MS1003SH･MS1004SH

Application Note Ver.2.2

SHINDENGEN ELECTRIC MFG. CO. , LTD

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3. Circuit operation

3.1 Startup

The diagram below shows the startup sequence.

Startup sequence

3.1.1 Startup circuit

The startup circuit does not require a startup resistor,

making it possible to easily start the IC with a small

number of components. A schematic diagram of the

startup circuit is shown to the right.

Until the IC starts up, the startup circuit current Icc

(stup) flows from the Vin pin to the Vcc pin to charge

C, as shown in the diagram.

Oscillation begins when the voltage at the Vcc pin

reaches Vcc (start). The startup circuit opens, and the

startup circuit current stops. The Vcc pin has hysteresis,

which begins oscillating at Vcc (start) and stops

oscillating at Vcc (stop stby) or Vcc (stop normal). A

bias assist function is provided for the Vcc voltage to ensure safe startup. For more information on the bias

assist function, see Section 3.1.3.

Vin

Nc coil

backup

Vcc

VccUVLO

Startup

UVLO

Standby

Vcc(start)=

Vcc(stup off)=12V

Off

On

Normal mode

Standby mode

Vcc(stop normal)=8V

Vcc(stop on normal)=9V

Vcc(stup on stby)=8V

Vcc(stop stby)=12V

Off

On

Off

On

Off

On

Normal mode

Startup circuit

Vcc pin

Vin pin