LT3008 Series
11
3008fc
PIN FUNCTIONS
SHDN (Pin 1/Pin 5): Shutdown. Pulling the SHDN pin
low puts the LT3008 into a low power state and turns the
output off. If unused, tie the SHDN pin to V
IN
. The LT3008
does not function if the SHDN pin is not connected. The
SHDN pin cannot be driven below GND unless tied to the
IN pin. If the SHDN pin is driven below GND while IN is
powered, the output will turn on. SHDN pin logic cannot
be referenced to a negative rail.
GND (Pins 2, 3, 4/Pin 6): Ground. Connect the bottom
of the resistor divider that sets output voltage directly to
GND for the best regulation.
IN (Pin 5/Pin 4): Input. The IN pin supplies power to the
device. The LT3008 requires a bypass capacitor at IN if
the device is more than six inches away from the main
input fi lter capacitor. In general, the output impedance of
a battery rises with frequency, so it is advisable to include
a bypass capacitor in battery-powered circuits. A bypass
capacitor in the range of 0.1µF to 10µF will suffi ce. The
LT3008 withstands reverse voltages on the IN pin with
respect to ground and the OUT pin. In the case of a reversed
input, which occurs with a battery plugged in backwards,
the LT3008 acts as if a blocking diode is in series with its
input. No reverse current fl ows into the LT3008 and no
reverse voltage appears at the load. The device protects
both itself and the load.
OUT (Pin 6/Pins 2, 3): Output. This pin supplies power
to the load. Use a minimum output capacitor of 2.2µF
to prevent oscillations. Large load transient applications
require larger output capacitors to limit peak voltage
transients. See the Applications Information section for
more information on output capacitance and reverse-output
characteristics.
ADJ (Pin 7/Pin 1): Adjust. This pin is the error amplifi er’s
inverting terminal. Its 400pA typical input bias current
fl ows out of the pin (see curve of ADJ Pin Bias Current vs
Temperature in the Typical Performance Characteristics
section). The ADJ pin voltage is 600mV referenced to GND
and the output voltage range is 600mV to 44.5V.
NC (Pin 8, TSOT-23 Package Only): No Connect. Pin 8
is an NC pin in the TSOT-23 package. This pin is not tied
to any internal circuitry. It may be fl oated, tied to V
IN
or
tied to GND.
GND (Exposed Pad Pin 7, DFN Package Only): Ground. The
exposed pad (backside) of the DFN package is an electrical
connection to GND. To ensure optimum performance,
solder Pin 7 to the PCB and tie directly to Pin 6.
SENSE (Pin 7/Pin 1): Sense. For fi xed voltage versions of
the LT3008 (LT3008-1.2, LT3008-1.5, LT3008-1.8, LT3008-
2.5, LT3008-3.3, LT3008-5), the SENSE pin is the input to
the error amplifi er. Optimum regulation is obtained at the
point where the SENSE pin is connected to the OUT pin of
the regulator. In critical applications, small voltage drops
are caused by the resistance (RP) of PC traces between
the regulator and the load. These may be eliminated by
connecting the SENSE pin to the output at the load as
shown in Figure 1 (Kelvin Sense Connection). Note that
the voltage drop across the external PC traces add to the
dropout voltage of the regulator. The SENSE pin bias current
is 1µA at the nominal rated output voltage. The SENSE pin
can be pulled below ground (as in a dual supply system
where the regulator load is returned to a negative supply)
and still allow the device to start and operate.
(TSOT-23/DFN)
IN
SHDN
3008 F01
R
P
OUT
V
IN
SENSE
GND
LT3008
R
P
+
+
LOAD
Figure 1. Kelvin Sense Connection
