AN4077

Test results and significant waveforms

Doc ID 022997 Rev 1

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must sink a current from the output bus which needs to be significantly higher than the

current biasing the error amplifier and PFC_OK comparator.

The OVP function described above is able to handle “normal” overvoltage conditions, i.e.

those resulting from an abrupt load/line change or occurring at startup. If the overvoltage is

generated by a feedback disconnection, for instance, when one of the upper resistors of the

output divider fails open, an additional circuitry detects the voltage drop of the INV pin. If the

voltage on the INV pin is lower than 1.66 V and at the same time the OVP is active, a

feedback failure is assumed. Therefore, the gate drive activity is immediately stopped, the

device is shut down, its quiescent consumption is reduced below 180 µA and the condition

is latched as long as the supply voltage of the IC is above the UVLO threshold. To restart the

goes below 6 V and that of the PWM controllers goes below its UVLO threshold.

Note that this function offers a complete protection against not only feedback loop failures or

erroneous settings, but also against a failure of the protection itself. Either resistor of the

PFC_OK divider failing short or open, or a PFC_OK pin floating, results in shutting down the

IC and stopping the pre-regulator. Moreover, the PFC_OK pin doubles its function as a not-

latched IC disable: a voltage below 0.23 V shuts down the IC, reducing its consumption

below 2 mA. To restart the IC simply let the voltage at the pin go above 0.27 V.

The event of an open loop is captured in

Figure 30, note that the protection intervention

latches the operation of the L6564H.

4.5

Power management and housekeeping functions

Differently from similar PFC controllers with more pins, the housekeeping functions of the

L6564H are minimized but still there, and the device, in spite of the low pin count, still has

some main functionalities that make it suitable to be implemented in high-end applications.

For example, in order to save power during light load operation or to put the converter in a

safe condition after detecting a failure of the DC-DC converter, a communication line can be

Figure 29.

EVL6564H-100W load transient at

Figure 30.

EVL6564H-100W open loop at 115