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LT3030HFE-PBF

Dual 750mA/250mA Low Dropout, Low Noise, Micropower Linear Regulator

Linear Technology 

LT3030

Applications Information

The LT3030 is a dual 750mA/250mA low dropout regulator

with independent inputs, micropower quiescent current

and shutdown. The device supplies up to 750mA/250mA

from the outputs of channel 1/channel 2 at a typical dropout

voltage of 300mV. The two regulators share common GND

pins and are thermally coupled. However, the two inputs

and outputs of the LT3030 operate independently. Each

channel can be shut down independently, but a thermal

shutdown fault on either channel shuts off the output on

both channels. The addition of a 10nF reference bypass ca-

pacitor lowers output voltage noise to 20μVRMS over a 10Hz

to 100kHz bandwidth. Additionally, the reference bypass

capacitor improves transient response of the regulator,

lowering the settling time for transient load conditions. The

low operating quiescent current (120μA/75μA for channel

1/2) drops to typically less than 1μA in shutdown. In ad-

dition to the low quiescent current, the LT3030 regulator

incorporates several protection features that make it ideal

for use in battery powered systems. Most importantly,

the device protects itself against reverse input voltages.

Adjustable Operation

Each of the LT3030’s channels has an output voltage range

of 1.220V to 19.5V. Figure 1 illustrates that the output

voltage is set by the ratio of two external resistors. The

device regulates the output to maintain the corresponding

ADJ pin voltage at 1.220V referenced to ground. R1’s cur-

rent equals 1.220V/R1. R2’s current equals R1’s current

plus the ADJ pin bias current. The ADJ pin bias current,

30nA at 25°C, flows through R2 into the ADJ pin. Use

the formula in Figure 1 to calculate output voltage. Linear

Technology recommends that the value of R1 be less than

243k to minimize errors in the output voltage due to the

ADJ pin bias current. In shutdown, the output turns off

and the divider current is zero. Curves of ADJ Pin Voltage

vs Temperature and ADJ Pin Bias Current vs Temperature

appear in the Typical Performance Characteristics section.

Linear Technology tests and specifies each LT3030 channel

with its ADJ pin tied to the corresponding OUT pin for a

1.220V output voltage. Specifications for output voltages

greater than 1.220V are proportional to the ratio of desired

output voltage to 1.220V:

VOUT / 1.220V

LT3030

OUT1/OUT2

VIN

IN1/IN2

R2

ADJ1/ADJ2

GND

R1

3030 F01

VOUT

COUT

VOUT

=

1.220V

⎛⎝⎜1+

R2⎞

R1⎠⎟

+

(IADJ)

(R2)

VADJ = 1.220V

IADJ = 30nA AT 25°C

OUTPUT RANGE = 1.220V TO 19.5V

Figure 1. Adjustable Operation

For example, load regulation on OUT2 for an output cur-

rent change of 1mA to full load current is typically –2mV

at VOUT2 = 1.220V. At VOUT2 = 2.5V, load regulation is:

(2.5V/1.220V) • (–2mV) = –4.1mV

Table 1 shows 1% resistor divider values for some com-

mon output voltages with a resistor divider current of

approximately 5μA.

Table 1. Output Voltage Resistor Divider Values

VOUT (V)

R1 (k)

1.5

237

1.8

237

2.5

243

3

232

3.3

210

5

200

R2 (k)

54.9

113

255

340

357

619

Bypass Capacitance and Low Noise Performance

Using a bypass capacitor connected between a channel’s

BYP pin and its corresponding OUT pin significantly low-

ers LT3030 output voltage noise, but is not required in

all applications. Linear Technology recommends a good

quality low leakage capacitor. This capacitor bypasses

the regulator’s reference, providing a low frequency noise

pole. A 10nF bypass capacitor introduces a noise pole that

decreases output voltage noise to as low as 20μVRMS. Using

a bypass capacitor provides the added benefit of improv-

ing transient response. With no bypass capacitor and a

10μF output capacitor, a 100mA to full load step settles to

within 1% of its final value in approximately 400μs. With

the addition of a 10nF bypass capacitor and evaluating

the same load step, output voltage excursion stays within

2% (see Transient Response in the Typical Performance

Characteristics section). Using a bypass capacitor makes

regulator start-up time proportional to the value of the

bypass capacitor. For example, a 10nF bypass capacitor

and 10μF output capacitor slow start-up time to 15ms.

3030fa

12

For more information www.linear.com/LT3030

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