WS2268
disabled and the gate driver can not be switched off.
Tons
Toffs
4
3
=
6. CCM Protection
The relationship between the output constant-current Iout
and secondary peak current Ipks is given by:
The WS2268 is designed to operate in discontinuous
conduction mode (DCM) in both CV and CC modes. To
avoid operating in continuous conduction mode (CCM),
the WS2268 detects the falling edge of the U input
voltage on each cycle. If a 0.1V falling edge of U is not
detected, the WS2268 will stop switching.
1
Tons
Iout = × Ipks ×
2
Tons + Toffs
At the instant of D1 turn-on, the primary current transfers to
the secondary at an amplitude of:
Np
Ipks =
× Ipk
Ns
7. OVP & OCkP
Thus the output constant-current is given by:
WS2268 include output over-voltage protection (OVP)
and open circuit protection (OckP) circuitry. If the voltage
at U pin exceeds 8V, 100% above the normal detection
voltage, or the -1V falling edge of U input can not be
monitored, the WS2268 will immediately shut off and
1
2
Np
Ns
Tons
2
7
Np
Ns
Iout =
×
× Ipk ×
=
×
× Ipk
Tons + Toffs
5. Leading Edge Blanking
When the power switch is turned on, a turn-on spike will
occur on the sense-resistor. To avoid false-termination of the
switching pulse, a 430ns leading-edge blanking is built in.
During this blanking period, the current sense comparator is
enter hiccup mode. The WS2268 sends out
a fault
detection pulse every 19ms in hiccup mode until the fault
has been removed.
7/8
Steady, keep for your advance
WINSEMI [ SHENZHEN WINSEMI MICROELECTRONICS CO., LTD ]
