L6566BHTR View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
'L6566BHTR' PDF : 51 Pages View PDF
Application information
L6566BH
Equation 15
D + TBLANK2 fsw ≤ 1
where TBLANK2 = 2 µs; this is also illustrated in the diagram of Figure 24.
Figure 24. Maximum allowed duty cycle vs. switching frequency for correct OVP
detection
0.8
0.725
0.7
0.6
Dmax 0.5
0.4
0.3
0.2
5 .104
1 .105
1.5.105
2 .105 2.5.105
fsw [Hz]
3 .105
3.5.105
4 .105
AM11500v1
5.12
Brownout protection
Brownout protection is basically a not-latched device shutdown function activated when a
condition of mains undervoltage is detected. There are several reasons why it may be
desirable to shut down a converter during a brownout condition, which occurs when the
mains voltage falls below the minimum specification of normal operation.
Firstly, a brownout condition may cause overheating of the primary power section due to an
excess of RMS current. Secondly, spurious restarts may occur during converter power
down, therefore causing the output voltage to not decay to zero monotonically.
L6566BH shutdown upon brownout is accomplished by means of an internal comparator, as
shown in the block diagram of Figure 25, which shows the basic usage. The inverting input
of the comparator, available on the AC_OK pin (16), is supposed to sense a voltage
proportional to the RMS (peak) mains voltage; the non-inverting input is internally
referenced to 0.485 V with 35 mV hysteresis. If the voltage applied on the AC_OK pin before
the device starts operating does not exceed 0.485 V or if it falls below 0.45 V while the
device is running, the AC_FAIL signal goes high and the device shuts down, with the soft-
start capacitor discharged and the gate-drive output low. Additionally, if the device has been
latched off by some protection function (testified by Vcc oscillating between VCCON and
VCCON - 0.5 V) the AC_OK voltage falling below 0.45 V clears the latch. This may allow a
quicker restart as the input source is removed.
While the brownout protection is active the startup generator keeps on working but, there
being no PWM activity, the Vcc voltage continuously oscillates between the startup and the
HV generator restart thresholds, as shown in the timing diagram of Figure 25.
36/51
Doc ID 16610 Rev 2
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