NCP102 データシートの表示（PDF） - ON Semiconductor

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NCP102

Low Dropout Linear Regulator Controller

ON Semiconductor 

NCP102

DETAILED OPERATING DESCRIPTION

The NCP102 is a low dropout linear regulator controller

for applications requiring high-current and ultra low

dropout voltages. The use of an external N-Channel

MOSFET allows the user to adapt the device to a multitude

of applications depending on system requirements for

current and dropout voltage.

An extremely accurate 0.8 V (±2%) reference allows the

implementation of sub 1 V voltage supplies. The reference

is guaranteed over the complete supply and temperature

ranges.

Other features of the NCP102 are a dedicated enable

input, internally compensated error amplifier and an

adjustable soft-start. A minimum drive capability of ±5 mA

provides fast transient response. The drive current is

internally limited to protect the controller in case of an

external MOSFET failure. The NCP102 is packaged in a

space saving TSOP-6.

SUPPLY VOLTAGE

The NCP102 supply voltage range is between 4.5 V and

13.5 V. The controller is enabled once the supply voltage

exceeds its minimum supply threshold, typically 4.5 V. The

minimum operating voltage is reduced to 4.2 V (typical)

once the controller is enabled to provide noise immunity.

A bypass capacitor is required on the VCC pin to provide

charge storage during power up and transient events. A

minimum of 0.1 mF is recommended.

DRIVE OUTPUT

A powerful error amplifier (EA) capable of driving an

external MOSFET is built into the NCP102. The output of

the error amplifier is connected to the DRV pin. It has a

minimum drive current capability of ±5 mA providing a fast

transient response.

The EA is biased directly from VCC. The DRV voltage

follows VCC up and it is internally clamped to 9.75 V (typ.).

This allows the use of external MOSFETs with a maximum

gate voltage of 12 V.

The DRV current is provided directly from VCC.

Therefore, the VCC capacitor should be large enough to

maintain a constant VCC during power up and transients.

Otherwise, the supply voltage may collapse reaching the

controller undervoltage lockout threshold.

Equation 1 relates the output voltage to the internal

reference voltage and external resistors R1 and R2.

ǒ Ǔ Vout + VREF @

R1 ) R2

R2

(eq. 1)

ERROR AMPLIFIER

The NCP102 has a wide bandwidth error amplifier. It

allows the user to implement a wide bandwidth feedback

loop resulting in better transient response and lower system

cost. It requires the user to compensate the system. A narrow

bandwidth error amplifier usually does not require external

compensation but it requires more output capacitance to

meet typical transient requirements.

The output of the error amplifier is available for frequency

compensation. A capacitor (CCOMP) can be placed between

the DRV and FB pins. In most cases the resistor is not

needed. The uncompensated error amplifier dominant pole

is approximately 1.65 Hz. Any external capacitance

between the DRV and FB pins reduces the dominant pole

frequency due to the Miller multiplication effect. Equation

2 relates the dominant pole frequency to CCOMP.

fpole + 6.7016 @ CCOMPā*0.846

(eq. 2)

EXTERNAL ENABLE

The EN input allows the NCP102 to be remotely enabled.

An internal 10 mA (typ.) current source pulls up the EN

voltage. The EN pin is internally pulled to VCC or 9.5 V,

whichever is lower.

The controller is enabled once the EN pin voltage exceeds

0.8 V (typ.). The controller is disabled by pulling down on

the EN pin. Figure 12 shows the relationship between enable

and soft-start.

EN

SOFT-S

Vout

INTERNAL REFERENCE

The internal 0.8 V reference facilitates the

implementation of sub 1 V supplies required in modern

computing equipment. The internal reference is trimmed

during manufacturing to obtain better than ±2% accuracy

over the complete operating range.

The output voltage, Vout, is programmed using a resistor

divider (R1 and R2) as shown in Figure 1.

The resistor divider senses the output voltage and

compares it to the internal 0.8 V reference.

tSOFT-S

Figure 12. Relationship Between Enable and

Soft-Start

The EN pin can be connected to VCC if the enable feature

is not used. If connected to VCC and VCC is higher than 9.5 V

a resistor in series should be used to limit the current into the

EN pin as the pin is internally clamped to 9.5 V. A minimum

of 40 kW is recommended.

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