SCYW99143 Datasheet, PDF (15/35 Pages) ON Semiconductor – Universal High Voltage Control Block

SCYW99143
CONFIDENTIAL AND PROPRIETARY
NOT FOR PUBLIC RELEASE
Introduction
This device is specifically designed for SMPS applications
targeting ultra−low no−load power consumption. SCYW99143
DIE implements an HV startup current source with X2
discharge circuitry and Brown−out protection.
• HV startup current source: Reaching a low no−load
standby power always represents a difficult exercise
when standard resistor startup network is used. Thanks
to its proprietary technology, the SCYW99143
implements HV startup current source that provides fast
and reliable startup sequence while cuts−off power
consumption when application operates under light load
and especially no–load conditions.
• X2 capacitor discharge circuitry: The X2 capacitor(s)
charge could result in electric shock to SMPS user if
not discharged after application is unplugged from the
mains. Thus, according to international standards, it is
mandatory to discharge X2 capacitor(s) in given time to
pass safety qualification. Built−in X2 discharger in
DAP029 controller together with external X2 sensing
network provides reliable and loss−less discharge
function when application is unplugged under any
operating conditions.
• Internal Brown−out protection: Brow−out (BO)
protection is required in adapter applications to
guarantee that the application won’t be operated under
too low input voltage. Internal high impedance
Brow−out sensing network consumes minimum power
from HV input and provides excellent noise and PCB
leakage currents immunity compare to standard
external BO networks composed from high resistance
SMT chip resistors.
• Auto recovery UVP on VCC: It is sometimes
interesting to implement a circuit protection by sensing
the VCC level. This is what SCYW99143 provides by
monitoring its VCC pin. When the voltage on this pin
drops under VCC_(off) threshold, the disable pin is
immediately activated and the part enters hiccup mode.
When the auto−recovery timer elapses SCYW99143
repeats start−up sequence.
• Off−mode: Off−mode helps to achieve low power
consumption of an SMPS during no load conditions.
The SCYW99143 goes into Off−mode when the REM
pin is brought higher than the internal reference voltage
V_{−REM−off} (Active_ON version). Similarly, for
active_OFF version, the SCYW99143 enters off mode
operation when the REM pin is brought below
reference voltage V_{−REM−off}. The disable input is pulled
low, Vcc capacitor is discharged and consumption of all
internal blocks is reduced once the off−mode is
activated. Off mode is terminated when remote pin
voltage crosses V_{−REM−on} threshold or application is
unplugged from the mains.
Brown−out Circuitry
The SCYW99143 features, on its HV pin, a true AC line
monitoring circuitry – refer to Figure 37. This system
includes a minimum start−up threshold and auto−recovery
brown−out protection; both of them independent of the input
voltage ripple. The thresholds are fixed, but they are
designed to fit most of the standard AC−DC converter
applications. When the HV pin voltage drops below
VBO_off threshold for longer time than Bo_timer, the
brown−out condition is detected and confirmed. Thus the
controller stops operation – refer to Figure 38. The HV
current source maintains V_CC at V_CC_bias level until the
input voltage is back above VBO_on. The controller then
discharges Vcc capacitor first to restart internal logic.
Standard startup attempt is then placed by the controller.
Refer to controller operation sequencing sections – case 2
for better understanding on how the SCYW99143 BO
protection operates.
Figure 37. Simplified Block Diagram of
Brown−out Detection Circuitry
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