LT1962 Series
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U
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PI FU CTIO S
R
P
8
1
SHDN pin can be driven either by 5V logic or open-
collector logic with a pull-up resistor. The pull-up resistor
is required to supply the pull-up current of the open-
collector gate, normally several microamperes, and the
SHDN pin current, typically 1µA. If unused, the SHDN pin
must be connected to VIN. The device will not function if
the SHDN pin is not connected.
IN
OUT
LT1962
5
2
+
+
SHDN SENSE
LOAD
V
IN
GND
4
R
P
1962 F01
NC (Pins 6, 7): No Connect. These pins are not internally
connected. For improved power handling capabilities,
these pins can be connected to the PC board.
Figure 1. Kelvin Sense Connection
pin.TheADJpinvoltageis1.22Vreferencedtogroundand
the output voltage range is 1.22V to 20V.
IN (Pin 8): Input. Power is supplied to the device through
the IN pin. A bypass capacitor is required on this pin if the
device is more than six inches away from the main input
filter 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 1µF to 10µF is sufficient. The
LT1962 regulators are designed to withstand reverse
voltages on the IN pin with respect to ground and the OUT
pin. In the case of a reverse input, which can happen if a
battery is plugged in backwards, the device will act as if
there is a diode in series with its input. There will be no
reverse current flow into the regulator and no reverse
voltage will appear at the load. The device will protect both
itself and the load.
BYP (Pin 3): Bypass. The BYP pin is used to bypass the
reference of the LT1962 to achieve low noise performance
from the regulator. The BYP pin is clamped internally to
±0.6V (one VBE). A small capacitor from the output to this
pin will bypass the reference to lower the output voltage
noise. A maximum value of 0.01µF can be used for
reducing output voltage noise to a typical 20µVRMS over a
10Hz to 100kHz bandwidth. If not used, this pin must be
left unconnected.
GND (Pin 4): Ground.
SHDN (Pin 5): Shutdown. The SHDN pin is used to put the
LT1962 regulators into a low power shutdown state. The
output will be off when the SHDN pin is pulled low. The
W U U
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APPLICATIO S I FOR ATIO
TheLT1962seriesare300mAlowdropoutregulatorswith
micropowerquiescentcurrentandshutdown.Thedevices
are capable of supplying 300mA at a dropout voltage of
300mV. Output voltage noise can be lowered to 20µVRMS
over a 10Hz to 100kHz bandwidth with the addition of a
0.01µFreferencebypasscapacitor. Additionally, therefer-
ence bypass capacitor will improve transient response of
the regulator, lowering the settling time for transient load
conditions. The low operating quiescent current (30µA)
drops to less than 1µA in shutdown. In addition to the low
quiescentcurrent, theLT1962regulatorsincorporatesev-
eral protection features which make them ideal for use in
battery-powered systems. The devices are protected
against both reverse input and reverse output voltages. In
battery backup applications where the output can be held
up by a backup battery when the input is pulled to ground,
the LT1962-X acts like it has a diode in series with its
output and prevents reverse current flow. Additionally, in
dual supply applications where the regulator load is re-
turnedtoanegativesupply,theoutputcanbepulledbelow
groundbyasmuchas20Vandstillallowthedevicetostart
and operate.
Adjustable Operation
The adjustable version of the LT1962 has an output
voltage range of 1.22V to 20V. The output voltage is set by
theratiooftwoexternalresistorsasshowninFigure2.The
device servos the output to maintain the ADJ pin voltage
at 1.22V referenced to ground. The current in R1 is then
equalto1.22V/R1andthecurrentinR2isthecurrentinR1
11
Linear [ Linear ]
