L6566BH View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
'L6566BH' PDF : 51 Pages View PDF
Application information
L6566BH
Figure 6. Timing diagram: normal power-up and power-down sequences
Vin
VHVstart
Vcc
(pin 5)
VccON
VccOFF
Vccrestart
GD
(pin 4)
HV_EN
regulation is lost here
t
t
t
cc_OK
t
Icharge
t
0.85 mA
Power-on
Normal
operation
Power-off
t
AM11482v1
As the Vcc voltage reaches the turn-on threshold (14 V typ.) the device starts operating and
the HV generator is cut off by the Vcc_OK signal asserted high. The device is powered by
the energy stored in the Vcc capacitor until the self-supply circuit (typically an auxiliary
winding of the transformer and a steering diode) develops a voltage high enough to sustain
the operation. The residual consumption of this circuit is just the one on the 15 MΩ resistor
(≈ 10 mW at 400 Vdc), typically 50-70 times lower, under the same conditions, as compared
to a standard startup circuit made with external dropping resistors.
At converter power-down the system loses regulation as soon as the input voltage is so low
that either peak current or maximum duty cycle limitation is tripped. Vcc then drops and
stops IC activity as it falls below the UVLO threshold (10 V typ.). The VCC_OK signal is de-
asserted as the Vcc voltage goes below a threshold VCCrest located at about 5 V. The HV
generator can now restart. However, if Vin < Vinstart, as illustrated in Figure 6, HV_EN is de-
asserted too and the HV generator is disabled. This prevents converter restart attempts and
ensures monotonic output voltage decay at power-down in systems where brownout
protection (see the relevant section) is not used.
The low restart threshold VCCrest ensures that, during short-circuits, the restart attempts of
the device have a very low repetition rate, as shown in the timing diagram of Figure 7, and
that the converter works safely with extremely low power throughput.
18/51
Doc ID 16610 Rev 2
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