L6564D STMicroelectronics, L6564D Datasheet - Page 19

• Manufacturer Part Number: L6564D
• Description: IC PFC CTRLR TRANSITION 10SSOP
• Manufacturer: STMicroelectronics

Specifications of L6564D

• Mode: Discontinuous (Transition)
• Frequency - Switching: 1MHz
• Current - Startup: 90µA
• Voltage - Supply: 10.3 V ~ 22.5 V
• Operating Temperature: -25°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 10-SSOP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: L6564; L6564

L6564
6.2
6.3
Feedback failure protection (FFP)
The OVP function above described handles “normal” over voltage conditions, i.e. those
resulting from an abrupt load/line change or occurring at start-up. In case the overvoltage is
generated by a feedback disconnection, for instance when the upper resistor of the output
divider (R1) fails open, comparator detects the voltage at pin INV. If the voltage is lower than
1.66V and the OVP is active, the FFP is triggered, 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 system it is necessary to recycle the input power, so that the Vcc voltage of
the L6564 goes below 6 V.
The pin PFC_OK doubles its function as a not-latched IC disable: a voltage below 0.23 V will
shut 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.
Note that these functions offer 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 will result in shutting down
the IC and stopping the pre-regulator.
Voltage feedforward
The power stage gain of PFC pre-regulators varies with the square of the RMS input
voltage. So does the crossover frequency fc of the overall open-loop gain because the gain
has a single pole characteristic. This leads to large trade-off in the design.
For example, setting the gain of the error amplifier to get fc = 20 Hz @ 264 Vac means
having fc 4 Hz @ 88 Vac, resulting in a sluggish control dynamics. Additionally, the slow
control loop causes large transient current flow during rapid line or load changes that are
limited by the dynamics of the multiplier output. This limit is considered when selecting the
sense resistor to let the full load power pass under minimum line voltage conditions, with
some margin. But a fixed current limit allows excessive power input at high line, whereas a
fixed power limit requires the current limit to vary inversely with the line voltage.
Voltage feedforward can compensate for the gain variation with the line voltage and allow
minimizing all of the above-mentioned issues. It consists of deriving a voltage proportional to
the input RMS voltage, feeding this voltage into a squarer/divider circuit (1/V
providing the resulting signal to the multiplier that generates the current reference for the
inner current control loop (see
Doc ID 16202 Rev 2
Figure
28).
Application information
2
corrector) and
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