LT3081
10
3081fc
block DiagraM
–
+
50µA
IN
I
MON
TEMPERATURE
DEPENDENT
CURRENT SOURCE
1µA/°C
SET
I
LIM
OUT
3081 BD
PROGRAMMABLE
CURRENT LIMIT
CURRENT
MONITOR
I
MON
= I
LOAD
/5000
TEMP
pin FuncTions
IN:
Input. This pin supplies power to regulate internal
circuitry and supply output load current. For the device
to operate properly and regulate, the voltage on this pin
must be between the dropout voltage and 36V above the
OUT pin (depending on output load current, see Dropout
Voltage Specifications).
OUT:
Output. This is the power output of the device. The
LT3081 requires a 5mA minimum load current for proper
output regulation.
TEMP:
Temperature Output. This pin delivers a current
proportional to the internal average junction temperature.
Current output is 1µA/°C for temperatures above 5°C. The
TEMP pin output current typically equals 25µA at 25°C.
The output of the TEMP pin is valid for voltages from V
OUT
+ 0.4V to V
OUT
– 40V. If unused, connect this pin to OUT.
I
LIM
:
Current Limit Program. A resistor between this pin
and OUT programs output current limit to a level propor-
tional to resistor value. Connect this resistor directly to
OUT at the pins of the package. The typical ratio of current
limit to resistor value is 360mA/kΩ with a 450Ω offset.
If programmable current limit is not used, leave this pin
open; the internal current limit of the LT3081 is still active,
keeping the device inside safe operating limits. External
voltage drops between the current limit resistor and V
OUT
will affect the current limit. Keep drops below 1mV.
I
MON
:
Output Current Monitor. The I
MON
pin sources a
current typically equal to I
LOAD
/5000 or 200µA per amp of
output current. Terminating this pin with a resistor to GND
produces a voltage proportional to I
LOAD
. For example,
at I
LOAD
= 1.5A, I
MON
typically sources 300µA. With a
1k resistor to GND, this produces 300mV. The output
of the I
MON
pin is valid for voltages from V
OUT
+ 0.4V to
V
OUT
– 40V. If unused, connect this pin to OUT.
SET:
Set. This pin is the error amplifier’s noninverting
input and also sets the operating bias point of the circuit.
A fixed 50μA current source flows out of this pin. A single
external resistor programs V
OUT
. Output voltage range is
0V to 34.5V.
Exposed Pad/Tab:
Output. The exposed pad of the DF and
FE packages and the tab of the R and T7 packages are tied
internally to OUT. As such, tie them directly to OUT (Pins
1-4/Pins 1-5, 8, 9, 16/Pin 4/Pin 4) at the PCB. The amount
of copper area and planes connected to OUT determine
the effective thermal resistance of the packages.
NC:
No Connection. No connect pins have no connection
to internal circuitry and may be tied to IN, OUT, GND or
floated.