is the no-load
quiescent output voltage of the regulator. The design of
these two feedback resistors follows:
R
FA
=
V
DROP
I
IOUT
I
IOUT
can be sized to be 100µA at full load current and
only this resistor creates the V
DROP
compensation voltage.
R
FB
=
V
REG
– V
FB
I
Q
– R
F
A
I
Q
is the no-load quiescent current flowing through the
resistor string.
Figure 4 is a circuit using the LT6110 and a three resistor
voltage setting technique to compensate the voltage loss
due to a 2A load connected through 6 feet of stranded
copper wire (300mΩ of wire resistance). The LT3980 is a
2A buck switching regulator programmed for 5V out with
only 10µA of current, I
Q
, through the feedback resistor
string when there is no load current. At the full 2A load the
LT6110 uses the internal 20mΩ sense resistor to produce
100µA at IOUT to compensate for the 640mV drop.
Compensating a Current Referenced
Regulator Power Source
Figure 5 shows a cable drop compensation circuit using a
current referenced regulator, the LT3080. A precision 10µA
set current, I
SET
, is sourced through two series connected
resistors to program the output voltage for the remote
load. To compensate for the load connecting cable drop
requires sourcing an additional current into this resistor
pair to increase the output voltage. The LT6110 provides
a sourced current at the IMON pin which is directly pro
-
portional to the current flowing to the load. This current
is three times the normal IOUT current. The following
equations are used to design this cir
cuit:
V
REG
= I
SET
• (R
SET1
+ R
SET2
)
V
SENSE
= I
LOAD
• R
SENSE
I
+IN
=
V
SENSE
R
IN
I
IMON
= 3 • I
+IN
Figure 4. LT3980 Buck Regulator with LT6110 Cable Drop Compensation Circuit
15k
1.5nF
0.1µF
100pF
V
IN
V
IN
BD
RUN/SS
0.47µF
47µF
10pF
V
REG
6.49k
422k
10µH
DFLS240L
LT3980
GND
100k
80.6k
V
FB
= 0.79V
97.6k
BOOST
NC +IN
IOUT
LT6110
V
+
RS
IMON
–INV
–
20mΩ
PGOOD SW
R
T
DA
V
C
FB
100µF
6110 F04
5V
2A
R
WIRE
0.3Ω
402Ω