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APPLICATION INFORMATION

Enable/Shutdown

Input Capacitor

Output Capacitor

Bypass Capacitor

Low-Voltage Operation

TL5209

500-mA LOW-NOISE LOW-DROPOUT VOLTAGE REGULATOR

WITH SHUTDOWN

SLVS581 – SEPTEMBER 2006

The enable function is only available in the SOIC (D) and TO-263 (KTT) packages. The EN pin is CMOS-logic

compatible. When EN is held high (>2 V), the regulator is active. Likewise, applying a low signal (<0.4 V at

25

°C) to EN or leaving it open shuts down the regulator. If the enable/shutdown feature is not needed, EN

If the input of the regulator is located more than ten inches from the power-supply filter, or if a battery is used to

power the regulator, a minimum 1-

µF input capacitor is recommended.

As with all PNP regulators, an output capacitor is needed for stability. The required minimum size of this output

capacitor depends on several factors, one of which is whether a bypass capacitor is used.

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Another factor that can determine the minimum size of the output capacitor is the load current. At low loads, a

smaller output capacitor is needed for stability.

have an ESR of

≈1 Ω, and it should have a resonant frequency above 1 MHz. Too low an ESR can cause the

output to have a low-amplitude oscillation and/or underdamped transient response. Most tantalum or aluminum

electrolytic capacitors can be used for the output capacitors. However, care should be used at low temperatures,

because aluminum electrolytics use electrolytes that can freeze at low temperature (

≈ –30°C). Solid tantalum

capacitors do not exhibit this problem and should be used below –25

°C.

noise performance (only for SOIC and TO-263 packages). Connected to the internal voltage divider and the

error amplifier of the regulator, this bypass capacitor filters the noise of the internal reference and reduces the

noise effects on the error amplifier. The overall result is a significant drop in output noise of the regulator. A

470-pF bypass capacitor is recommended.

Adding a bypass capacitor has several effects on the regulator that must be taken into account. First, the bypass

µF, as previously mentioned. Second, upon startup of the regulator, the bypass capacitor has an effect on the

If a bypass capacitor is not needed, BYP should be left open.

When using the TL5209-18 and TL5209-25 in voltage-sensitive applications, special considerations are required.

If appropriate output and bypass capacitors are not chosen properly, these devices may experience a temporary

overshoot of their nominal voltages.

At start-up, the full input voltage is initially applied across the regulator pass transistor, causing it to be

temporarily fully turned on. By contrast, the error amplifier and voltage-reference circuits, being powered from

the output, are not powered up as fast. In order to slow down the output ramp and give the error amplifier time to

respond, select larger values of output and bypass capacitors. The longer ramp time of the output allows the

regulator enough time to respond and keeps the output from overshooting its nominal value.

To prevent an overshoot when starting up into a light load (

≈100 µA), 4.7-µF and 470-pF capacitors are

recommended for the output and bypass capacitors, respectively. At higher loads, 10-

µF and 470-pF capacitors

should be used.

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