LT3060_15 datasheet(21/26 Pages) LINER

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LT3060 Series

3060fc

For more information www.linear.com/LT3060

applicaTions inForMaTion

The LT3060 IN pin withstands reverse voltages up to 50V.

The device limits current flow to less than 300µA (typi-

cally less than 50µA) and no negative voltage appears at

OUT. The device protects both itself and the load against

batteries that are plugged in backwards.

The SHDN pin cannot be driven below GND unless tied to

the IN pin. If the SHDN pin is driven below GND while IN is

powered, the output may turn on. SHDN pin logic cannot

be referenced to a negative supply voltage.

The LT3060 incurs no damage if its output is pulled be-

low ground. If the input is left open-circuit or grounded,

the output can be pulled below ground by 50V. No cur-

rent flows through the pass transistor from the output.

However, current flows in (but is limited by) the resistor

divider that sets the output voltage. Current flows from

the bottom resistor in the divider and from the ADJ pin’s

internal clamp through the top resistor in the divider to

the external circuitry pulling OUT below ground. If the

input is powered by a voltage source, the output sources

current equal to its current limit capability and the LT3060

protects itself by thermal limiting. In this case, grounding

the SHDN pin turns off the device and stops the output

from sourcing current.

The LT3060 incurs no damage if the ADJ pin is pulled

above or below ground by less than 50V. For the adjust-

able version, if the input is left open-circuit or grounded,

the ADJ pin performs like a large resistor (typically 30k)

in series with a diode when pulled below ground, and like

30k in series with two diodes when pulled above ground.

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 left open-

circuit. Current flow back into the output follows the curve

shown in Figures 7 and 8.

If the LT3060’s IN pin is forced below the OUT pin or the

OUT pin is pulled above the IN pin, input current typically

drops to less than 1µA. This occurs if the LT3060 input

is connected to a discharged (low voltage) battery and

either a backup battery or a second regulator holds up

the output. The state of the SHDN pin has no effect on

the reverse current if the output is pulled above the input.

OUTPUT VOLTAGE (V)

1.4

1.6

1.8

1.2

1.0

0.8

0.4

0.6

0.2

2.0

30 35 40 45

10 15 20

3060 F07

ADJ

OUT

TJ = 25°C

VIN = 0V

CURRENT FLOWS

INTO OUT PIN

VOUT = VADJ

Figure 7. LT3060 Reverse Output Current

Figure 8. LT3060-1.2/-1.5/-1.8/-2.5/-3.3/-5/-15

Reverse Output Current

OUTPUT VOLTAGE (V)

250

150

200

100

350

300

30 35 40 45

10 15 20

3060 F08

LT3060-1.2

LT3060-5

LT3060-15

LT3060-1.5

LT3060-1.8

LT3060-2.5

LT3060-3.3

TJ = 25°C

VIN = 0V

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