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Application Note : LDO Regulators (Linear Regulators)

Technical Notes

Typical Applications



PCB Layout

Ensure the VDD and GND lines are sufficiently robust. If their impedance is too high, noise pickup or unstable operation may result.
Connect a capacitor with a suitable value between the VDD and GND pins, and as close as possible to the pins.

Phase Compensation

In LDO regulators, phase compensation is provided to secure stable operation even when the load current is varied.
For this purpose, use a capacitor COUT with good frequency characteristics and proper ESR (Equivalent Series Resistance), value in the hatched area.

If a capacitor with large ESR value, especially a tantalum type capacitor, is used, the output might be unstable. Evaluate a circuit including consideration of frequency characteristics.
Depending on the capacitor size, manufacturer, and part number, the bias characteristics and temperature characteristics are different. Evaluate the circuit taking actual characteristics into account.

Equivalent Series Resistance vs. Output Current

Equivalent Series Resistance vs. Output Current

R1116 Series Example

The relations between IOUT (Output Current) and ESR of an output capacitor are shown right.
The conditions when the white noise level is under 40 µV (Avg.) are shown by the hatched area in the graph.

Measurement conditions
C2 GRM155B30J105KE18B (Murata)
Noise Frequency Band 10 Hz to 1 MHz
Measurement Temperature 25°C
Hatched Area Noise level below 40 µV
(average value)

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