OB2273A

High Performance Current Mode PWM Controller

GENERAL DESCRIPTION FEATURES

OB2273A is a highly integrated current mode Level 5 compliance with <100mW standby
PWM control IC optimized for high performance, power at universal AC input.
low standby power and cost effective offline Power on Soft Start Reducing MOSFET Vds
flyback converter applications. Stress
PWM switching frequency at normal operation is Frequency shuffling for EMI

internally fixed and is trimmed to tight range. At no Extended Burst Mode Control For Improved
load or light load condition, the IC operates in Efficiency and Minimum Standby Power
extended burst mode to minimize switching loss. Design

Lower standby power and higher conversion Audio Noise Free Operation
efficiency is thus achieved. Fixed 65KHZ Switching Frequency
VDD low startup current and low operating current Comprehensive Protection Coverage

contribute to a reliable power on startup and low o VDD Under Voltage Lockout with
standby design with OB2273A. Hysteresis (UVLO)
OB2273A offers complete protection coverage o Cycle-by-cycle over current threshold

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with auto-recovery including Cycle-by-Cycle setting for constant output power limiting
current limiting (OCP), over load protection (OLP), over universal input voltage range

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VDD under voltage lockout (UVLO), over o Overload Protection (OLP) with auto-
temperature protection (OTP), and over voltage
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(fixed or adjustable) protection (OVP). Excellent o Over Temperature Protection (OTP) with
EMI performance is achieved with On-Bright auto-recovery
proprietary frequency shuffling technique. o VDD Over voltage Protection(OVP) with
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The tone energy at below 20KHZ is minimized in auto-recovery
the design and audio noise is eliminated during o Adjustable OVP through external Zener
operation.
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OB2273A is offered in SOT23-6 package.

APPLICATIONS
Offline AC/DC flyback converter for
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Battery Charger
Power Adaptor
Set-Top Box Power Supplies
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Open-frame SMPS
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TYPICAL APPLICATION
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On-Bright Electronics Confidential Datasheet

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 OB2273A
High Performance Current Mode PWM Controller

Package Dissipation Rating

GENERAL INFORMATION Package RJA(/W)
Pin Configuration SOT23-6 200
The OB2273A is offered in SOT23-6 package,
shown as below.
Absolute Maximum Ratings
Parameter Value

VDD DC Supply Voltage VOVP-1V
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

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Min/Max Storage
-55 to 150

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Temperature Tstg
Lead Temperature
260
Ordering Information
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Part Number Description Note: VDD_Clamp has a typical value of 32V
Stresses beyond those listed under absolute maximum
OB2273AMP SOT23-6, Pb-free in T&R ratings may cause permanent damage to the device. These
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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
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may affect device reliability.

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OB2273A X X
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Current Mode PWM Controller with Package Package Pb-free

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Frequency shuffling
M:SOT23-6 P:Pb-free
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Marking Information
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73YWW S
. ZZZA
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Y:Year Code
WW:Week Code(01-52)
s: Internal code
ZZZ: Lot code
A: Character code

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 OB2273A
High Performance Current Mode PWM Controller

TERMINAL ASSIGNMENTS
Pin Name I/O Description
GND P Ground
Feedback input pin. The PWM duty cycle is determined by voltage level into this pin
FB I
and the current-sense signal at Pin 4.

Dual function pin. Either connected through a NTC resistor to ground for over
RT I temperature shutdown/latch control or connected through Zener to VDD for
adjustable over voltage protection

CS I Current sense input
VDD P Power Supply

Gate O Totem-pole gate driver output for power Mosfet

C: Optional Internal Code

RECOMMENDED OPERATING CONDITION

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Symbol Parameter Min/Max Unit

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VDD VDD Supply Voltage 12 to 25 V
TA Operating Ambient Temperature -20 to 85
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BLOCK DIAGRAM
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 OB2273A
High Performance Current Mode PWM Controller

ELECTRICAL CHARACTERISTICS
(TA = 25, VDD=18V, unless otherwise noted)
Symbol Parameter Test Conditions Min Typ Max Unit
Supply Voltage (VDD)
VDD=UVLO(OFF)-
1V, measure
Istartup VDD Start up Current 5 20 uA
leakage current

into VDD
I_VDD_Operation Operation Current VFB=3V 1.8 2.5 mA
VDD Under Voltage Lockout

UVLO(ON) 8 9 10 V
Enter
VDD Under Voltage Lockout
UVLO(OFF) 14.3 15.3 16.3 V

Exit (Recovery)
Vpull-up Pull-up PMOS active 13 V
Vdd_clamp Ivdd=10mA 30 32 34 V
CS=0V,FB=3V

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Over voltage protection
OVP(ON) Ramp up VDD until 26 28 30 V
voltage
gate clock is off

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Feedback Input Section(FB Pin)
VFB_Open VFB Open Loop Voltage 3.9 4.2 V
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Avcs PWM input gain VFB/VCS 2 V/V
Maximum duty Max duty cycle @
75 80 85 %
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cycle VDD=14V,VFB=3V,VCS=0V
The threshold enter green
Vref_green 2 V
mode
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Vref_burst_H The threshold exit burst mode 1.275 V

The threshold enter burst
Vref_burst_L 1.175 V
mode
on

Short FB pin to
IFB_Short FB pin short circuit current GND and measure 0.4 mA
current
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Power Limiting FB Threshold

VTH_PL 3.7 V
Voltage
TD_PL Power limiting Debounce Time 80 88 96 mSec
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ZFB_IN Input Impedance 16 Kohm

Current Sense Input(CS Pin)
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SST Soft start time 4 ms

T_blanking Leading edge blanking time 220 ns
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ZSENSE_IN Input Impedance 40 Kohm

From Over Current
Over Current Detection and Occurs till the
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TD_OC 120 nSec

Control Delay Gatedrive output
start to turn off
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Internal Current Limiting

VTH_OC Threshold Voltage with zero 0.725 0.75 0.775 V
duty cycle
Vocp_clamping CS voltage clamper 0.9 V
Oscillator
VDD=14V, FB=3V,
FOSC Normal Oscillation Frequency 60 65 70 KHZ
CS=0V
f_OSC Frequency jittering +/-4 %
F_shuffling Shuffling frequency 32 Hz
Frequency Temperature
f_Temp 1 %
Stability

On-Bright Electronics Confidential Datasheet

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 OB2273A
High Performance Current Mode PWM Controller

f_VDD Frequency Voltage Stability 1 %

F_Burst Burst Mode Switch Frequency 22 KHZ
Gate driver
Ouput low level @ VDD=14V,
VOL 1 V
Io=5mA
Ouput high level @ VDD=14V,
VOH 6 V
Io=20mA
V_clamping Output clamp voltage 12 V

Output rising time 1V ~ 12V @
T_r 175 nS
CL=1000pF
Output falling time 12V ~ 1V

T_f 85 nS
@ CL=1000pF
Over temperature protection
IRT Output current of RT pin 95 100 105 uA

VOTP Threshold voltage for OTP 0.95 1 1.05 V
Td_OTP OTP debounce time 6 Cycle
VRT_FL Float voltage at RT pin 2.3 V

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External OVP threshold
Vth_OVP 4 V
voltage

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 OB2273A
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( )

5.0
1.02
4.5

Istartup(uA)

1.01

Vth_otp(V)
4.0 1.00

3.5 0.99

3.0 0.98
-40 0 40 80 120 -40 0 40 80 120
Temperature() Temperature()

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UVLO(on)(V) vs Temperature( ) UVLO(off)(V) vs Temperature( )

9.6
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UVLO(on)(V)

15.2
UVLO(off)(V)

9.4
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15
9.2
14.8
9
14.6
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8.8 14.4
-40 0 40 80 120 -40 0 40 80 120
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Temperature( ) Temperature( )
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Vth_OC(V)vs duty(%) Fosc(KHz) vs Temperature( )

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0.95 64.0

63.8
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0.90
Fosc(KHz)
Vth_OC(V)

0.85 63.5
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0.80 63.3
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63.0
0.75
-40 0 40 80 120
0 14 28 42 56 70
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Duty(%) Temperature()

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 OB2273A
High Performance Current Mode PWM Controller

OPERATION DESCRIPTION
OB2273A is a highly integrated current mode no load condition, the FB input drops below burst
PWM control IC optimized for high performance, mode threshold level and device enters Burst
low standby power and cost effective offline Mode control. The Gate drive output switches
flyback converter applications. The Extended when VDD voltage drops below a preset level and
burst mode control greatly reduces the standby FB input is active to output an on state. Otherwise

power consumption and helps the design easily to the gate drive remains at off state to minimize the
meet the international power conservation switching loss and reduces the standby power
requirements. consumption to the greatest extend.

The switching frequency control also eliminates
Startup Current and Start up Control the audio noise at any loading conditions.
Startup current of OB2273A is designed to be

very low so that VDD could be charged up above Oscillator Operation
UVLO threshold level and device starts up quickly. The switching frequency is internally fixed at
A large value startup resistor can therefore be 65KHZ. No external frequency setting

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used to minimize the power loss yet achieve a components are required for PCB design
reliable startup in application. simplification.

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Operating Current Current Sensing and Leading Edge Blanking
The Operating current of OB2273A is low at
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1.8mA. Good efficiency is achieved with OB2273A OB2273A current mode PWM control. The switch
low operating current together with the Extended current is detected by a sense resistor into the cs
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burst mode control features. pin. An internal leading edge blanking circuit
chops off the sensed voltage spike at initial
Soft Start internal power MOSFET on state due to snubber
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OB2273A features an internal 4ms soft start to diode reverse recovery and surge gate current of
soften the electrical stress occurring in the power power MOSFET. The current limiting comparator
supply during startup. It is activated during the is disabled and cannot turn off the internal power
on

power on sequence. As soon as VDD reaches MOSFET during the blanking period. The PWM
UVLO(OFF), the CS peak voltage is gradually duty cycle is determined by the current sense
increased to the maximum level. Every restart up input voltage and the FB input voltage.
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is followed by a soft start.

Internal Synchronized Slope Compensation
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Frequency shuffling for EMI improvement Built-in slope compensation circuit adds voltage
The frequency Shuffling (switching frequency ramp onto the current sense input voltage for
modulation) is implemented in OB2273A. The PWM generation. This greatly improves the close
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oscillation frequency is modulated so that the tone loop stability at CCM and prevents the sub-
energy is spread out. The spread spectrum harmonic oscillation and thus reduces the output
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minimizes the conduction band EMI and therefore ripple voltage.

eases the system design.
Drive
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Extended Burst Mode Operation The power MOSFET is driven by a dedicated gate
At light load or zero load condition, most of the driver for power switch control. Too weak the gate
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power dissipation in a switching mode power drive strength results in higher conduction and
supply is from switching loss on the MOSFET, the switch loss of MOSFET while too strong gate
core loss of the transformer and the loss on the drive results the compromise of EMI.
snubber circuit. The magnitude of power loss is in A good tradeoff is achieved through the built-in
proportion to the switching frequency. Lower totem pole gate design with right output strength
switching frequency leads to the reduction on the and dead time control. The low idle loss and good
power loss and thus conserves the energy. EMI system design is easier to achieve with this
The switching frequency is internally adjusted at dedicated control scheme.
no load or light load condition. The switch
frequency reduces at light/no load condition to
improve the conversion efficiency. At light load or

On-Bright Electronics Confidential Datasheet

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 OB2273A
High Performance Current Mode PWM Controller

Protection Controls With On-Bright Proprietary technology, the OCP is

Good power supply system reliability is achieved line voltage compensated to achieve constant
with auto-recovery protection features including output power limit over the universal input voltage
Cycle-by-Cycle current limiting (OCP), Over Load range.
Protection (OLP), Under Voltage Lockout on VDD At overload condition when FB input voltage
(UVLO), over temperature protection (OTP) and exceeds power limit threshold value for more than
fixed or adjustable VDD over voltage protection TD_PL, control circuit reacts to shut down the
(OVP). converter. It restarts when VDD voltage drops

below UVLO limit.

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 OB2273A
High Performance Current Mode PWM Controller

PACKAGE MECHANICAL DATA

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Dimensions In Millimeters Dimensions In Inches

Symbol
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Min Max Min Max

A 1.000 1.450 0.039 0.057
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A1 0.000 0.150 0.000 0.006

A2 0.900 1.300 0.035 0.051
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b 0.300 0.500 0.012 0.020

c 0.080 0.220 0.003 0.009
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D 2.800 3.020 0.110 0.119

E 1.500 1.726 0.059 0.068
E1 2.600 3.000 0.102 0.118
e 0.950 (BSC) 0.037 (BSC)
e1 1.800 2.000 0.071 0.079
L 0.300 0.600 0.012 0.024
0 8 0 8

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 OB2273A
High Performance Current Mode PWM Controller

IMPORTANT NOTICE
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.

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-Brights components, data sheet
and application notes. To minimize the risks associated with customer products and applications,

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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
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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
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military applications.
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