LT3024EDE データシートの表示（PDF） - Linear Technology

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LT3024EDE

Dual 100mA/500mA Low Dropout, Low Noise, Micropower Regulator

Linear Technology 

LT3024

APPLICATIONS INFORMATION

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.

Current limit protection and thermal overload protection

are intended to protect the device against current overload

conditions at the output of the device. For normal operation,

the junction temperature should not exceed 125°C.

The input of the device will withstand reverse voltages

of 20V. Current flow into the device will be limited to less

than 1mA (typically less than 100μA) and no negative

voltage will appear at the output. The device will protect

both itself and the load. This provides protection against

batteries which can be plugged in backward.

The output of the LT3024 can be pulled below ground

without damaging the device. If the input is left open circuit

or grounded, the output can be pulled below ground by

20V. The output will act like an open circuit; no current will

flow out of the pin. If the input is powered by a voltage

source, the output will source the short-circuit current of

the device and will protect itself by thermal limiting. In

this case, grounding the SHDN1/SHDN2 pins will turn off

the device and stop the output from sourcing the short-

circuit current.

The ADJ pins can be pulled above or below ground by as

much as 7V without damaging the device. If the input is

left open circuit or grounded, the ADJ pins will act like an

open circuit when pulled below ground and like a large

resistor (typically 100k) in series with a diode when pulled

above ground.

In situations where the ADJ pins are connected to a resistor

divider that would pull the pins above their 7V clamp volt-

age if the output is pulled high, the ADJ pin input current

must be limited to less than 5mA. For example, a resistor

divider is used to provide a regulated 1.5V output from the

1.22V reference when the output is forced to 20V. The top

resistor of the resistor divider must be chosen to limit the

current into the ADJ pin to less than 5mA when the ADJ

pin is at 7V. The 13V difference between output and ADJ

pin divided by the 5mA maximum current into the ADJ pin

yields a minimum top resistor value of 2.6k.

In circuits where a backup battery is required, several

different input/output conditions can occur. The output

voltage may be held up while the input is either pulled

to ground, pulled to some intermediate voltage or is left

open circuit. Current flow back into the output will follow

the curve shown in Figure 7.

When the IN pin of the LT3024 is forced below either OUT

pin or either OUT pin is pulled above the IN pin, input cur-

rent for the corresponding regulator will typically drop to

less than 2μA. This can happen if the input of the device

is connected to a discharged (low voltage) battery and the

output is held up by either a backup battery or a second

regulator circuit. The state of the SHDN1/SHDN2 pin will

have no effect on the reverse output current when the

output is pulled above the input.

100

TA = 25°C

90 VIN = 0V

80

VOUT = VADJ

CURRENT FLOWS

70 INTO OUTPUT PIN

60

50

40

30

20

10

0

01234567 8

OUTPUT VOLTAGE (V)

9 10

3024 F07

Figure 7. Reverse Output Current

3024fa

17

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