Datasheet

LT6110
12
6110fa
For more information www.linear.com/LT6110
applicaTions inForMaTion
+IN and –IN
The +IN and –IN inputs can have a maximum differential
voltage equal to the supply voltage. This protects the
LT6110 if the –IN pin (the remote load side) is accidentally
shorted to ground. In this case, the IOUT current must be
limited to less than 2mA (see the Limiting the Regulator
Boost Voltage section).
The +IN to IOUT voltage must be kept below 36V to avoid
the breakdown of internal transistors.
IOUT and IMON
The IOUT to IMON outputs can have a maximum differ
-
ential voltage
of 36V for IOUT above IMON and –0.6V for
IOUT below IMON. A 36V Zener diode can be connected
from IOUT to IMON to prevent damage to the output NPN
transistor in the event of a fault condition. In this case, a
low leakage Zener diode should be used to reduce error
in the IOUT current.
RS (Internal R
SENSE
)
The internal sense resistor can reliably carry a continuous
current up to 3A and transient currents of 5A for up to 0.1
seconds. For currents greater than this, an external sense
resistor should be used. The internal sense resistor has a
temperature coefficient similar to copper.
DESIGN PROCEDURE
The design
of an LT6110 compensation circuit is a simple
3-step
process. To start, the following parameters must
be known:
R
WIRE
, total wire resistance to the load
R
SENSE
, resistor used to sense the load current
R
F
, feedback resistor of the regulator
I
LOADMAX
, maximum load current
The circuit in Figure 2 shows an adjustable voltage regula-
tor with
an LT6110 compensation circuit. The regulator
has
an internal ground referred voltage reference to set
its output voltage. There are two wires to the load, one
source (R
SWIRE
) and one return (R
RWIRE
). Since it is the
most common configuration it will be used for the follow-
ing design
example. Current referenced regulators and
regulators
with an output referred reference are covered
in later sections.
Step 1: Determine the drop in voltage at the load due to
the wire resistance and sense resistor at the maximum
load current.
V
DROP
= (R
SWIRE
+ R
RWIRE
+ R
SENSE
) • I
LOADMAX
V
DROP
= (0.125Ω + 0.125Ω + 0.02Ω) • 2A = 0.54V
IOUT
+IN –IN
R
IN
I
+IN
I
LOADMAX
= 2A
LT6110
V
+
V
–
RS
R
F
3.65k
R
G
IMON
+
–
V
IN
V
REG
I
LOAD
R
SWIRE
0.125Ω
V
DROP
V
DROP
R
RWIRE
0.125Ω
6110 F02
R
SENSE
20mΩ
V
SENSE
+
–
FB
REGULATOR
V
LOAD
LOAD
CIRCUIT
OR
BATTERY
+
–
Figure 2. 2-Wire Compensation, One Wire Is Connected to the Load and One Wire Is the Ground Return Wire