Preliminary Datasheet CURRENT MODE PWM CONTROLLER FOR BJT General Description Features The AP3720 is a low startup current, current mode PWM controller with green-mode operation. The PWM switching frequency at normal operation is 65k, but when the output power drops below the specifically level, the device enters the frequency-drop mode and the typical operating frequency is 20kHz (no audible noise). Additionally, when the load drops to a very low level or zero, the IC operates in so called ‘burst mode’ to minimize switching loss. • • • • • • • • • • The IC integrated a lot of functions such as the Lead-Edge Blanking (LEB) of the current sensing, internal slope compensation, line compensation, and several protection features. The protection functions include cycle-by-cycle current limit (OCP), VCC over voltage protection (OVP), OTP and OLP. AP3720 Low Startup Current （ 2.5µA ） and Low Operating Current (1.2mA) Off-line Converter Applied in Sub 25W Range Skip Cycle Mode Achieves Low Standby Power (<200mW) Cycle-by-Cycle Power Limited Frequency-drop Mode Soft Start with 2ms Programmable Drive Current for BJT Leading Edge Blanking Pre-shutdown Decreases Turn-off Losses Reliable Protection: Accurate OCP with Line Compensation Short Circuit Protection Over Voltage Protection for VCC Hysteretic Thermal Shutdown Protection Applications The AP3720 is available in DIP-8 and SOIC-8 packages. • • • • DIP-8 STB Cable Modem ADSL Modem DVD Recorder SOIC-8 Figure 1. Package Types of AP3720 Jul. 2009 Rev. 1. 0 BCD Semiconductor Manufacturing Limited 1 Preliminary Datasheet CURRENT MODE PWM CONTROLLER FOR BJT AP3720 Pin Configuration P Package (DIP-8) M Package (SOIC-8) LINE 1 8 CS NC 2 7 FB 3 BIAS 4 LINE 1 8 CS GND NC 2 7 GND 6 DRV FB 3 6 DRV 5 VCC BIAS 4 5 VCC Figure 2. Pin Configuration of AP3720 (Top View) Pin Description Pin Number Pin Name 1 LINE 2 NC Line compensation for OLP No connection Connect opto-coupler to this pin. The voltage of FB controls the mode of operation in one of the three modes: burst mode, frequency-drop mode (20kHz) and normal mode (65kHz). When the voltage of FB reaches a limit-point, the system enters the OLP mode This pin sets the driver current inside AP3720 with an external resistor to GND This pin is the positive supply voltage input. During start up, the power is supplied from line voltage. When VCC reaches 20V, the system begins running and the power is supplied from the auxiliary transformer winding 3 FB 4 BIAS 5 VCC 6 DRV This pin supplies the drive current for the external power NPN switch 7 GND This pin is the control ground 8 Jul. 2009 Function CS This pin senses the primary current and routes it to internal comparator. By changing the value of the sense resistor, the primary peak current set point is adjusted according to the output power demand Rev. 1. 0 BCD Semiconductor Manufacturing Limited 2 Preliminary Datasheet CURRENT MODE PWM CONTROLLER FOR BJT AP3720 Functional Block Diagram VCC 5 VF4 Skip VF4 VF3 VF2 COMP VF2 FB Regulator &UVLO OLP COMP 3 Internal Supply Vref&Vbias OVP COMP COMP V1 VF3 OSC PWM Comp 8 CS 65K/20K Duty S Slope Compensation 4 1 LINE K1 DRV R OCP COMP V2 6 Drive Q Skip BIAS Line compensation OLP 7 Protect Logic OTP OVP Fault GND Figure 3. Functional Block Diagram of AP3720 Ordering Information AP3720 Package - Circuit Type G1: Green Package P: DIP-8 M: SOIC-8 TR: Tape and Reel Blank: Tube Temperature Range DIP-8 Part Number Marking ID AP3720P-G1 AP3720P-G1 AP3720MTR-G1 3720M-G1 Packing Type Tube -40 to 85°C SOIC-8 Tape & Reel BCD Semiconductor's Pb-free products, as designated with "G1" suffix in the part number, are RoHS compliant and green. Jul. 2009 Rev. 1. 0 BCD Semiconductor Manufacturing Limited 3 Preliminary Datasheet CURRENT MODE PWM CONTROLLER FOR BJT AP3720 Absolute Maximum Ratings (Note 1) Parameter Supply Voltage Symbol Value Unit VCC -0.3 to 28 V -0.3 to 7 V Internally limited A Voltage at DRV, FB, CS, BIAS, LINE Output Current at DRV IDRV DIP-8 1.35 SOIC-8 0.55 Power Dissipation at TA=25ºC PD Operating Junction Temperature TJ 160 ºC Storage Temperature TSTG -65 to 150 ºC Lead Temperature (Soldering, 10 sec) TLEAD 300 ºC Thermal Resistance (Junction-to-Ambient) θJA DIP-8 83 SOIC-8 186 ESD (Machine Model) 400 W ºC/W V Note 1: Stresses greater than those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and 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 Ratings” for extended periods may affect device reliability. Recommended Operating Conditions Parameter Symbol Min Max Unit Supply Voltage VCC 12 18 V Ambient Temperature TA -40 85 ºC Jul. 2009 Rev. 1. 0 BCD Semiconductor Manufacturing Limited 4 Preliminary Datasheet CURRENT MODE PWM CONTROLLER FOR BJT AP3720 Electrical Characteristics VCC =15V, TA=25°C, unless otherwise specified. Parameter Supply Voltage ( VCC Pin ) Startup Current Operating Current UVLO (on) UVLO (off) VCC OVP Conditions Min VCC=15V VFB=VCS=0V 18.5 7.1 PWM Section / Oscillator Section Maximum Duty Cycle Normal Frequency VFB=3V Green Frequency VFB=2V From 65k to 20k Frequency Switch Delay Time From 20k to 65k Frequency Temperature Stability -40ºC to 85ºC Frequency Voltage Stability VCC=8V to 18V 67 60 Typ Max Unit 2.5 1.2 20 8 26.5 8 2.5 21.5 8.9 28.5 µA mA V V V 75 65 20 64 0 ±5 1.5 83 70 % kHz kHz ms ms % % ±8 3 Current Sense Section ( CS Pin ) Maximum CS Voltage Line Compensation Coefficient LEB Time Soft Start Time VLINE=0.95V 0.983 250 1.032 4.6 350 2 1.081 9.5 400 V % ns ms 3 10 -0.5 3.5 13 V/V kΩ mA Feedback Input Section ( FB Pin ) The Ratio of FB to CS Input Impedance Source Current GFB RFB IFB 2.5 7 -1 Output Section ( Gate Pin ) Output Maximum Current Output Sink Current RBIAS=1M VFB=VCS=0V 32 VFB=5.1V 64 160 0.5 mA mA Protection Section OLP Delay Time Shutdown Temperature Jul. 2009 Rev. 1. 0 ms ºC BCD Semiconductor Manufacturing Limited 5 Preliminary Datasheet CURRENT MODE PWM CONTROLLER FOR BJT AP3720 Control Flow Chart START Zero Pulses VCC > 20V Over Load Short Circuit Over Temperature Soft Start (2ms) Monitor VFB VFB < 1.45V 1.45V<VFB< 2.45V 2.45V<VFB<4.85V VFB > 4.85V Skip Cycle Mode Operating Frequency: 20K (Light Load) Operating Frequency: 65K (High Load) Protection Mode Jul. 2009 Rev. 1. 0 BCD Semiconductor Manufacturing Limited 6 Preliminary Datasheet CURRENT MODE PWM CONTROLLER FOR BJT AP3720 Typical Performance Characteristics 3.0 100 2.9 2.8 Start up Current (µA) Drive Current (mA) 80 60 40 2.7 2.6 2.5 2.4 2.3 2.2 20 2.1 0 0 500 1000 1500 2000 2500 3000 2.0 -50 3500 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90 o RBIAS (KΩ) Temperature ( C) Figure 4. Drive Current vs. RBIAS Figure 5. Start-up Current vs. Temperature 65 21.0 64 20.5 20.0 62 Switch Frequency (kHz) Switch Frequency (kHz) 63 61 60 59 58 57 56 The Highest fSW 55 54 53 52 -50 -40 -30 -20 -10 0 10 20 30 40 19.0 18.5 18.0 17.5 The Highest fSW The Lowest fSW 17.0 The Lowest fSW The Average fSW 16.5 The Average fSW 50 60 70 80 16.0 -50 -40 -30 -20 -10 90 o Temperature ( C) 0 10 20 30 40 50 60 70 80 90 100 o Temperature ( C) Figure 6. Switch Frequency (65k) vs. Temperature Jul. 2009 19.5 Figure 7. Switch Frequency (20k) vs. Temperature Rev. 1. 0 BCD Semiconductor Manufacturing Limited 7 Preliminary Datasheet CURRENT MODE PWM CONTROLLER FOR BJT AP3720 Typical Performance Characteristics (Continued) 370 365 360 LEB (nS) 355 350 345 340 335 330 325 320 -50 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90 o Temperature ( C) Figure 8. LEB vs. Temperature Operation Description Figure 9. Operation Diagram of AP3720 Jul. 2009 Rev. 1. 0 BCD Semiconductor Manufacturing Limited 8 Preliminary Datasheet CURRENT MODE PWM CONTROLLER FOR BJT AP3720 Operation Description (Continued) Start Sequence Normal Mode (65kHz) When the VCC capacitor reaches the UVLO(on) level (typically 20V), the controller runs. At this time, VCC capacitor supplies the controller and the auxiliary supply takes over before VCC collapses below UVLO(off). At the higher load, the device operates in normal mode and the frequency is 65kHz (typical). Cycle-by-Cycle Current Limit The cycle terminates when the CS voltage exceeds 1.074V. Soft Start The AP3720 operates as a current mode controller, whereby output switch conduction is initiated by the oscillator and terminated when the peak inductor current reaches the threshold level established by VFB. The inductor current is converted to a voltage by inserting the ground referenced sense resistor RS in series with the emitter of the power transistor. The internal soft start function is activated at start-up with a duration of 2ms (typical). The current sense compensation starts from 1.0V and slowly decreases to zero at the end of the 2ms duration. This function is activated at each auto-restart attempt due to OLP or TSD condition. The feature also helps minimize output overshoot and prevents saturation of transformer during start-up. When the power supply output is overload or the control loop is open, the current sense comparator threshold will be internally clamped to about 1.074V. Therefore the maximum peak inductor current is: FB Pin Operation The AP3720 can automatically adjust the operating mode according to the loading condition. The voltage of FB controls the mode of operation in one of the three modes: burst mode, frequency-drop mode (20kHz) and normal mode (65kHz). To prevent saturation of transformer and achieve good transient load performance, the switch from frequency-drop mode to normal mode occurs with no delay time and that from normal mode to frequency-drop mode occurs with 64ms delay time when the load condition changes. I PK (max) = ( k=0.0444 ) Leading Edge Blanking (LEB) At the instant the power transistor is turned on, there usually exists a high current spike through the BJT, caused by primary-side capacitance and secondary-side rectifier reverse recovery. Excessive voltage across the RS can lead to incorrect feedback operation in the current mode PWM control. To counter this effect, the AP3720 employs a leading edge blanking (LEB) circuit. This circuit inhibits the PWM comparator for a short time (tLEB) after the BJT is turn on. Burst Mode Operation At zero load or light load condition, majority of the power dissipation is in proportion to the number of switch events within a fixed period of time. To reduce the loss in this situation, the device enters burst mode control which makes some switching cycle skip when VFB drops below the burst mode threshold level. Line Compensation The AP3720 has an adjustable line compensation so that achieves constant output power limit over the universal input voltage range. Frequency-drop Mode (20kHz) When the output power drops below a specific level, the device enters the frequency-drop mode and the typical operating frequency is 20kHz. In this mode, the system efficiency at specific load will improve obviously. Jul. 2009 1.074 − k ∗ VLINE RS Drive Current Control The AP3720 drive current is programmable through an external resistor to GND (see Figure 4). Rev. 1. 0 BCD Semiconductor Manufacturing Limited 9 Preliminary Datasheet CURRENT MODE PWM CONTROLLER FOR BJT AP3720 Operation Description (Continued) Protection Circuit current through the opto-coupler LED, which also reduces the opto-coupler transistor current, thus increasing VFB. If VFB exceeds 4.85V and holds the situation beyond 64ms, the over load protection circuit is activated. The AP3720 has several self-protective functions such as over load protection (OLP), open loop protection, over voltage protection for VCC, thermal shutdown (TSD). Because these protection circuits are fully integrated into the IC without external components, the reliability can be improved without increasing cost. Once the fault condition occurs, switching is terminated and the power transistor remains off. This causes VCC to fall. When VCC reaches the UVLO stop voltage of 8V, the current consumed by the AP3720 decreases to the start-up current (typically 2.5µA) and the current supplied from the DC link charges the VCC capacitor. When VCC reaches the start voltage of 20V, the AP3720 resumes its normal operation. In this manner, the auto-restart can alternately enable and disable the switching of the power transistor until the fault condition is eliminated. Open Loop Protection: In this abnormal situation, OLP or OVP will be activated. Over Voltage Protection: If the control loop is open, the current through the opto-coupler transistor becomes almost zero. Then VFB climbs up to the over load situation and the over load protection is activated. But maybe the output voltage exceed the rated voltage before the over load protection is activated, resulting in the breakdown of the devices in the secondary side and the primary side. To prevent this situation, an over voltage protection circuit is employed. In general, VCC is proportional to the output voltage. If VCC exceeds 26.5V, an OVP circuit is activated resulting in the termination of the switching operation. To avoid undesired activation of OVP during normal operation, VCC should be designed to be below 20V. Over Load Protection: In this situation, the protection circuit should be activated to protect the SMPS. However, even when the SMPS is in the normal operation, the over load protection circuit can be activated during the load transition. To avoid this undesired operation, the over load protection circuit is designed to be activated after a specified time (typically 64ms) to determine whether it is a transient situation or an overload situation. Because of the cycle-by-cycle current limit, the maximum peak current through the BJT is limited, and therefore the maximum input power is restricted. If the output consumes exceeds this maximum power, the voltage decreases below the rated voltage. This reduces the Jul. 2009 Thermal Shutdown Thermal shutdown is provided by a precision analog circuit that turns the power transistor off when the junction temperature exceeds the thermal shutdown temperature (typically 160ºC). When the junction temperature drops about the hysteretic temperature, normal operation resumes. Rev. 1. 0 BCD Semiconductor Manufacturing Limited 10 Preliminary Datasheet CURRENT MODE PWM CONTROLLER FOR BJT AP3720 Mechanical Dimensions DIP-8 Unit: mm(inch) 0.700(0.028) 7.620(0.300)TYP 1.524(0.060) TYP 5° 3.200(0.126) 3.600(0.142) 3.710(0.146) 4.310(0.170) 0.510(0.020)MIN 3.000(0.118) 3.600(0.142) 0.204(0.008) 0.360(0.014) 8.200(0.323) 9.400(0.370) 0.254(0.010)TYP 0.360(0.014) 0.560(0.022) 2.540(0.100) TYP 0.130(0.005)MIN 6.200(0.244) 6.600(0.260) R0.750(0.030) Φ3.000(0.118) Depth 0.100(0.004) 0.200(0.008) 9.000(0.354) 9.400(0.370) Note: Eject hole, oriented hole and mold mark is optional. Jul. 2009 Rev. 1. 0 BCD Semiconductor Manufacturing Limited 11 Preliminary Datasheet CURRENT MODE PWM CONTROLLER FOR BJT AP3720 Mechanical Dimensions (Continued) SOIC-8 4.700(0.185) 5.100(0.201) Unit: mm(inch) 0.320(0.013) 1.350(0.053) 1.750(0.069) 0.675(0.027) 5.800(0.228) 0.725(0.029) 1.270(0.050) 6.200(0.244) TYP 0.800(0.031) 0.100(0.004) 0.300(0.012) 0.200(0.008) 1.000(0.039) 3.800(0.150) 4.000(0.157) 0.330(0.013) 0.510(0.020) 0.190(0.007) 0.250(0.010) 1° 5° 0.900(0.035) 0.450(0.017) 0.800(0.031) Note: Eject hole, oriented hole and mold mark is optional. 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