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

APPLICATIONS INFORMATION

General

The NCV8705 is a high performance 500 mA Low

Dropout Linear Regulator. This device delivers excellent

noise and dynamic performance. Thanks to its adaptive

ground current feature the device consumes only 13 mA of

quiescent current at no*load condition. The regulator

features ultra*low noise of 12 mVRMS, PSRR of 71 dB at

1 kHz and very good load/line transient performance. Such

excellent dynamic parameters and small package size make

the device an ideal choice for powering the precision analog

and noise sensitive circuitry in portable applications. The

LDO achieves this ultra low noise level output without the

need for a noise bypass capacitor. A logic EN input provides

ON/OFF control of the output voltage. When the EN is low

the device consumes as low as typ. 10 nA from the IN pin.

The device is fully protected in case of output overload,

output short circuit condition and overheating, assuring a

very robust design.

Input Capacitor Selection (CIN)

It is recommended to connect a minimum of 1 mF Ceramic

X5R or X7R capacitor close to the IN pin of the device. This

capacitor will provide a low impedance path for unwanted

AC signals or noise modulated onto constant input voltage.

There is no requirement for the min. /max. ESR of the input

capacitor but it is recommended to use ceramic capacitors

for their low ESR and ESL. A good input capacitor will limit

the influence of input trace inductance and source resistance

during sudden load current changes. Larger input capacitor

may be necessary if fast and large load transients are

encountered in the application.

Output Decoupling (COUT)

The NCV8705 requires an output capacitor connected as

close as possible to the output pin of the regulator. The

minimal capacitor value is 1 mF and X7R or X5R dielectric

due to its low capacitance variations over the specified

temperature range. The NCV8705 is designed to remain

stable with minimum effective capacitance of 1 mF to

account for changes with temperature, DC bias and package

size. Especially for small package size capacitors such as

0402 the effective capacitance drops rapidly with the

applied DC bias. Refer to the Figure 64, for the capacitance

vs. package size and DC bias voltage dependence.

There is no requirement for the minimum value of

Equivalent Series Resistance (ESR) for the COUT but the

maximum value of ESR should be less than 900 mΩ. Larger

output capacitors and lower ESR could improve the load

transient response or high frequency PSRR as shown in

typical characteristics. It is not recommended to use

tantalum capacitors on the output due to their large ESR. The

equivalent series resistance of tantalum capacitors is also

strongly dependent on the temperature, increasing at low

temperature. The tantalum capacitors are generally more

costly than ceramic capacitors.

10

0

−10

−20

−30

−40

−50

Package Size

1206

−60

0805

−70

0603

0402

−80

0 1 2 3 4 5 6 7 8 9 10

DC BIAS (V)

Figure 64. Capacitance Change vs. DC Bias

No−load Operation

The regulator remains stable and regulates the output

voltage properly within the ±2% tolerance limits even with

no external load applied to the output.

Adjustable Operation

The output voltage range can be set from 0.8 V to

5.5 V−VDO by resistor divider network. Use Equations 1

and 2 to calculate appropriate values of resistors and output

voltage. Typical current to ADJ pin is 1 nA. For output

voltage 0.8 V ADJ pin can be tied directly to Vout pin.

ǒ Ǔ VOUT + 0.8 @

1

)

R1

R2

) R1 @ IADJ

(eq. 1)

R2

^

R1

@

1

VOUT

0.8

*

1

(eq. 2)

The resistor divider should be designed carefully to

achieve the best performance. Recommended current

through divider is 10 mA and more. Too high values of

resistors (MW) cause increasing noise and longer start−up

time. The suggested values of the resistors are in Table 5. To

improve dynamic performance capacitor C1 should be at

least 1 nF. Recommended range of capacity is between

10 nF and 100 nF. Higher value of capacitor C1 increasing

start−up time.

Table 5. Proposal Resistor Values for Variuos VOUT

VOUT

R1

R2

1.5 V

130k

150k

3.3 V

256k

82k

5.0 V

430k

82k

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