SCYW99143 Datasheet, PDF (21/35 Pages) ON Semiconductor – Universal High Voltage Control Block

SCYW99143
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NOT FOR PUBLIC RELEASE
mode. The voltage on remote pin thus drops fast below
V_REM_on threshold. Vcc is fully discharged and the
controller enables the HV startup current source to built Vcc
bias up again. The BO block bias is enabled at point H. This
Vcc_bias level (5 V) is maintained until the controller
receives BO_OK information from the BO block. If the line
voltage is high enough to enable operation the startup
current source continues to ramp up Vcc voltage (point I) up
to Vcc_on threshold (point J) where controller PWM is
enabled (PWM_ON signal). The remote timer is now not
activated like during first start because there was line voltage
present all the time during off−mode operation (the remote
timer latch is reset by X2 discharge signal). Application then
operates normally under any load conditions (e.g. standard
PWM operation, frequency foldback or skip mode).
Application has been unplugged from the mains at point
K. Let us consider the light load operation mode during this
event as a worst case for X2 capacitor discharging process.
The X2 capacitor stays charged on its actual voltage level
(line peak voltage in worst case). The X2 capacitor provides
DC bias to HV pin. The X2 sense input voltage starts to drop
in the same time because there is no AC voltage and charge
pump cannot transfer any charge to X2 pin. The 100 ms X2
timer is activated when the X2 input voltage drops below
internal X2 timer disable switch threshold voltage (Vth_X2)
point L. After the X2 timer elapses (point M), the PWM
block operation is disabled by pulling down the FB pin via
internal FB switch and the discharge switches (X2 and VCC)
are activated and X2 capacitor discharges via HV startup
current source until the X2 capacitor voltage drops to safe
level and internal bias is lost. The over temperature
protection is active during discharging process to overcome
HV startup damage that would occur otherwise under fault
cases – like when X2 pin is not connected.
2. Application start, AC line dropout, low line off,
BO restart, AC line off – Figure 47:
Application operation from point A to point F is the same
like in 1^st case described above. The line dropout occurs at
point F. BO timer starts to count down and X2 pin voltage
drops below threshold voltage of internal X2 disable switch
– thus also X2 timer is initiated. The line however recovers
before the BO and X2 timer periods elapsed and Vcc has
been lost. Application operation is thus is not interrupted.
The energy for power stage operation is provided by bulk
capacitor during dropout period in this case. The line voltage
drops below V_BO_off threshold at point G. The BO timer
is initiated and elapses after 50 ms thus the PWM block
operation is disabled by pulling down the FB pin via internal
FB switch. The Vcc capacitor is discharged by Vcc
discharge switch to Vcc_bias level. The Vcc is then
maintained at VCC_bias level by HV startup current source
to keep BO block operation (VHV > 60 V).
The line voltage increases above V_BO_on threshold at
point I. The BO_OK signal is received (point J) and internal
Vcc discharge switch is activated to fully discharge Vcc
capacitor and thus restart whole circuit. The HV startup
current source is activated after discharge and ramps−up the
Vcc voltage to Vcc_bias (5 V) level. The BO block is
activated at point K and correct line voltage is confirmed at
point L thus the HV startup current source continues to
ramp−up the Vcc voltage up to Vcc_on threshold where is
the PWM block operation enabled (point M). The remote
pin is pulled down by internal switch to assure correct
application restart even if the external bias remains on the
remote pin. Application then operates normally under any
load conditions (e.g. standard PWM operation, frequency
foldback or skip mode).
User unplugged power supply from the mains at point N.
The X2 discharge process takes place after 100 ms similarly
as in case 1.
3. Off−mode operation – restart by primary remote
discharge then AC line off – Figure 48:
The secondary controller turns−off the remote
opto−coupler and off−mode is initiated at point A. The
auxiliary voltage on remote input discharges very slowly
during off−mode. If the off−mode is active for too long time
the remote pin bias voltage will disappear. Thus the remote
pin voltage crosses V_REM_on threshold at point B. Vcc
capacitor is fully discharged and the HV startup current
source is activated to build Vcc bias for BO block (point C).
Once the BO_OK information is received (point D) the HV
startup current source ramps up to Vcc_on level (point E).
PWM block operation is enabled and remote pin bias voltage
thus grows. The PWM block is disabled via FB pin, Vcc
capacitor is internally discharged to 5 V and application
enters off−mode again when remote pin voltage crosses
V_REM_off threshold (point F). This operation mode is
called automatic primary restart during off−mode. Restart
occurs because remote pin bias is lost.
User unplugged application from the mains at point G.
The application was operating in off−mode at that time. The
X2 pin voltage drops because charge pump does not operate
and X2 timer disable switch is opened at point H (X2 timer
start counting). The X2 and Vcc dischargers are activated
after X2 timer elapses (point I).
4. Application start into short circuit, auto−recovery
restart, overloads then AC line off – Figure 49:
Application operation from point A to point E is the same
like in 1^st case described in paragraph 1. However, the short
circuit is present at the converter output during startup
sequence thus the Vcc voltage is not maintained and Vcc_off
threshold is reached in point F. The PWM block is disabled
via FB pin and 1 s auto−recovery timer is activated. The Vcc
capacitor is discharged by Vcc discharge switch to Vcc_bias
level where it is maintained by the HV startup current
source. This Vcc bias provides powers to all needed blocks
including auto−recovery timer.
The auto−recovery timer elapses at point G and controller
places new restart by fully discharging Vcc capacitor and
then enabling HV startup current source to ramp up Vcc
voltage again. The BO block is enabled at point H as Vcc
bias is available. The BO_OK information is received at
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