Datasheet

LT6110
14
6110fa
For more information www.linear.com/LT6110
applicaTions inForMaTion
Without the compensation circuit (no R
SENSE
) the load
regulation in percent would be,
LoadReg
UNCOMP
%
( )
=
–0.5V
5V
• 100 = –10
%
The regulator’s output will also change due to its own
load regulation effects (per the regulator’s specification).
In general, this change in voltage is small compared to
the wire-drop, and can be ignored. If it is considered to
be a significant source of error, it can be included as part
of the wire-drop compensation. To include the regulator’s
load regulation effect, simply add the voltage drop due to
the regulator’s load regulation at I
LOADMAX
to V
DROP
, when
calculating the compensation circuit parameters.
PCB Trace Resistance
Printed circuit trace resistance between the output of the
regulator and the load will cause additional voltage drops.
As with the regulator’s load regulation effects, these drops
can be compensated for by adding them to V
DROP
when
calculating the compensation circuit parameters. This also
allows the use of narrower traces to deliver power to the
load and still retain good load regulation. See the PCB
Copper Resistor section for more information on how to
determine trace resistance.
Kelvin Sense Connection to R
SENSE
To reduce R
SENSE
error due to trace resistance, the –IN pin
and R
IN
resistor should be connected as close to R
SENSE
as possible, as reflected in Figure 2.
Compensating a Low Quiescent Current Design
Switching
regulator circuits are used for high power ef
-
ficiency. Many are required to maintain high efficiency at
light or no load conditions. In these cases the quiescent
operating current is minimized by using larger valued
resistors to program the output voltage so very little cur
-
rent is wasted in the feedback network.
A
large value for resistor R
F
could require too low of a
compensating current (<30µA) from IOUT of the LT6110.
In this situation the feedback resistor, R
F
, can be split
into two resistor values. A small value resistor to conduct
I
IOUT
from the LT6110 and compensate the output voltage
when the load current is high, and a second, larger valued
resistor, to keep the no-load quiescent current drain low.
With this arrangement, as shown in Figure 3, I
IOUT
can
be designed for 100µA to preserve V
DROP
compensation
accuracy. At no load the quiescent current drawn through
the feedback resistors, I
Q
, can be kept very low.
IOUT
+IN –IN
R
IN
LT6110
V
+
V
–
RS
R
FA
R
FB
R
G
IMON
+
–
V
IN
V
REG
I
LOAD
R
WIRE
V
LOAD
6110 F03
20mΩ
+
–
FB
I
Q
<30µA
REGULATOR
LOAD
I
+IN
V
SENSE
Figure 3. Low Quiescent Current Wire Compensation Using Three Regulator Resistors