NCV47701 查看數據表（PDF） - ON Semiconductor

零件编号

产品描述 (功能)

生产厂家

NCV47701

Low Dropout Regulator - Adjustable Current Limit 5 V to 20 V

ON Semiconductor 

NCV47701

APPLICATIONS INFORMATION

Circuit Description

The NCV47701 is an integrated low dropout regulator

that provides a regulated voltage at 350 mA to the output. It

is enabled with an input to the enable pin. The regulator

voltage is provided by a PNP pass transistor controlled by an

error amplifier with a bandgap reference, which gives it the

lowest possible dropout voltage. The output current

capability is 350 mA, and the base drive quiescent current is

controlled to prevent oversaturation when the input voltage

is low or when the output is overloaded. The integrated

current sense feature provides diagnosis and system

protection functionality. The current limit of the device is

adjustable by resistor connected to CSO pin. Voltage on

CSO pin is proportional to output current. The regulator is

protected by both current limit and thermal shutdown.

Thermal shutdown occurs above 150°C to protect the IC

during overloads and extreme ambient temperatures.

Regulator

The error amplifier compares the reference voltage to a

sample of the output voltage (Vout) and drives the base of a

PNP series pass transistor via a buffer. The reference is a

bandgap design to give it a temperature−stable output.

Saturation control of the PNP is a function of the load current

and input voltage. Oversaturation of the output power

device is prevented, and quiescent current in the ground pin

is minimized.

Calculating Bypass Capacitor

If usage of low ESR ceramic capacitors is demanded,

connect the bypass capacitor Cb between Adjustable Input

pin and Vout pin according to Applications circuit at

Figure 1. Parallel combination of bypass capacitor Cb with

the feedback resistor R1 contributes in the device transfer

function as an additional zero and affects the device loop

stability, therefore its value must be optimized. Attention to

the Output Capacitor value and its ESR must be paid. See

also Stability in High Speed Linear LDO Regulators

Application Note, AND8037/D for more information.

Optimal value of bypass capacitor is given by following

expression:

Cb + 2

1

p fz

R1

(eq. 1)

where

R1 − the upper feedback resistor

fz − the frequency of the zero added into the device

transfer function by R1 and Cb external components.

Set the R1 resistor according to output voltage requirement.

Chose the fz with regard on the output capacitance Cout, refer

to the table below.

Cout (mF)

fZ range (kHz)

10

3.3−48.2

22

1.5−33

47

1.5−33

100

2.2−22

Regulator Stability Considerations

The input capacitor (Cin) is necessary to stabilize the input

impedance to avoid voltage line influences. The output

capacitor (Cout) helps determine three main characteristics

of a linear regulator: startup delay, load transient response

and loop stability. The capacitor value and type should be

based on cost, availability, size and temperature constraints.

The aluminum electrolytic capacitor is the least expensive

solution, but, if the circuit operates at low temperatures

(−25°C to −40°C), both the value and ESR of the capacitor

will vary considerably. The capacitor manufacturer’s data

sheet usually provides this information. The value for the

output capacitor Cout, shown in Figure 1 should work for

most applications; see also Figure 17 for output stability at

various load and Output Capacitor ESR conditions. Stable

region of ESR in Figure 17 shows ESR values at which the

LDO output voltage does not have any permanent

oscillations at any dynamic changes of output load current.

Marginal ESR is the value at which the output voltage

waving is fully damped during four periods after the load

change and no oscillation is further observable.

ESR characteristics were measured with ceramic

capacitors and additional series resistors to emulate ESR.

Low duty cycle pulse load current technique has been used

to maintain junction temperature close to ambient

temperature.

Ceramic capacitors and its part numbers listed bellow

have been used as low ESR output capacitors Cout from the

table above to define the frequency ranges of additional zero

required for stability:

GRM31CR71C106KAC7 (10 mF, 16 V, X7R, 1206)

GRM32ER71C226KE18 (22 mF, 16 V, X7R, 1210)

GRM32ER61C476ME15 (47 mF, 16 V, X5R, 1210)

GRM32ER60J107ME20 (100 mF, 6.3 V, X5R, 1210)

Enable Input

The enable pin is used to turn the regulator on or off. By

holding the pin down to a voltage less than 0.8 V, the output

of the regulator will be turned off. When the voltage on the

enable pin is greater than 3.5 V, the output of the regulator

will be enabled to power its output to the regulated output

voltage. The enable pin may be connected directly to the

input pin to give constant enable to the output regulator.

Setting the Output Voltage

The output voltage range can be set between 5 V and 20 V.

This is accomplished with an external resistor divider

feeding back the voltage to the IC back to the error amplifier

by the voltage adjust pin ADJ. The internal reference voltage

is set to a temperature stable reference (VREF1) of 1.275 V.

www.onsemi.com

9

Share Link: