AN3011 datasheet(32/37 Pages) STMICROELECTRONICS

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Efficiency

AN3011

32/37

Doc ID 16043 Rev 1

Figure 36.

Brown-out protection, internal block diagram

The current hysteresis provides an additional degree of freedom. It is possible to set the ON

threshold and the OFF threshold for the flyback input voltage separately by properly

choosing the external divider resistors. The following relationships can be established for the

ON (VIN_ON) and OFF (VIN_OFF) thresholds of the input voltage:

Equation 2

Equation 3

Where IBRhyst=10 µA (typ.) is the current hysteresis, VBRhyst=50 mV (typ.) is the voltage

hysteresis and VBRth=450 mV (typ.) is the brown-out comparator internal reference.

One purpose of this protection is to stop operation of the converter when the line voltage is

too low, avoiding too high root mean square current value flowing inside the main switch an

then its overheating. Another purpose is to avoid a false restart of the converter and then

Figure 34.

J7 jumper setting. Brown-out

disabled

Figure 35.

J7 jumper setting. Brown-out

enabled

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

⋅

BRth

OFF

()

BRhyst

BRth

⋅

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

⋅

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