R7731
Burst Triple Mode PWM Flyback Controller
General Description
The R7731 is a high performance, low cost, low start-up current, current mode PWM controller with burst triple mode to support green mode power saving operation. The R7731 integrates functions of Soft-Start, Under Voltage Lockout (UVLO), Leading Edge Blanking (LEB), Over Temperature Protection (OTP), 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 R7731 output driver is clamped at 12V. Furthermore, R7731 features fruitful protections like OLP (Over Load Protection) ,OVP (Over Voltage Protection) to eliminate the external protection circuits and provide reliable operation. R7731 is available in SOT-23-6 and DIP-8 packages.
Features
zVery Low Start-Up Current (<30μA)
z10/14V UVLO
zSoft-Start Function
zCurrent Mode Control
zJittering Switching Frequency
zInternal Leading Edge Blanking
zBuilt-in Slope Compensation
zBurst Triple Mode PWM for Green-Mode
zCycle-by-Cycle Current Limiting
zFeedback Open Protection
zOutput Over Voltage Protection
zOver Temperature Protection
zOver Load Protection
zSoft Driving for Reducing EMI
zHigh Noise Immunity
zOpto Coupler Short Protection
zRoHS Compliant and Halogen Free
Applications
zAdaptor and Battery Charger
zATX Standby Power
zSet Top Boxes (STB)
zDVDand CD(R)
zTV/Monitor Standby Power
zPC Peripherals
Typical Application Circuit
VO+ AC Mains 
(90V to 265V)
VO-
RT |
VDD |
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R7731 |
COMP |
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GATE |
GND |
CS |
DS7731-03 March 2011 |
www.richtek.com |
1
R7731
Ordering Information
R7731 
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 requirements of IPC/JEDEC J-STD-020.
`Suitable for use in SnPb or Pb-free soldering processes.
Marking Information
For marking information, contact our sales representative directly or through a Richtek distributor located in your area.
Pin Configurations
(TOP VIEW)
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GATE |
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VDD CS |
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GND COMP RT |
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SOT-23-6 |
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GND COMP NC |
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RT |
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8 |
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GATE VDD |
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NC |
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CS |
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DIP-8
www.richtek.com |
DS7731-03 March 2011 |
2
R7731
Function Block Diagram
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OVP + |
VDD |
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POR |
- |
27V |
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Shutdown |
OTP |
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Logic |
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+ |
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Brown out |
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UVLO |
- |
14V/10V |
sensing |
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COMP open |
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Counter |
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Bias & |
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sensing |
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Bandgap |
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OLP |
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Jittering Oscillator |
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Constant |
SS |
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RT |
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Dmax |
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Power |
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Soft |
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S |
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Driver |
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- |
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Q |
GATE |
COMP |
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- |
R |
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+ |
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PWM |
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CS |
Slope |
comparator |
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Ramp |
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COMP |
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Burst |
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VBURL |
LEB |
X3 |
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Triple Mode |
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VBURH |
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VDD |
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GND |
Functional Pin Description
Pin No. |
Pin Name |
Pin Function |
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SOT-23-6 |
DIP8 |
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1 |
8 |
GND |
Ground. |
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2 |
7 |
COMP |
Comparator Input Pin. By connecting a photo-coupler to this pin, the peak |
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current set point is adjusted accordingly to the output power requirement. |
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3 |
5 |
RT |
Set the switching frequency by connecting a resistor to GND. |
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4 |
4 |
CS |
Primary Current Sense Pin. |
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5 |
2 |
VDD |
IC Power Supply Pin. |
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6 |
1 |
GATE |
Gate driver output to drive the external MOSFET. |
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-- |
3, 6 |
NC |
No Internal Connection. |
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DS7731-03 March 2011 |
www.richtek.com |
3
R7731
Absolute Maximum Ratings (Note 1)
z Supply Input Voltage, VDD ------------------------------------------------------------------------------------------- |
30V |
z GATE Pin ---------------------------------------------------------------------------------------------------------------- |
20V |
z FB, RT, COMP, CS Pin ---------------------------------------------------------------------------------------------- |
6.5V |
z IDD ------------------------------------------------------------------------------------------------------------------------- |
10mA |
z Power Dissipation, PD @ TA = 25°C |
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SOT-23-6 ---------------------------------------------------------------------------------------------------------------- |
0.4W |
DIP-8 --------------------------------------------------------------------------------------------------------------------- |
0.714W |
z Package Thermal Resistance (Note 2) |
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z SOT-23-6, θJA ----------------------------------------------------------------------------------------------------------- |
250°C/W |
z DIP-8, θJA ---------------------------------------------------------------------------------------------------------------- |
140°C/W |
z Junction Temperature ------------------------------------------------------------------------------------------------- |
150°C |
z Lead Temperature (Soldering, 10 sec.) --------------------------------------------------------------------------- |
260°C |
z Storage Temperature Range ---------------------------------------------------------------------------------------- |
−65°C to 150°C |
z ESD Susceptibility (Note 3) |
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HBM (Human Body Mode) ------------------------------------------------------------------------------------------ |
4kV |
MM (Machine Mode) -------------------------------------------------------------------------------------------------- |
250V |
Recommended Operating Conditions |
(Note 4) |
z Supply Input Voltage, VDD ------------------------------------------------------------------------------------------- |
12V to 25V |
z Operating Frequency ------------------------------------------------------------------------------------------------- |
50k to 130kHz |
z Junction Temperature Range ---------------------------------------------------------------------------------------- |
−40°C to 125°C |
z Ambient Temperature Range ---------------------------------------------------------------------------------------- |
−40°C to 85°C |
Electrical Characteristics
(VDD = 15V, RT = 100kΩ, TA = 25°C, unless otherwise specified)
Parameter |
Symbol |
Test Conditions |
Min |
Typ |
Max |
Unit |
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VDD Section |
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VDD Over Voltage Protection Level |
VOVP |
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25.5 |
27 |
28.5 |
V |
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On Threshold Voltage |
VTH_ON |
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13 |
14 |
15 |
V |
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VDD On/Off Hysteresis |
VDD_hys |
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3 |
4 |
5 |
V |
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Start-Up Current |
IDD-ST |
VDD = VTH_ON – 0.1V |
-- |
20 |
30 |
μA |
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Operating Current |
IDD-OP |
VDD = 15V, RT = 100kΩ, |
-- |
1.1 |
2.2 |
mA |
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GATE = Open, VCOMP = 2.5V |
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VDD Hold Up Mode Hysteresis |
VDD_hys |
VCOMP < 1.6V |
-- |
11.5 |
-- |
V |
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Ending Level |
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VDD Hold Up Mode Entry Level |
VDD_Low |
VCOMP < 1.6V |
-- |
11 |
-- |
V |
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VDD Clamp Voltage |
VDD_Clamp |
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-- |
29 |
-- |
V |
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Oscillator Section (RT pin) |
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Normal PWM Frequency |
fOSC |
RT = 100kΩ |
60 |
65 |
70 |
kHz |
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Frequency Jittering Range |
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-- |
± 4 |
-- |
% |
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Maximum Duty Cycle |
DMAX |
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70 |
75 |
80 |
% |
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To be continued |
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www.richtek.com |
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DS7731-03 March 2011 |
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