OB2004AMP

OB2004A High Performance synchronous rectification controller GENERAL DESCRIPTION FEATURES OB2004A is a high performance and highly integrated secondary side synchronous rectification controller used for secondary side rectification in switch mode power supply system. It drivers a much lower voltage drop N-channel MOSFET to emulate the traditional diode rectifier at the secondary side of flyback converter, which can reduce heat dissipation, increases output current capability and efficiency, and simplify thermal design. It can support wide range of system output voltage 5V~12V. It is suitable for multiple mode applications including discontinuous conduction mode (DCM), quasi-resonant mode (QR) and continuous conduction mode (CCM). Specially for CCM, to guarantee system reliability, innovative property prediction algorithm is used in SR turn-off control. In addition, to balance reliability and efficiency, OB2004A generates a driving signal with optimized dead time with respect to the primary side PWM signal from the information on the secondary side of the isolation transformer with the help of innovative property dead time control algorithm. The externally adjustable minimum on time and innovative property off time control effectively avoid the ring impact induced by parasitic elements so that a reliable and noise free operation of the SR system is insured. OB2004A is offered in SOT23-6 package. ■ Secondary-side synchronous rectification controller for 5V~12V output system Up to 85V VD pin high voltage tolerance Externally adjustable minimum on time Suitable for DCM, QR and CCM operation Prediction algorithm for CCM Accurate secondary side MOSFET Vds sensing SR turn on/off dead-time control for high efficiency and low thermal with immunity of interference Adaptive off time control effectively avoid the ring impact induced by parasitic elements 3A/2A peak current sink/source driver capability VDD UVLO protection ■ ■ ■ ■ ■ ■ ■ 源 ■ 辉 ■ o AC/DC 5V~12V adaptors Low voltage rectification circuits Br ig ht co nf id en t ia lt ■ ■ 英 APPLICATIONS O n- TYPICAL APPLICATION ©On-Bright Electronics Confidential 1 Preliminary Datasheet OB_DOC_DS_2004A00 OB2004A W High Performance synchronous rectification controller GENERAL INFORMATION Pin Configuration The OB2004A is offered in SOT23-6 package, shown as below. Parameter VIN pin VDD pin VD pin Gate pin RT pin Min/Max Operating Junction Temperature TJ Operating Ambient Temperature TA Min/Max Storage Temperature Tstg Lead Temperature (Soldering, 10secs) Value -0.6V to 24V -0.6V to 8V -2.5V to 85V Note2 -0.6V to 8V -0.6V to 7V -40 to 150 ℃ -20 to 85 ℃ -55 to 150 ℃ 260 ℃ 辉 源 Note1: Stresses beyond those listed under “absolute maximum ratings” may cause permanent damage to the device. These are stress ratings only, functional operation of the device at these or any other conditions beyond those indicated under “recommended operating conditions” is not implied. Exposure to absolute maximum-rated conditions for extended periods may affect device reliability. Note2: -2.5V applies to minimum duty cycle during normal operation only. ia lt o 英 Ordering Information Part Number Description SOT23-6, Halogen-free in OB2004AMP T&R id en t nf Br ig ht Absolute Maximum Ratings Recommended Operating Range Symbol Parameter Min/Max VDD VDD Supply Voltage 5V to 7.5V co Package Dissipation Rating Package RJA(℃/W) SOT23-6 200 X X O n- OB2004A High Performance synchronous rectification controller Package M:SOT23-6 ©On-Bright Electronics Confidential 2 Package Pb-free P: Green (Halogen-free) Preliminary Datasheet OB_DOC_DS_2004A00 OB2004A W High Performance synchronous rectification controller Marking Information 004YWW . ZZZAs 英 辉 源 Y:Year Code WW:Week Code(01-52) ZZZ: Lot code A:Character Code s: Internal code lt nf id en t ia Description This pin is connected to external n-channel MOSFET drain Driver output for external N-channel MOSFET Ground Power Supply System output voltage detection Minimum on time control pin. A resistor is connected from this pin to GND co I/O I O P P I O O n- Br ig ht Pin Name VD Gate GND VDD VIN RT o TERMINAL ASSIGNMENTS ©On-Bright Electronics Confidential -3- Preliminary Datasheet OB_DOC_DS_2004A00 OB2004A W High Performance synchronous rectification controller BLOCK DIAGRAM VDD VIN Regulator1 Bias GND System Output Detection PG UVLO Regulator2 AVDD RT AVDD R 辉 85V HV Switch SR 英 Min on time 源 200mV VD Driver Gate id en t ia lt o S Logic Control Demag_Det Prdiction O n- Br ig ht co Ring Detection nf GND ©On-Bright Electronics Confidential 4 Preliminary Datasheet OB_DOC_DS_2004A00 OB2004A W High Performance synchronous rectification controller ELECTRICAL CHARACTERISTICS (TA = 25℃, VDD=6.5V, unless otherwise noted) Symbol Parameter Test Conditions Min Typ. Max Unit Supply Voltage (VDD) 辉 源 Frequency@Vd=65KHz,VDD=5 V,1nF Cap load at GATE. I_Vdd_operation Operation current Frequency@Vd=2KHz,VDD=5V, No load at GATE. Frequency@Vd=50KHz, Vdd_regulation Vdd regulation voltage 6.3 Duty=25%, High level @Vd=20V UVLO(OFF) VDD Under Voltage Lockout Entry 4.4 VDD Under Voltage Lockout Exit UVLO(ON) 4.2 (Recovery) VD Detection Section SR MOSFET turn on threshold Vth_SR_act -150 voltage detection at VD Adjustable SR MOSFET turn off threshold voltage detection at Vd, Vth_SR_deact Rd=85 ohm Which is 0.06*Rd mV, and Rd is the resistor connected to Vd. (Note2) SR MOSFET fast path turn-on propagation delay Tdelay_on SR MOSFET slow path turn-on propagation delay SR MOSFET turn-off propagation Tdelay_off delay 6.5 6.7 V 4.6 4.8 V 4.4 4.6 V -200 -250 mV ns 200 ns 75 ns 1.9 us 2.2 2.5 2.8 V No sub-harmonic condition 70 75 75 % With sub-harmonic condition 12 15 18 % Maximum SR turn-on time 35 40 45 us Voltage reference at RT pin 0.95 1 nf id en t ia lt o 英 100 co RT=25KΩ Br ig ht n- Prediction ratio O Tsr_on_max 1.0 mA mV Voltage level at VIN when SR is disable CCM Prediction Section Rpre 0.8 mA -5 T_minimum_on SR MOSFET minimum on time Vin_sr_disable 1.5 2.0 RT Section Vrt 1.05 V Dead-time Control Section Tdt_off_max Maximum SR turn-off dead time GATE driver Section VOH Output high level @ VDD=6.5V VOL Output low level @ VDD=6.5V 0.8 us 6 1 V V Tf Falling time Gate voltage falling from 6V to 1V @ C L =1nF 50 ns Tr Rising time Gate voltage rising from 1V to 6V @ C L =1nF 50 ns Note1：Suggesting primary side controller operating at 65kHz frequency Note2： Rd can be choosed between 10~100 ohm ©On-Bright Electronics Confidential 5 Preliminary Datasheet OB_DOC_DS_2004A00 OB2004A W High Performance synchronous rectification controller O n- Br ig ht co nf id en t ia lt o 英 辉 源 CHARACTERIZATION PLOTS ©On-Bright Electronics Confidential 6 Preliminary Datasheet OB_DOC_DS_2004A00 OB2004A W High Performance synchronous rectification controller Operation Description OB2004A is a high performance and highly integrated secondary side synchronous rectification controller in switch mode power supply system. It drivers a much lower voltage drop N-channel MOSFET to emulate the traditional diode rectifier, which can reduce heat dissipation, increases output current capability and efficiency, and simplify the thermal design. regardless of VDD. Refer to the following timing diagram. 英 辉 源 Startup and under voltage lockout (UVLO) Whether OB2004 can operate normally or not depends on UVLO function implemented on chip and system output voltage. When power system is plugged in, VDD cap is charged from transformer secondary winding. When VDD rises above UVLO(off), the IC wakes up from under voltage lock out state and monitors the system output voltage through Vin pin. OB2004 will output SR gate based on correct timing after Vin rises above 2.7V(typical). Refer to the following timing diagram. o Fig.3 System output SCP timing diagram id en t ia lt Additionally, there is a pull down on-chip 15Kohm resistor to avoid the misconducting by VD pulse coupling. Besides, a hysteresis window between UVLO(off) and UVLO(on) makes system work reliably. co nf Synchronization rectifier OB2004A controls the turn-on and turn-off of synchronization rectifier MOSFET (SR MOSFET) by detection of drain-source voltage and prediction control. When demagnetization of transformer starts, the secondary-side current will flow through the body diode of SR MOSFET and the voltage at the drain will drop to below -200mV (typical). As soon as OB2004A detects this negative voltage, the driver voltage is pulled high to turn on the SR MOSFET after variable delay time depending on input line voltage and loading condition, refer to Fig.4.This variable delay time can improve system immunity to noise． After the SR MOSFET is turned on, the drain voltage of SR MOSFET begins to rise based on its Rdson and secondary-side current. The drain voltage becomes higher with demagnetization goes on. For reliable operation,OB2004 generate a adjustable SR turn-off threshold voltage based on resistor Rd on Vd pin， which is determined by 0.06*Rd mV. For DCM and QR, when the drain voltage rises above -5mV （ Rd=85 ohm ） , the gate of SR MOSFET will be pulled down to ground very quickly, refer to Fig.4. However, when the system works in CCM mode, the drain voltage may not rise above -5mV. In this situation, the property prediction algorithm would turn off SR O n- Br ig ht Fig.1 System start up timing diagram With enough high Vin, OB2004 would be powered from VDD and system output (Vin), which can lead to better system efficiency. When VDD drops below UVLO(on), to guarantee thermal stability, as long as the primary side is in operation, the OB2004 still can work normally until the Vin is lower than 2.9V. Refer to the following timing diagram. Fig.2 System shut down timing diagram For system reliability, the SR gate would be pulled low when Vin is lower than 2.5V (typical) ©On-Bright Electronics Confidential 7 Preliminary Datasheet OB_DOC_DS_2004A00 OB2004A W High Performance synchronous rectification controller gate in advance. The details are described in CCM section. Primary-side PWM Vp VD Tdemag(n) Tdemag(n+1) Demag Prediction Tsr_on(n) Tsr_on(n+1) Gate Tsr_on(n+1) = Tdemag(n) * 75% 英 辉 源 Fig.5 Prediction in stable CCM lt ia co nf id en t Prediction control in CCM When system works in CCM mode, drain voltage can not rise above -5mV when primary side turns on. In this case the property prediction algorithm implemented in OB2004A turns off the SR. OB2004A would detect the demagnetization time of current cycle and use this information to turn off SR in next cycle. For stable CCM, there is little variation between consecutive demagnetization phase, so the next cycle SR can be turn off predictively with pre-set prediction ratio, such as 75%. This means the next SR turn-on would last 75% of current demagnetization time before turn off. However when sub-harmonic switching happens, there is risk of short-circuit of transformer if both primary side and secondary side switch controllers are in turn-on phase. To avoid this risk, OB2004A would detect the primary side turn on time. If the primary side turn on time of current cycle is 600ns (typical) longer than the previous cycle, the pre-set prediction ratio would be changed from 75% to 15% so that the SR turnon time is significantly reduced to avoid the risk of short-circuit of transformer. Fig.5 and Fig.6 illustrates the control scheme. In the next consecutive cycles, the SR on-time will be gradually increased that improve the efficiency. o Fig.4 SR MOSFET turn-on and turn-off timing Br ig ht Fig.6 Prediction in CCM with sub-harmonic O n- Dead time control For efficiency and thermal issue, the demagnetization current flowing through SR MOSFET body diode after SR turn off should be as small as possible, i.e the dead time between SR turn off and demagnetization ending is as short as possible. But when SR MOSFET Rdson is too small or interference riding on Vds, SR maybe turn off prematurely. In this case, an adaptive dead time control algorithm used in OB2004A can correct the dead time to 1uS (typical) for good efficiency and thermal performance. Adjustable minimum on time OB2004A offers adjustable minimum on time control. This timer can avoid effectively false turnoff due to high frequency interference caused by parasitic element at the start of secondary-side demagnetization. Tonmin=8*RT*10E(-11) In addition, a adaptive dead time control is implemented (described in next section). It regulates the time period (dead time) between the SR tune off instance and turn on instance of the primary side to be 1uS in stable CCM operation to further improve the efficiency while ensure the safe operation. ©On-Bright Electronics Adaptive minimum off time At the end of demagnetization, SR MOSFET will be turn off. The remaining current will flow through body diode again, which may result in negative voltage (about -700mV) appears at drain and SR Confidential 8 Preliminary Datasheet OB_DOC_DS_2004A00 OB2004A W High Performance synchronous rectification controller MOSFET will turn on again. In addition, the resonance oscillation between the magnetization inductance and parasitic capacitance after demagnetization may cause negative drain voltage. These may turn on SR MOSFET unexpectedly. To avoid above mis-turn-on of SR MOSFET, constant minimum off time can be used to screen it. But it may disturb SR MOSFET operation. For reliable SR operation achieve reliable SR operation, an adaptive minimum off time control is implemented in OB2004A, which can guarantee reliable synchronous rectification operation. O n- Br ig ht co nf id en t ia lt o 英 辉 源 Gate driver For good and efficient synchronous rectification operation, the SR MOSFET should be turned on/off in very short time. Therefore strong driver capability is needed. OB2004A can offer typical source capability 2A and typical sink capability 3A. This guarantees fast turn-on and turn-off of SR MOSFET. The gate driver voltage high level is typically 6.5V regardless of the output voltage which is ranging from 5V to 12V (typical). ©On-Bright Electronics Confidential 9 Preliminary Datasheet OB_DOC_DS_2004A00 OB2004A W High Performance synchronous rectification controller Symbol Br ig ht co nf id en t ia lt o 英 辉 源 PACKAGE MECHANICAL DATA Dimensions In Millimeters Dimensions In Inches Max Min Max 1.000 1.450 0.039 0.057 0.000 0.150 0.000 0.006 A2 0.900 1.300 0.035 0.051 b 0.300 0.500 0.012 0.020 c 0.080 0.220 0.003 0.009 D 2.800 3.020 0.110 0.119 E 1.500 1.726 0.059 0.068 E1 2.600 3.000 0.102 0.118 A1 O A n- Min e 0.950 (BSC) 0.037 (BSC) e1 1.800 2.000 0.071 0.079 L 0.300 0.600 0.012 0.024 θ 0º 8º 0º 8º ©On-Bright Electronics Confidential 10 Preliminary Datasheet OB_DOC_DS_2004A00 OB2004A W High Performance synchronous rectification controller IMPORTANT NOTICE RIGHT TO MAKE CHANGES On-Bright Electronics Corp. reserves the right to make corrections, modifications, enhancements, improvements and other changes to its products and services at any time and to discontinue any product or service without notice. Customers should obtain the latest relevant information before placing orders and should verify that such information is current and complete. 源 WARRANTY INFORMATION On-Bright Electronics Corp. warrants performance of its hardware products to the specifications applicable at the time of sale in accordance with its standard warranty. Testing and other quality control techniques are used to the extent it deems necessary to support this warranty. Except where mandated by government requirements, testing of all parameters of each product is not necessarily performed. On-Bright Electronics Corp. assumes no liability for application assistance or customer product design. Customers are responsible for their products and applications using On-Bright’s components, data sheet and application notes. To minimize the risks associated with customer products and applications, customers should provide adequate design and operating safeguards. lt o 英 辉 LIFE SUPPORT On-Bright Electronics Corp.’s products are not designed to be used as components in devices intended to support or sustain human life. On-bright Electronics Corp. will not be held liable for any damages or claims resulting from the use of its products in medical applications. O n- Br ig ht co nf id en t ia MILITARY On-Bright Electronics Corp.’s products are not designed for use in military applications. On-Bright Electronics Corp. will not be held liable for any damages or claims resulting from the use of its products in military applications. ©On-Bright Electronics Confidential 11 Preliminary Datasheet OB_DOC_DS_2004A00