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LT3029

3029fa

The LT3029 is a dual 500mA/500mA low dropout regulator

with independent inputs, micropower quiescent current

and shutdown. The device supplies up to 500mA from each

channel’s output at a typical dropout voltage of 300mV.

The two regulators share a common GND pin and are

thermally coupled. However, the two inputs and outputs of

the LT3029 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 capacitor 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 (55μA per channel) drops to

less than 1μA in shutdown. In addition to the low quies-

cent current, the LT3029 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. Current limiting with

foldback necessitates a minimum load current of 20μA

for input/output voltage differentials of more than 10V to

keep the output regulated.

Adjustable Operation

Each of the LT3029’s channels has an output voltage range

of 1.215V to 19.5V. Figure 1 illustrates that output voltage

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

regulates the output to maintain the corresponding ADJ

pin voltage at 1.215V referenced to ground. R1’s current

equals 1.215V/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.

APPLICATIONS INFORMATION

Figure 1. Adjustable Operation

IN1/IN2

3029 F01

LT3029

OUT1/OUT2

VIN

VOUT

ADJ1/ADJ2

GND

Linear Technology tests and speciﬁes each LT3029 channel

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

1.215V output voltage. Speciﬁcations for output voltages

greater than 1.215V are proportional to the ratio of desired

output voltage to 1.215V:

VOUT

1.215V

For example, load regulation on either output for an output

current change of 1mA to 500mA is typically –2.5mV at

VOUT = 1.215V. At VOUT = 2.5V, load regulation is:

2.5V

1.215V

•(

−2.5mV) =− 5.14mV

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)

(k)

1.5

237

54.9

1.8

237

113

2.5

243

255

232

340

3.3

210

357

200

619

OUT = 1.215V 1+

⎛

⎝⎜

⎞

⎠⎟

+ I

ADJ

() R2

()

ADJ = 1.215V

ADJ = 30nA AT 25°C

OUTPUT RANGE = 1.215V TO 19.5V

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