L6566BH View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
'L6566BH' PDF : 51 Pages View PDF
L6566BH
Figure 18. Hiccup-mode OCP: timing diagram
Application information
Vcc
(pin 5)
VccON
VccOFF
Vccrestart
Secondary diode is shorted here
VCS
1.5 V
t
(pin 7)
GD
t
(pin 4)
OCP latch
t
Vcc_OK
t
t
AM11494v1
To distinguish an actual malfunction from a disturbance (e.g. induced during ESD tests), the
first time the comparator is tripped the protection circuit enters a “warning state”. If in the
next switching cycle the comparator is not tripped, a temporary disturbance is assumed and
the protection logic is reset in its idle state; if the comparator is again tripped, a real
malfunction is assumed and the L6566BH is stopped. Depending on the time relationship
between the detected event and the oscillator, the device may occasionally stop after the
third detection.
This condition is latched as long as the device is supplied. While it is disabled, however, no
energy comes from the self-supply circuit; hence the voltage on the VCC capacitor decays
and crosses the UVLO threshold after some time, which clears the latch. The internal
startup generator is still off, and the VCC voltage still needs to go below its restart voltage
before the VCC capacitor is charged again and the device restarted. Ultimately, this results in
a low-frequency intermittent operation (Hiccup-mode operation), with very low stress on the
power circuit. This special condition is illustrated in the timing diagram of Figure 18.
5.8
Frequency modulation
To alleviate the converter’s EMI emissions and reduce cost and size of the line filter, it is
advantageous to modulate its switching frequency, so that the resulting spread-spectrum
action distributes the energy of each harmonic of the switching frequency over a number of
side-band harmonics. Their overall energy is unchanged but the individual amplitudes are
smaller. This is what naturally occurs with QR operation, due to the twice-mains-frequency
ripple appearing on the input bulk capacitor, which translates into different DCM-CCM
boundary frequencies.
The L6566BH is provided with a dedicated pin, FMOD (6), to perform this function if FF mode
is selected.
Doc ID 16610 Rev 2
29/51
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