LT3013

12

3013fe

APPLICATIONS INFORMATION

3013 F01

R2

R1

+

R2

R1

OUTPUT RANGE = 1.24V TO 60V

1 +

IN

LT3013

OUT

ADJ

GND

Figure 1. Adjustable Operation

The LT3013 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

(65μA) drops to 1μA in shutdown. In addition to the

low quiescent current, the LT3013 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

LT3013 acts like it has a diode in series with its output

and prevents reverse current flow.

Adjustable Operation

The LT3013 has an output voltage range of 1.24V to 60V.

The output voltage is set by the ratio of two external

resistors 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.

The adjustable device is tested and specified with the

ADJ pin tied to the OUT pin and a 5μA DC load (unless

otherwise specified) for an output voltage of 1.24V. Speci-

fications for output voltages greater than 1.24V will be

proportional to the ratio of the desired output voltage to

output current change of 1mA to 250mA is –7mV typical at

(12V/1.24V) • (–7mV) = –68mV

Output Capacitance and Transient Response

The LT3013 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 3.3μF with an ESR of 3Ω or less is

recommended to prevent oscillations. The LT3013 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 LT3013, will increase the

effective output capacitor value.