High Performance Current Mode PWM Controller
This information can be detected by the resistor
divider R3 and R4 at Demag pin and is sampled
by chip to implement Output over voltage
If VOUT ramp high, VDemag will ramp high too.
When VOUT ramp to predetermined voltage
threshold of output OVP,
VDeamg Vth _ ref happen and system enter
auto-recovery shut down mode after 6 cycle
debounce time to avoid mis-trigger.
VBUCK _ BOP _ Enter
* (R1 R2)
When the BO voltage level falls blow 0.8V
(typical) ， the brownout protection is triggered
and controller stops pulsing until this voltage goes
back to 1.05V(typical).
VBUCK _ BOP _ Exit
By adjusting the resistor ratio, the window
between brownout enter voltage and exit voltage
can be programmed.
Fig.1 Output OVP implementation scheme
To protect the SMPS under low line voltage
condition, Brownout protection is implemented in
OB2276A. Refer to Fig.2.The line voltage is
monitored with resistor ratio from buck capacitor
to ground and is averaged by the RC filter (R2
and C1) at BO pin. This protection is active or not
depends on voltage level on BO pin.
Fig.2 Diagram of BOP
Besides Brownout Protection and Output OVP,
OB2276A also provides other protection features
with auto-recovery including Cycle-by-Cycle
current limiting (OCP), Over Load Protection (OLP)
with auto-recovery, Under Voltage Lockout on
VDD (UVLO), VDD over voltage protection (OVP),
over temperature protection (OTP). With On-
Bright Proprietary technology, the OCP is line
voltage compensated to achieve constant output
power limit over the universal input voltage range.
At overload condition when FB input voltage
exceeds power limit threshold value for more than
TD_PL, control circuit reacts to shut down the
converter. It restarts when VDD voltage drops
below UVLO limit.