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PDF R7731A Data sheet ( Hoja de datos )

Número de pieza R7731A
Descripción Burst Triple Mode PWM Flyback Controller
Fabricantes Richtek Technology 
Logotipo Richtek Technology Logotipo



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R7731A
Burst Triple Mode PWM Flyback Controller
General Description
The R7731A is a high-performance, low cost, low start-up
current and current mode PWM controller with burst triple
mode to support green mode power saving operation. The
R7731A integrates functions of soft start, Under Voltage
LockOut (UVLO), Leading Edge Blanking (LEB), Over
Temperature Protection (OTP) and internal slope
compensation. It provides the users a superior AC/DC
power application of higher efficiency, low external
component counts and lower cost solution.
To protect the external power MOSFET from being
damaged by supply over voltage, the R7731A output driver
is clamped at 12V. Furthermore, R7731A features fruitful
protections like Over Load Protection (OLP) and Over
Voltage Protection (OVP) to eliminate the external
protection circuits and provide reliable operation. R7731A
is available in SOT-23-6 and DIP-8 packages.
Ordering Information
R7731A
Package Type
E : SOT-23-6
N : DIP-8
Lead Plating System
G : Green (Halogen Free and Pb Free)
Note :
Richtek products are :
` RoHS compliant and compatible with the current require-
ments of IPC/JEDEC J-STD-020.
` Suitable for use in SnPb or Pb-free soldering processes.
Features
z Very Low Start-up Current (<30μA)
z 10/14V UVLO
z Soft Start Function
z Current Mode Control
z Jittering Switching Frequency
z Internal Leading Edge Blanking
z Built-in Slope Compensation
z Burst Triple Mode PWM for Green-Mode
z Cycle-by-Cycle Current Limit
z Feedback Open Protection
z Over Voltage Protection
z Over Temperature Protection
z Over Load Protection
z Soft Driving for Reducing EMI
z Driver Capability ±200mA
z High Noise Immunity
z Opto-Coupler Short Protection
z RoHS Compliant and Halogen Free
Applications
z Adaptor and Battery Charger
z ATX Standby Power
z Set-Top Box (STB)
z DVD and CD(R)
z TV/Monitor Standby Power
z PC Peripherals
Marking Information
R7731AGE
IDP=W
IDP= : Product Code
W : Date Code
R7731AGE
RichTek
R7731A
GNYMDNN
R7731AGN : Product Number
YMDNN : Date Code
R7731A-10 August 2011
www.richtek.com
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R7731A pdf
R7731A
Parameter
Frequency Jittering Range
Symbol
Test Conditions
Min Typ Max Unit
-- ±6 -- %
PWM Frequency Jitter Period
Maximum Duty Cycle
Frequency Variation Versus VDD
Deviation
TJIT
DMAX
fDV
For 65 kHz
VDD = 12V to 25V
-- 4 -- ms
70 75 80 %
-- -- 2 %
Frequency Variation Versus
Temperature Deviation
fDT
TA = 30°C to 105°C (Note 5)
--
--
5
%
COMP Input Section
Open Loop Voltage
VCOMP_OP COMP pin open
COMP Open-loop Protection Delay
Cycles
TOLP
RT = 100kΩ
5.2 5.6 6
V
-- 60 -- ms
Short Circuit Current
Current-Sense Section
IZERO
VCOMP = 0V
-- 1.2 2.2 mA
Initial Peak Current Limit Offset
Leading Edge Blanking Time
Propagation Delay Time
GATE Section
VCSTH
TLEB
TPD
0.8 0.85 0.9
-- 420 520
-- 100 --
V
ns
ns
Rising Time
Falling Time
Gate Output Clamping Voltage
Over Temperature Protection
OTP Hysteresis
TR
TF
VCLAMP
TOTP
TOTP_HYS
VDD = 15V, CL = 1nF
VDD = 15V, CL = 1nF
VDD = 22V
-- 250 350
-- 150 250
-- 12 --
140 --
--
-- 30 --
ns
ns
V
°C
°C
Note 1. Stresses listed as the above "Absolute Maximum Ratings" may cause permanent damage to the device. These are for
stress ratings. Functional operation of the device at these or any other conditions beyond those indicated in the
operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended
periods may remain possibility to affect device reliability.
Note 2. θJA is measured in the natural convection at TA = 25°C on a low effective single layer thermal conductivity test board of
JEDEC 51-3 thermal measurement standard.
Note 3. Devices are ESD sensitive. Handling precaution is recommended.
Note 4. The device is not guaranteed to function outside its operating conditions.
Note 5. Guaranteed by design.
R7731A-10 August 2011
www.richtek.com
5

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R7731A arduino
R7731A
Protection
R7731A provides fruitful protection functions that intend
to protect system from being damaged. All the protection
functions can be listed as below :
` Cycle-by-Cycle Current Limit
This is a basic but very useful function and it can be
implemented easily in current mode controller.
` Over Load Protection
Long time cycle-by-cycle current limit will lead to system
thermal stress. To further protect system, system will
be shut down after about 4096 clock cycles. it's about
60ms delay in 67kHz operation. After shutdown, system
will resume and behave as hiccup. By proper start-up
resistor design, thermal will be averaged to an
acceptable level over the ON/OFF cycle of IC. This will
last until fault is removed. #It's highly recommended to
add a resistor in parallel with the opto-coupler. To provide
sufficient bias current to make TL-431 regulate properly,
1.2kΩ resistor is suggested.
` Brownout Protection
During heavy load, this will trigger 60ms protection and
shut down the system. If it's in light load condition,
system will be shut down after VDD is running low and
triggers UVLO.
` OVP
Output voltage can be roughly sensed by VDD pin.If the
sensed voltage reaches 27V threshold, system will be
shut down after 20μs deglitch delay.
` Feedback Open and Opto-Coupler Short
This will trigger OVP or 60ms delay protection. It
depends on which one occurs first.
` OTP
Internal OTP function will protect the controller itself
from suffering thermal stress and permanent damage. It
stops the system from switching until the temperature
is under threshold level. Meanwhile, if VDD reaches VDD
turn off threshold voltage, system will hiccup till over
temperature condition is gone.
Negative Voltage Spike on Each Pin
Negative voltage (< 0.3V) on each pin will cause substrate
injection. It leads to controller damage or circuit false
trigger. Generally, it happens at CS pin due to negative
spike because of improper layout or inductive current
sense resistor. Therefore, it is highly recommended to
add a R-C filter to avoid CS pin damage, as shown in
Figure 4. Proper layout and careful circuit design should
be done to guarantee yield rate in mass production.
AC Mains
(90V to 265V)
VDD
R7731A
GATE
CS
R-C Filter
Figure 4. R-C Filter on CS Pin
R7731A-10 August 2011
www.richtek.com
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