LT3023EMSE datasheet(9/16 Pages) LINER

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LT3023

3023f

APPLICATIO S I FOR ATIO

The LT3023 is a dual 100mA low dropout regulator with

micropower quiescent current and shutdown. The device

is capable of supplying 100mA per channel at a dropout

voltage of 300mV. Output voltage noise can be lowered to

µVRMS over a 10Hz to 100kHz bandwidth with the

addition of a 0.01

µF reference bypass capacitor. Addition-

ally, the reference bypass capacitor will improve transient

response of the regulator, lowering the settling time for

transient load conditions. The low operating quiescent

current (20

µA per channel) drops to less than 1µA in

shutdown. In addition to the low quiescent current, the

LT3023 regulator incorporates several protection features

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 LT3023 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 isreturned to a negative supply, the output

can be pulled below ground by as much as 20V and still

allow the device to start and operate.

Adjustable Operation

The LT3023 has an output voltage range of 1.22V to 20V.

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 corresponding ADJ1/ADJ2 pin voltage 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 ADJ1/ADJ2 pin bias current. The ADJ1/ADJ2 pin bias

current, 30nA at 25

°C,flowsthroughR2intotheADJ1/ADJ2

pin. The output voltage can be calculated using the formula

in Figure 1. The value of R1 should be no greater than 250k

to minimize errors in the output voltage caused by the ADJ1/

ADJ2 pin bias current. Note that in shutdown the output is

turned off and the divider current will be zero. Curves of

ADJ1/ADJ2 Pin Voltage vs Temperature and ADJ1/ADJ2 Pin

Bias Current vs Temperature appear in the Typical Perfor-

mance Characteristics.

The device is tested and specified with the ADJ1/ADJ2 pin

tied to the corresponding OUT1/OUT2 pin for an output

voltage of 1.22V. Specifications for output voltages greater

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

output voltage to 1.22V: VOUT/1.22V. For example, load

regulation for an output current change of 1mA to 100mA

is –1mV typical at VOUT = 1.22V. At VOUT = 12V, load

regulation is:

(12V/1.22V)(–1mV) = – 9.8mV

Bypass Capacitance and Low Noise Performance

The LT3023 regulator may be used with the addition of a

bypass capacitor from VOUT to the corresponding BYP1/

BYP2 pin to lower output voltage noise. A good quality low

leakage capacitor is recommended. This capacitor will

bypass the reference of the regulator, providing a low fre-

quency noise pole. The noise pole provided by this bypass

capacitor will lower the output voltage noise to as low as

µVRMS with the addition of a 0.01µF bypass capacitor.

Using a bypass capacitor has the added benefit of improv-

ing transient response. With no bypass capacitor and a

µF output capacitor, a 10mA to 100mA load step will

settle to within 1% of its final value in less than 100

µs.With

the addition of a 0.01

µF bypass capacitor, the output will

stay within 1% for a 10mA to 100mA load step (see Tran-

sient Reponse in Typical Performance Characteristics sec-

tion). However, regulator start-up time is inversely pro-

portional to the size of the bypass capacitor, slowing to

15ms with a 0.01

µF bypass capacitor and 10µF output

capacitor.

3023 F01

LT3023

OUT1/OUT2

VIN

VOUT

ADJ1/ADJ2

GND

InA

OUT

ADJ









()( )

=°

122

AT 25 C

OUTPUT RANGE = 1.22V TO 20V

Figure 1. Adjustable Operation

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