L4984D STMicroelectronics, L4984D Datasheet - Page 21

• Manufacturer Part Number: L4984D
• Description: Power Factor Correction ICs Current Mode PFC CCM Line Modulated Bi
• Manufacturer: STMicroelectronics

Specifications of L4984D

• Rohs: yes

L4984
6
Note:
Overvoltage protection (OVP)
Normally, the voltage control loop keeps the output voltage Vout 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 Vout that can be expected.
Figure 30. Output voltage setting, OVP and FFD functions: internal block diagram
Example: V
Select: R3 = 8.8 M; then: R4 = 8.8 M ·2.5/(434-2.5) = 51 k.
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. Notice that R1, R2, R3 and R4 can be
selected without any constraints. The unique criterion is that both dividers must sink a
current from the output bus which needs to be significantly higher than the bias current of
both pins INV and PFC_OK (< 1 μA).
out
= 400 V, V
R3
R3a
R3b
R4
outx
R1
Vout
= 434 V.
R1a
R1b
Doc ID 023489 Rev 3
R2
compensation
Frequency
PFC_OK
COMP
INV
Figure 30
6
2
1
0.23 V
0.27 V
1.66 V
2.5 V
2.4 V
2.5 V
). This divider is selected so that
+
+
+
-
-
-
+
-
Overvoltage protection (OVP)
Disable
OVP
Error Amplifier
L_OVP
L4984
AM13246v1
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