Datasheet

LT6110
27
6110fa
For more information www.linear.com/LT6110
applicaTions inForMaTion
The maximum operating ambient temperature T
AMAX
is
equal to T
JMAX
– θ
JA
• Power.
T
JMAX
is 150°C and θ
JA
is 195°C/W for a TSOT-23 pack-
age and
T
JMAX
is 150°C and θ
JA
is 80.6°C/W for a DFN package.
T
AMAX
= 150°C – 0.301W • 195°C/W = 91°C for the TSOT-
23 package and
T
AMAX
= 150°C – 0.301W • 80.6°C/W = 126°C for the
DFN package.
Limiting the Regulator Boost Voltage (V
REGMAX
)
In some wire drop compensation applications it may be
necessary to limit the maximum voltage at the regulator
output to ensure the safe operation of all load circuitry.
Adding a resistor, R
IOUT
, in series with the output pin limits
the maximum compensation current. This in turn limits
the maximum voltage boosting at the regulator output,
V
REGMAX
. The increasing I
IOUT
current through R
IOUT
drops the voltage at the IOUT pin to a minimum level and
limits the maximum IOUT current (refer to the Minimum
IOUT to IMON Voltage vs Temperature graph under Typical
Performance Characteristics). If the limited IOUT current
is greater than 1mA, a 0.1µF capacitor should be placed
from the IOUT pin to ground to ensure stable operation.
The R
IOUT
resistor limits the regulator’s voltage to an
arbitrary value higher than V
LOAD
+ R
FA
• I
IOUT
.
Design Procedure:
1. Select a V
REGMAX
voltage > V
LOAD
+ R
FA
• I
IOUT
.
2. Calculate R
IOUT
:
R
IOUT
=
V
LOAD
–
R
FA
R
G
• V
FB
⎛
⎝
⎜
⎞
⎠
⎟
•R
FA
V
REGMAX
– V
LOAD
Example: Limit the output of a 5V regulator to less than 6V.
V
LOAD
= 5V, I
LOADMAX
= 2A and I
IOUT
= 100µA.
R
FA
= 6.49k, R
FB
= 422k and R
G
= 80.6k, R
IN
= 402Ω, V
FB
= 0.79V (Figure 4).
Calculate R
IOUT
:
R
IOUT
=
5 –
6490
80600
• 0.79
⎛
⎝
⎜
⎞
⎠
⎟
• 6490
6 – 5
R
IOUT
= 32k and 5.649V ≤ V
REGMAX
≤ 6V.
Limiting V
IOUT
The absolute maximum voltage at the IOUT pin (V
IOUT
) is
36V. If V
IOUT
is greater than 36V then a Zener diode from
the IOUT pin to the regulator resistors and a resistor from
the IOUT pin to V
–
can limit the V
IOUT
voltage to ≤36V.
The Zener diode voltage, V
ZENER
, is typically specified as
a nominal voltage with a minimum and a maximum. For
limiting V
IOUT
, use the minimum Zener voltage rating,
V
ZENERMIN
. V
ZENERMIN
is typically specified at a current
of 2mA to 5mA and at the low LT6110 I
IOUT
currents
(≤1mA), the actual V
ZENERMIN
can be up to 2V less than
the minimum voltage listed in a diode data sheet. Therefore
select a Zener diode with a minimum voltage at least 2V
Figure 17. LT6110 Power Dissipation
IOUT
+IN –IN
R
IN
LT6110
V
+
V
–
RS
R
FA
R
FB
R
IOUT
R
G
IMON
+
–
V
IN
V
REG
I
LOAD
I
IOUT
R
WIRE
V
DROP
20mΩ
6110 F18
FB
SWITCHING
REGULATOR
V
LOAD
LOAD
IOUT
+IN –IN
R
IN
LT6110
V
+
V
–
RS
IMON
+
–
V
IN
V
REG
I
LOAD
I
OUT
I
+IN
I
SUPPLY
V
IOUT
20mΩ
6110 F17
SWITCHING
REGULATOR
FB
Figure 18. Limiting Regulator Voltage Boost (V
REGMAX
)