MD3221N 데이터 시트보기 (PDF) - Shindengen

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MD3221N

DC-DC Converter Power IC

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voltage applied must be no higher than VCC.

When the remote ON / OFF function is used, a

condenser is connected across the R / C and GND pins

to prevent malfunctioning due to noise. If the

capacitance of this condenser is too high, the output

voltage will be produced instantaneously when an input

voltage is applied while the MD3221N is OFF. The

capacitance of this condenser should be approximately

1/ 3 of that of the S / S condenser (C2) as obtained from

the graph in 'Soft Start Function' (P11).

● Remote Control Circuit

1

R/C

C

MD3221N

To turn the timer latch off, use the R / C function to

switch OFF the MD3221N, or switch OFF the power

supply voltage.

This function also employs the S / S pin condenser as

a timer. Determine the capacitance of this condenser

in reference to the section on soft start.

● Over-current Protection

Itimer

32

S/S

C2

MD3221N

◆The Reference Voltage (Vref)

The MD3221N provides an internal temperature

compensated reference voltage (4V) which may be

used as a reference voltage up to 1mA for external

circuits. A condenser (C8) of approximately 0.1μF

is connected across the Vref and GND pins to

prevent malfunctioning due to noise.

＊Note that this voltage differs from the error amp

reference voltage.

◆The Over-current Protection Function (timer latch)

The MD3221N incorporates an over-current protection

function. As the over-current condition is detected with

the use of the voltage drop resulting from the ON

resistance of the internal MOSFET, an external

detection resistance is not required. When the over-

current condition is detected the condenser (C2)

connected to the S / S pin is charged again, and

when a level of 3.45V is reached the latch is halted.

Vi

2.9V

Vss

Vo

3.45V

Over-current

In the process of increasing the output voltage at start-

up, the converter generally charges the output

condenser resulting in the over-current condition. When

the over-current protection circuit operates the latch

is halted and start-up becomes impossible. The

MD3221N timer circuit is locked to prevent its

operation until the voltage at the S / S pin reaches 2.9V,

and when the S / S pin is fully charged the lock is

cleared and the timer circuit is ready for operation.

If, however, the output voltage does not rise by the

time the S / S pin is charged to 2.9V, the over-current

protection circuit operates and the latch is halted. The

output voltage must therefore reach the set voltage

before the voltage at the S / S pin reaches 2.9V.

12

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