L6566B View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
'L6566B' PDF : 51 Pages View PDF
Application information
L6566B
Equation 9
β = ∆fsw
fm
which is the parameter that the amplitude of the generated side-band harmonics depends
on.
The minimum frequency fsw_min (occurring on the peak of the triangle) and the maximum
frequency fsw_max (occurring on the valley of the triangle) will be symmetrically placed
around the centre value fsw, so that:
Equation 10
fsw _ min
=
fsw
−
1
2
∆fsw
;
fsw _ max
= fsw
+
1
2
∆fsw
Then, RT will be found from (5) (see Section 5.2: Zero current detection and triggering block;
oscillator block on page 21), while RMOD and CMOD can be calculated as follows:
Equation 11
RMOD
=
2 ⋅ 103
∆fsw
CMOD
=
75
fm
where ∆fsw and fm (in kHz, with CMOD in nF and RMOD in kΩ) will be selected by the user so
to achieve the best compromise between attenuation of peak EMI emissions and clean
converter operation.
5.9
Latched disable function
The device is equipped with a comparator having the non-inverting input externally available
at the pin DIS (8) and with the inverting input internally referenced to 4.5 V. As the voltage
on the pin exceeds the internal threshold, the device is immediately shut down and its
consumption reduced to a low value.
The information is latched and it is necessary to let the voltage on the Vcc pin go below the
UVLO threshold to reset the latch and restart the device. To keep the latch supplied as long
as the converter is connected to the input source, the HV generator is activated periodically
so that Vcc oscillates between the start-up threshold VccON and VccON - 0.5 V. Activating the
HV generator in this way cuts its power dissipation approximately by three (as compared to
the case of continuous conduction) and keeps peak silicon temperature close to the average
value.
To let the L6566B restart it is then necessary to disconnect the converter from the input
source. Pulling pin 16 (AC_OK) below the disable threshold (see Section 5.12: Brownout
protection on page 37) will stop the HV generator until Vcc falls below Vccrestart, so that the
latch can be cleared and a quicker restart is allowed as the input source is removed. This
operation is shown in the timing diagram of Figure 20 on page 33.
32/51
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