UNISONIC TECHNOLOGIES CO., LTD UC3846 LINEAR INTEGRATED CIRCUIT LOW COST POWER-SAVING MODE PWM CONTROLLER FOR FLYBACK CONVERTERS DESCRIPTION The UTC UC3846 is a high performance current mode PWM controller ideally suited for low standby power and cost effective off-line flyback converter. Low VDD startup current make the power reliable in startup design and a large value resistor could be used in the startup circuit to minimize the standby power. At no load condition, the IC operates in burst mode for lower standby power and in decreasing frequency for higher conversion efficiency at light load condition. The PWM switching frequency is programmable externally at normal operation. The UTC UC3846 contains protection coverage with automatic self-recovery including OCP (cycle-by-cycle current limiting), OTP (over temperature protection), UVLO (VDD over voltage clamp and under voltage lockout).To protect the power MOSFET, Gate-drive output is fixed up to 15V max. The internal slope compensation improves system stability at high PWM duty cycle output. Leading-edge blanking on current sense (CS) input removes the signal glitch that offers minimal reqnirement of external component and lower system cost. Excellent EMI performance is achieved by UTC proprietary frequency hopping technique together with soft driver control. Audio noise is eliminated because switch frequency is more than 20kHz during operation. The UTC UC3846 can be used in the applications, such as battery charger, power adaptor, set-top box power supplies, ink jet printers open-frame SMPS DIP-8 FEATURES * UTC proprietary frequency hopping technology for Improved EMI * performance. * Power-saving mode for high light-load efficiency * Burst mode for minimum standby power * Dynamic peak current limiting for constant output power * Built-in synchronized slope compensation * OTP,OVP and VDD clamp for higher security * Programmable PWM Frequency * Gate output voltage clamped at 15V * Low start-up current * Cycle-by-cycle Current Limiting * Under voltage lockout (UVLO) * Few external components required ORDERING INFORMATION Ordering Number Lead Free Halogen Free UC3846L-D08-T UC3846G-D08-T UC3846L-D08-T Package Packing DIP-8 Tube (1)Packing Type (1) T: Tube (2)Package Type (2) D08: DIP-8 (3)Lead Free (3) G: Halogen Free, L: Lead Free www.unisonic.com.tw Copyright © 2011 Unisonic Technologies Co., Ltd 1 of 10 QW-R103-053.B UC3846 LINEAR INTEGRATED CIRCUIT PIN CONFIGURATION PIN DESCRIPTION PIN NO. 1 2 3 PIN NAME GATE VDD NC 4 SENSE 5 RI 6 NC 7 FB 8 GND PIN TYPE DESCRIPTION O The totem-pole output driver for driving the power MOSFET. P Power supply. NC pin. Current sense input pin. Connected to MOSFET current sensing resistor I node. A resistor connected between RI and GND sets switching frequency. A I 100kΩ resistor Ri results in a 70kHz switching frequency. NC pin. Feedback input pin. The PWM duty cycle is determined by voltage level I into this pin and SENSE pin input. P Ground. UNISONIC TECHNOLOGIES CO., LTD www.unisonic.com.tw 2 of 10 QW-R103-053.B UC3846 LINEAR INTEGRATED CIRCUIT BLOCK DIAGRAM VDD RI 2/5 5/3 Frequency Hopping Oscillator UVLO Reference voltage Driver OVP 1/6 GATE Latch Logic Control Burstmode OTP FB 7/2 S Q R Q PWM COMP Slope Compensation Constant Power Limit OCP LEB 4/4 SENSE 8/1 GND UNISONIC TECHNOLOGIES CO., LTD www.unisonic.com.tw 3 of 10 QW-R103-053.B UC3846 LINEAR INTEGRATED CIRCUIT ABSOLUTE MAXIMUM RATINGS (Ta＝25°C, VDD=15V, unless otherwise specified) PARAMETER SYMBOL RATINGS UNIT Supply Voltage 25 V VDD Zener Clamp 28 V Zener Current 10 mA Input Voltage to FB Pin VFB 7 V Input Voltage to CS Pin VSENSE 7 V Junction Temperature TJ +150 °C Operating Temperature TOPR -40 ~ +125 °C Storage Temperature TSTG -50 ~ +150 °C Note: Absolute maximum ratings are those values beyond which the device could be permanently damaged. Absolute maximum ratings are stress ratings only and functional device operation is not implied. OPERATING RANGE PARAMETER Supply Voltage SYMBOL VDD RATINGS 8.2 ~ 21 UNIT V ELECTRICAL CHARACTERISTICS (Ta＝25°C, VDD=15V, RI=100kΩ ,unless otherwise specified) PARAMETER SUPPLY SECTION Start Up Current IC Operating current UNDER-VOLTAGE LOCKOUT SECTION Start Threshold Voltage Min. Operating Voltage Hysteresis INTERNAL VOLTAGE REFERENCE Reference Voltage CONTROL SECTION VFB Operating Level Burst-Mode Out FB Voltage Reduce-Frequency end FB Voltage Burst-Mode Enter FB Voltage Normal Switch Frequency Power-Saving Duty Cycle Frequency Hopping Frequency Variation VS VDD Deviation Frequency Variation VS Temperature Deviation Feedback Resistor PROTECTION SECTION OVP threshold OTP threshold CURRENT LIMITING SECTION Peak Current Limitation DRIVER OUTPUT SECTION Output Voltage Low State Output Voltage High State Output Voltage Rise Time Output Voltage Fall Time SYMBOL ISTR IOP VREF VMIN VMAX VFB(OUT) VFB(END) VFB(IN) F(SW) DMAX DMIN FJ(SW) FDV FDT RFB MIN TYP MAX UNIT 22 7 45 9 μA mA 13.5 7.5 14.2 8.2 6 15 9 V V V 6.3 6.5 6.7 V VDD = VDD(ON)-0.1V FB PIN OPEN VTHD(ON) VDD(MIN) VDD(HY) measured at pin VFB 0.5 4.4 VSENSE =0 VSENSE =0 VSENSE =0 FB PIN OPEN Before enter burst mode FB PIN OPEN, VSENSE =0 VFB<0.5V VDD=10 to 20V T=-40 to 105°C VFB=0V VOVP T(THR) FB PIN OPEN VCS FB PIN OPEN VOL VOH tR tF ISOURCE = 200 mA ISINK = 200 mA CL = 1.0 nF CL = 1.0 nF UNISONIC TECHNOLOGIES CO., LTD www.unisonic.com.tw TEST CONDITIONS 61 24 68 0 ±1.5 1.7 1.6 1.5 68 74 ±3 75 31 80 V V V V V kHz kHz % % kHz % % kΩ 16 21 ±4.5 5 5 26 120 28 135 150 V °C 0.85 1 V 2.5 V V ns ns 12.2 200 50 300 90 4 of 10 QW-R103-053.B UC3846 LINEAR INTEGRATED CIRCUIT OPERATION DESCRIPTION The UTC UC3846 devices integrate many useful designs into one controller for low-power switch-mode power supplies. The following descriptions highlight some of the features of the UTC UC3846 series. Start-up Current The start-up current is only 22μA. Low start-up current allows a start-up resistor with a high resistance and a low-wattage to supply the start-up power for the controller. For AC/DC adaptor with universal input range design, a 1 MΩ, 1/8 W startup resistor could be used together with a VDD capacitor to provide a fast startup and low power dissipation solution. Power-Saving Mode Operation The proprietary Power-Saving Mode function provides linearly decrease the switching frequency under light-load conditions for higher efficiency. The feedback voltage, which is sampled from the voltage feedback loop, is taken as the reference. Once the feedback voltage exceeds the threshold voltage, the switching frequency starts to decrease. This Power-Saving Mode function dramatically reduces power consumption under light-load conditions. The frequency control also eliminates the audio noise at any loading conditions. Burst Mode Operation At zero load condition, majority of the power dissipation in a switching mode power supply is from switching loss on the MOSFET transistor, the core loss of the transformer and the loss on the snubber circuit. The magnitude of power loss is in proportion to the number of switching events within a fixed period of time. Reducing switching events leads to the reduction on the power loss and thus conserves the energy. The UTC UC3846 enter burst mode at standby condition to minimize the switching loss and reduces the standby power consumption. The frequency control also eliminates the audio noise at any loading conditions. Power supplies using the UTC UC3846 can easily meet even the strictest regulations regarding standby power consumption. Switch Frequency Set The maximum switch frequency is set to 68kHz. Switch frequency is modulated by output power POUT during IC operating. At no load or light load condition, most of the power dissipation in a switching mode power supply is from switching loss on the MOSFET transistor, the core loss of the transformer and the loss on the subber circuit. The magnitude of power loss is in proportion to the number of switching events within a fixed period of time. So lower switch frequency at lower load, which more and more improve IC’s efficiency at light load. At from no load to light load condition, The IC will operate at from Burst mode to Reducing Frequency Mode. The relation curve between fSW and POUT/POUT (MAX) as followed FIG.1. FIG.1 The relation curve between fSW and relative output power POUT/ POUT (MAX) UNISONIC TECHNOLOGIES CO., LTD www.unisonic.com.tw 5 of 10 QW-R103-053.B UC3846 LINEAR INTEGRATED CIRCUIT OPERATION DESCRIPTION(Cont.) Frequency Hopping For EMI Improvement The Frequency hopping is implemented in the IC; there are two oscillators built-in the IC. The first oscillator is to set the normal switching frequency; the switching frequency is modulated with a period signal generated by the 2nd oscillator. The relation between the first oscillator and the 2nd oscillator as followed FIG.2. So the tone energy is evenly spread out, the spread spectrum minimizes the conduction band EMI and therefore eases the system design in meeting stringent EMI requirement. FIG.2 Frequency Hopping Built-in Slope Compensation Built-in slope compensation circuit adds voltage ramp onto the current sense input voltage for PWM generation, this greatly improves the close loop stability at CCM and prevents the sub-harmonic oscillation and thus reduces the output ripple voltage. Leading-Edge Blanking Each time the power MOSFET is switched on, a turn-on spike will inevitably occur at the sense-resistor. To avoid premature termination of the switching pulse, a 400ns 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. Constant Output Power Limit When the SENSE voltage, across the sense resistor RS, reaches the threshold voltage, around 0.8V, the output GATE drive will be turned off after a small propagation delay tD. This propagation delay will introduce an additional current proportional to tD×VIN/Lp. Since the propagation delay is nearly constant regardless of the input line voltage VIN. Higher input line voltage will result in a larger additional current and hence the output power limit is also higher than that under low input line voltage. To compensate this variation for wide AC input range, the threshold voltage is adjusted by the VIN current. Since VIN pin is connected to the rectified input line voltage through a resistor RVIN, a higher line voltage will generate higher VIN current into the VIN pin. The threshold voltage is decreased if the VIN current is increased. Smaller threshold 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 line input. This proprietary internal compensation ensures a constant output power limit for wide AC input voltage from 90VAC to 264VAC. Under Voltage Lockout (UVLO) The turn-on and turn-off thresholds of the UTC UC3846 are fixed internally at 14.2V/8.2V. During start-up, the hold-up capacitor must be charged to 14.2V through the start-up resistor, so that the UTC UC3846 will be enabled. The hold-up capacitor will continue to supply VDD until power can be delivered from the auxiliary winding of the main transformer. VDD must not drop below 8.2V during this start-up process. This UVLO hysteresis window ensures that hold-up capacitor will be adequate to supply VDD during start-up. Gate Output The UTC UC3846 output stage is a fast totem pole gate driver. Cross conduction has been avoided to minimize heat dissipation, increase efficiency, and enhance reliability. A good tradeoff is achieved through dead time control. The low idle loss and good EMI system design is easier to achieve with this dedicated control scheme. An internal 18V clamp is added for MOSFET gate protection at higher than expected VDD input. UNISONIC TECHNOLOGIES CO., LTD www.unisonic.com.tw 6 of 10 QW-R103-053.B UC3846 LINEAR INTEGRATED CIRCUIT OPERATION DESCRIPTION(Cont.) Protection Controls The IC takes on more protection functions such as OVP and OTP etc. In case of those failure modes for continual blanking time, the driver is shut down. Driver is reset after failure is eliminated. OVP The OVP will shut down the switching of the power MOSFET whenever VDD>VOVP. The OVP case as followed FIG.3. The test circuit as followed FIG.4. FIG.3 OVP case FIG.4 OVP test circuit OTP OTP will shut down driver when junction temperature TJ>T (THR) for continual a blanking time. PCB Layout Note Noise from the current sense or the control signal can cause significant pulse width jitter in continuous-conduction mode. While slope compensation helps alleviate these problems. Good placement and layout practices should be followed. Avoiding long PCB traces and component leads, locating compensation and filter components near the UTC UC3846, and increasing the power MOS gate resistance is advised. UNISONIC TECHNOLOGIES CO., LTD www.unisonic.com.tw 7 of 10 QW-R103-053.B UC3846 L LINEAR INTEGRATED CIRCUIT REFRENCE CIRCUIT F1 L1 1 1 CX1 2 BD1 2 + 4 C1 R1 C2 C3 R3 R5 R4 T1 1, 2 2 D4 1 L2 1 2 VO 10 N 3 R2 D1 9 R10 8 U1 8 7 C6 6 5 GND GATE VDD FB NC NC RI SENSE 22 1 R7 C8 5 Q1 1 C7 1 + D5 C9 2 3 2 + 7 3 4 R8 R9 + 1 D2 GND 3, 4 R6 2 R11 C4 U2 4 3 R13 1 R14 2 3 CY1 U3 C10 1 R12 2 Reference BD1 CX1 (Optional) CY1 (Optional) C2 C1 C3 C4 C6 C7 (Optional) C8 C9 C10 D1 D2 D4 D5 (Optional) F1 L1 Component BD 1A/500V YC 472P/400V (Y1) YC 102P/400V (Y1) EC 10μF/400V 105℃ CC 103P/500V CC 1000P/500V EC 10u/50V CC 472P 0805 CC 102P/100V 1206 EC 470u/10V 105℃ EC 220u/10V 105℃ CC 222P 0805 Diode FRI07 Diode FR102 Diode SB360 ZD 6.8V 0.5W R1Ω/0.5W 20mH 6*8mm UNISONIC TECHNOLOGIES CO., LTD www.unisonic.com.tw Reference L2 Q1 R1,R2 R4,R3 R5 R6 R7 R8 R10 (Optional) R9 R11 R12 R13 R14 T1 U1 U2 U3 Component 10μH 6mm 1N60 R 750KΩ 1206 R 47KΩ 1206 R 47Ω 1206 R 4.7Ω 1206 R 100Ω 0805 R 10Ω 1206 R 10Ω 1206 R 100KΩ 0805 R 100Ω 1/8W R 33KΩ 0805 R 33KΩ 1/8W R 4.7KΩ 0805 EE-16 IC UC3846 PC817 TL431 8 of 10 QW-R103-053.B UC3846 LINEAR INTEGRATED CIRCUIT IDD ST (µA) FOSC (kHz) VTH(ON) (V) VDD(min) (V) TYPICAL CHARACTERISTICS Frequency in green mode (FOSC-green) vs Temperature Max. Duty Cycle (DC(MAX)) vs Temperature 80 79 15 78 13 DC(MAX) (%) FOSC-green (KHz) 14 12 11 77 76 75 74 73 10 72 9 71 8 -40-25 -10 5 20 35 50 65 80 95110 125 Temperature (℃) UNISONIC TECHNOLOGIES CO., LTD www.unisonic.com.tw 70 -40-25 -10 5 20 35 50 65 80 95110 125 Temperature (℃) 9 of 10 QW-R103-053.B UC3846 LINEAR INTEGRATED CIRCUIT TYPICAL CHARACTERISTICS(Cont.) UTC assumes no responsibility for equipment failures that result from using products at values that exceed, even momentarily, rated values (such as maximum ratings, operating condition ranges, or other parameters) listed in products specifications of any and all UTC products described or contained herein. UTC products are not designed for use in life support appliances, devices or systems where malfunction of these products can be reasonably expected to result in personal injury. Reproduction in whole or in part is prohibited without the prior written consent of the copyright owner. The information presented in this document does not form part of any quotation or contract, is believed to be accurate and reliable and may be changed without notice. UNISONIC TECHNOLOGIES CO., LTD www.unisonic.com.tw 10 of 10 QW-R103-053.B