NCP121 datasheet(6/8 Pages) ONSEMI

Part #	NCP121

Description	150 mA, High Accuracy, Very Low Dropout Bias Rail CMOS Voltage Regulator

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Manufacturer	ONSEMI [ON Semiconductor]

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NCP121

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APPLICATIONS INFORMATION

The NCP121 dual−rail very low dropout voltage regulator

is using NMOS pass transistor for output voltage regulation

from VIN voltage. All the low current internal controll

circuitry is powered from the VBIAS voltage.

The use of an NMOS pass transistor offers several

advantages in applications. Unlike a PMOS topology

devices, the output capacitor has reduced impact on loop

stability. VIN to VOUT operating voltage difference can be

very low compared with standard PMOS regulators in very

low VIN applications.

The NCP121 offers smooth monotonic start-up. The

controlled voltage rising limits the inrush current.

The Enable (EN) input is equipped with internal

hysteresis.

NCP121 is a Fixed Voltage linear regulator.

Dropout Voltage

Because of two power supply inputs VIN and VBIAS and

one VOUT regulator output, there are two Dropout voltages

specified.

The first, the VIN Dropout voltage is the voltage

difference (VIN – VOUT) when VOUT starts to decrease by

percents specified in the Electrical Characteristics table.

VBIAS is high enough, specific value is published in the

Electrical Characteristics table.

The second, VBIAS dropout voltage is the voltage

difference (VBIAS – VOUT) when VIN and VBIAS pins are

joined together and VOUT starts to decrease.

Input and Output Capacitors

The device is designed to be stable for ceramic output

capacitors with Effective capacitance in the range from 1

mF

to 10

mF. The device is also stable with multiple capacitors

in parallel, having the total effective capacitance in the

specified range.

In applications where no low input supplies impedance

available (PCB inductance in VIN and/or VBIAS inputs as

example), the recommended CIN = 1

mF and CBIAS = 0.1 mF

or greater. Ceramic capacitors are recommended. For the

best performance all the capacitors should be connected to

the NCP121 respective pins directly in the device PCB

copper layer, not through vias having not negligible

impedance.

When using small ceramic capacitor, their capacitance is

not constant but varies with applied DC biasing voltage,

temperature and tolerance. The effective capacitance can be

much lower than their nominal capacitance value, most

importantly in negative temperatures and higher LDO

output voltages. That is why the recommended Output

capacitor capacitance value is specified as Effective value in

the specific application conditions.

Enable Operation

The enable pin will turn the regulator on or off. The

threshold limits are covered in the electrical characteristics

table in this data sheet. If the enable function is not to be used

then the pin should be connected to VIN or VBIAS.

Current Limitation

The internal Current Limitation circuitry allows the

device to supply the full nominal current and surges but

protects the device against Current Overload or Short.

Thermal Protection

Internal thermal shutdown (TSD) circuitry is provided to

protect the integrated circuit in the event that the maximum

junction temperature is exceeded. When TSD activated , the

regulator output turns off. When cooling down under the low

temperature threshold, device output is activated again. This

TSD feature is provided to prevent failures from accidental

overheating.

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