LXXLD50L-SH2-R datasheet(7/11 Pages) UTC

7 / 11 page

LXXLD50

CMOS IC

UNISONICTECHNOLOGIESCO.,LTD

7 of 11

www.unisonic.com.tw

QW-R502-474.B

APPLICATION INFORMATION

Power Sequencing

Less consideration could be taken into the power sequencing of VIN and VCNTL. But do not apply a voltage to

VOUT for a long time when the main voltage applied at VIN is not present. The reason is the internal parasitic diode

from VOUT to VIN conducts and dissipates power without protections due to the forward-voltage.

Output Capacitor

For the maximum device performance and improving system stability, transient response over temperature and

current, a well-suitable output capacitor is needed. The selected output capacitor should be qualified perfect ESR

(equivalent series resistance) and capacitor value for a better system stability and load transient.

The UTC LXXLD50 is designed with a programmable feedback compensation adjusted by an external

feedback network for the use of wide ranges of ESR and capacitance in all applications. The output capacitors can

be ultra-low-ESR capacitors, such as ceramic chip capacitors; low-ESR bulk capacitors, such as solid Tantalum,

POSCap, and Aluminum electrolytic capacitors, and their values can be increased without limit.

During load transients, the output capacitors, depending on the stepping amplitude and slew rate of load

current, are used to reduce the slew rate of the current seen by the UTC LXXLD50 and help the device to minimize

the variations of output voltage for good transient response. Therefore, low-ESR bulk capacitors are universally to be

expected for the applications with large stepping load current.

In addition, decoupling ceramic capacitors must be located to the load and GND as close as possible and the

layout’s impedance should be maintained minimum.

Input Capacitor

The input capacitors should be chosen properly due to supply current to protect the input rail against dropping

during stepping load transients. Because the parasitic inductor from the voltage sources or other bulk capacitors to

the VIN pin limit the slew rate of the surge currents. More parasitic inductance needs more input capacitance. More

capacitance reduces the variations of the VIN pin voltage.

For the UTC LXXLD50, input capacitors with low-ESR are not needed. Ultra-low-ESR capacitors (such as

ceramic chip capacitors) are good options, and an aluminum electrolytic capacitor (>100μF, ESR <300mΩ) is

recommended as the input capacitor.

Feedback Network

In the following, the feedback network between VOUT, GND and FB pins is shown in Figure 1. It works with the

internal error amplifier to provide proper frequency response for the linear regulator.

As seen in Figure 1, the ESR is the equivalent series resistance of the output capacitor. The COUT is ideal

capacitance in the output capacitor. The VOUT is the setting of the output voltage.

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