NCV8675(2007) データシートの表示（PDF） - ON Semiconductor

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NCV8675
(Rev.:2007)

350 mA Very Low Iq Low Dropout Linear Regulator with Reset and Reset Delay

ON Semiconductor 

NCV8675

VIN

CIN

100 nF

IN

1

OUT

5

NCV8675

IOUT

COUT

22 mF

VOUT

REXT

5.0 K

ID D

RO

4

2

CD

3

IRO

VRO

47 nF

GND

IG

Figure 34. Application Circuits

Circuit Description

The NCV8675 is an integrated low dropout regulator that

provides 5.0 V 350 mA, or 3.3 V 350 mA protected output

and a signal for power on reset. The regulation is provided

by a PNP pass transistor controlled by an error amplifier

with a bandgap reference, which gives it the lowest possible

drop out voltage and best possible temperature stability. The

output current capability is 350 mA, and the base drive

quiescent current is controlled to prevent over saturation

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. The delay time for the reset output is

adjustable by selection of the timing capacitor. See

Figure 34, Test Circuit, for circuit element nomenclature

illustration.

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 by 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.

Regulator Stability Considerations

The input capacitor (CIN) is necessary to stabilize the

input impedance to avoid voltage line influences. 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.

Ceramic, tantalum, or electrolytic capacitors of 22 mF, or

greater, are stable with very low ESR values. Refer to

Figure 2 for specific ESR ratings. The aluminum

electrolytic capacitor is the least expensive solution, but, if

the circuit operates at low temperatures (-25°C to -40°C),

both the capacitance 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 13, Test Circuit, should

work for most applications; however, it is not necessarily the

optimized solution.

Reset Output

The reset output is used as the power on indicator to the

microcontroller. This signal indicates when the output

voltage is suitable for reliable operation of the controller. It

pulls low when the output is not considered to be ready. RO

is pulled up to VOUT by an external resistor, typically 5.0 kW

in value. The input and output conditions that control the

Reset Output and the relative timing are illustrated in

Figure 35, Reset Timing. Output voltage regulation must be

maintained for the delay time before the reset output signals

a valid condition. The delay for the reset output is defined as

the amount of time it takes the timing capacitor on the delay

pin to charge from a residual voltage of 0 V to the upper

timing threshold voltage VDU of 1.3 V. The charging current

for this is ID of 4 mA. By using typical IC parameters with

a 47 nF capacitor on the D Pin, the following time delay is

derived:

tRD + CD * VDUńID

tRD + 47ĂnF * (1.3ĂV)ń4ĂmA + 15.3Ăms

Other time delays can be obtained by changing the CD

capacitor value. The Delay Time can be reduced by

decreasing the capacitance of CD. Using the formula above,

Delay can be reduced as desired. Leaving the Delay Pin

open is not desirable as it can result in unwanted signals

being coupled onto the pin.

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