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PDF ( 数据手册 , 数据表 ) OB2500N

零件编号 OB2500N
描述 High Precision CC/CV Primary-Side Power Switch
制造商 On-Bright Electronics
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OB2500N 数据手册, 描述, 功能
OB2500N
High Precision CC/CV Primary-Side Power Switch
GENERAL DESCRIPTION
OB2500N is a high performance offline PSR
power switch 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 at large load
condition and it operates in PWM with frequency
reduction at light/medium load. The chip
consumes very low operation current. It achieves
less than 75mW standby power to meet strict
standby power standard.
OB2500N offers comprehensive protection
coverage with auto-recovery feature 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.
OB2500N is offered in SOP7 packages.
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
Integrated 1A 650V MOSFET
Good dynamic response
Programmable CV and CC regulation
Built-in primary winding inductance
compensation
Programmable cable drop compensation
No need for control loop compensation
Audio noise free operation
Built-in leading edge blanking (LEB)
Ultra low start-up current and low operating
current
Comprehensive protection coverage with
auto-recovery
On-chip OTP and external OTP
VDD over voltage protection
VDD under voltage lockout with
hysteresis (UVLO)
Cycle-by-Cycle current limiting
Feedback loop open protection
Output short circuit protection
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
Figure.1. Typical CC/CV Curve
TYPICAL APPLICATION
©On-Bright Electronics
Confidential
-1-
Preliminary Datasheet
OB_DOC_DS_2500N00







OB2500N pdf, 数据表
OB2500N
High Precision CC/CV Primary-Side Power Switch
PoMAX
1
2
LP FSW
I
2
p
(3)
Where Lp indicate the inductance of primary
winding and Ip is the peak current of primary
winding.
Refer to the equation 3, the change of the primary
winding inductance results in the change of the
maximum output power and the constant output
current in CC mode. To compensate the change
from variations of primary winding inductance, the
switching frequency is locked by an internal loop
and the switching frequency is
FSW
1
2TDemag
(4)
Since TDemag is inversely proportional to the
inductance, as a result, the product Lp and fsw is
constant, thus the maximum output power and
constant current in CC mode will not change as
primary winding inductance changes. Up to ±7%
variation of the primary winding inductance can be
compensated.
On Time OCP Compensation
The variation of max output current in CC mode
can be rather large if no compensation is provided.
The OCP threshold value is self adjusted higher at
higher AC voltage. This OCP threshold slope
adjustment helps to compensate the increased
output current limit at higher AC voltage. In
OB2500N, a proprietary OCP compensation block
is integrated and no external components are
needed. The OCP threshold in OB2500N series is
a function of the switching ON time. For the ON
time between 1.6us to 6.4us (typical), the OCP
threshold changes linearly from 500mV to 590mV.
For the ON time larger than 6.4us, the OCP
threshold is clamped to 590mV, as shown in
Figure 4.
internal current flowing into the resister divider.
The current is proportional to the switching off time,
as a result, it is inversely proportional to the output
load current, and the drop due to the cable loss
can be compensated. As the load current
decreases from full-load to no-load, the offset
voltage at INV will increase. It can also be
programmed by adjusting the resistance of the
divider to compensate the drop for various cable
lines used.
The percentage of maximum compensation is
V Icomp _ cable(R1// R2) 106 100%
Vout 2.5
V is load compensation voltage and Vout is
output voltage;
For example: R1//R2=6.2Kohm, the percentage of
maximum compensation is
V 456200 106 100% 11.16%
Vout 2.5
Current Sensing and Leading Edge Blanking
Cycle-by-Cycle current limiting is offered in
OB2500N. 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 power MOSFET on state so that the
external RC filtering on sense input is no longer
needed.
Gate Driver
The GATE pin is connected to the gate of an
external power switch. An internal 11V (typical)
clamp is added for MOSFET gate protection at
high VCC voltage. When VCC voltage drops below
UVLO(ON), the GATE pin is internally pull low to
maintain the off state.
Figure.4. On time OCP compensation
Programmable Cable Drop Compensation
In OB2500N, cable drop compensation is
implemented to achieve good load regulation. An
offset voltage is generated at INV pin by an
CC mode shutdown function
In OB2500N, to prevent the controller operating
under abnormal conditions, the minimum output
voltage of CC mode is limited to predetermined
voltage. The CC output voltage is sampled through
FB pin from auxiliary winding at the middle of the
de-magnetization. When the FB sampled voltage
is below 1.55V and last 1024-2048 cycle, the
controller will shut down.
Protection Control
Good power supply system reliability is achieved
©On-Bright Electronics
Confidential
-8-
Preliminary Datasheet
OB_DOC_DS_2500N00














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