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.
Features
μ
Very Low Start-up Current (<30μA)
10/14V UVLO
Soft Start Function
Current Mode Control
Jittering Switching Frequency
Internal Leading Edge Blanking
Built-in Slope Compensation
Burst Triple Mode PWM for Green-Mode
Cycle-by-Cycle Current Limit
Feedback Open Protection
Over Voltage Protection
Over Temperature Protection
Over Load Protection
Soft Driving for Reducing EMI
Driver Capability
±
200mA
High Noise Immunity
Opto-Coupler Short Protection
RoHS Compliant and Halogen Free
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.
Applications
Adaptor and Battery Charger
ATX Standby Power
Set-Top Box (STB)
DVD and CD(R)
TV/Monitor Standby Power
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
1
R7731A
Pin Configurations
(TOP VIEW)
GND COMP NC
8
7
6
RT
5
GATE VDD CS
6
5
4
2
3
2
3
4
GND COMP RT
GATE VDD
NC
CS
SOT-23-6
DIP-8
Typical Application Circuit
AC Mains
(90V to 265V)
VO+
VO-
RT
VDD
R7731A
*
COMP
GATE
GND
CS
* : See Application Information
Functional Pin Description
Pin No.
SOT-23-6
1
2
3
4
5
6
--
DIP8
8
7
5
4
2
1
3, 6
GND
COMP
RT
CS
VDD
GATE
NC
Ground.
Comparator Input. By connecting an opto-coupler to this pin, the peak
current set point is adjusted accordingly to the output power requirement.
Set the switching frequency by connecting a resistor to GND.
Primary Current Sense.
IC Power Supply.
Gate Driver Output to drive the external MOSFET.
No Internal Connection.
Pin Name
Pin Function
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2
R7731A-10 August 2011
R7731A
Function Block Diagram
OVP
+
-
VDD
27V
Shutdown
Logic
Brown out
sensing
COMP open
sensing
OLP
Constant
Power
SS
Counter
OTP
POR
+
UVLO
-
14V/10V
Bias &
Bandgap
Jittering Oscillator
RT
Soft
Driver
Q
R
GATE
Dmax
S
COMP
-
-
+
PWM
comparator
CS
Slope
Ramp
COMP
Burst
Triple Mode
V
BURL
V
BURH
V
DD
GND
LEB
X3
R7731A-10 August 2011
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3
R7731A
Absolute Maximum Ratings
(Note 1)
Supply Input Voltage, V
DD
-------------------------------------------------------------------------------------------------
−0.3V
to 30V
GATE Pin ----------------------------------------------------------------------------------------------------------------------
−0.3V
to 20V
RT, COMP, CS Pin ----------------------------------------------------------------------------------------------------------
−0.3V
to 6.5V
I
DD
------------------------------------------------------------------------------------------------------------------------------- 10mA
Power Dissipation, P
D
@ T
A
= 25°C
SOT-23-6 ---------------------------------------------------------------------------------------------------------------------- 0.4W
DIP-8 --------------------------------------------------------------------------------------------------------------------------- 0.714W
Package Thermal Resistance (Note 2)
SOT-23-6,
θ
JA
----------------------------------------------------------------------------------------------------------------- 250°C/W
DIP-8,
θ
JA
---------------------------------------------------------------------------------------------------------------------- 140°C/W
Junction Temperature ------------------------------------------------------------------------------------------------------- 150°C
Lead Temperature (Soldering, 10 sec.) --------------------------------------------------------------------------------- 260°C
Storage Temperature Range ----------------------------------------------------------------------------------------------
−65°C
to 150°C
ESD Susceptibility (Note 3)
HBM (Human Body Mode) ------------------------------------------------------------------------------------------------ 4kV
MM (Machine Mode) -------------------------------------------------------------------------------------------------------- 250V
Recommended Operating Conditions
(Note 4)
Supply Input Voltage, V
DD
------------------------------------------------------------------------------------------------- 12V to 25V
Operating Frequency ------------------------------------------------------------------------------------------------------- 50k to 130kHz
Junction Temperature Range ----------------------------------------------------------------------------------------------
−40°C
to 125°C
Ambient Temperature Range ----------------------------------------------------------------------------------------------
−40°C
to 85°C
Electrical Characteristics
(V
DD
= 15V, VDD bypass capacitor=0.1μF, R
T
= 100kΩ, T
A
= 25°C, unless otherwise specified)
Parameter
VDD Section
V
DD
Over Voltage Protection Level
On Threshold Voltage
V
DD
On/Off Hysteresis
Start-up Current
Operating Current
VDD Holdup Mode Hysteresis
Ending Level
VDD Holdup Mode Entry Level
V
DD
Clamp Voltage
Oscillator Section (RT pin)
Normal PWM Frequency
Symbol
Test Conditions
Min
Typ
Max
Unit
V
OVP
V
TH_ON
V
DD_HYS
I
DD_ST
I
DD_OP
V
DD_HYS
V
DD_LOW
V
DD_CLAMP
V
DD
= V
TH_ON
– 0.1V
V
DD
= 15V, R
T
= 100kΩ,
GATE = Open, V
COMP
= 2.5V
V
COMP
< 1.6V
V
COMP
< 1.6V
25.5
13
3
--
--
--
--
--
27
14
4
20
1.1
11.5
11
29
28.5
15
5
30
2.2
--
--
--
V
V
V
μA
mA
V
V
V
f
OSC
R
T
= 100kΩ
60
65
70
kHz
To be continued
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4
R7731A-10 August 2011
R7731A
Parameter
Frequency Jittering Range
PWM Frequency Jitter Period
Maximum Duty Cycle
Frequency Variation Versus V
DD
Deviation
Frequency Variation Versus
Temperature Deviation
COMP Input Section
Open Loop Voltage
V
COMP_OP
COMP pin open
R
T
= 100kΩ
V
COMP
= 0V
5.2
--
--
5.6
60
1.2
6
--
2.2
V
ms
mA
T
JIT
D
MAX
f
DV
f
DT
V
DD
= 12V to 25V
T
A
=
−30°C
to 105°C (Note 5)
For 65 kHz
Symbol
Test Conditions
Min
--
--
70
--
--
Typ
±6
4
75
--
--
Max
--
--
80
2
5
Unit
%
ms
%
%
%
COMP Open-loop Protection Delay
T
OLP
Cycles
Short Circuit Current
Current-Sense Section
Initial Peak Current Limit Offset
Leading Edge Blanking Time
Propagation Delay Time
GATE Section
Rising Time
Falling Time
Gate Output Clamping Voltage
Over Temperature Protection
OTP Hysteresis
T
R
T
F
V
CLAMP
T
OTP
T
OTP_HYS
V
CSTH
T
LEB
T
PD
I
ZERO
0.8
--
--
0.85
420
100
0.9
520
--
V
ns
ns
V
DD
= 15V, C
L
= 1nF
V
DD
= 15V, C
L
= 1nF
V
DD
= 22V
--
--
--
140
--
250
150
12
--
30
350
250
--
--
--
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.
θ
JA
is measured in the natural convection at T
A
= 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
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5
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