Datasheet

LT6110
20
6110fa
For more information www.linear.com/LT6110
applicaTions inForMaTion
FREQUENCY RESPONSE AND TRANSIENTS
The LT6110 has a –3dB bandwidth of 180kHz. This
smooth frequency response is shown in Figure 8. This
defines the response time from the sensed input voltage
to the compensation output currents. Power sources will
typically have a large output capacitance making their
loop response bandwidth much slower than the LT6110.
The cable drop compensation loop is much faster than
the power source so there should be little impact on loop
stability in driving a remote load.
For fast or step change variations in load current some
transients will be observed at the power source output
and at the remote load due to the finite reaction time of
the compensation loop. The amount of voltage transient
seen will depend mostly on the size and quality of the
supply bypass capacitors used at each end of the load
connecting wire. An example of these transients is shown
in Figure9. Any ringing while settling out can be smoothed
by additional filtering components in the control loop. A
small feedback capacitor across the regulator feedback
resistor, R
F
, can provide effective smoothing of transients.
Specific values to use depend on the particular application
component values.
One important consideration
for transients is a sudden
open or removal of the load current from a high current
condition. There is a risk of overvoltage at the load before
the LT6110 can reduce the compensation voltage. A good
solution to this potential issue is to bypass the remote
load with a capacitance greater than the capacitance at the
output of the regulator or power source. Figure 10 shows
a load removal transient using a 100µF load. Fortunately
the amount of compensation in most applications should
not be so large as to cause a serious overvoltage risk but
should always be considered.
Table 1. Compensation Error Using Typical Variances Expected at 25°C.
FIGURE 7 DESIGN EXAMPLE. TOTAL V
DROP
TO COMPENSATE = 744mV,
I
+IN
= 74.6µA FOR MAXIMUM V
COMP
FOR MINIMUM V
COMP
TERM DESIGN VALUE/SPEC UNITS COMMENT/CALCULATION TYPICAL ERROR VALUE TYPICAL ERROR VALUE
R
SENSE
20 mΩ Internal Sense Resistor 7.50% 21.5 –7.50% 18.5
R
IN
499 Ω –0.5% 496.5 0.5% 501.5
V
OS
0 µV –100 –100 100 100
∆V
OS
/∆I
+IN
0 mV/mA Relative to I
+IN
= 100µA –0.15 –0.15 0.15 0.15
∆V
OS
/∆V
IOUT
0 mV/V Relative to V
IOUT
= 1.2V –0.005 –0.005 0.005 0.005
∆V
OS
/∆V
IMON
0 mV/V Relative to V
IMON
= 0V –0.3 –0.3 0.3 0.3
Total V
OS
V
OS
+ ∆V
OS
/∆I
+IN
(100µA – 80µA) + ∆V
OS
/∆V
IOUT
(1.2V – 0.8V) + ∆V
OS
/∆V
IMON
•0V
µV –105 105
I
IOUT
Error 0 % % IOUT Current Error Relative to I
+IN
0.5 0.5 –0.5 –0.5
I
IMON
Error 0 % % IMON Current Error Relative to 3 • I
+IN
1.5 1.5 –1.5 –1.5
Summary of Terms
V
SENSE
40 mV I
LOAD(MAX)
• R
SENSE
43 37
I
+IN
80.2 µA (V
SENSE
– Total V
OS
)/R
IN
86.8 73.6
I
IOUT
80.2 µA I
+IN
• (1 + I
IOUT
Error) 87.2 73.2
I
IMON
240.6 µA 3 • I
+IN
• (1 + I
IMON
Error) 264.4 219.6
R
F
10 kΩ Fixed Resistor Value in Power Source 0.5% 10.05 –0.5% 9.95
V
COMP
802 mV I
IOUT
• R
F
876 728
V
COMP
Error 0 % 9.2 –9.2
With Compensation
V
LOAD_ERROR
2 mV V
COMP
– V
DROP
76 –72
Load Regulation 0.03 % 1.52 –1.44