LT3085 Просмотр технического описания (PDF) - Linear Technology

Номер в каталоге

Компоненты Описание

производитель

LT3085

3µA IQ, 20mA, 45V Low Dropout Fault Tolerant Linear Regulators

Linear Technology 

LT3007 Series

APPLICATIONS INFORMATION

The LT3007 is a low dropout linear regulator with ultra-

low quiescent current and shutdown. Quiescent current is

extremely low at 3µA and drops well below 1µA in shut-

down. The device supplies up to 20mA of output current.

Dropout voltage at 20mA is typically 300mV. The LT3007

incorporates several protection features, making it ideal for

use in battery-powered systems. The device protects itself

against both reverse-input and reverse-output voltages.

In battery backup applications, where a backup battery

holds up the output when the input is pulled to ground,

the LT3007 acts as if a blocking diode is in series with its

output and prevents reverse current flow. In applications

where the regulator load returns to a negative supply, the

output can be pulled below ground by as much as 50V

without affecting start-up or normal operation.

Adjustable Operation

The LT3007 has an output voltage range of 0.6V to 44.5V.

Figure 2 shows that output voltage is set by the ratio of two

external resistors. The IC regulates the output to maintain

the ADJ pin voltage at 600mV referenced to ground. The

current in R1 equals 600mV/R1 and the current in R2 is

the current in R1 minus the ADJ pin bias current. The

ADJ pin bias current, typically 400pA at 25°C, flows out

of the pin. Calculate the output voltage using the formula

in Figure 2. An R1 value of 619k sets the divider current

to 0.97µA. Do not make R1’s value any greater than 619k

to minimize output voltage errors due to the ADJ pin bias

current and to insure stability under minimum load condi-

tions. 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.

Specifications for output voltages greater than 0.6V are

proportional to the ratio of the desired output voltage to

0.6V: VOUT/0.6V. For example, load regulation for an output

current change of 100µA to 20mA is –0.5mV typical at

VOUT = 0.6V. At VOUT = 5V, load regulation is:

5V • (−0.5mV) = −4.17mV

0.6V

Table 1 shows resistor divider values for some com-

mon output voltages with a resistor divider current of

about 1µA.

Table 1. Output Voltage Resistor Divider Values

VOUT

R1

1V

604k

1.2V

590k

1.5V

590k

1.8V

590k

2.5V

590k

3V

590k

3.3V

619k

5V

590k

R2

402k

590k

887k

1.18M

1.87M

2.37M

2.8M

4.32M

VOUT = 600mV • (1 + R2/R1) – (IADJ • R2)

VADJ = 600mV

IADJ = 0.4nA at 25°C

OUTPUT RANGE = 0.6V to 44.5V

IN

OUT

VOUT

VIN

LT3007

R2

SHDN

ADJ

GND

R1

3007 F02

Figure 2. Adjustable Operation

3007f

10

For more information www.linear.com/LT3007

Share Link: