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OB2279
Current Mode PWM ControllerFreq Shuffling with Latch Shutdown
GENERAL DESCRIPTION
OB2279 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
externally programmable and 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 design with
OB2279. A large value resistor could thus be used in
the startup circuit for reduced power loss.
The internal slope compensation improves system
large signal stability and reduces the possible sub-
harmonic oscillation at high PWM duty cycle output.
Leading-edge blanking on current sense input
removes the signal glitch due to snubber circuit diode
reverse recovery and greatly reduces the external
component count and system cost in the design.
OB2279 offers comprehensive protection coverage
including Cycle-by-Cycle current limiting(OCP),
VDD Under Voltage Lockout(UVLO), VDD Over
Voltage Protection(OVP), VDD Clamp, Gate Clamp,
Over Load protection(OLP) and Over Temperature
protection (OTP), etc.
Different latch shutdown options are offered on
OB2279 in different device version. V version has
OVP Latch shutdown. T version supports both OVP
and OTP latch shutdown. L version provides all OVP,
OTP and OLP latch shutdown control.
Excellent EMI performance is achieved with On-
Bright proprietary frequency shuffling technique
together with soft switching control at the totem pole
gate drive output.
OB2279 is offered in SOP-8 and DIP-8 packages.
FEATURES
On-Bright Proprietary Frequency Shuffling
Technology for Improved EMI Performance
Power On Soft Start
Extended Burst Mode Control For Improved
Efficiency and Minimum Standby Power Design
Audio Noise Free Operation
External Programmable PWM Switching
Frequency
Internal Synchronized Slope Compensation
Low VIN/VDD Startup Current(3uA) and Low
Operating Current (2.3mA)
Leading Edge Blanking on Current Sense Input
Complete Protection Coverage with selective
protections for Latch Shutdown
o VDD Over Voltage Protection(OVP) – Latch
Shutdown
o Over Temperature Protection(OTP) – Auto
recovery or Latch Shutdown
o Over Load Protection. (OLP) – Auto recovery
or Latch Shutdown
o VDD Under Voltage Lockout with Hysteresis
(UVLO)
o Gate Output Voltage Clamp (16.5V)
o Built-in OCP Compensation to Achieve
Minimum OPP Variation over Universal AC
Input Range.
APPLICATIONS
Offline AC/DC flyback converter for
Adaptor
Notebook Adaptor
LCD Monitor/TV/PC/Set-Top Box Power
Supplies
Open-frame SMPS
Printer Power
TYPICAL APPLICATION
©On-Bright Electronics
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OB_DOC_DS_79A1

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OB2279
Current Mode PWM ControllerFreq Shuffling with Latch Shutdown
GENERAL INFORMATION
Pin Configuration
The pin map of OB2279 in DIP8 and SOP8 package
is shown as below.
OB2279CP-L
SOP8, tube package, L
version with OVP/OTP/OLP
latch
OB2279CPA-L
SOP8, taping package, L
version with OVP/OTP/OLP
latch
Note: All Devices are offered in Pb-free Package if not otherwise
noted.
Package Dissipation Rating
Package
DIP8
SOP8
RθJA (°C/W)
90
150
Ordering Information
Part Number
OB2279AP-V
Description
DIP8, tube package, V
version with OVP Latch
OB2279AP-T
DIP8, tube package, T
version with OVP/OTP latch
OB2279AP-L
DIP8, tube package, L
version with OVP/OTP/OLP
latch
OB2279CP-V
SOP8, tube package, V
version with OVP latch
OB2279CPA-V SOP8, taping package, V
version with OVP latch
OB2279CP-T
SOP8, tube package, T
version with OVP/OTP latch
OB2279CPA-T SOP8, taping package, T
version with OVP/OTP latch
Absolute Maximum Ratings
Parameter
VDD Clamp Voltage (Vclamp)
VDD Clamp Continuous
Current
VIN / VDD Input Voltage
FB Input Voltage
Sense Input Voltage
RT Input Voltage
RI Input Voltage
Min/Max Operating Junction
Temperature TJ
Min/Max Storage Temperature
Tstg
Lead Temperature (Soldering,
10 seconds)
Value
35 V
10 mA
-0.3V to Vclamp
-0.3 to 7V
-0.3 to 7V
-0.3 to 7V
-0.3 to 7V
-20 to 150 oC
-55 to 150 oC
260 oC
Note: 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.
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Marking Information
OB2279
Current Mode PWM ControllerFreq Shuffling with Latch Shutdown
TERMINAL ASSIGNMENTS
Pin Num Pin Name
1 GND
2 FB
3 VIN
4 RI
5 RT
6 SENSE
7 VDD
8 GATE
I/O Description
P Ground
I Feedback input pin. PWM duty cycle is determined by voltage level into this
pin and current-sense signal level at Pin 6.
I Connected through a large value resistor to rectified line input for startup
and line voltage sensing.
I Internal oscillator frequency setting pin. A resistor connected between RI
and GND sets the PWM frequency.
I Dual function pin. Either connected through a NTC resistor to GND for over
temperature shutdown control or used as latch shutdown control input.
I Current sense input pin. Connected to MOSFET current sensing resistor
node.
P DC power supply pin.
O Totem-pole gate drive output for power MOSFET.
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BLOCK DIAGRAM
OB2279
Current Mode PWM ControllerFreq Shuffling with Latch Shutdown
RECOMMENDED OPERATING CONDITION
Symbol
VDD
TA
Parameter
VDD Supply Voltage
Operating Ambient Temperature
Min Max Unit
11.5 25
V
-20 85
oC
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OB2279
Current Mode PWM ControllerFreq Shuffling with Latch Shutdown
ELECTRICAL CHARACTERISTICS
(TA = 25, RI=100K ohm, VDD=16V, if not otherwise noted)
Symbol
Parameter
Supply Voltage (VDD)
I_VDD_Startup VDD Start up Current
I_VDD_Ops
Operation Current
UVLO(Enter)
VDD Under Voltage
Lockout Enter
UVLO(Exit)
VDD Under Voltage
Lockout Exit
(Startup)
OVP(Latch)
VDD Over Voltage
Latch Trigger
OVP(De-Latch) VDD Latch Release
Voltage Threshold
I(Vdd)_latch
VDD bleeding current
at latch shutdown
when VDD = 9V
TD_OVP
VDD OVP Debounce
time
VDD_Clamp
VDD Zener Clamp
Voltage
T_Softstart
Soft Start Time
Feedback Input Section(FB Pin)
AVCS
PWM Input Gain
VFB_Open
VFB Open Voltage
Test Conditions
VDD =15VMeasure
current into VDD
VFB=3V
I(VDD ) = 5 mA
ΔVFB /ΔVcs
IFB_Short
FB pin short circuit
current
VTH_0D
Zero Duty Cycle FB
Threshold Voltage
VTH_BM
Burst Mode FB
Threshold Voltage
VTH_PL
Power Limiting FB
Threshold Voltage
TD_PL
Power limiting
Debounce Time
ZFB_IN
Input Impedance
Current Sense Input(Sense Pin)
T_blanking
Sense Input Leading
Edge Blanking Time
ZSENSE_IN
Sense Input
Impedance
TD_OC
Over Current
Detection and Control
Delay
VTH_OC_0
Current Limiting
Threshold at No
Compensation
Short FB pin to GND,
measure current
CL=1nf at GATE,
I(VIN) = 0uA
Min Typ Max Unit
3 20 uA
2.3 mA
8.8 9.8 10.8 V
15.5 16.5 17.5 V
26.5 28
7.5
45
29.5 V
V
uA
80 uSec
35 V
3 mSec
2.8 V/V
6.2 V
0.75 mA
0.95 V
1.6 V
4.4 V
80 mSec
9.0 Kohm
300 nSec
30 Kohm
70 nSec
0.85 0.90 0.95 V
©On-Bright Electronics
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OB_DOC_DS_79A1