AS1358/AS1359
Datasheet - Application Information
9 Application Information
Capacitor Selection and Regulator Stability
For normal operation, use a 1µF capacitor at pin IN and a 1µF capacitor at pin OUT. Larger input capacitor values and
lower ESR provide better noise rejection and line-transient response. Reduce output noise and improve load-transient
response, stability, and power-supply rejection by using large output capacitors.
Note: Some ceramic dielectrics exhibit large capacitance and ESR variation with temperature. With dielectrics such
as Z5U and Y5V, it may be necessary to use a 2.2µF or larger output capacitor to ensure stability at tempera-
tures below -10°C. With X7R or X5R dielectrics, 1µF is sufficient at all operating temperatures.
Bypass Capacitor
Use a 0.01µF bypass capacitor at pin BYPASS for low-output voltage noise reduction. The leakage current going into
pin BYPASS should be less than 10nA. Increasing the capacitance slightly decreases the output noise. Values above
0.1µF and below 0.001µF are not recommended.
Noise, PSRR, and Transient Response
The AS1358/AS1359 are designed to deliver ultra-low noise and high PSRR, as well as low dropout and low quiescent
currents in battery-powered systems. The power-supply rejection is 92dB at 1kHz and 62dB at 100kHz. (see PSRR vs.
Frequency; IOUT = 10mA on page 7).
When operating from sources other than batteries, improved supply-noise rejection and transient response can be
achieved by increasing the values of the input and output capacitors, and through passive filtering techniques.
The Figure 16 and Figure 14 on page 8 show the AS1358/AS1359 line- and load-transient responses.
Dropout Voltage
The AS1358/AS1359 minimum dropout voltage determines the lowest usable supply voltage. In battery-powered sys-
tems, this determines the useful end-of-life battery voltage.
Since the AS1358/AS1359 use a P-channel MOSFET pass transistor, the dropout voltage is a function of drain-to-
source on-resistance (RDS(ON)) multiplied by ILOAD (see Figure 6 on page 6).
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