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PDF ( 数据手册 , 数据表 ) CR6237

零件编号 CR6237
描述 High Precision CC/CV Primary-Side PWM Power Switch
制造商 Chip Rail
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CR6237 数据手册, 描述, 功能
CR623XCR6235/6236/6237/6238
High Precision CC/CV Primary-Side PWM Power Switch
Features
Up to 5% Precision for Constant
Voltage Regulation and Constant
Current Regulation at Universal AC
input
Primary-side Sensing and Regulation
Without TL431 and Opto-coupler
Flyback Topology In DCM Operation
Soft-start
Built-in Leading Edge Blanking (LEB)
Frequency Jitter to Reduce System EMI
Programmable CV and CC Regulation
Adjustable Constant Current and
Output Power Setting
Built-in Secondary Constant Current
Applications
Cell Phone /Digital Cameras Charger
Small Power Adaptor
General Description
CR623X is a high performance offline PWM
power switch for low power AC/DC charger
and adaptor applications. It operates in
primary-side sensing and provides constant
voltage (CV) and constant current (CC)
regulation without TL431 and opto-coupler.
A typical output CC/CV curve is shown as in
the Fig.1.
Fig.1. Typical CC/CV Curve
Control with Primary Side Feedback
Built-in Secondary Constant Voltage
Sampling Controller
Program Cable Drop Compensation
Rich Protections For System Reliability
including
VDD Under Voltage Lockout with
Hysteresis (UVLO)
Cycle-by-Cycle Current Limiting
and Peak Current Protection (OCP)
Over Temperature Protection (OTP)
VDD Over Voltage Protection (OVP)
VDD Clamp
Lead-free SOP-8L & DIP-8L
Auxiliary Power for PC, TV etc.
Linear Regulator/RCC Replacement
In CC mode, the current point and maximum
output power setting can be adjusted by the
sense resistor RS at CS pin. In CV mode,
CR623X captures the auxiliary flyback
signal at Pin INV and then regulates the
output voltage. IN this mode, multi-mode
operations are utilized to achieve high
performance and high efficiency. In addition,
built-in cable drop compensation further
enhances output accuracy.
CR623X offers power on soft-start control
and ensures safe operation with complete
protections against all the fault conditions.
Built-in protection circuitry includes
Cycle-by-Cycle current limiting, peak current
protection, OTPVDD OVP, VDD clamp and
UVLO. Excellent EMI performance is
achieved with frequency jitter and soft-drive.
V2.0
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CR6237 pdf, 数据表
CR623X
High Precision CC/CV Primary-Side PWM Power Switch
The current IC is inversely proportional to
the output COMP of the error amplifier. As a
result, it is inversely proportional to the
output load current. Thus the drop due to the
cable loss can be compensated. The
integrate equation is shown as below.
Vref
(1 +
R1
R2
)
IC
R1
=
N AUX
NS
(VO
+ ∆V
+ Vcable )
(3)
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. This feature allows for better output
voltage accuracy by compensating for the
output voltage droop due to the output cable
resistance. In CR623X, cable drop
compensation is implemented to achieve
good load regulation in the CV mode.
Switching frequency
In CR623X, the switching frequency is
adaptively controlled by the load conditions
and the operation modes. The maximum
operation switching frequency is set to 60
KHz internally.
For flyback operating in DCM, The
maximum output power is given by
PoMAX
=
1
2
LP
FSW
I
2
P
(3)
Where LP indicates the inductance of
primary winding and IP is the peak current of
primary winding.
The primary-side sensing topology must
work in DCM. Refer to the equation 3, to
prevent from working in continuous
conduction mode (CCM), the switching
frequency is locked by an internal loop such
that 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 is limited.
Current Sensing and Leading Edge
Blanking
CR623X detects primary MOSFET current
from the CS pin, which is not only for the
peak current mode control but also for the
cycle-by-cycle current limit. The maximum
voltage threshold of the current sensing pin
is set as 0.9V. Thus the MOSFET peak
current can be calculated as:
I peak (max)
=
0.9V
RS
(4)
A 540 ns leading-edge blanking (LEB) time
is included in the input of CS pin to prevent
the false-trigger caused by the current spike.
So that the external R-C filter can be
eliminated. The current sense input voltage
and the EA output COMP determine the
switch duty cycle, and then regulation the
output voltage.
EMI improvement
To improve EMI of the CR623X system, two
methods are designed in the chip. One is
the frequency jitter. This control is achieved
by changing the operation frequency. The
oscillation frequency is modulated so that
the tone energy is spread out. The spread
spectrum minimizes the conduction band
EMI. The other one is soft drive which is
designed to open the power MOSFET
gradually. The internal power MOSFET in
CR623X is driven by a dedicated gate driver
for power switch control. Too weak gate
drive strength will result in higher conduction
and switch loss of MOSFET, while too
strong drive will produce EMI problem. A
good tradeoff is achieved through the built-in
totem pole driver design with right output
strength control. In this way, the EMI will be
improved much better.
V2.0
8/12














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