LT3024IDE datasheet(13/20 Pages) LINER

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LT3024

3024fa

APPLICATIONS INFORMATION

The LT3024 is a dual 100mA/500mA low dropout regulator

with micropower quiescent current and shutdown. The

device is capable of supplying 100mA from Output 2 at a

dropout voltage of 300mV. Output 1 delivers 500mA at a

dropout voltage of 300mV. The two regulators have com-

mon VIN and GND pins and are thermally coupled, however,

the two outputs of the LT3024 operate independently. They

can be shut down independently and a fault condition on

one output will not affect the other output electrically.

Output voltage noise can be lowered to 20μVRMS over a

10Hz to 100kHz bandwidth with the addition of a 0.01μF

reference bypass capacitor. Additionally, the reference

bypass capacitor will improve transient response of the

regulator, lowering the settling time for transient load

conditions. The low operating quiescent current (30μA per

output) drops to less than 1μA in shutdown. In addition to

the low quiescent current, the LT3024 regulator incorpo-

rates 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 LT3024 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 is

returned 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 LT3024 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 ADJ 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 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 no greater 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. Curves of ADJ Pin Voltage

vs Temperature and ADJ Pin Bias Current vs Temperature

appear in the Typical Performance Characteristics.

The device is tested and speciﬁed with the ADJ pin tied to

the corresponding OUT 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 on

Output 2 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 LT3024 regulator may be used with the addition of a

bypass capacitor from VOUT to the corresponding BYP 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 frequency noise

pole. The noise pole provided by this bypass capacitor will

lower the output voltage noise to as low as 20μVRMS with

the addition of a 0.01μF bypass capacitor. Using a bypass

capacitor has the added beneﬁt of improving transient

response. With no bypass capacitor and a 10μF output

capacitor, a 10mA to 100mA load step on Output 2 will settle

to within 1% of its ﬁnal value in less than 100μs. With the

addition of a 0.01μF bypass capacitor, the output will stay

Figure 1. Adjustable Operation

3024 F01

LT3024

OUT1/OUT2

VIN

VOUT

ADJ1/ADJ2

GND

InA

OUT

ADJ

⎛

⎝⎜

⎞

⎠⎟

()( )

=°

122

AT 25 C

OUTPUT RANGE = 1.22V TO 20V

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