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http://www.union-ic.com

Rev.01 Nov.2010

7/10

UM365XX

Applications Information

The UM365XXS series are 300mA very low dropout regulators with micropower quiescent

current . The maximum dropout is only 90mV at the load current of 150mA. Output voltage noise

In addition to the low quiescent current, the UM365XXS regulators incorporate several protection

features which make them ideal for use in battery-powered systems. The devices are protected

against both reverse input voltages and reverse voltages from output to input (reverse current

protection). The devices also include current limit and thermal overload protection, and will

survive an output short circuit indefinitely. The fast transient response over comes the traditional

tradeoff between dropout voltage, quiescent current and load transient response inherent in most

regulators by using a proprietary new architecture.

Output Capacitance and Transient Response

The UM365XXS regulators are designed to be stable with a wide range of output capacitors. The

ESR of the output capacitor affects stability, most notably with small capacitors. A minimum

output capacitor of 1μF with an ESR of 0.3Ω or less is recommended to ensure stability. The

UM365XXS series are micropower devices and output transient response will be a function of

output capacitance. Larger values of output capacitance decrease the peak deviations and provide

improved transient response for larger load current changes. The shaded region of Figure 1 defines

the region over which the UM365XXS regulators are stable. The maximum ESR allowed is 0.3Ω.

High ESR tantalum and electrolytic capacitors may be used, but a low ESR ceramic capacitor

must be in parallel at the output. There is no minimum ESR requirement.

Figure 1

Extra consideration must be given to the use of ceramic capacitors. Ceramic capacitors are

manufactured with a variety of dielectrics, each with different behavior across temperature and

applied voltage. The most common dielectrics used are Z5U, Y5V, X5R and X7R. The Z5U and

Y5V dielectrics are good for providing high capacitances in a small package, but exhibit strong

voltage and temperature coefficients as shown in Figures 2 and 3. When used with a 5V regulator,

a 10μF Y5V capacitor can exhibit an effective value as low as 1μF to 2μF over the operating

temperature range. The X5R and X7R dielectrics result in more stable characteristics and are more

suitable for use as the output capacitor. The X7R type has better stability across temperature,

while the X5R is less expensive and is available in higher values.