Flyback Controller. RT7738M Datasheet

RT7738M Controller. Datasheet pdf. Equivalent

RT7738M Datasheet
Recommendation RT7738M Datasheet
Part RT7738M
Description Multi-Mode Flyback Controller
Feature RT7738M; RT7738M SmartJitterTM Multi-Mode Flyback Controller General Description The RT7738M is enhanced hi.
Manufacture Richtek
Datasheet
Download RT7738M Datasheet




Richtek RT7738M
RT7738M
SmartJitterTM Multi-Mode Flyback Controller
General Description
The RT7738M is enhanced high efficient multi-mode PWM
flyback controller with proprietary SmartJitterTM technology.
The innovative SmartJitterTM technology can not only
reduces the EMI emissions of SMPS when the system
enters green mode, but also eliminates the output jittering
ripple. Also, the RT7738M feature Continuous Conduction
Mode (CCM) and valley switching multi-mode control to
optimize the product performance. To meet the stringent
trend toward performance in recent years, the RT7738M is
the best choice for product designers.
The RT7738M is available in SOT-23-6 package, and it is a
current mode PWM controller. Comprehensive protection
and programmable functions are built-in, including a
programmable propagation delay time compensation, a
programmable output Over-Voltage Protection (OVP), a
programmable external Over-Temperature Protection (OTP),
and a programmable bulk capacitor Brown-in/Brown-out
protection. With the above features, the RT7738M is a
cost-effective and compact solution for AC/DC products.
Features
Proprietary SmartJitterTM Technology
Reducing EMI Emissions of SMPS
Output Jittering Ripple Elimination
Continuous Conduction Mode (CCM) and Valley
Switching Mode Control
Ultra-low Start-up current (<3A)
Accurate Over-Load Protection (OLP)
Programmable Propagation Delay Time
Compensation
Programmable Output Over-Voltage Protection
Programmable External Over-Temperature
Protection
Programmable Bulk Capacitor Brown-in/Brown-out
Protection
Driver Capability : 200mA/300mA
High Noise Immunity
Applications
Switching AC/DC Adaptor
NB Adaptor
TV/Monitor Standby Power
PC Peripherals
Simplified Application Circuit
Mains
(90V to 265V)
CCOMP
VDD
DMAG
GATE
COMP
RT7738M
GND
CS
(Optional)
(Optional)
(Optional)
(Optional)
VO+
VO-
Copyright © 2014 Richtek Technology Corporation. All rights reserved.
DS7738M-00 November 2014
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
1



Richtek RT7738M
RT7738M
Ordering Information
RT7738M
Package Type
E : SOT-23-6
Lead Plating System
G : Green (Halogen Free and Pb Free)
Note :
Richtek products are :
RoHS compliant and compatible with the current
requirements of IPC/JEDEC J-STD-020.
Suitable for use in SnPb or Pb-free soldering processes.
Marking Information
2D=DNN
2D= : Product Code
DNN : Date Code
Pin Configurations
(TOP VIEW)
GATE VDD CS
654
23
GND COMP DMAG
SOT-23-6
Functional Pin Description
Pin No.
Pin Name
Pin Function
1 GND
Ground of the Controller.
2 COMP
Feedback Voltage Input. Connect an opto-coupler to close the control loop and
achieve output voltage regulation.
3 DMAG
Demagnetization Pin. Input and output voltage detection from auxiliary winding.
4 CS
Current Sense Input. The current sense resistor between this pin and GND is used
for current limit setting.
5 VDD
Supply Voltage Input. The controller will be enabled when VDD exceeds VTH_ON
and disabled when VDD decreases lower than VTH_OFF.
6 GATE
Gate Driver Output Pin.
Function Block Diagram
VDD
DMAG
COMP
CS
VDMAG_OVP
IDMAG_BNI/BNO
Vin/Vo
Detection
+
-
+
-
+
VSRSP_TH -
VOTP_TH
+
-
GATEOFF
COMP Open
Sensing
VCOMP_OP
Constant
Power
LEB X3
OVP
+
-
27V
Shutdown
Logic
Counter
POR
UVLO
+
-
VTH_ON/OFF
Bias &
Bandgap
Oscillator
Slope
Ramp
VS_Oscillator
TON_MAX
S
-
-
+
PWM
Comparator
R
Green Mode
Soft Driver
Q
COMP
VDD
GATE
GND
Copyright © 2014 Richtek Technology Corporation. All rights reserved.
www.richtek.com
2
is a registered trademark of Richtek Technology Corporation.
DS7738M-00 November 2014



Richtek RT7738M
RT7738M
Operation
Multi-mode PWM
The RT7738M is a multi-mode PWM controller, and a
constant oscillator is built-in to allow the system
operating in CCM. As the load decreases, the system
enters DCM, and the oscillator converts to valley
switching mode control. In lighter load or no load
conditions, the controller enters green mode. The
RT7738M provides multi-mode control to optimize the
product performance under different load conditions.
Oscillator
The oscillator runs at 65kHz and features frequency
jittering function. The saw-tooth slope compensation,
maximum duty cycle pulse and over-load protection
slope are built-in. Its jitter depth is proportion of
oscillator frequency where f is frequency jittering
range, and TJIT is frequency jittering period.
Leading Edge Blanking (LEB)
To prevent unexpectedly gate switching interruption
from the initial spike on CS pin, the LEB delay is
designed to block this spike at the beginning of gate
switching.
Gate Driver
A totem pole gate driver is designed to meet both EMI
and efficiency requirements in low power applications.
An internal pull-low circuit is activated after pretty low
VDD to prevent external MOSFET from accidentally
turning on during UVLO.
DMAG Pin
The DMAG pin detects the input voltages of bulk
capacitor and output voltage by auxiliary winding and
resistor divider. According to the DMAG signal, the
RT7738M provides protections, including output
over-voltage protection, and programmable bulk
capacitor Brown-in/Brown-out protection.
Over-Load Protection
In over-load conditions, current limit for a long time will
lead to system thermal stress problem. To further
protect the system, the RT7738M is designed with a
proprietary prolonged turn-off period during hiccup. The
power loss and temperature during OLP are averaged
to an acceptable level over the ON/OFF cycle.
CS Pin Open Protection
When the CS pin is opened, the controller will shut
down after a few cycles.
Internal VDD Over-Voltage Protection
Output voltage can be roughly sensed by the VDD pin.
If the sensed voltage reaches VOVP threshold, the
controller shuts down after deglitch delay.
Feedback Open and Opto-Coupler Short
If the output voltage feedback loop is open or the
opto-coupler is shorted, the OVP/OLP function will be
triggered depending on which one occurs first.
Output Short Protection
The RT7738M implements output short protection by
detecting output signal of DMAG pin. It can minimize
the power loss and temperature during output short,
especially at high line input voltage.
Secondary Rectifier Short Protection
The current spike during secondary rectifier short test
is extremely high because of the saturated main
transformer. Meanwhile, the transformer acts like a
leakage inductance. During high line, the current in
power MOSFET is sometimes too high in OLP delay
time. To offer better and easier protection design, the
RT7738M shuts down after a few of cycles before fuse
is impacted.
Copyright © 2014 Richtek Technology Corporation. All rights reserved.
DS7738M-00 November 2014
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
3







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