SCYW99143 Datasheet, PDF (18/35 Pages) ON Semiconductor – Universal High Voltage Control Block

CONFIDENTIAL AND PROPRIETARY
NOT FOR PUBLIC RELEASE
SCYW99143
Active OFF Off−mode
The remote input is designed for direct connection to FB
pin of a flyback controller. The voltage on remote pin
follows FB pin voltage except during off−mode.
The FB pin is not biased in off−mode because Vcc is
disabled by SCYW99143. The internal current source of
(2.5 mA typically) then pulls−up the remote when FB
optocoupler instructs the primary side to restart normal
operation. The feedback pin of the flyback controller thus
has to feature protection against reverse current from FB to
Vcc pins. The easiest way how to overcome this reverse
current is to use a diode in FB pin. Connection between
remote and FB pins with simplified block diagram of remote
control input are shown in Figure 41.
The off mode is activated when the remote pin is low and
Vcc _off threshold is crossed i.e. when the skip mode takes
so long time that Vcc is lost. Vcc capacitor is then discharged
by internal consumption of the SCYW99143 and
consumption of slave SMPS controller in skip mode.
Maximum skip mode duration before the SCYW99143
enters off−mode is thus given by value of Vcc capacitor,
total consumption during skip mode and voltage level on
Vcc capacitor in the time when flyback controller enters skip
mode.
The remote pin information is ignored in the case the FB
pin is pulled down by SCYW99143 itself (i.e. like during
BO event or Vcc fault cases) – refer to next paragraph
“Disable input”.
Figure 41. Simplified Block Diagram of Remote Control Input for Active OFF Off−mode
Refer to controller operation sequencing section – cases
1 − 5 for better understanding on how the SCYW99143
remote circuitry works.
Disable Switch Output
The SCYW99143 features internal open drain MOSFET
switch that is connected to the disable pin/pad. This pad can
be used to pull down FB pin of the slave SMPS controller in
order to stop its operation immediately by activating skip
mode. More specifically − this function is used for fast
disabling of SMPS controller driver in these cases: remote
mode (only Active ON option), auto−recovery mode,
latch−off mode, after X2 discharge condition is confirmed,
BO event and during every new start−up sequence. All these
cases can be represent by one “/PWM_ON” signal (refer to
Figure 42).
Figure 42. Simplified Block Diagram of Disable
Switch Output
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