Data Sheet

ADPL42010A

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Rev. 0

21 of 28

voltage noise gains up accordingly. This results in RMS noise over the 10Hz to 100kHz bandwidth of 22µVRMS for the

ADPL42010A increasing to 83µVRMS for the ADPL42010A-3.3.

Higher values of output voltage noise may be measured when care is not exercised with regard to circuit layout and

testing. Crosstalk from nearby traces can induce unwanted noise onto the output of the ADPL42010A-X. Power supply

ripple rejection must also be considered, the ADPL42010A regulators do not have unlimited power supply rejection

and pass a small portion of the input noise through to the output.

Protection Features

The ADPL42010A incorporates several protection features, which makes it ideal for use in battery-powered circuits.

In addition to the normal protection features associated with monolithic regulators, such as current limiting and

thermal limiting, the devices are protected against reverse input voltages, reverse output voltages, and reverse

voltages from output to input.

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 withstands reverse voltages of 20V. Current flow into the device is limited to less than 1mA

(typically less than 100µA) and no negative voltage appears at the output. The device protects both itself and the

load. This provides protection against batteries that can be plugged in backward.

The output of the ADPL42010A 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. For fixed voltage versions, the output acts as a

large resistor, typically 5k or higher, limiting current flow to typically less than 600µA. For adjustable versions, the

output acts as an open circuit, no current flows out of the pin. If the input is powered by a voltage source, the output

sources the short-circuit current of the device and protects itself by thermal limiting. In this case, grounding the

SHDN

pin turns off the device and stop the output from sourcing the short-circuit current.

The ADJ pin of the adjustable device 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 pin acts as an open circuit when pulled below ground and

as a large resistor (typically 5k) in series with a diode when pulled above ground.

In situations where the ADJ pin is connected to a resistor divider that pulls 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 1.21V 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 OUT and ADJ pins 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 follows the curve, as shown in Figure 33.

When the IN pin of the ADPL42010A is forced below the OUT pin or the OUT pin is pulled above the IN pin, input

current typically drops 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

SHDN

pin have no effect on the reverse output current when the output is pulled above the input.