L6563S datasheet(33/42 Pages) STMICROELECTRONICS

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L6563S

Application information

Doc ID 16116 Rev 3

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Figure 46.

Interface circuits for actual power-up sequencing (master PFC)

Another possible use of the RUN and PWM_STOP pins (again, in systems where the PFC

stage is the master) is the brownout protection, thanks to the hysteresis provided.

The brownout protection is basically a not-latched device shutdown function that is activated

when a condition of mains undervoltage is detected. This condition may cause overheating

of the primary power section due to an excess of RMS current. Brownout can also cause the

PFC pre-regulator to work open loop and this could be dangerous to the PFC stage itself

and the downstream converter, should the input voltage return abruptly to its rated value.

Another problem is the spurious restarts that may occur during converter power down and

that cause the output voltage of the converter not to decay to zero monotonically. For these

reasons it is usually preferable to shutdown the unit in case of brownout.

IC shutdown upon brownout can be easily realized as shown in Figure 47. The scheme on

the left is of general use, that one on the right can be used if the bias levels of the multiplier

and the RFF·CFF time constant are compatible with the specified brownout level and with the

specified holdup time respectively. In this latest case, an additional resistor voltage divider

and one capacitor are not needed.

In table 1 it is possible to find a summary of all of the above mentioned working conditions

that cause the device to stop operating.

Figure 47.

Brownout protection (master PFC)

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