7

LT3014

3014fb

The LT3014 is a 20mA high voltage low dropout regulator

with micropower quiescent current and shutdown. The

device is capable of supplying 20mA at a dropout voltage

of 350mV. The low operating quiescent current (7

µA)

drops to 1

µA in shutdown. In addition to the low quiescent

current, the LT3014 incorporates several protection fea-

tures which make it ideal for use in battery-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 LT3014 acts

like it has a diode in series with its output and prevents

reverse current flow.

Adjustable Operation

The LT3014 has an output voltage range of 1.22V to 60V.

The output voltage is set by the ratio of two external

resistors as shown in Figure 2. The device servos the

output to maintain the voltage at the adjust pin at 1.22V

referenced to ground. The current in R1 is then equal to

1.22V/R1 and the current in R2 is the current in R1 plus

the ADJ pin bias current. The ADJ pin bias current, 4nA

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 1.62M 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. The device is tested

and specified with the ADJ pin tied to the OUT pin and a

5

µA DC load (unless otherwise specified) for an output

voltage of 1.22V. Specifications for output voltages greater

APPLICATIO S I FOR ATIO

than 1.22V will be proportional to the ratio of the desired

regulation for an output current change of 1mA to 20mA

regulation is:

(12V/1.22V) • (–13mV) = –128mV

IN

LT3014

OUT

ADJ

GND

3014 F01

R2

R1

+

R2

R1

OUTPUT RANGE = 1.22V TO 60V

1 +

()

•

Figure 1. Adjustable Operation

ADJ (Pin 4/Pin 2): Adjust. This is the input to the error

amplifier. This pin is internally clamped to

±7V. It has a

bias current of 4nA which flows into the pin (see curve of

ADJ Pin Bias Current vs Temperature in the Typical Perfor-

mance Characteristics). The ADJ pin voltage is 1.22V

referenced to ground, and the output voltage range is

1.22V to 60V.

OUT (Pin 5/Pin 1): Output. The output supplies power to

the load. A minimum output capacitor of 0.47

µF is re-

quired to prevent oscillations. Larger output capacitors

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.

Output Capacitance and Transient Response

The LT3014 is designed to be stable with a wide range of

output capacitors. The ESR of the output capacitor affects

stability, most notably with small capacitors. A minimum

output capacitor of 0.47

µF with an ESR of 3Ω or less is

recommended to prevent oscillations. The LT3014 is a

micropower device and output transient response will be

a function of output capacitance. Larger values of output

capacitance decrease the peak deviations and provide

improved transient response for larger load current

changes. Bypass capacitors, used to decouple individual

components powered by the LT3014, will increase the

effective output capacitor value.