OB2268
OB2268
OB2268
OB2269
Current Mode PWM Controller
OB2268/9 is offered in SOP-8 and DIP-8 packages.
GENERAL DESCRIPTION
OB2268/9 is a highly integrated current mode PWM FEATURES
control IC optimized for high performance, low ■ Green Mode and Burst Mode Control For
standby power and cost effective offline flyback Improved Efficiency and Minimum Standby
converter applications in above 20W power level. Power Design
The external programmable PWM frequency was ■ Audio Noise Free Operation
internally adjusted according to the load condition. ■ External Programmable PWM Switching
Consequently, a better power efficiency is achieved Frequency
over full load range. At no load condition, the IC ■ Internal Synchronized Slope Compensation
operates in ‘burst mode’ and the standby power is ■ Low VIN/VDD Startup Current(4uA) and Low
reduced to minimum. At light load condition, the Operating Current (2.3mA)
device enters frequency reduction ‘green mode’. ■ Leading Edge Blanking on Current Sense Input
Switching loss is reduced and higher conversion ■ Complete Protection Coverage With Auto Self-
efficiency is thus achieved. Recovery
VDD low startup current and low operating current o External Programmable Over Temperature
contribute to a reliable power on startup design with Protection (OTP)
OB2268/9. A large value resistor could thus be used o With or Without On-chip VDD OVP for
in the startup circuit to minimize the standby power. Output Over Voltage Protection.
The internal slope compensation improves system o Under Voltage Lockout with Hysteresis
large signal stability and reduces the possible sub- (UVLO)
harmonic oscillation at high PWM duty cycle output. o Gate Output Maximum Voltage Clamp (18V)
Leading-edge blanking on current sense input o Line Compensated Cycle-by-Cycle Over-
removes the signal glitch due to snubber circuit diode current Threshold Setting For Constant Output
reverse recovery. and greatly reduces the external Current Limiting Over Universal Input Voltage
component count and system cost in the design. Range (OCP)
OB2268/9 offers complete protection coverage with o Over Load Protection. (OLP)
automatic self-recovery feature including Cycle-by- ■ On-Bright Proprietary Frequency Shuffling
Cycle current limiting (OCP), over load protection Technology for Improved EMI Performance
(OLP), over temperature protection (OTP), VDD (OB2269 only)
over voltage protection (OVP) and under voltage
lockout (UVLO). The Gate-drive output is clamped APPLICATIONS
to maximum 18V to protect the power MOSFET. Offline AC/DC flyback converter for
Excellent EMI performance is achieved with On- ■ Laptop Power Adaptor
Bright proprietary frequency shuffling technique ■ PC/TV/Set-Top Box Power Supplies
(OB2269 only) together with soft switching control at ■ Open-frame SMPS
the totem pole gate drive output. ■ Battery Charger
The tone energy at below 20KHZ is minimized in
operation. Consequently, audio noise performance is
greatly improved..
TYPICAL APPLICATION
1
EMI
AC IN 4 2
F i l te r
+ +
D C O UT
+
3
V I N V DD
RT GA TE
NTC
O B 2 2 6 8/ 9
RI S E NSE
OB 43 1
FB GND
GENERAL INFORMATION
Pin Configuration Package Dissipation Rating
The OB2268/9 is offered in DIP and SOP packages Package RθJA (°C/W)
shown as below.
DIP8 90
SOP8 150
TERMINAL ASSIGNMENTS
Pin Num Pin Name I/O Description
1 GND P Ground
2 FB I Feedback input pin. PWM duty cycle is determined by voltage level into this
pin and current-sense signal level at Pin 6.
3 VIN I Connected through a large value resistor to rectified line input for Start up
chip supply and line voltage sensing.
4 RI I Internal Oscillator frequency setting pin. A resistor connected between RI
and GND sets the PWM frequency.
5 RT I Temperature sensing input pin. Connected through a NTC resistor to GND.
Once the voltage of the RT pin drops below a fixed limit of 1.05V, PWM
output will be disabled.
6 SENSE I Current sense input pin. Connected to MOSFET current sensing resistor
node.
7 VDD P DC power supply pin.
8 GATE O Totem-pole gate drive output for power MOSFET.
BLOCK DIAGRAM
ESD INFORMATION
Symbol Parameter Test Conditions Min Typ Max Unit
HBMNote Human Body Model MIL-STD 2 KV
MM Machine Model on JEDEC-STD 250 V
All Pins
Note: HBM all pins pass 2KV except VIN pin. The details are VIN passes 1kV, VDD and GATE pass 2KV, all other I/Os pass 8KV. In
system application, VIN pin is either a high impedance input or left floating. The lower rating has minimum impacts on system ESD
performance.
ELECTRICAL CHARACTERISTICS
(TA = 25OC if not otherwise noted)
Symbol Parameter Test Conditions Min Typ Max Unit
Supply Voltage (VDD, VIN)
I_VDD_Startup VDD Start up VDD =15V, RI=100K 4 20 uA
Current Measure current into VDD
I_VDD_Operation Operation Current VDD=18V, RI=100Kohm, 2.3 mA
VFB=3V, Gate floats
UVLO(ON) VDD Under 9.5 10.5 11.5 V
Voltage Lockout
Enter
UVLO(OFF) VDD Under 15.5 16.5 17.5 V
Voltage Lockout
Exit (Recovery)
*Optional
OVP(ON) VDD Over Voltage 23.5 25 26.5 V
Protection Enter
OVP(OFF)*Optional VDD Over Voltage 21.5 23 24.5 V
Protection Exit
(Recovery)
OVP_Hysteresis OVP(ON)- 2 V
OVP(OFF)
TD_OVP VDD OVP 80 uSec
Debounce time
VDD_Clamp VDD Zener Clamp I(VDD ) = 10 mA 35 V
Voltage
Feedback Input Section(FB Pin)
VFB_Open VFB Open Loop 6.0 V
Voltage
IFB_Short FB pin short circuit Short FB pin to GND and 0.65 mA
current measure current
VTH_GM Green Mode FB 2.3 V
Threshold Voltage
VTH_BM Burst Mode FB 1.8 V
Threshold Voltage
VTH_PL Power Limiting FB 4.4 V
Threshold Voltage
TD_PL Power limiting 80 mSec
Debounce Time
ZFB_IN Input Impedance 9.0 Kohm
Current Sense Input(Sense Pin)
T_blanking Leading edge RI = 100Kohm 400 ns
CHARACTERIZATION PLOTS
VDD Start-up Current vs. Voltage VDD UVLO and Operation Current
11 3
S tart-up C urrent (uA )
10
9 2.5
6 120
I(VDD) (mA)
RI (Kohm)
5 100
4 80
60
3
40
2
20
1 50 80 110 140 170 200 230
0 500 1000 1500 2000
Frequency (KHz)
Gatedrive Loading (pf)
0.94
70
Frequency(K H Z)
60 0.89
Vth_OC (V)
50
0.84
40
30 0.79
20
0.74
10
0 0.69
1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4 3.6 3.8 4.0 0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300
FB Voltage(V) Ivin(uA)
OPERATION DESCRIPTION
The OB2268/9 is a highly integrated PWM below a preset level and FB input is active to output
controller IC optimized for offline flyback an on state. Otherwise the gate drive remains at off
converter applications in above 20W power range. state to minimize the switching loss thus reduce the
The Green mode and burst mode control greatly standby power consumption to the greatest extend.
reduces the standby power consumption and helps The frequency control also eliminates the audio
the design easily meet the international power noise at any loading conditions.
conservation requirements.
• Oscillator Operation
• Startup Current and Start up Control A resistor connected between RI and GND sets the
Startup current of OB2268/9 is designed to be very constant current source to charge/discharge the
low so that VDD could be charged up above UVLO internal cap and thus the PWM oscillator frequency
threshold level and device starts up quickly. A large is determined. The relationship between RI and
value startup resistor can therefore be used to switching frequency follows the below equation
minimize the power loss yet reliable startup in within the specified RI in Kohm range at nominal
application. For AC/DC adaptor with universal loading operational condition.
input range design, a 2 MΩ, 1/8 W startup resistor
could be used together with a VDD capacitor to FPWM = 6500/RI (KHZ)
provide a fast startup and yet low power dissipation
design solution.
• Current Sensing and Leading Edge Blanking
• Operating Current Cycle-by-Cycle current limiting is offered in
The Operating current of OB2268/9 is low at OB2268/9 current mode PWM control. The switch
2.3mA. Good efficiency is achieved with current is detected by a sense resistor into the sense
OB2268/9 low operating current together with pin. An internal leading edge blanking circuit chops
green mode, burst mode control schemes. off the sense voltage spike at initial MOSFET on
state due to Snubber diode reverse recovery so that
• Frequency shuffling for EMI improvement the external RC filtering on sense input is no longer
The frequency Shuffling/jittering (switching needed. The current limit comparator is disabled
frequency modulation) is implemented in OB2269. and cannot turn off the external MOSFET during
The oscillation frequency is modulated with a the blanking period. The PWM duty cycle is
random source so that the tone energy is spread out. determined by the current sense input voltage and
The spread spectrum minimizes the conduction the FB input voltage.
band EMI and therefore eases the system design.
• Internal Synchronized Slope Compensation
• Green Mode and Burst Mode Operation Built-in slope compensation circuit adds voltage
At light load or zero load condition, most of the ramp onto the current sense input voltage for PWM
power dissipation in a switching mode power generation. This greatly improves the close loop
supply is from switching loss on the MOSFET stability at CCM and prevents the sub-harmonic
transistor, the core loss of the transformer and the oscillation and thus reduces the output ripple
loss on the snubber circuit. The magnitude of voltage.
power loss is in proportion to the switching
frequency. Lower switching frequency leads to the • Over Temperature Protection
reduction on the power loss and thus conserves the An NTC resistor in series with a regular resistor
energy. should connect between RT and GND for
OB2268/9 self adjusts the switching frequency temperature sensing and protection. NTC resistor
(Green-mode) according to the loading condition. value becomes lower when the ambient temperature
The switch frequency reduces at lighter load rises. With the fixed internal current IRT flowing
condition to improve the conversion efficiency. At through the resistors, the voltage at RT pin
light load or no load condition, the FB input drop becomes lower at high temperature. The internal
below burst mode threshold level (1.6V) and the OTP circuit is triggered and shutdown the
device enters Burst Mode control. The Gate drive MOSFET when the sensed input voltage is lower
output switches only when VDD voltage drops than VTH_OTP.
IMPORTANT NOTICE
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 applications 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.
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.
MILITARY
On-Bright Electronics Corp.’s products are not designed for use in military applications. On-Bright Electronics
Corp. and Lite-on Semiconductor Corp. will not be held liable for any damages or claims resulting from the use
of its products in military applications.