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기능 High Performance Current Mode PWM Controller
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OB2273A 데이터시트, 핀배열, 회로
OB2273A
High Performance Current Mode PWM Controller
GENERAL DESCRIPTION
OB2273A is a highly integrated current mode
PWM control IC optimized for high performance,
low standby power and cost effective offline
flyback converter applications.
PWM switching frequency at normal operation is
internally fixed and is trimmed to tight range. At no
load or light load condition, the IC operates in
extended ‘burst mode’ to minimize switching loss.
Lower standby power and higher conversion
efficiency is thus achieved.
VDD low startup current and low operating current
contribute to a reliable power on startup and low
standby design with OB2273A.
OB2273A offers complete protection coverage
with auto-recovery including Cycle-by-Cycle
current limiting (OCP), over load protection (OLP),
VDD under voltage lockout (UVLO), over
temperature protection (OTP), and over voltage
(fixed or adjustable) protection (OVP). Excellent
EMI performance is achieved with On-Bright
proprietary frequency shuffling technique.
The tone energy at below 20KHZ is minimized in
the design and audio noise is eliminated during
operation.
OB2273A is offered in SOT23-6 package.
FEATURES
Level 5 compliance with <100mW standby
power at universal AC input.
Power on Soft Start Reducing MOSFET Vds
Stress
Frequency shuffling for EMI
Extended Burst Mode Control For Improved
Efficiency and Minimum Standby Power
Design
Audio Noise Free Operation
Fixed 65KHZ Switching Frequency
Comprehensive Protection Coverage
o VDD Under Voltage Lockout with
Hysteresis (UVLO)
o Cycle-by-cycle over current threshold
setting for constant output power limiting
over universal input voltage range
o Overload Protection (OLP) with auto-
recovery
o Over Temperature Protection (OTP) with
auto-recovery
o VDD Over voltage Protection(OVP) with
auto-recovery
o Adjustable OVP through external Zener
APPLICATIONS
Offline AC/DC flyback converter for
Battery Charger
Power Adaptor
Set-Top Box Power Supplies
Open-frame SMPS
TYPICAL APPLICATION
©On-Bright Electronics
Confidential
-1-
Datasheet
OB_DOC_DS_2273AA2




OB2273A pdf, 반도체, 판매, 대치품
OB2273A
High Performance Current Mode PWM Controller
ELECTRICAL CHARACTERISTICS
(TA = 25, VDD=18V, unless otherwise noted)
Symbol
Parameter
Supply Voltage (VDD)
Istartup
VDD Start up Current
I_VDD_Operation
UVLO(ON)
UVLO(OFF)
Vpull-up
Vdd_clamp
Operation Current
VDD Under Voltage Lockout
Enter
VDD Under Voltage Lockout
Exit (Recovery)
Pull-up PMOS active
OVP(ON)
Over voltage protection
voltage
Feedback Input Section(FB Pin)
VFB_Open
VFB Open Loop Voltage
Avcs
PWM input gain ΔVFB/ΔVCS
Maximum duty Max duty cycle @
cycle
VDD=14V,VFB=3V,VCS=0V
Vref_green
The threshold enter green
mode
Vref_burst_H
The threshold exit burst mode
Vref_burst_L
The threshold enter burst
mode
IFB_Short
FB pin short circuit current
VTH_PL
Power Limiting FB Threshold
Voltage
TD_PL
Power limiting Debounce Time
ZFB_IN
Input Impedance
Current Sense Input(CS Pin)
SST Soft start time
T_blanking
Leading edge blanking time
ZSENSE_IN
Input Impedance
TD_OC
Over Current Detection and
Control Delay
VTH_OC
Vocp_clamping
Oscillator
FOSC
f_OSC
F_shuffling
f_Temp
Internal Current Limiting
Threshold Voltage with zero
duty cycle
CS voltage clamper
Normal Oscillation Frequency
Frequency jittering
Shuffling frequency
Frequency
Temperature
Stability
Test Conditions
VDD=UVLO(OFF)-
1V, measure
leakage current
into VDD
VFB=3V
Ivdd=10mA
CS=0V,FB=3V
Ramp up VDD until
gate clock is off
Short FB pin to
GND and measure
current
From Over Current
Occurs till the
Gatedrive output
start to turn off
VDD=14V, FB=3V,
CS=0V
Min
8
14.3
30
26
3.9
75
80
0.725
60
Typ
5
1.8
9
15.3
13
32
28
4.2
2
80
2
1.275
1.175
0.4
3.7
88
16
4
220
40
120
0.75
0.9
65
+/-4
32
1
Max
20
2.5
10
16.3
34
30
85
96
0.775
70
Unit
uA
mA
V
V
V
V
V
V
V/V
%
V
V
V
mA
V
mSec
Kohm
ms
ns
Kohm
nSec
V
V
KHZ
%
Hz
%
©On-Bright Electronics
Confidential
-4-
Datasheet
OB_DOC_DS_2273AA2

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OB2273A 전자부품, 판매, 대치품
OB2273A
High Performance Current Mode PWM Controller
OPERATION DESCRIPTION
OB2273A is a highly integrated current mode
PWM control IC optimized for high performance,
low standby power and cost effective 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.
Startup Current and Start up Control
Startup current of OB2273A is designed to be
very low so that VDD could be charged up above
UVLO threshold level and device starts up quickly.
A large value startup resistor can therefore be
used to minimize the power loss yet achieve a
reliable startup in application.
Operating Current
The Operating current of OB2273A is low at
1.8mA. Good efficiency is achieved with OB2273A
low operating current together with the ‘Extended
burst mode’ control features.
Soft Start
OB2273A features an internal 4ms soft start to
soften the electrical stress occurring in the power
supply during startup. It is activated during the
power on sequence. As soon as VDD reaches
UVLO(OFF), the CS peak voltage is gradually
increased to the maximum level. Every restart up
is followed by a soft start.
Frequency shuffling for EMI improvement
The frequency Shuffling (switching frequency
modulation) is implemented in OB2273A. The
oscillation frequency is modulated so that the tone
energy is spread out. The spread spectrum
minimizes the conduction band EMI and therefore
eases the system design.
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 on the MOSFET, the
core loss of the transformer and the loss on 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 switch
frequency reduces 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 level and device enters Burst
Mode control. The Gate drive output switches
when VDD voltage drops below a preset level and
FB input is active 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.
Oscillator Operation
The switching frequency is internally fixed at
65KHZ. No external frequency setting
components are required for PCB design
simplification.
Current Sensing and Leading Edge Blanking
Cycle-by-Cycle current limiting is offered in
OB2273A current mode PWM control. The switch
current is detected by a sense resistor into the cs
pin. An internal leading edge blanking circuit
chops off the sensed voltage spike at initial
internal power MOSFET on state due to snubber
diode reverse recovery and surge gate current of
power MOSFET. The current limiting comparator
is disabled and cannot turn off the internal power
MOSFET during the blanking period. The PWM
duty cycle is determined by the current sense
input voltage and the FB input voltage.
Internal Synchronized Slope Compensation
Built-in slope compensation circuit adds voltage
ramp onto the current sense input voltage for
PWM generation. This greatly improves the close
loop stability at CCM and prevents the sub-
harmonic oscillation and thus reduces the output
ripple voltage.
Drive
The power MOSFET is driven by a dedicated gate
driver for power switch control. Too weak the gate
drive strength results in higher conduction and
switch loss of MOSFET while too strong gate
drive results the compromise of EMI.
A good tradeoff is achieved through the built-in
totem pole gate design with right output strength
and dead time control. The low idle loss and good
EMI system design is easier to achieve with this
dedicated control scheme.
©On-Bright Electronics
Confidential
7
Datasheet
OB_DOC_DS_2273AA2

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