LT3012 LINER [Linear Technology], LT3012 Datasheet - Page 8

• Manufacturer Part Number: LT3012
• Description: 250mA, 4V to 80V Low Dropout Micropower Linear Regulator
• Manufacturer: LINER [Linear Technology]

PIN FUNCTIONS
LT3012
NC (Pins 1, 6, 7, 9, 12)/(Pins 2, 7, 10, 12, 15): No Con-
nect. These pins have no internal connection; connecting
NC pins to a copper area for heat dissipation provides a
small improvement in thermal performance.
OUT (Pins 2, 3)/(Pins 3, 4): Output.The output supplies
power to the load. A minimum output capacitor of 3.3μF
is required to prevent oscillations. Larger output capaci-
tors will be required for applications with large transient
loads to limit peak voltage transients. See the Applications
Information section for more information on output ca-
pacitance and reverse output characteristics.
ADJ (Pin 4)/(Pin 5): Adjust. This is the input to the error
amplifi er. This pin is internally clamped to ±7V. It has a
bias current of 30nA which fl ows into the pin (see curve
of ADJ Pin Bias Current vs Temperature in the Typical
Performance Characteristics). The ADJ pin voltage is
1.24V referenced to ground, and the output voltage range
is 1.24V to 60V.
GND (Pins 5, 13)/(Pins 1, 6, 8, 9, 16, 17): Ground. The
exposed backside of the package is an electrical connection
for GND. As such, to ensure optimum device operation and
thermal performance, the exposed pad must be connected
directly to pin 5/pin 6 on the PC board.
APPLICATIONS INFORMATION
The LT3012 is a 250mA high voltage low dropout regula-
tor with micropower quiescent current and shutdown.
The device is capable of supplying 250mA at a dropout
voltage of 400mV. The low operating quiescent current
(40μA) drops to 1μA in shutdown. In addition to the
low quiescent current, the LT3012 incorporates several
protection features which make it ideal for use in bat-
tery-powered systems. The device is 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
LT3012 acts like it has a diode in series with its output
and prevents reverse current fl ow.
8
(DFN Package/TSSOP Package)
SHDN (Pin 8)/(Pin 11): Shutdown. The SHDN pin is used
to put the LT3012 into a low power shutdown state. The
output will be off when the ⎯ S HDN pin is pulled low. The
SHDN pin can be driven either by 5V logic or open-collector
logic with a pull-up resistor. The pull-up resistor is only
required to supply the pull-up current of the open-collec-
tor gate, normally several microamperes. If unused, the
SHDN pin must be tied to a logic high or to V
IN (Pins 10, 11)/(Pins 13,14): 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 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 1μF to 10μF is
suffi cient. The LT3012 is designed to withstand reverse
voltages on the IN pin with respect to ground and the OUT
pin. In the case of a reversed input, which can happen if
a battery is plugged in backwards, the LT3012 will act as
if there is a diode in series with its input. There will be no
reverse current fl ow into the LT3012 and no reverse volt-
age will appear at the load. The device will protect both
itself and the load.
Adjustable Operation
The LT3012 has an output voltage range of 1.24V to 60V.
The output voltage is set by the ratio of two external resis-
tors as shown in Figure 1. The device servos the output to
maintain the voltage at the adjust pin at 1.24V referenced
to ground. The current in R1 is then equal to 1.24V/R1
and the current in R2 is the current in R1 plus the ADJ
pin bias current. The ADJ pin bias current, 30nA at 25°C,
fl ows through R2 into the ADJ pin. The output voltage
can be calculated using the formula in Figure 1. The value
of R1 should be less than 250k to minimize errors in the
output voltage caused by the ADJ pin bias current. Note
that in shutdown the output is turned off and the divider
current will be zero.
IN
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