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AS13986

Datasheet - A p p l i c a t i o n I n f o r m a t i o n

External Component Selection

Input Capacitor

to a clean analog ground (see Figure 15).

Note: Tantalum capacitors can suffer catastrophic failures due to surge current when connected to a low impedance

source of power (like a battery or a very large capacitor). If a tantalum capacitor is used at the input, it must be

guaranteed by the manufacturer to have a surge current rating sufficient for the application. There are no

requirements for the ESR on the input capacitor, but tolerance and temperature coefficient must be considered

when selecting the capacitor to ensure the capacitance will be approximately 1µF over the entire operating

temperature range.

Output Capacitor

The AS13986 was specifically designed to use very small ceramic output capacitors (temperature characteristics X7R,

X5R, Z5U or Y5V) in 1 to 22µF range (ESR of 0.005 to 5

Ω). Tantalum or film capacitors can be used at the output,

however these types of capacitors require more PCB space and are more expensive than ceramic capacitors.

Note: The output capacitor must meet the minimum capacitance requirement and also have an ESR value which is

within a stable range.

Bypass Capacitor

between pin BYPASS and GND (see Figure 15), with virtually no effect on the transient response of the AS13986.

Using a bypass capacitor will also prevent output overshoot during start up. This capacitor should be connected

directly to a high-impedance node in the band gap reference circuit. See also Fast Turn-On Time on page 8.

Note: Any significant loading on the high-impedance node will effect the regulated output voltage. For this reason,

DC leakage current through pin BYPASS must be kept as low as possible for best output voltage accuracy.

High-quality ceramic capacitors with NPO or COG dielectric are ideal as bypass capacitors as they typically exhibit

very low leakage current. Polypropylene and polycarbonate film capacitors are also a good choice as these capacitors

typically have extremely low leakage current and are available in small surface-mount packages.

Layout and Grounding Considerations

Well designed PC board layout is essential for optimizing device performance. In addition to providing electrical con-

nections, the AS13986 pins also channel heat away from the die.

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Wide circuit-board traces and large, solid copper polygons should be used to improve power dissipation.

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Multiple vias to buried ground planes should be used to further enhance thermal conductivity.