NCV47701 查看數據表（PDF） - ON Semiconductor

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NCV47701

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

ON Semiconductor 

NCV47701

The output voltage is calculated from the following formula.

Ignoring the bias current into the ADJ pin:

ǒ Ǔ Vout + VREF1

1 ) R1

R2

(eq. 2)

Use R2 < 50 kW to avoid significant voltage output errors

due to ADJ bias current.

Designers should consider the tolerance of R1 and R2 during

the design phase.

Setting the Output Current Limit

The output current limit can be set between 10 mA and

350 mA by external resistor RCSO (see Figure 1). Capacitor

CCSO of 1 mF in parallel with RCSO is required for stability

of current limit control circuitry (see Figure 1).

ǒ Ǔ VCSO + Iout RCSO

1

100

(eq. 3)

ILIM

+

100

1

2.55

RCSO

(eq. 4)

RCSO

+

100

1

2.55

ILIM

(eq. 5)

Where

RCSO

− current limit setting resistor

VCSO

− voltage at CSO pin proportional to Iout

ILIM

− current limit value

Iout

− output current actual value

CSO pin provides information about output current actual

value. The CSO voltage is proportional to output current

according to Equation 3.

Once output current reaches its limit value (ILIM) set by

external resistor RCSO than voltage at CSO pin is typically

2.55 V. Calculations of ILIM or RCSO values can be done

using equations Equation 4 and Equation 5, respectively.

Thermal Considerations

As power in the NCV47701 increases, it might become

necessary to provide some thermal relief. The maximum

power dissipation supported by the device is dependent

upon board design and layout. Mounting pad configuration

on the PCB, the board material, and the ambient temperature

affect the rate of junction temperature rise for the part. When

the NCV47701 has good thermal conductivity through the

PCB, the junction temperature will be relatively low with

high power applications. The maximum dissipation the

NCV47701 can handle is given by:

ƪ ƫ TJ(MAX) * TA

PD(MAX) +

RqJA

(eq. 6)

Since TJ is not recommended to exceed 150°C, then the

NCV47701 soldered on 645 mm2, 1 oz copper area, FR4

can dissipate up to 1.8 W (SOIC−8 EP) or 1 W (SOIC−8) and

up to 4.3 W (SOIC−8 EP) or 1.6 W (SOIC−8) for 4 layers

PCB (all layers are 1 oz) when the ambient temperature (TA)

is 25°C. See Figure 18 for RthJA versus PCB area. The power

dissipated by the NCV47701 can be calculated from the

following equations:

PD + VinǒIq@IoutǓ ) IoutǒVin * VoutǓ

(eq. 7)

or

PD(MAX) ) ǒVout

Vin(MAX) [

Iout ) Iq

IoutǓ

(eq. 8)

Hints

Vin and GND printed circuit board traces should be as

wide as possible. When the impedance of these traces is

high, there is a chance to pick up noise or cause the regulator

to malfunction. Place external components, especially the

output capacitor, as close as possible to the NCV47701 and

make traces as short as possible.

220

200

180

160

140

120

100

1 oz

80

1 oz

2 oz

1 oz

2 oz 2 oz

SO−8 single layer PCB

SO−8 EP single layer PCB

60 SO−8 4 layers PCB

40 SO−8 EP 4 layers PCB

1 oz 2 oz

20

0 100 200 300 400 500 600 700

COPPER HEAT SPREADER AREA (mm2)

Figure 18. Thermal Resistance vs. PCB Copper Area

ORDERING INFORMATION

Device

Output Voltage

Marking

Package

Shipping†

NCV47701PDAJR2G

Adjustable

47701

SOIC−8 EP

(Pb−Free)

2500 / Tape & Reel

NCV47701DAJR2G

Adjustable

47701

SOIC−8

(Pb−Free)

2500 / Tape & Reel

†For information on tape and reel specifications,including part orientation and tape sizes, please refer to our Tape and Reel Packaging

Specifications Brochure, BRD8011/D.

www.onsemi.com

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