NCP623 查看數據表（PDF） - ON Semiconductor

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NCP623

Ultra Low Noise 150 mA Low Dropout Voltage Regulator with ON/OFF Control

ON Semiconductor 

NCP623

NCP623 Wake−up Improvement − In portable

applications, an immediate response to an enable signal is

vital. If noise is not a concern, the NCP623 without a bypass

capacitor settles in nearly 20 ms and typically delivers

65 mVRMS between 100 Hz and 100 kHz.

In ultra low−noise systems, the designer needs a 10 nF

bypass capacitor to decrease the noise down to 25 mVRMS

between 100 Hz and 100 kHz. With the addition of the 10 nF

capacitor, the wake−up time expands up to 1.0 ms as shown

on the data−sheet curves. If an immediate response is

wanted, Figure 5 provides a solution to charge the bypass

capacitor with the enable signal without degrading the noise

response of the NCP623.

At power−on, C4 is discharged. When the control logic

sends its wake−up signal by going high, the PNP base is

momentarily tied to ground. The PNP switch closes and

immediately charges the bypass capacitor C1 toward its

operating value. After a few ms, the PNP opens and becomes

totally transparent to the regulator.

This circuit improves the response time of the regulator

which drops from 1.0 ms down to 30 ms. The value of C4

needs to be tweaked in order to avoid any bypass capacitor

overload during the wake−up transient.

C4

470 pF

MMBT2902LT1

Q1

C1

10 nF

R2

220 k

On/Off

C3

1.0 mF

+

65 4

NCP623

1 23

Input

Output

C2

+ 1.0 mF

Output

876 5

C2

1.0 mF

+

NCP623

1 23 4

C1

10 nF

MMBT2902LT1

Q1

Input

C3

1.0 mF

+

On/Off

R2

220 k

C4

470 pF

Figure 4. A PNP Transistor Drives the

Bypass Pin when Enable Goes High (DFN6)

Figure 5. A PNP Transistor Drives the

Bypass Pin when Enable Goes High (Micro8)

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