NCV4276BDT50RKG datasheet(11/18 Pages) ONSEMI

Part #	NCV4276BDT50RKG

Description	400 mA Low?륞rop Voltage Regulator

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Manufacturer	ONSEMI [ON Semiconductor]

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NCV4276B

http://onsemi.com

11

Circuit Description

The NCV4276B is an integrated low dropout regulator

that provides a regulated voltage at 400 mA to the output.

It is enabled with an input to the inhibit 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 400 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

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 (VQ) 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. See Figure 4, Test Circuit, for

circuit element nomenclature illustration.

Regulator Stability Considerations

The input capacitors (CI1 and CI2) are necessary to

stabilize the input impedance to avoid voltage line

influences. Using a resistor of approximately 1.0

W in

series with CI2 can stop potential oscillations caused by

stray inductance and capacitance.

The output capacitor 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 CQ, shown in Figure 3,

should work for most applications; see also Figures 5 to 7

for output stability at various load and Output Capacitor

ESR conditions. Stable region of ESR in Figures 5 to 7

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.

Minimum ESR for CQ =22 mF is native ESR of ceramic

capacitor with which the fixed output voltage devices are

performing stable. Murata ceramic capacitors were used,

GRM32ER71C226KE18 (22

mF, 16 V, X7R, 1210),

GRM31CR71C106KAC7 (10

mF, 16 V, X7R, 1206).

Calculating Bypass Capacitor

If usage of low ESR ceramic capacitors is demand in case

of Adjustable Regulator, connect the bypass capacitor Cb

between Voltage Adjust pin and Q pin according to

Applications circuit at Figure 4.

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 +

1

2

p

fz

R1

@ (F)

(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 CQ, refer to the table below.

CQ (mF)

10

22

47

100

fz Range (kHz)

20 - 50

14 - 35

10 - 20

7 – 14

Ceramic capacitors and its part numbers listed bellow

have been used as low ESR output capacitors CQ 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)

Inhibit Input

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

holding the pin down to a voltage less than 1.8 V, the output

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

Inhibit pin is greater than 2.8 V, the output of the regulator

will be enabled to power its output to the regulated output

voltage. The inhibit pin may be connected directly to the

input pin to give constant enable to the output regulator.

Setting the Output Voltage (Adjustable Version)

The output voltage range of the adjustable version can be

set between 2.5 V and 20 V. This is accomplished with an

external resistor divider feeding back the voltage to the IC

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NCV4276BDT50RKG Datasheet(PDF) 11 Page - ON Semiconductor

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