NCP690(2009) 데이터 시트보기 (PDF) - ON Semiconductor

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NCP690
(Rev.:2009)

1 A, Low IGND, Very Low Dropout Regulator (VLDO) with/without Enable

ON Semiconductor 

NCP690, NCP691, NCP692

divider network as shown on Figure 4. The output voltage

and resistors should be chosen using Equations 1 and 2.

ǒ Ǔ VOUT + 1.250

1

)

R1

R2

) (IADJ @ R1)

(eq. 1)

R2

^

R1

1

VOUT

1.25

*

1

(eq. 2)

Input bias current IADJ is typically less than 210 nA.

Choose R1 arbitrarily to minimize errors due to the bias

current and to minimize noise contribution to the output

voltage. Use Equation 2 to find the required value for R2.

Thermal Characteristics

As power dissipated in the NCP690 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 NCP690 has good thermal

conductivity through the PCB, the junction temperature will

be relatively low with high power applications. The

maximum dissipation the NCP690 can handle is given by:

PD(MAX)

+

[TJ(MAX) *

RqJA

TA]

(eq. 3)

Since TJ is not recommended to exceed 125°C (TJ(MAX)),

then the NCP690 can dissipate up to 1 W when the ambient

temperature (TA) is 25°C.

The power dissipated by the NCP690 can be calculated

from the following equations:

PD [ VIN(IGND@IOUT) ) IOUT(VIN * VOUT) (eq. 4)

or

VIN(MAX)

[

PD(MAX) ) (VOUT

IOUT ) IGND

IOUT)

(eq. 5)

250

200

150

FR4 − 1.0 oz

100

FR4 − 2.0 oz

50

0

0

200

400

600

800

COPPER AREA (mm2)

Figure 32. Thermal Resistance vs. Copper Area

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 NCP690, and

make traces as short as possible.

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