Application Note : LDO Regulators (Linear Regulators)
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.
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.
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.
|Noise Frequency Band||10 Hz to 1 MHz|
|Hatched Area||Noise level below 40 µV