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High-integrated Green Mode PWM Controller - SG6840
Product Specification
SG6840 SG6840 Data Sheet
DESCRIPTION
FEATURES OVERVIEW
Green-mode PWM to support "Blue Angle"Norm Low start up current 30uA Low operation current 3mA Leading-edge blanking Built-in synchronized slope compensation Totem pole output includes soft driving Constant output power Current mode operation Cycle-by-cycle current limiting Under voltage lockout (UVLO) Short circuit protection Programmable over-temperature protection Few external components & low cost solution
This
high-integrated PWM controller provides
several special enhancements to satisfy the needs for low power standby and protection features. In standby mode, PWM frequency reduction is used to lower the power consumption and support a stable output voltage. Due to Bi-CMOS process, the SG6840 reduces startup and operation current to achieve a higher efficiency power conversion. Start-up current has been reduced to 30uA typical and operating current has been shrunk to 3mA. The SG6840 is a fixed frequency PWM controller in normal operation; its patented green-mode function will decrease the PWM frequency in response to the decrease of the load. This green function dramatically reduces the power loss in no load and light load conditions that assist the power supply to meet the power conservation requirement. The proprietary synchronized slope compensation ensures the stability of the current loop for continuous-mode operation. Built-in line -voltage compensation maintains an identical output power for a wide input range. An NTC thermistor is applied to sense the temperature for over-temperature protection. The SG6840 is available in 8-pin DIP and SO packages.
PIN CONFIGURATION
APPLICATIONS
General-purpose switching mode power supplies and flyback power converters, and Power Adapter Open-frame SMPS Battery Charger Adapter
-12002 System General Corporation Ver1.0 http://www.sg.com.tw
High-integrated Green Mode PWM Controller - SG6840
Product Specification
SG6840
PIN DESCRIPTIONS
Name VDD VIN Pin No. 7 3 Type Supply Function Power supply.
The start-up current input. A start-up resistor is connected from the Analog inline-input to this pin, such as 1.5M for off-line converter. Adjust the put start-up resistor to vary the line voltage compensation for constant Analog in- Feedback. The FB pin provides the information of the regulation, it put effects to the internal PWM comparator to control the duty cycle. Current sense. It senses the voltage developed on a sensed resistor. Analog in- When it reaches the internal threshold, the PWM output is disabled. put Therefore, the over-current protection is realized. Besides, the current information is providing for the current mode control. For over-temperature protection. A constant current is output. Analog in- An NTC thermistor is connected from this pin to ground to sense the put/output temperature. When the voltage in this pin is lower than the limit, which will enable the over-temperature protection. Driver out- The totem-pole output driver to drive the power MOSFET. Program- Reference setting. Connect a resistor to ground to generate a conSupply Ground.
FB
2
Sense
6
RT Gate Ri GND
5 8 4 1
BLOCK DIAGRAM
Ri
4 VDD
0.8V
Soft ON/OFF Driver
8
Gate
VIN
3
+
_AI Q S R
Internal BIAS
OSC
Green Mode Controller
VDD
7
+
_
UVLO
6
16V/10V Comp Slope Compensation IRT
Sense
5V
RT
5
+
_
2
Comp 0.7V
FB
1
GND
-22002 System General Corporation Ver1.0 http://www.sg.com.tw
High-integrated Green Mode PWM Controller - SG6840
Product Specification
SG6840
ABSOLUTE MAXIMUM RATINGS
Symbol VDD Iout VFB VSense Pd TJ TA Tstg Parameter DC Supply Voltage - note 1 Gate Output Current Input Voltage to FB Pin Input Voltage to Sense Pin Power Dissipation Operating Junction Temperature Operating Ambient Temperature Storage Temperature Range Value 20 500 -0.3 to 7 V -0.3 to 7V 1 150 -25 to 85 -55 to +150 Unit V mA V V W C C C
Note: All voltage values, except differential voltage, are with respect to network ground terminal.
ELECTRCIAL CHARACTERISTICS(VDD=15V, TA=25) Feedback Input Section
Symbol Av Zfb Ifb Voz Parameter Input-voltage to current-sense attenuation Input impedance Bias current Input voltage for zero duty cycle Test Condition Min. 1/4.5 3 Typ. 1/5 4.5 Max. 1/5.5 6 2 1.2 Unit V/V K mA V
Current Sense Section
Symbol Zcs TPD Vth Vth @ Iin Parameter Input impedance Delay to Output Threshold voltage for current limit The change of threshold voltage versus the input current of the Vin 0.8 Iin = 220 uA -0.09 Test Condition Min. 8 Typ. 12 150 0.85 -0.15 Max. 16 200 0.9 -0.21 Unit K nS V V
Oscillator Section
Symbol Fosc Fosc-green Vg Vn Sg Fdv Fdt Parameter Frequency Frequency in green mode Green mode voltage (Vg = Vfb - Vd) Normal mode voltage (Vn = Vfb - Vd) Vn = 4 V for maximum duty cycle Slope for green mode modulation Frequency variation versus VDD deviation Frequency variation versus Temp. deviation Ri=26KOhms VDD=10 to 20V TA=-25 to 85 Test Condition Ri=26KOhms Ri=26KOhms Min. 60 Typ. 65 10 1.3 1.7 50 2 80 2.3 120 5 5 Max. 70 15 Unit KHz KHz V V Hz/ mV % %
-32002 System General Corporation Ver1.0 http://www.sg.com.tw
High-integrated Green Mode PWM Controller - SG6840
Product Specification
SG6840
PWM Section
Symbol DC (MAX) DC (MIN) Bnk Parameter Maximum Duty Cycle Minimum Duty Cycle Leading edge blanking time Test Condition Min. 75 200 Typ. 80 270 Max. 90 0 350 Unit % % nsec
Output Section
Symbol Vol Voh tr tf Parameter Output Voltage Low Output Voltage High Rising Time Falling Time Test Condition VDD= 12V, Io = 150mA VDD= 12V, Io = 50mA VDD=13V, CL=1nF VDD=13V, CL=1nF Min. 8V 150 30 250 50 350 90 Typ. Max. 1.5 Unit V V NS NS
Under-voltage Lockout Section
Symbol VTH(ON) VDD(min) Parameter Start Threshold Voltage Min. Operating Voltage Test Condition Min. 15 9 Typ. 16 10 Max. 17 11 Unit V V
Over-temperature Protection Section
Symbol Irt Vtov Parameter Output current of pin RT Threshold voltage for over-temperature protection Test Condition Ri=26KOhms Min. 92 0.665 Typ. 100 0.7 Max. 108 0.735 Unit uA V
Total Standby Current Section
Symbol IDD ST IDD OP Parameter Start-up Current Operating Supply Current Test Condition Min. Typ. 30 3 Max. 40 5 Unit uA mA
-42002 System General Corporation Ver1.0 http://www.sg.com.tw
High-integrated Green Mode PWM Controller - SG6840
Product Specification
SG6840
Start-up Current (IDD ST) vs Tem perature
25.5 35
Start-up Current (IDD ST) vs VDD Voltage
Start-up Current (uA)
Start-up Current (uA)
-40 -25 -10 5 20 35 50 65 80 95 110 125
25.0 24.5 24.0 23.5 23.0 22.5 22.0
30 25 20 15 10 5 0 0 2 4 6 8 10 12 14 16
TEMPERATURE ( )
VDD VOLTAGE (V)
FB Voltage vs Frequency
70
Frequency in green m ode (Fosc-green) vs Tem perature
10.55
Frequency (KHz)
60 50 40 30 20 10 0 1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 3.0
Fosc-green (KHz)
10.50 10.45 10.40 10.35 10.30 -40 -25 -10 5 20 35 50 65 80 95 110 125
FB VOLTAGE (V)
TEMPERATURE ( )
PWM Oscillator Frequency (Fosc) vs Tem perature
Max. Duty Cycle (%)
64.4 64.3
Maxim um Duty Cycle DC( MAX.)vs Tem perature
84.80 84.70 84.60 84.50 84.40 84.30 84.20 -40 -25 -10 5 20 35 50 65 80 95 110 125
Fosc (KHz)
64.2 64.1 64.0 63.9 63.8 63.7 -40 -25 -10 5 20 35 50 65 80 95 110 125
TEMPERATURE ( )
TEMPERATURE ( )
-52002 System General Corporation Ver1.0 http://www.sg.com.tw
High-integrated Green Mode PWM Controller - SG6840
Product Specification
SG6840
Min. Operating Voltage (VDD(min)) vs Tem perature
10.20 10.15 10.10 10.05 10.00 9.95 9.90 9.85 9.80 9.75 9.70 -40 -25 -10 5 20 35 50 65 80 95 110 125 16.60 16.55 16.50 16.45 16.40 16.35 16.30 16.25 16.20
Start Threshold Voltage (V TH(ON)) vs Tem perature
VDD(min) (V)
VTH(ON) (V)
-40
-25
-10
5
20
35
50
65
80
95
110
125
TEMPERATURE ( )
TEMPERATURE ( )
RT Voltage vs Ton
14 12 10
101.5 101.0
Output Current of pin RT (IRT) vs Tem perature
Ton (uS)
6 4 2 0 -2 0.620 0.628 0.636 0.644 0.652 0.660
I RT (uA)
8
100.5 100.0 99.5 99.0 98.5 -40 -25 -10 5 20 35 50 65 80 95 110 125
RT VOLTAGE (V)
TEMPERATURE ( )
V OTP, STOP vs Tem perature
0.63 0.62
VOTP, STOP (V)
0.62 0.61 0.61 0.60 0.60 -40 -25 -10 5 20 35 50 65 80 95 110 125
TEMPERATURE ( )
-62002 System General Corporation Ver1.0 http://www.sg.com.tw
High-integrated Green Mode PWM Controller - SG6840
Product Specification
SG6840
OPERATION DESCRIPTION
Start-up Current
Typical start-up current is only 30uA This ultra low start-up current allows users to use a high resistance, and lowwattage, start-up resistor to supply the start-up power required by SG6840. Take a wide input-range (100VAC~240VAC) of AC-to-DC power adapter as an example, an 1.5 M, 0.25W, start-up resistor and a 10uF/25V VDD hold-up
Current sensing and PWM current limiting
SG6840 consists of two feedback loops: voltage loop and current loop, to control the load regulation. SG6840's current sense input is designed for the current-mode control. A current-to-voltage conversion is done externally through a current-sense resistor Rs. Under normal operation, the FB voltage VFB controls the peak voltage across the sense resistor Rs, hence the PWM duty cycle, as follows: Ipk = (VFB - 1.4) / 5Rs; where VFB is the voltage on pin FB
Operating Current
Operating current has been reduced to 3mA. The low operating current enables a better efficiency and reduces the
Green Mode Operation
The patented green-mode function provides an off-time modulation to reduce the switching frequency in the light load and no load conditions. The feedback voltage, which is derived from the voltage feedback loop, is taken as the reference. Once the feedback voltage is lower than the threshold voltage, switching frequency will linearly decrease until the minimum green mode frequency around 10kHz (Ri =26k). We can find that all of the losses are in proportional to the switching frequency, such as the switching loss of the transistor, the core loss of the transformer and inductors, and the power loss of the snubber, etc. The off-time modulation in the PWM controller can reduce the power consumption of the power supply in light load and no load conditions. In normal load and high load conditions, the PWM frequency is at its maximum frequency around 65kHz (Ri =26k) and not affected by the off-time modulation.
When the DC output voltage of secondary side decreases due to heavy load conditions, the FB voltage VFB will increase such that the PWM duty cycle increases to regulate the output voltage of secondary side back to its normal voltage. The inverting input to SG6840's current-sense comparator is internally clamped to a variable voltage around 0.85V (note: see Constant Output Power Limit section). The current limiting occurs if the voltage of SENSE pin reaches this 0.85V threshold value, such as Ipk (max) = 0.85V/Rs. The value of sense resistor Rs decides the maximum power limit. Larger Rs, whose Ipk is smaller, results in a smaller power limit
Leading Edge Blanking
Each time when the power MOSFET is switched on, a leading spike is generated due to parasitic capacitance. To avoid premature termination of the switching pulse, this leading edge spike is blanked out with a time constant 270 nsec. During this time period, the current-limit comparator is disabled and cannot switch off the gate drive regardless how big the SENSE voltage is.
Oscillator Operation
An external resistor Ri determines the PWM oscillation frequency. A 26k resistor Ri creates a 50uA constant current Ii and generates 65kHz switching frequency. Ii (mA) = 1.3V / Ri (k);
Under-voltage lockout (UVLO)
The UVLO Under-Voltage Lockout (UVLO) function ensures the supply voltage VDD for SG6840 is adequate to fully function before enabling the output stage. The turn-on and turn-off threshold voltages are fixed internally at 16V/10V. The hysteresis voltage between turn-on and turn-off prevents VDD from being unstable during power on/off sequencing. Start-up current is typically 30uA for efficient bootstrapping from the rectified input for an off-line converter. During the normal operation, VDD is developed from an auxiliary winding of the transformer. At the moment of start-up, VDD hold-up capacitor CIN must be charged up to 16V through the start-up resistor RIN before enabling the output switch. With an ultra small start-up current of 30uA, RIN can be as large as 1.5 M and still be able to charge up the hold-up capacitor CIN even when VAC = 90Vrms. Power dissipation of this large resistance RIN would then be less than 70mW (0.07W) even under high line (VAC = -7-
fPWM =
1690 RI (k )
(kHz )
(1)
2002 System General Corporation
Ver1.0
http://www.sg.com.tw
High-integrated Green Mode PWM Controller - SG6840
Product Specification
SG6840 Gate Output / Soft Driving
The SG6840 BiCMOS output stage is a fast totem pole gate driver, which is designed to avoid cross conduction current. This minimizes heat dissipation, increases efficiency and enhances reliability. The output driver is clamped by an internal 18V Zener diode in order to improve the control of the power MOSFET transistors and protect them against undesirable gate over-voltage. By controlling the rising time of the switch-on waveform and falling shape of the switch-off waveform, the output stage is optimized to reduce switching noise, improve EMI, and to provide a stable MOSFET gate drive.
Noise immunity
Noise on the current sense or control signal can cause significant pulse width jitter, particularly with the continuousmode operation. While slope compensation helps alleviate this problem. Note that the SG6840 has a single ground pin. High sink current in the output therefore cannot be returned separately. Good high frequency or RF layout practices should be followed. Avoid long PCB traces and component leads. Locate components such as Ri, Rt and VDD capacitor near to the SG6840. The noise, which often causes the problem, is caused by the output (pin 8) being pulled below ground at turn-off by external parasitic. This is particularly true when driving MOSFET. A resistor (10 ~ 20 ohms) series connected from the output (pin 8) to the gate of MOSFET will prevent such output noise.
Built-in Slope Compensation
Current mode control regulates the peak transformer/inductor current via the current control loop. In a continuous mode operation, the current is the average current, and composed of both AC and DC components. Since the output is proportional to the average, not the peak current, this causes oscillation when input voltage is changed. Adding the slope compensation to the current loop (reduce the current loop gain) to correct the problem is a simple approach. The SG6840 inserts a synchronized 0.33V positive-going ramp at every switching cycle to stabilize the current loop. Vs-comp = 0.33V.
Constant Output Power Limit
Every time when the SENSE voltage, across the sense resistor Rs, is larger than the threshold voltage around 0.85V, the output GATE drive is turned off after a small propagation delay tD. Since the propagation delay is constant regardless the input line voltage VIN, the output power would not be equal for the wide input voltage VIN of 90Vrms to 265Vrms. To compensate the different output power limit between high line voltage and low line voltage, the internal threshold voltage is adjusted dependent on the input line voltage VIN through the VIN pin. The threshold voltage is decreased from 0.85V to a smaller voltage when input line voltage VIN increases. Smaller threshold voltage, at higher input line voltage, forces the output GATE drive to terminate earlier, thus reduce the total PWM turn-on time and make the output power equal to that of low input line voltage.
Thermal Protection
A constant current IRT is output from pin RT. The resistor in pin Ri decides the current IRT. IRT = 2 x (1.3V / Ri); An NTC thermistor Rntc in series with a resistor Ra can be connected from pin RT to ground. The over-temperature
-82002 System General Corporation Ver1.0 http://www.sg.com.tw
High-integrated Green Mode PWM Controller - SG6840
Product Specification
SG6840
APPLICATION CIRCUIT
BOM
Reference BD1 C1 C2 C3,C6,C7 C4 C5 C8 C9 C10 D1 D3 F1 L1 L2 Q1 Component BD 1A/600V XC 0.22u EC 0.1u 250V YC 222p EC 68u/400V CC 102p/1KV EC 1200u/16V EC 680u/16V EC 10u/25V LED ZD 12V FUSE 2A/250V UU10.5 L04 DIODE Reference Q2 R1,R2 R3 R4 R5 R6 R8,R12 R9 R10 THER1 T1 U1 U2 U3 VZ1 Component MOS 2A/600V R 470Kohm 1/4W R 47ohm 1/4W R 22ohm 1/4W R 4.7Kohm 1/4W R 0.5ohm 1W R 510Kohm 1/4W R 20Kohm 1/8W 1% R 100ohm 1/8W Thermistor SCK054 Transformer EI28 IC SG6840 IC 4N35D IC TL431 VZ 9G
-92002 System General Corporation Ver1.0 http://www.sg.com.tw
High-integrated Green Mode PWM Controller - SG6840
Product Specification
SG6840
MECHANICAL DIMENSIONS
8 PINS - PLASTIC DIP (D)
8
5
E
1 D
4
b A
A1
A2 b2 e b1 d H d
Symbol A A1 A2 b b1 b2 d D E e H
Min.
Millimeter Typ. 3.4
Max. 4.5
Min.
Inch Typ. 0.134
Max. 0.177
3.0 0.4 0.25 0 1.5 0.5 0.3 9.3 2.29 6.5 2.54 7.6 2.79 0.6 0.4 15
0.118 0.016 0.010 0 0.059 0.020 0.012 0.366 0.090 0.256 0.100 0.299 0.110 0.024 0.016 15
-102002 System General Corporation Ver1.0 http://www.sg.com.tw
High-integrated Green Mode PWM Controller - SG6840
Product Specification
SG6840
MECHANICAL DIMENSIONS
8 PINS - PLASTIC SMD (S) Dimension:
b
8
5
E
H d L
1
4
Detail
D
A2 A1
A c
e
L1 See Detail
Symbol A A1 A2 b c d D E e H L L1 Y
Min. 1.35 0.10 1.30 0.33 0.19 0 4.80 3.80 5.80 0.40 -
Millimeter Typ. 1.63 0.15 1.40 0.41 4.90 3.90 1.27 6.00 0.64 1.07 -
Max. 1.75 0.25 1.50 0.51 0.25 8 5.00 4.00 6.20 1.27 0.10
Min. 0.053 0.004 0.051 0.013 0.007 0 0.189 0.150 0.228 0.016 -
Inch Typ. 0.064 0.006 0.055 0.016 0.193 0.154 0.050 0.236 0.025 0.042 -
Max. 0.069 0.010 0.059 0.020 0.010 8 0.197 0.157 0.244 0.050 0.004
-112002 System General Corporation Ver1.0 http://www.sg.com.tw

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