NCV8705(2014) 데이터 시트보기 (PDF) - ON Semiconductor

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NCV8705
(Rev.:2014)

500 mA, Ultra-Low Quiescent Current, IQ 13 μA, Ultra-Low Noise, LDO Voltage Regulator

ON Semiconductor 

NCV8705

VIN

IN

OUT

NCV8705

1 mF CIN

EN

ADJ

ON

GND

OFF

R1 C1

R2

VOUT

COUT

1 mF

Internal Soft−Start circuit

NCV8705 contains an internal soft−start circuitry to

protect against large inrush currents which could otherwise

flow during the start−up of the regulator. Soft−start feature

protects against power bus disturbances and assures a

controlled and monotonic rise of the output voltage.

Figure 65. NCV8705 Adjustable with Noise

Improvement Capacitor

Enable Operation

The NCV8705 uses the EN pin to enable/disable its device

and to deactivate/activate the active discharge function.

If the EN pin voltage >0.9 V the device is guaranteed to

be enabled. The NCV8705 regulates the output voltage and

the active discharge transistor is turned−off.

The EN pin has internal pull−down current source with

typ. value of 110 nA which assures that the device is

turned−off when the EN pin is not connected. Build in 2 mV

hysteresis into the EN prevents from periodic on/off

oscillations that can occur due to noise.

In the case where the EN function isn’t required the EN

should be tied directly to IN.

Undervoltage Lockout

The internal UVLO circuitry assures that the device

becomes disabled when the VIN falls below typ. 1.5 V. When

the VIN voltage ramps−up the NCV8705 becomes enabled, if

VIN rises above typ. 1.6 V. The 100 mV hysteresis prevents

from on/off oscillations that can occur due to noise on VIN line.

Output Current Limit

Output Current is internally limited within the IC to a

typical 750 mA. The NCV8705 will source this amount of

current measured with a voltage drops on the 90% of the

nominal VOUT. If the Output Voltage is directly shorted to

ground (VOUT = 0 V), the short circuit protection will limit

the output current to 800 mA (typ). The current limit and

short circuit protection will work properly up to

VIN = 5.5 V at TA = 125°C. There is no limitation for the

short circuit duration.

220

Thermal Shutdown

When the die temperature exceeds the Thermal Shutdown

threshold (TSD − 160°C typical), Thermal Shutdown event

is detected and the device is disabled. The IC will remain in

this state until the die temperature decreases below the

Thermal Shutdown Reset threshold (TSDU − 140°C typical).

Once the IC temperature falls below the 140°C the LDO is

enabled again. The thermal shutdown feature provides the

protection from a catastrophic device failure due to

accidental overheating. This protection is not intended to be

used as a substitute for proper heat sinking.

Power Dissipation

As power dissipated in the NCV8705 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.

The maximum power dissipation the NCV8705 can

handle is given by:

ƪ ƫ TJ(MAX) * TA

PD(MAX) +

qJA

(eq. 3)

The power dissipated by the NCV8705 for given

application conditions can be calculated from the following

equations:

PD [ VINǒIGND@IOUTǓ ) IOUTǒVIN * VOUTǓ (eq. 4)

1.6

200

1.4

PD(MAX), TA = 25°C, 2 oz Cu

180

1.2

160

1

PD(MAX), TA = 25°C, 1 oz Cu

140

0.8

qJA, 1 oz Cu

120

0.6

100

qJA, 2 oz Cu

0.4

80

0

0.2

100 200 300 400 500 600 700

COPPER HEAT SPREADER AREA (mm2)

Figure 66. qJA and PD(MAX) vs. Copper Area (WDFN6)

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