MC7731N6

CYStech Electronics Corp.
Spec. No. : C494N6
Issued Date : 2012.04.02
Revised Date :
Page No. : 1/10
Current Mode PWM Controller
MC7731N6
Description
MC7731N6 is highly integrated current mode PWM control IC optimized for high performance low
standby power offline fly back converter applications. To meet the international power conservation
requirements, optimized green mode is integrated to
improve the efficiency at light or no load conditions with no audible noise. Slope compensation is
integrated to ensure the stability at high load. Lead edge blanking is integrated to prevent the false trigger
at the transition of the switch. Soft switching control at the gate drive can improve the EMI performance of
the power supply. The Gate-drive output is clamped at 18V to protect the power MOS.
MC7731N6 offers many protection functions with auto self-recovery features, including cycle-by-cycle
current limiting, over-load protection (OLP) and under voltage lockout(UVLO).
Excellent EMI performance is achieved with frequency jitter technique together with soft switching
control at the totem pole gate driver.
Features
●Frequency jitter function to improve EMI performance of power supply
●No-audible-noise green mode Control
● External Programmable PWM Switching Frequency
● Internal Slope Compensation
● Low VDD Startup Current and Low Operating Current
● Leading Edge Blanking
● UVLO
● Gate Max Output Voltage Clamp at 18V
● Overload Protection (OLP).
● Line Compensation Over Current Protection (OCP)
Applications
Offline AC/DC flyback converter for
● Battery Charger
● Power Adaptor
● Set-Top Box Power Supplies
● Open-frame SMPS
● PC 5V Standby Power
MC7731N6
CYStek Product Specification
CYStech Electronics Corp.
Spec. No. : C494N6
Issued Date : 2012.04.02
Revised Date :
Page No. : 2/10
Ordering Information
Device
Package
Shipping
MC7731N6
SOT-23-6L
(Pb-free lead plating)
3000 pcs / tape & reel
Typical Application Circuit
Pin Configuration
MC7731N6
CYStek Product Specification
CYStech Electronics Corp.
Spec. No. : C494N6
Issued Date : 2012.04.02
Revised Date :
Page No. : 3/10
Pin Assignment
Pin Name
Pin Number
Pin Function
GND
1
FB
2
Ground
Feedback input pin. The PWM duty cycle is determined by voltage level into
this pin and the current-sense signal at Pin 6.
RI
3
Internal Oscillator frequency setting pin. A resistor connected between RI and GND
sets the PWM frequency.
SENSE
VDD
GATE
4
5
6
Current sense input pin. Connected to MOSFET current sensing resistor node.
Chip DC power supply pin.
Totem-pole gate drive output for the power MOSFET.
Function Block Diagram
Absolute Maximum Ratings
Parameter
VDD to GND
VDD clamped current
VDD clamped voltage
VFB, VSENSE and VRI to GND
Maximum Junction Temperature (Tj MAX)
Storage Temperature Range
Value
-0.3 to +30
10
29
-0.3~+7
-20° to +150
-55 ~ +150
Unit
V
mA
V
V
°C
°C
Note：Stresses beyond those listed under “Absolute Maximum Ratings" may cause permanent damage to the device.
MC7731N6
CYStek Product Specification
Spec. No. : C494N6
Issued Date : 2012.04.02
Revised Date :
Page No. : 4/10
CYStech Electronics Corp.
Recommended Operating Conditions
● Supply
Voltage, VDD………………………………………………………………………................25V
● Operating Temperature Range……………………………………………………………-20°C to 85°C
● RI resistor value …………………………………………………………………………………100 kΩ
Electrical Characteristics
(TA = 25°C, RI=100kΩ, VDD=16V if not otherwise noted)
Parameter
Symbol
Test Conditions
Min
Typ
Max
Units
5
20
uA
SUPPLY SECTION
Vdd=12V, measure current into VDD
pin
VDD=16V,VFB=3V
Chip start up current via VDD pin
I_set
Operation current
I_op
VDD Off(Turn-off threshold)
UVLO_L
8
9
10
V
VDD on(Turn-on threshold)
UVLO_H
13
14
15
V
VZ(VDD clamp voltage)
VDD_CLP
Iz(Idd)=10mA
34
V
PWM input gain
A_PWM
ΔVFB/ΔVCS
2
V/V
VFB open loop voltage
VFB_O
5.3
V
FB pin short circuit current
VFB_S
0.8
mA
Zero duty cycle FB threshold
VFB_th_L
0.75
V
Power limiting FB threshold
VFB_th_P
3.7
V
Power limiting delay time
T_PL_D
35
ms
Input impedance
R_FB
6
KΩ
Maxim duty cycle
D_MAX
80
%
1.4
mA
FEEDBACK SECTION
Short FB pin to gnd and measure
current
VDD=18V, FB=3V,CS=0
OSCILLATOR
Normal oscillation frequency
FOSC
60
Frequency temperature stability
Δf_Temp
TA = -20°C to +100°C
5
%
Frequency supply stability
Δf_Sup
VDD =12-25V
5
%
50
65
100
70
KΩ
Operating RI range
RI_range
RI open load voltage
RI_open
2
V
Burst mode base frequency
FOSC-BM
22
KΩ
Frequency modulate range (jitter)
Δf_OSC
Jitter frequency
f_jitter
32
Hz
Leading edge blanking time
T_blank
300
nS
Sense pin input impedance
R_sense
40
kΩ
Over current threshold voltage at
sense pin
VTH_OC
FB=3.3V
Over current protect delay
T_OC_D
CS>VTH_OC, FB=3.3V
Output low level
VOL
Io=20mA
Output high level
VOH
Io=20mA
-3
150
kHz
3
%
CURRENT SENSE SECTION
0.7
0.75
0.8
75
V
nS
GATE OUTPUT
MC7731N6
0.8
10V
V
V
CYStek Product Specification
Spec. No. : C494N6
Issued Date : 2012.04.02
Revised Date :
Page No. : 5/10
CYStech Electronics Corp.
Output voltage clamped level
VO_clamp
Output rising time
Tr
Output falling time
Tf
18
V
Cl=1nf
220
nS
Cl=1nf
70
ns
OPERATION DESCRIPTION
Over-view description
The MC7731N6 includes all necessary function to build an easy and cost effective solution for low power supplies to
meet the international power conservation requirements.
Start-up current
Startup current of MC7731N6 is designed to be very low so that VDD could be charged up above UVLO (exit)
threshold level and device starts up quickly. Also a large value startup resistor can be used to minimize the power
loss.
Green Mode Operation （Patent）
At light load or no load condition, the switch loss become the major loss of the power supply, to reduce the power
wasted in light and no load condition, based on a special designed voltage controlled oscillator, green mode
operation of the power supply can be achieved by using MC7731N6. The controller will judge the load condition
based on the voltage of FB pin. In light load the FB voltage will decrease, when VFB is lower than a set threshold
voltage, a FB depending time (TR2) will be generated by the oscillator and decrease the operating frequency of the
power supply, the minimum frequency is set about 22kHZ. The function block and the working waveform can be
depicted as below:
MC7731N6
CYStek Product Specification
CYStech Electronics Corp.
Spec. No. : C494N6
Issued Date : 2012.04.02
Revised Date :
Page No. : 6/10
When VFB decreases further, the power supply will enter into burst mode operation to decrease the power
consumed at no load condition. Besides there is no audible noise in any load condition.
Oscillator Operation
A resistor from RI pin to ground will generate a constant current source for MC7731N6. This current is
used to charge/discharge an internal capacitor and hence the internal clock and switching frequency are
determined. Increase the resistance will decrease the current source and reduce the switching frequency.
The relation between Ri and switching frequency is:
Built-in Slope Compensation
The sensed voltage across the sense resistor is used for pwm control, and pulse by pulse current limit.
Built-in slope compensation circuit adds a voltage ramp onto the current sense input voltage. This greatly
improves the close loop stability and prevents the sub-harmonic oscillation of peak current mode pwm
control scheme.
Leading Edge Blanking
Each time when the power MOSFET is switched on, a turn-on spike will inevitably occur on the
sense-resistor. To avoid premature termination of the switching pulse, a 270 nsec leading-edge blanking
time is built in. Conventional RC filtering can therefore be omitted. During this blanking period, the
current-limit comparator is disabled and it cannot switch off the gate driver.
Gate Driver
The output stage of MC7731N6 is a fast totem pole gate driver. Cross conduction has been avoided to
minimize heat dissipation, increases efficiency and enhances reliability. The output driver is clamped by an
internal 18V Zener diode in order to protect power MOSFET transistors against undesirable gate over
voltage. A soft driving waveform is implemented to minimize EMI.
Frequency Jitter
The frequency jitter function is integrated in the controller, the jitter is modulated by a periodic signal,
the modulate signal frequency is much smaller than the oscillator frequency, By this way，the EMI noise
has a wider spectrum with lower amplitudes.
MC7731N6
CYStek Product Specification
CYStech Electronics Corp.
Spec. No. : C494N6
Issued Date : 2012.04.02
Revised Date :
Page No. : 7/10
Protect Functions
To increase the reliability of power supply system, many protection functions are integrated in this
controller, including Cycle-by-Cycle current limiting (OCP), Over Load Protection (OLP) and over
voltage clamp, Under Voltage Lockout on VDD (UVLO). At overload condition when FB input voltage
exceeds power limit threshold value for more than TD_PL (power limit debounce time), the controller
reacts to shut down the output power MOSFET. Device restarts when VDD voltage drops below UVLO
limit. VDD is supplied by transformer auxiliary winding output. It is clamped when VDD is higher than
threshold value. The power MOSFET is shut down when VDD drops below UVLO limit and device enters
power on start-up sequence thereafter.
MC7731N6
CYStek Product Specification
CYStech Electronics Corp.
Spec. No. : C494N6
Issued Date : 2012.04.02
Revised Date :
Page No. : 8/10
Reel Dimension
Carrier Tape Dimension
MC7731N6
CYStek Product Specification
CYStech Electronics Corp.
Spec. No. : C494N6
Issued Date : 2012.04.02
Revised Date :
Page No. : 9/10
Recommended wave soldering condition
Product
Pb-free devices
Peak Temperature
260 +0/-5 °C
Soldering Time
5 +1/-1 seconds
Recommended temperature profile for IR reflow
Profile feature
Average ramp-up rate
(Tsmax to Tp)
Preheat
−Temperature Min(TS min)
−Temperature Max(TS max)
−Time(ts min to ts max)
Time maintained above:
−Temperature (TL)
− Time (tL)
Peak Temperature(TP)
Time within 5°C of actual peak
temperature(tp)
Ramp down rate
Time 25 °C to peak temperature
Sn-Pb eutectic Assembly
Pb-free Assembly
3°C/second max.
3°C/second max.
100°C
150°C
60-120 seconds
150°C
200°C
60-180 seconds
183°C
60-150 seconds
240 +0/-5 °C
217°C
60-150 seconds
260 +0/-5 °C
10-30 seconds
20-40 seconds
6°C/second max.
6 minutes max.
6°C/second max.
8 minutes max.
Note : All temperatures refer to topside of the package, measured on the package body surface.
MC7731N6
CYStek Product Specification
Spec. No. : C494N6
Issued Date : 2012.04.02
Revised Date :
Page No. : 10/10
CYStech Electronics Corp.
SOT-23-6L Dimension
A
D
Marking:
d1
d2
6
5
4
Style:
Pin 1. GND
Pin 2. FB
Pin 3. DEM
Pin 4. SENSE
Pin 5. VDD
Pin 6. GATE
B C
○
1
2
3
63ABC
Device Name
Date Code
E
6-Lead SOT-23-6L Plastic
Surface Mounted Package
CYStek Package Code: N6
I
F
L
H
J
G
Inches
Min.
Max.
0.1063
0.1220
0.1024
0.1181
0.0551
0.0709
0.0748 REF
0.0374 REF
0.0374 REF
0.0118
0.0217
DIM
A
B
C
D
d1
d2
E
Millimeters
Min.
Max.
2.70
3.10
2.60
3.00
1.40
1.80
1.90 REF
0.95 REF
0.95 REF
0.30
0.55
K
DIM
F
G
H
I
J
K
L
Inches
Min.
Max.
0.0472 REF
0
0.0059
0.0086
0.0047 REF
0.0146 REF
0.0236 REF
0°
10°
Millimeters
Min.
Max.
1.20 REF
0
0.15
0.22
0.12 REF
0.37 REF
0.60 REF
0°
10°
Notes : 1.Controlling dimension : millimeters.
2.Maximum lead thickness includes lead finish thickness, and minimum lead thickness is the minimum thickness of base material.
3.If there is any question with packing specification or packing method, please contact your local CYStek sales office.
Material :
• Mold Compound : Epoxy resin family, flammability solid burning class:UL94V-0
Important Notice:
• All rights are reserved. Reproduction in whole or in part is prohibited without the prior written approval of CYStek.
• CYStek reserves the right to make changes to its products without notice.
• CYStek semiconductor products are not warranted to be suitable for use in Life-Support Applications, or systems.
• CYStek assumes no liability for any consequence of customer product design, infringement of patents, or application assistance.
MC7731N6
CYStek Product Specification