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LT3013

3013fe

APPLICATIONS INFORMATION

In situations where the ADJ pin is connected to a resistor

divider that would pull the ADJ pin above its 7V clamp

voltage 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

1.24V reference when the output is forced to 60V. 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 53V difference between the OUT and ADJ

pins divided by the 5mA maximum current into the ADJ

pin yields a minimum top resistor value of 10.6k.

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 5. The rise in reverse output

current above 7V occurs from the breakdown of the 7V

clamp on the ADJ pin. With a resistor divider on the

regulator output, this current will be reduced depending

on the size of the resistor divider.

When the IN pin of the LT3013 is forced below the OUT

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

will typically drop to less than 2μA. This can happen if

the input of the LT3013 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 SHDN pin will have no effect on the reverse output

current when the output is pulled above the input.

OUTPUT VOLTAGE (V)

120

160

200

3013 F05

100

140

180

ADJ

PIN CLAMP

(SEE ABOVE)

TJ = 25°C

VIN = 0V

VOUT = VADJ

CURRENT FLOWS

INTO OUTPUT PIN

Figure 5. Reverse Output Current

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