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LT3012EDE

250mA, 4V to 80V Low Dropout Micropower Linear Regulator

Linear Technology 

LT3012

PIN FUNCTIONS (DFN Package/TSSOP Package)

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

amplifier. This pin is internally clamped to ±7V. It has a

bias current of 30nA which flows 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.

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 ⎯SHDN 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 VIN.

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 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 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 flow into the LT3012 and no reverse volt-

age will appear at the load. The device will protect both

itself and the load.

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 flow.

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,

flows 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.

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