OB2273
High Performance Current Mode PWM Controller
GENERAL DESCRIPTION
FEATURES
OB2273 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 OB2273.
OB2273 offers complete protection coverage with
auto-recovery including Cycle-by-Cycle current
limiting (OCP), over load protection (OLP), and
VDD under voltage lockout (UVLO). It also
provides the protections with latched shut down
including over temperature protection (OTP), and
over voltage (fixed or adjustable) protection (OVP).
Excellent EMI performance is achieved with OnBright proprietary frequency shuffling technique.
The tone energy at below 20KHZ is minimized in
the design and audio noise is eliminated during
operation.
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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 autorecovery
o Over Temperature Protection (OTP) with
latch shut down
o VDD Over voltage Protection(OVP) with
latch shut down
o Adjustable OVP through external Zener
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APPLICATIONS
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OB2273 is offered in SOT23-6 and DIP-8 package.
Offline AC/DC flyback converter for
■ Battery Charger
■ Power Adapter
■ Set-Top Box Power Supplies
■ Open-frame SMPS
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TYPICAL APPLICATION
©On-Bright Electronics
Confidential
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Preliminary Datasheet
OB_DOC_DS_227305
OB2273
High Performance Current Mode PWM Controller
Pin Configuration
The OB2273 is offered in SOT23-6 and DIP8
package, shown as below.
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Package Dissipation Rating
Package
RθJA(℃/W)
SOT23-6
200
DIP8
90
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Ordering Information
Part Number
Description
OB2273MP
SOT23-6, Pb-free in T&R
OB2273AP
DIP8, Pb-free in Tube
GENERAL INFORMATION
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Absolute Maximum Ratings
Parameter
Value
VDD DC Supply Voltage
30 V
VDD Zener Clamp
VDD_Clamp+0.1V
VoltageNote
VDD DC Clamp Current
10 mA
FB Input Voltage
-0.3 to 7V
Sense Input Voltage
-0.3 to 7V
RT Input Voltage
-0.3 to 7V
Min/Max Operating
-40 to 150 ℃
Junction Temperature TJ
Min/Max Storage
-55 to 160 ℃
Temperature Tstg
Lead
Temperature
260 ℃
(Soldering, 10secs)
Note: VDD_Clamp has a nominal value of 32V.
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Stresses beyond those listed under “absolute maximum
ratings” may cause permanent damage to the device. These
are stress ratings only, functional operation of the device at
these or any other conditions beyond those indicated under
“recommended operating conditions” is not implied. Exposure
to absolute maximum-rated conditions for extended periods
may affect device reliability.
OB2273
On
Current Mode PWM Controller with
Frequency shuffling
©On-Bright Electronics
X
Package
M:SOT23-6
A: DIP8
Confidential
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X
Package Pb free
Blank:Normal
P:lead-free
Preliminary Datasheet
OB_DOC_DS_227305
OB2273
High Performance Current Mode PWM Controller
Marking Information
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73YWW
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Y:Year Code
WW:Week Code(01-52)
S:Internal Code(Optional)
TERMINAL ASSIGNMENTS
I
RT
I
CS
VDD
Gate
I
P
O
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FB
Description
Ground
Feedback input pin. The PWM duty cycle is determined by voltage level into this pin
and the current-sense signal at Pin 4.
Dual function pin. Either connected through a NTC resistor to ground for over
temperature shutdown/latch control or connected through Zener to VDD for
adjustable over voltage protection
Current sense input
Power Supply
Totem-pole gate driver output for power Mosfet
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Pin Name
GND
Parameter
VDD Supply Voltage
Operating Ambient Temperature
Min/Max
12 to 25
-40 to 85
Unit
V
℃
On
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Symbol
VDD
TA
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RECOMMENDED OPERATING CONDITION
©On-Bright Electronics
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Preliminary Datasheet
OB_DOC_DS_227305
OB2273
High Performance Current Mode PWM Controller
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BLOCK DIAGRAM
©On-Bright Electronics
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Preliminary Datasheet
OB_DOC_DS_227305
OB2273
High Performance Current Mode PWM Controller
ELECTRICAL CHARACTERISTICS
VDD Start up Current
I_VDD_Operation
Operation Current
Over
voltage
voltage
OVP(ON)
protection
Ivdd=10mA
CS=0V,FB=3V
Ramp up VDD until
gate clock is off
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Vlatch_release
Latch release voltage
Feedback Input Section(FB Pin)
VFB_Open
VFB Open Loop Voltage
PWM input gain Δ VFB/ Δ
Avcs
VCS
Maximum
duty Max
duty
cycle
@
cycle
VDD=18V,VFB=3V,VCS=0V
The threshold enter green
Vref_green
mode
Vref_burst_H
The threshold exit burst mode
The threshold enter burst
Vref_burst_L
mode
FB pin short circuit current
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IFB_Short
VTH_OC
Vocp_clamping
Oscillator
Normal Oscillation Frequency
△f_OSC
F_shuffling
Frequency jittering
Shuffling frequency
©On-Bright Electronics
5
20
uA
1.8
2.5
mA
14.3
15.3
-5-
V
V
V
26
28
30
V
3.9
75
60
5
V
4.2
V
2
V/V
80
85
%
2
V
1.275
V
1.175
V
0.4
mA
3.7
V
88
96
mSec
16
Kohm
4
220
40
ms
ns
Kohm
120
nSec
0.75
V
0.9
V
65
+/-4
32
Confidential
16.3
34
From Over Current
Occurs
till
the
Gatedrive output start
to turn off
FB=3V,
V
13
32
80
VDD=18V,
CS=0V
10
30
Internal
Current
Limiting
Threshold Voltage with zero
duty cycle
CS voltage clamper
FOSC
Unit
9
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On
TD_OC
Over Current Detection and
Control Delay
Max
8
Short FB pin to GND
and measure current
Power Limiting FB Threshold
Voltage
Power limiting Debounce
TD_PL
Time
ZFB_IN
Input Impedance
Current Sense Input(CS Pin)
SST
Soft start time
T_blanking
Leading edge blanking time
ZSENSE_IN
Input Impedance
VTH_PL
Typ
to
Vpull-up
Vdd_clamp
VDD Under Voltage Lockout
Enter
VDD Under Voltage Lockout
Exit (Recovery)
Pull-up PMOS active
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UVLO(OFF)
VDD=UVLO(OFF)1V, measure leakage
current into VDD
VDD=18V,VFB=3V,
CS=0V,Cgate=1nF
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UVLO(ON)
Min
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Istartup
Test Conditions
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(TA = 25℃, VDD=18V, unless otherwise noted)
Symbol
Parameter
Supply Voltage (VDD)
70
KHZ
%
Hz
Preliminary Datasheet
OB_DOC_DS_227305
OB2273
High Performance Current Mode PWM Controller
△f_VDD
F_Burst
Gate driver
Frequency
Temperature
Stability
Frequency Voltage Stability
Burst Mode Switch Frequency
Output low level @ VDD=18V,
Io=5mA
Output
high
level
@
VOH
VDD=18V, Io=20mA
V_clamping
Output clamp voltage
Output rising time 1V ~ 12V
T_r
@ CL=1000pF
Output falling time 12V ~ 1V
T_f
@ CL=1000pF
Over temperature protection
IRT
Output current of RT pin
VOTP
Threshold voltage for OTP
Td_OTP
OTP debounce time
VRT_FL
Float voltage at RT pin
External
OVP
threshold
Vth_OVP
voltage
1
%
1
22
%
KHZ
VOL
1
6
V
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△f_Temp
V
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12
nS
85
nS
to
175
100
1
32
2.3
4
105
1.05
uA
V
Cycle
V
V
On
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0.95
V
©On-Bright Electronics
Confidential
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Preliminary Datasheet
OB_DOC_DS_227305
OB2273
High Performance Current Mode PWM Controller
CHARACTERIZATION PLOTS
VDD = 18V, TA = 25℃ condition applies if not otherwise noted.
Istartup(uA) vs Temperature(℃ )
Vth_otp(V) vs Temperature(℃ )
3.5
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4.0
1.01
1.00
0.99
0.98
3.0
-40
0
40
80
-40
120
80
120
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UVLO(on)(V) vs Temperature(℃ )
UVLO(off)(V) vs Temperature(℃ )
15.4
15.2
15
UVLO(off)(V)
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9.6
9.4
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9.2
9
8.8
0
40
80
14.8
14.6
14.4
120
-40
0
nf
-40
Temperature(℃ )
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0.95
120
64.0
Fosc(KHz)
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0.85
0.80
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80
Fosc(KHz) vs Temperature(℃ )
0.90
63.8
63.5
63.3
63.0
0.75
14
28
42
Duty(%)
56
-40
70
0
40
80
120
Temperature(℃)
On
0
40
Temperature(℃ )
Vth_OC(V)vs duty(%)
Vth_OC(V)
40
Temperature(℃)
Temperature(℃)
UVLO(on)(V)
0
to
4.5
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1.02
Vth_otp(V)
Istartup(uA)
5.0
©On-Bright Electronics
Confidential
7
Preliminary Datasheet
OB_DOC_DS_227305
OB2273
High Performance Current Mode PWM Controller
OPERATION DESCRIPTION
OB2273 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.
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Vref_burst_L (the threshold enter burst mode) and
device enters Burst Mode control. The Gate drive
output switches when FB input rises back to
Vref_burst_H (the threshold exit burst mode).
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.
• Startup Current and Start up Control
Startup current of OB2273 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.
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• Soft Start
OB2273 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 from 0.05V to the maximum level.
Every restart up is followed by a soft start.
• Current Sensing and Leading Edge Blanking
Cycle-by-Cycle current limiting is offered in
OB2273 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.
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• Operating Current
The Operating current of OB2273 is low at 1.8mA.
Good efficiency is achieved with OB2273 low
operating current together with the ‘Extended
burst mode’ control features.
• Oscillator Operation
The switching frequency is internally fixed at
65KHZ.
No
external
frequency
setting
components are required for PCB design
simplification.
• 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 subharmonic oscillation and thus reduces the output
ripple voltage.
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• Frequency shuffling for EMI improvement
The frequency Shuffling (switching frequency
modulation) is implemented in OB2273. 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.
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• 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
• 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
©On-Bright Electronics
•
Confidential
8
Protection Controls
Preliminary Datasheet
OB_DOC_DS_227305
OB2273
High Performance Current Mode PWM Controller
Good power supply system reliability is achieved
with auto-recovery protection features including
Cycle-by-Cycle current limiting (OCP), Over Load
Protection (OLP), and Under Voltage Lockout on
VDD (UVLO), and latch shutdown features
including over temperature protection (OTP), fixed
or adjustable VDD over voltage protection (OVP).
With On-Bright Proprietary technology, the OCP is
line voltage compensated to achieve constant
output power limit over the universal input voltage
range.
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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. For protection with latch shut
down mode, control circuit shutdowns (latch) the
power MOSFET when an Over Temperature
condition or Over Voltage condition is detected
until VDD drops below 5V (Latch release voltage) ,
and device enters power on restart-up sequence
thereafter.
©On-Bright Electronics
Confidential
-9-
Preliminary Datasheet
OB_DOC_DS_227305
OB2273
High Performance Current Mode PWM Controller
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PACKAGE MECHANICAL DATA
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A1
A2
b
c
D
E
E1
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L
θ
Dimensions In Millimeters
Min
Max
1.000
1.300
0.000
0.150
1.000
1.200
0.300
0.500
0.100
0.200
2.800
3.020
1.500
1.700
2.600
3.000
0.950 (BSC)
1.800
2.000
0.300
0.600
0º
8º
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©On-Bright Electronics
Confidential
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Dimensions In Inches
Min
Max
0.039
0.051
0.000
0.006
0.039
0.047
0.012
0.020
0.004
0.008
0.110
0.119
0.059
0.067
0.102
0.118
0.037 (BSC)
0.071
0.079
0.012
0.024
0º
8º
Preliminary Datasheet
OB_DOC_DS_227305
OB2273
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High Performance Current Mode PWM Controller
Dimensions In Millimeters
Min
Max
3.710
5.334
0.381
2.921
4.953
0.350
0.650
1.524 (BSC)
0.200
0.360
9.000
10.160
6.096
7.112
7.320
8.255
2.540 (BSC)
2.921
3.810
7.620
10.920
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Symbol
On
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A1
A2
B
B1
C
D
E
E1
e
L
E2
©On-Bright Electronics
Confidential
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Dimensions In Inches
Min
Max
0.146
0.210
0.015
0.115
0.195
0.014
0.026
0.06 (BSC)
0.008
0.354
0.240
0.288
0.014
0.400
0.280
0.325
0.1 (BSC)
0.115
0.300
0.150
0.430
Preliminary Datasheet
OB_DOC_DS_227305
OB2273
High Performance Current Mode PWM Controller
IMPORTANT NOTICE
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RIGHT TO MAKE CHANGES
On-Bright Electronics Corp. reserves the right to make corrections, modifications, enhancements,
improvements and other changes to its products and services at any time and to discontinue any product
or service without notice. Customers should obtain the latest relevant information before placing orders
and should verify that such information is current and complete.
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WARRANTY INFORMATION
On-Bright Electronics Corp. warrants performance of its hardware products to the specifications
applicable at the time of sale in accordance with its standard warranty. Testing and other quality control
techniques are used to the extent it deems necessary to support this warranty. Except where mandated
by government requirements, testing of all parameters of each product is not necessarily performed.
On-Bright Electronics Corp. assumes no liability for application assistance or customer product design.
Customers are responsible for their products and applications using On-Bright’s components, data sheet
and application notes. To minimize the risks associated with customer products and applications,
customers should provide adequate design and operating safeguards.
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LIFE SUPPORT
On-Bright Electronics Corp.’s products are not designed to be used as components in devices intended to
support or sustain human life. On-bright Electronics Corp. will not be held liable for any damages or
claims resulting from the use of its products in medical applications.
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MILITARY
On-Bright Electronics Corp.’s products are not designed for use in military applications. On-Bright
Electronics Corp. will not be held liable for any damages or claims resulting from the use of its products in
military applications.
©On-Bright Electronics
Confidential
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Preliminary Datasheet
OB_DOC_DS_227305
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