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OB5269CP View Datasheet(PDF) - Unspecified

Part Name
Description
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OB5269CP Datasheet PDF : 11 Pages
1 2 3 4 5 6 7 8 9 10
OB5269
High Voltage Green Mode PWM Controller
OPERATION DESCRIPTION
OB5269 is a highly integrated current mode PWM power on sequence. As soon as VDD reaches
control IC optimized for high performance, low UVLO(OFF), the CS peak voltage is gradually
standby power consumption and cost effective increased from 0V to the maximum level. Every
offline flyback converter applications. The
‘Extended burst mode’ control greatly reduces the
standby power consumption and helps the design
easily to meet the international power
conservation requirements.
Internal High Voltage Startup and Under
Voltage Lockout (UVLO)
Ktec restart up begins with a soft start.
Frequency shuffling for EMI improvement
The frequency shuffling (switching frequency
modulation) is implemented in OB5269. The
oscillation frequency is modulated so that the tone
energy is spread out. The spread spectrum
minimizes the conduction band EMI and therefore
OB5269 integrates HV startup circuit, and
provides about 2.8mA current to charge VDD pin
during power on state from HV pin. When VDD
to cap voltage is higher than UVLO(OFF), the
charge current is switched off. At this moment,
l the VDD capacitor provides current to OB5269
until the auxiliary winding of the main transformer
tia starts to provide the operation current.
In general application, a 51K Ω resistor is
recommended to be placed in the high voltage
path to limit the current.
n VDD
e UVLO_off
fid UVLO_on
n HV Current
t
2.8mA
Co VDD
t Current
t
Operation Current
h Startup Current
rig t
Fig1 Startup current timing
-B Operating Current
The typical operating current of OB5269 is 1.8mA.
nGood efficiency is achieved with this low operating
current together with the ‘Extended burst mode’
Ocontrol features.
eases the system design.
Green-Mode Operation
OB5269 provides green-mode control to reduce
the switching frequency in light-load and no-load
conditions. VFB, which is derived from the voltage
feedback loop, is taken as the reference. Once
VFB is lower than the threshold voltage
(Vref_green), switching frequency is continuously
decreased to the minimum green-mode frequency
of around 22KHz.
Extended Burst Mode Operation
At light load or zero load condition, most of the
power dissipation in a switching mode power
supply is from switching loss in the MOSFET, the
core loss of the transformer and the loss in the
snubber circuit. The magnitude of power loss is in
proportion to the switching frequency. Lower
switching frequency leads to the reduction on the
power loss and thus conserves the energy.
The switching frequency is internally adjusted at
no load or light load condition. The switching
frequency is reduced at light/no load condition to
improve the conversion efficiency. At light load or
no load condition, the FB input drops below burst
mode threshold voltage (Vref_burst_L) and device
enters Burst Mode control. The gate driver output
switches only when FB voltage is higher than the
threshold voltage (Vref_burst_H) to output an on
state. Otherwise the gate drive remains at off
state to minimize the switching loss and reduces
the standby power consumption to the greatest
extend.
The switching frequency control also eliminates
the audio noise at any loading conditions.
Soft Start
OB5269 features an internal 4ms soft start to
soften the electrical stress occurring in the power
supply during startup. It is activated during the
Oscillator Operation
The switching frequency is internally fixed at
65KHZ. No external frequency setting
components are required for PCB design
simplification.
©On-Bright Electronics
Confidential
-8-
Preliminary Datasheet
OB_DOC_DS_526902
 

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