STMicroelectronics 19 V - 75 W SMPS using the L6563 and the L6566A EVL6566A-75WES4 EVL6566A-75WES4 Data Sheet
Product codes
EVL6566A-75WES4
L6563S
Application information
Doc ID 16116 Rev 4
31/43
occasionally slightly saturate when the PFC stage is restarted because of a larger load
demand. This happens when the restart occurs at an unfavorable line voltage phase, i.e.
when the output voltage is significantly below the rectified peak voltage. As a result, in the
boost inductor the inrush current coming from the bridge rectifier adds up to the switched
current and, furthermore, there is little or no voltage available for demagnetization.
demand. This happens when the restart occurs at an unfavorable line voltage phase, i.e.
when the output voltage is significantly below the rectified peak voltage. As a result, in the
boost inductor the inrush current coming from the bridge rectifier adds up to the switched
current and, furthermore, there is little or no voltage available for demagnetization.
To cope with a saturated inductor, the L6563S is provided with a second comparator on the
current sense pin (CS, pin 4) that stops the IC if the voltage, normally limited within 1.1 V,
exceeds 1.7 V. After that, the IC will be attempted to restart by the internal starter circuitry;
the starter repetition time is twice the nominal value to guarantee lower stress for the
inductor and boost diode. Hence, the system safety will be considerably increased.
current sense pin (CS, pin 4) that stops the IC if the voltage, normally limited within 1.1 V,
exceeds 1.7 V. After that, the IC will be attempted to restart by the internal starter circuitry;
the starter repetition time is twice the nominal value to guarantee lower stress for the
inductor and boost diode. Hence, the system safety will be considerably increased.
Figure 42.
Effect of boost inductor saturation on the MOSFET current and detection method
6.7
Power management/housekeeping functions
A special feature of this IC is that it facilitates the implementation of the “housekeeping”
circuitry needed to co-ordinate the operation of the PFC stage to that of the cascaded DC-
DC converter. The functions realized by the housekeeping circuitry ensure that transient
conditions like power-up or power down sequencing or failures of either power stage be
properly handled.
circuitry needed to co-ordinate the operation of the PFC stage to that of the cascaded DC-
DC converter. The functions realized by the housekeeping circuitry ensure that transient
conditions like power-up or power down sequencing or failures of either power stage be
properly handled.
This device provides some pins to do that. One communication line between the IC and the
PWM controller of the cascaded dc-dc converter is the pin PWM_LATCH (
PWM controller of the cascaded dc-dc converter is the pin PWM_LATCH (
b
),
which is normally open (high impedance) when the PFC works properly, and goes high if it
loses control of the output voltage (because of a feedback loop disconnection) with the aim
of latching off the PWM controller of the cascaded dc-dc converter as well (see “Feedback
failure protection” section for more details).
loses control of the output voltage (because of a feedback loop disconnection) with the aim
of latching off the PWM controller of the cascaded dc-dc converter as well (see “Feedback
failure protection” section for more details).
A second communication line can be established via the disable function included in the
PFC_OK pin (see “Feedback failure protection” section for more details). Typically this line is
used to allow the PWM controller of the cascaded dc-dc converter to drive in burst mode
operation the L6563S in case of light load and to minimize the no-load input consumption.
Interface circuits like those are shown in
PFC_OK pin (see “Feedback failure protection” section for more details). Typically this line is
used to allow the PWM controller of the cascaded dc-dc converter to drive in burst mode
operation the L6563S in case of light load and to minimize the no-load input consumption.
Interface circuits like those are shown in