LXXLD50

CMOS IC

UNISONICTECHNOLOGIESCO.,LTD

6 of 11

www.unisonic.com.tw

QW-R502-474.B

FUNCTIONAL DESCRIPTION

Power-On-Reset

avoid the unexpected operations. During powering on process, the POR circuit would initiate a soft-start process

Internal Soft-Start

The built-in soft-start circuit controls rise rate of the output voltage to limit the current surge at start-up. The

soft-start interval is approximately 1.2mS (TYP.).

Output Voltage Regulation

The error amplifier compares a temperature-compensated 0.8V reference with the feedback voltage, which is

characterized with high bandwidth and DC gain to provide fast transient response and less load regulation.

The output voltage can be adjusted by an output NMOS to get the preset voltage. The difference which is

Current-Limit

The current-limit protection circuit is used to protect this device against the maximum current, which occurs in

overload or short-circuit conditions. For the UTC LXXLD50, the current is monitored through the output NMOS.

Under-Voltage Protection (UVP)

The UTC LXXLD50 monitors the voltage on internal feed back signal after soft-start process is finished. Thus,

the Under-Voltage circuit is inactive during soft-start. When the voltage on FB signal goes below the under-voltage

threshold, the UVP circuit shuts off the output immediately. Last for a period, this device starts a new soft-start to

regulate output.

Over-Voltage Protection (OVP)

regulation voltage by 25%, the OVP circuit shuts off the output immediately. After a while, the LXXLD50 starts a new

soft-start to regulate output.

Thermal Shutdown

The thermal shutdown protection circuit is designed to prevent the junction temperature beyond a certain value.

If the junction temperature becomes higher than +150°C, the output NMOS is turned off through a thermal sensor,

allowing the device to cool down. The regulator regulates the output again through initiation of a new soft-start cycle

after the junction temperature cools by 25°C, resulting in a pulsed output during continuous thermal overload

conditions.

The average junction temperature is reduced by the 25°C hysteresis during continuous thermal overload

conditions, making this device use longer. Also, the power dissipation should be externally limited to ensure junction

temperature under +125°C during normal operation.

Enable Control

a logic high signal re-enables the output through initiation of a new soft-start cycle. Left open, this pin is pulled up by

an internal current source (10μA Typical) to enable operation. For a low cost-effectiveness, an external transistor is

not required.

Power-OK and Delay

For the UTC LXXLD50, the Power-OK circuit indicates the status of the output voltage by monitoring the

an internal delay function starts to perform a delay time. At the end of the delay time, the IC shuts off the internal

NMOS of the POK to indicate the output is OK. When the feedback voltage becomes equal to the falling Power-OK

time.