L6564H datasheet(25/35 Pages) STMICROELECTRONICS

25 / 35 page

L6564H

Application information

Doc ID 022960 Rev 2

25/35

Figure 37.

Interface circuits that let the DC-DC converter’s controller IC disable the

L6564H

Another function available is the brownout protection which is basically a not-latched

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 function in open loop and this

may 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 shut down the unit

in case of brownout. The brownout threshold is internally fixed at 0.8 V and is sensed on the

VFF pin (#5) during the voltage falling and an 80 mV threshold hysteresis prevents

rebounding at input voltage turn-off. In

Table 5 it is possible to find a summary of all of the

above mentioned working conditions that cause the device to stop operating.

L6564H Datasheet(PDF) 25 Page - STMicroelectronics