L6564T STMicroelectronics, L6564T Datasheet - Page 18

• Manufacturer Part Number: L6564T
• Description: 10 pin transition-mode PFC controller for outdoor applications
• Manufacturer: STMicroelectronics

Application information
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6.1
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Application information
Overvoltage protection
Normally, the voltage control loop keeps the output voltage Vo of the PFC pre-regulator
close to its nominal value, set by the ratio of the resistors R1 and R2 of the output divider. A
pin of the device (PFC_OK) has been dedicated to monitor the output voltage with a
separate resistor divider (R3 high, R4 low, see
the voltage at the pin reaches 2.5 V if the output voltage exceeds a preset value, usually
larger than the maximum Vo that can be expected.
Example: V
51 kΩ .
When this function is triggered, the gate drive activity is immediately stopped until the
voltage on the pin PFC_OK drops below 2.4 V. Note that R1, R2, R3 and R4 can be selected
without any constraints. The unique criterion is that both dividers have to sink a current from
the output bus which needs to be significantly higher than the bias current of both INV and
PFC_OK pins.
Figure 27. Output voltage setting, OVP and FFP functions: internal block diagram
O
= 400 V, V
OX
= 434 V. Select: R3 = 8.8 MΩ; then: R4 = 8.8 MΩ ·2.5/(434-2.5) =
Doc ID 022671 Rev 1
Figure 27
). This divider is selected so that
L6564T