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APPLICATION INFORMATION

Capacitors

Load Current − mA

LP2985

150-mA LOW-NOISE LOW-DROPOUT REGULATOR

WITH SHUTDOWN

SLVS522F – JULY 2004 – REVISED AUGUST 2005

A minimum value of 1

µF (over the entire operating temperature range) is required at the input of the LP2985. In

addition, this input capacitor should be located within 1 cm of the input pin and connected to a clean analog

ground. There are no equivalent series resistance (ESR) requirements for this capacitor, and the capacitance

can be increased without limit.

As an advantage over other regulators, the LP2985 permits the use of low-ESR capacitors at the output,

including ceramic capacitors that can have an ESR as low as 5 m

Ω. Tantalum and film capacitors also can be

used if size and cost are not issues. The output capacitor also should be located within 1 cm of the output pin

and be returned to a clean analog ground.

As with other PNP LDOs, stability conditions require the output capacitor to have a minimum capacitance and an

ESR that falls within a certain range.

•

•

ESR range: see Figure 28

Figure 28. 2.2-V/3.3-

µF ESR Curves

It is critical that both the minimum capacitance and ESR requirement be met over the entire operating

temperature range. Depending on the type of capacitors used, both these parameters can vary significantly with

temperature (see capacitor characteristics).

The LP2985 allows for low-noise performance with the use of a bypass capacitor that is connected to the internal

bandgap reference via the BYPASS pin. This high-impedance bandgap circuitry is biased in the microampere

range and, thus, cannot be loaded significantly, otherwise, its output – and, correspondingly, the output of the

much as possible and never should exceed 100 nA.

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