L6564H STMicroelectronics, L6564H Datasheet - Page 19

• Manufacturer Part Number: L6564H
• Description: Power Factor Correction ICs High Voltage Startup Trans-Mode PFC 700V
• Manufacturer: STMicroelectronics

Specifications of L6564H

• Rohs: yes

L6564H
6.3
Figure 32. Voltage feedforward: squarer/divider (1/V
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
V
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.
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 voltage divider in a short condition or open, or the PFC_OK pin left floating, results
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 f
has a single pole characteristic. This leads to a large trade-off in the design.
For example, setting the gain of the error amplifier to get f
having f
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
the minimizing of all the issues mentioned above. It consists of deriving a voltage
proportional to the input RMS voltage, feeding this voltage into a squarer/divider circuit (1/V
corrector) and providing the resulting signal to the multiplier that generates the current
reference for the inner current control loop (see
CC
voltage of the L6564H goes below 6 V.
c
≈ 4 Hz @ 88 Vac, resulting in sluggish control dynamics. Additionally, the slow
Doc ID 022960 Rev 2
c
2
of the overall open-loop gain because the gain
) block diagram and transfer characteristics
Figure 32
).
c
= 20 Hz @ 264 Vac means
Application information
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