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OB2550
High Precision CC/CV Primary-Side Controller
GENERAL DESCRIPTION
OB2550 is a high performance offline PSR
controller for low power AC/DC charger and
adapter applications. It operates in primary-side
sensing and regulation. Consequently,
opto-coupler and TL431 could be eliminated.
Proprietary Constant Voltage (CV) and Constant
Current (CC) control is integrated as shown in the
figure below.
In CC control, the current and output power setting
can be adjusted externally by the sense resistor
Rs at CS pin. In CV control, multi-mode operations
are utilized to achieve high performance and high
efficiency. In addition, good load regulation is
achieved by the built-in cable drop compensation.
Device operates in PFM in CC mode as well at
large load condition and it operates in PWM with
frequency reduction at light/medium load. The chip
consumes very low operation current, it can
achieve less than 30mW standby power to meet
strict standby power standard.
OB2550 offers comprehensive protection
coverage with auto-recovery features including
Cycle-by-Cycle current limiting, VDD over voltage
protection, feedback loop open protection, short
circuit protection, built-in leading edge blanking,
VDD under voltage lockout (UVLO), OTP etc.
OB2550 is offered in SOT23-6 package.
Figure.1. Typical CC/CV Curve
TYPICAL APPLICATION
Product Specification
FEATURES
Primary-side Sensing and Regulation Without
TL431 and Opto-coupler
High Precision Constant Voltage and Current
Regulation at Universal AC Input
Multi-mode PWM/PFM operation for efficiency
improving
Meet 30mW no load standby power standard
Good dynamic response
Programmable CV and CC Regulation
Built-in Line Voltage and Primary Winding
Inductance Compensation
Programmable Cable Drop Compensation
No Need For Control Loop Compensation
Precise Internal Over Temperature Protection
Audio Noise Free Operation
Drive BJT Switch
Built-in Leading Edge Blanking (LEB)
Ultra Low Start-up Current (Typ. 1uA) and Low
Operating Current (Typ. 360uA)
Comprehensive Protection Coverage with
auto-recovery
VDD Over Voltage Protection
VDD Under Voltage Lockout with
Hysteresis (UVLO)
Cycle-by-Cycle Current Limiting
Feedback Loop Open Protection
Output Short Circuit Protection
Over Temperature Protection (OTP)
APPLICATIONS
Low Power AC/DC offline SMPS for
Cell Phone Charger
Digital Cameras Charger
Small Power Adapter
Auxiliary Power for PC, TV etc.
Linear Regulator/RCC Replacement
©On-Bright Electronics
Confidential
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Preliminary datasheet
OB_DOC_DS_255000

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GENERAL INFORMATION
Pin Configuration
The pin map is shown as below for SOT23-6.
Ordering Information
Part Number
Description
OB2550MP
SOT23-6, Pb-free, T&R
OB2550
High Precision CC/CV Primary-Side Controller
Package Dissipation Rating
Package
RθJA (/W)
SOT23-6
200
Absolute Maximum Ratings
Parameter
Value
VDD Voltage
-0.3 to 30V
FB Input Voltage
-0.3 to 7V
CS Input Voltage
-0.3 to 7V
ED Input Voltage
-0.3 to 7V
BD Input Voltage
-0.3 to 7V
Min/Max Operating
Junction Temperature TJ
Min/Max Storage
Temperature Tstg
Lead Temperature
(Soldering, 10secs)
-40 to 150
-55 to 150
260
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.
©On-Bright Electronics
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Preliminary datasheet
OB_DOC_DS_255000

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Marking Information
OB2550
High Precision CC/CV Primary-Side Controller
TERMINAL ASSIGNMENTS
Pin Num
1
2
3
4
5
6
Pin Name
FB
GND
CS
ED
BD
VDD
I/O Description
I
The voltage feedback from auxiliary winding. Connected to resistor
divider from auxiliary winding reflecting output voltage.
P Ground
I Power Mosfet source
O Enable driver.
O Base drive with current limit for power BJT.
P Power Supply
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Preliminary datasheet
OB_DOC_DS_255000

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BLOCK DIAGRAM
OB2550
High Precision CC/CV Primary-Side Controller
©On-Bright Electronics
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Preliminary datasheet
OB_DOC_DS_255000

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OB2550
High Precision CC/CV Primary-Side Controller
ELECTRICAL CHARACTERISTICS
(TA = 25, VDD=15V, if not otherwise noted)
Symbol
Parameter
Test Conditions
Min
Supply Voltage (VDD) Section
I start-up
Start up current
VDD=UVLO_OFF-1V
I static
Static current
UVLO(OFF) VDD under voltage lockout exit
18.4
UVLO(ON) VDD under voltage lockout enter
6.5
VDD_OVP VDD over voltage protection
26.5
Max.
Operating
Voltage
Current Sense Input Section
TLEB
LEB time
Vth_ocp_min Minimum over current threshold
485
Vth_ocp_max Maximum over current threshold
Vcs_mini
Minimum CS threshold
Ton_max
Maximum Ton
Td_oc
OCP propagation delay
FB Input Section
Vref_fb
Reference voltage for feedback
threshold
2.475
Tpause_min Minimum Toff
F_min
Minimum frequency
720
Icomp_cable
Maximum cable compensation
current
44
BASE Drive Section
Is_max
Base sourcing maximum current
20
Is_preoff
Base sourcing current after
pre-off
Rdson_l
Base drive low side on resistor
IED_leak
Before startup,
current
ED
pin
leakage
VED=VDD-1V
Output Over Voltage Protection
V_OVP
Output Over voltage threshold
2.85
On chip Over temperature Section
T_otp
Over temperature protection
trigger point
150
T_otp_rec
Over temperature protection
recovery point
115
Typ Max
5 15
0.65 1.0
19.4 20.4
7.1 7.8
28.0 29.5
26
0.5
500 515
555
100
50
100
2.50 2.525
2.0
800 880
48 52
30 40
1.5
1.0 2
01
3.0 3.15
165 180
130 145
Unit
uA
mA
V
V
V
V
uS
mV
mV
mV
uS
nS
V
uS
Hz
uA
mA
mA
ohm
uA
V
©On-Bright Electronics
Confidential
-5-
Preliminary datasheet
OB_DOC_DS_255000