Datasheet

LT6110
28
6110fa
For more information www.linear.com/LT6110
applicaTions inForMaTion
greater than the calculated V
ZENERMIN
voltage.
V
ZENERMIN
V
REGMAX
V
IOUT
+
I
IOUT
R
FA
+
R
FA
R
G
V
FB
V
REGMAX
= V
LOAD
+ I
LOADMAX
• (R
SENSE
+ R
WIRE
).
Example: Limit V
IOUT
to 20V.
V
LOAD
= 48V and I
LOADMAX
= 2A, R
WIRE
= 1Ω.
R
SENSE
= 20mΩ, R
FA
= 20.5k, R
FB
= 453k, R
G
= 12.4k, R
IN
= 402Ω, V
FB
= 1.223V, I
IOUT
= 100µA.
Calculate V
REGMAX
= 48 + 2(0.02 + 1) = 50.04V.
Calculate V
ZENERMIN
:
V
ZENERMIN
50.04
20+ 100 10
6
( )
20.5 10
3
( )
+
20.5 10
3
12.4 10
3
1.223
V
ZENERMIN
= 26V.
The minimum Zener diode voltage must be ≥28V.
Setting the Wire Compensation Threshold
With light load currents, wire drop compensation may not
be desirable. An additional resistor, R
IN2
, from the +IN
pin to ground provides the option to set a load current
threshold, I
LOADCOMP
, for the start of wire drop compen-
sation. When
the load current is equal to I
LOADCOMP
the
maximum error in voltage at the load occurs. For I
LOAD
greater than I
LOADCOMP
the error in voltage at the load
decreases to zero at I
LOADMAX
.
Design Procedure:
1. Choose a threshold current.
2. Calculate R
IN1
and R
IN2
:
R
IN1
=
I
LOADMAX
R
SENSE
I
IOUT
V
LOAD
+
I
LOADMAX
R
WIRE
I
IOUT
V
LOAD
I
LOADCOMP
R
SENSE
1
R
IN2
=
V
LOAD
I
LOADCOMP
R
SENSE
1
R
IN1
Example: Design the start of wire drop compensation at 1A.
V
LOAD
= 5V, I
LOADMAX
= 3.5A, R
WIRE
= 0.25Ω, R
SENSE
=
25mΩ and I
IOUT
= 100µA.
Figure 19. Limiting the Voltage at the IOUT Pin (V
OUT
≤ 36V)
Figure 20. Setting the Wire Drop Compensation Threshold
IOUT
+IN –IN
R
IN
LT6110
V
+
V
RS
R
FA
R
FB
R
G
R
Z
10M
IMON
+
V
IN
V
REG
I
LOAD
R
WIRE
V
DROP
20mΩ
6110 F19
FB
SWITCHING
REGULATOR
V
LOAD
V
ZENER
V
IOUT
LOAD
IOUT
+IN –IN
R
IN1
LT6110
I
LOADMAX
I
LOAD
V
REG
V
REGMAX
I
LOADCOMP
WIRE DROP
COMPENSATION
THRESHOLD
V
+
V
RS
R
FA
R
FB
R
G
IMON
R
IN2
+
V
IN
V
REG
I
LOAD
R
WIRE
V
DROP
20mΩ
6110 F20
FB
SWITCHING
REGULATOR
V
LOAD
V
IOUT
LOAD
I
OUT