UC3844_06

UC3844, UC3845, UC2844, UC2845 High Performance Current Mode Controllers The UC3844, UC3845 series are high performance fixed frequency current mode controllers. They are specifically designed for Off−Line and DC−to−DC converter applications offering the designer a cost effective solution with minimal external components. These integrated circuits feature an oscillator, a temperature compensated reference, high gain error amplifier, current sensing comparator, and a high current totem pole output ideally suited for driving a power MOSFET. Also included are protective features consisting of input and reference undervoltage lockouts each with hysteresis, cycle−by−cycle current limiting, a latch for single pulse metering, and a flip−flop which blanks the output off every other oscillator cycle, allowing output dead times to be programmed for 50% to 70%. These devices are available in an 8−pin dual−in−line plastic package as well as the 14−pin plastic surface mount (SOIC−14). The SOIC−14 package has separate power and ground pins for the totem pole output stage. The UCX844 has UVLO thresholds of 16 V (on) and 10 V (off), ideally suited for off−line converters. The UCX845 is tailored for lower voltage applications having UVLO thresholds of 8.5 V (on) and 7.6 V (off). Features http://onsemi.com PDIP−8 N SUFFIX CASE 626 1 14 1 8 1 SOIC−14 D SUFFIX CASE 751A SOIC−8 D1 SUFFIX CASE 751A 8 PIN CONNECTIONS Compensation 1 Voltage Feedback 2 Current Sense 3 RT/CT 4 (Top View) 8 7 6 5 Vref VCC Output GND • • • • • • • • • • Current Mode Operation to 500 kHz Output Switching Frequency Output Deadtime Adjustable from 50% to 70% Automatic Feed Forward Compensation Latching PWM for Cycle−By−Cycle Current Limiting Internally Trimmed Reference with Undervoltage Lockout High Current Totem Pole Output Input Undervoltage Lockout with Hysteresis Low Startup and Operating Current Direct Interface with ON Semiconductor SENSEFETt Products Pb−Free Packages are Available VCC Vref 8(14) R R RTCT 4(7) Vref Undervoltage Lockout Oscillator Flip Flop & Latching PWM 5.0V Reference 7(12) Compensation NC Voltage Feedback NC Current Sense NC RT/CT 1 2 3 4 5 6 7 (Top View) 14 Vref 13 NC 12 VCC 11 VC 10 Output 9 8 GND Power Ground VCC Undervoltage Lockout VC 7(11) ORDERING INFORMATION See detailed ordering and shipping information in the package dimensions section on page 14 of this data sheet. Output 6(10) PWR GND 5(8) Current Sense 3(5) Voltage Feedback 2(3) 1(1) Output Comp. + − DEVICE MARKING INFORMATION See general marking information in the device marking section on page page 14 of this data sheet. Error Amplifier GND 5(9) Pin numbers in parenthesis are for the D suffix SOIC−14 package. Figure 1. Simplified Block Diagram © Semiconductor Components Industries, LLC, 2006 July, 2006 − Rev. 7 1 Publication Order Number: UC3844/D UC3844, UC3845, UC2844, UC2845 MAXIMUM RATINGS Rating Total Power Supply and Zener Current Output Current, Source or Sink (Note 1) Output Energy (Capacitive Load per Cycle) Current Sense and Voltage Feedback Inputs Error Amp Output Sink Current Power Dissipation and Thermal Characteristics D Suffix, Plastic Package, Case 751A Maximum Power Dissipation @ TA = 25°C Thermal Resistance Junction−to−Air N Suffix, Plastic Package, Case 626 Maximum Power Dissipation @ TA = 25°C Thermal Resistance Junction−to−Air Operating Junction Temperature Operating Ambient Temperature UC3844, UC3845 UC2844, UC2845 Storage Temperature Range Symbol (ICC + IZ) IO W Vin IO Value 30 1.0 5.0 − 0.3 to + 5.5 10 Unit mA A mJ V mA PD RqJA PD RqJA TJ TA 862 145 1.25 100 + 150 0 to + 70 − 25 to + 85 − 65 to + 150 mW °C/W W °C/W °C °C Tstg °C Stresses exceeding Maximum Ratings may damage the device. Maximum Ratings are stress ratings only. Functional operation above the Recommended Operating Conditions is not implied. Extended exposure to stresses above the Recommended Operating Conditions may affect device reliability. 1. Maximum Package power dissipation limits must be observed. ELECTRICAL CHARACTERISTICS (VCC = 15 V, (Note 2), RT = 10 k, CT = 3.3 nF, TA = Tlow to Thigh (Note 3), unless otherwise noted.) UC284X Characteristics REFERENCE SECTION Reference Output Voltage (IO = 1.0 mA, TJ = 25°C) Line Regulation (VCC = 12 V to 25 V) Load Regulation (IO = 1.0 mA to 20 mA) Temperature Stability Total Output Variation over Line, Load, Temperature Output Noise Voltage (f = 10 Hz to kHz, TJ = 25°C) Long Term Stability (TA = 125°C for 1000 Hours) Output Short Circuit Current OSCILLATOR SECTION Frequency TJ = 25°C TA = Tlow to Thigh Frequency Change with Voltage (VCC = 12 V to 25 V) Frequency Change with Temperature TA = Tlow to Thigh Oscillator Voltage Swing (Peak−to−Peak) Discharge Current (Vosc = 2.0 V, TJ = 25°C) ERROR AMPLIFIER SECTION Voltage Feedback Input (VO = 2.5 V) Input Bias Current (VFB = 2.7 V) Open Loop Voltage Gain (VO = 2.0 V to 4.0 V) VFB IIB AVOL 2.45 − 65 2.5 −0.1 90 2.55 −1.0 − 2.42 − 65 2.5 −0.1 90 2.58 −2.0 − V mA dB fosc 47 46 − − − − 52 − 0.2 5.0 1.6 10.8 57 60 1.0 − − − 47 46 − − − − 52 − 0.2 5.0 1.6 10.8 57 60 1.0 − − − kHz Vref Regline Regload TS Vref Vn S ISC 4.95 − − − 4.9 − − − 30 5.0 2.0 3.0 0.2 − 50 5.0 − 85 5.05 20 25 − 5.1 − − − 180 4.9 − − − 4.82 − − − 30 5.0 2.0 3.0 0.2 − 50 5.0 − 85 5.1 20 25 − 5.18 − − − 180 V mV mV mV/°C V mV mV mA Symbol Min Typ Max Min UC384X Typ Max Unit Dfosc/DV Dfosc/DT Vosc Idischg % % V mA 2. Adjust VCC above the Startup threshold before setting to 15 V. 3. Low duty cycle pulse techniques are used during test to maintain junction temperature as close to ambient as possible. Thigh = +70°C for UC3844, UC3845 Tlow = 0°C for UC3844, UC3845 −25°C for UC2844, UC2845 +85°C for UC2844, UC2845 http://onsemi.com 2 UC3844, UC3845, UC2844, UC2845 ELECTRICAL CHARACTERISTICS (VCC = 15 V, (Note 4), RT = 10 k, CT = 3.3 nF, TA = Tlow to Thigh (Note 5), unless otherwise noted.) UC284X Characteristics ERROR AMPLIFIER SECTION (continued) Unity Gain Bandwidth (TJ = 25°C) Power Supply Rejection Ratio (VCC = 12 V to 25 V) Output Current Sink (VO = 1.1 V, VFB = 2.7 V) Source (VO = 5.0 V, VFB = 2.3 V) Output Voltage Swing High State (RL = 15 k to ground, VFB = 2.3 V) Low State (RL = 15 k to Vref, VFB = 2.7 V) CURRENT SENSE SECTION Current Sense Input Voltage Gain (Notes 6 & 7) Maximum Current Sense Input Threshold (Note 6) Power Supply Rejection Ratio VCC = 12 V to 25 V (Note 6) Input Bias Current Propagation Delay (Current Sense Input to Output) OUTPUT SECTION Output Voltage Low State (ISink = 20 mA) (ISink = 200 mA) High State (ISink = 20 mA) (ISink = 200 mA) Output Voltage with UVLO Activated VCC = 6.0 V, ISink = 1.0 mA Output Voltage Rise Time (CL = 1.0 nF, TJ = 25°C) Output Voltage Fall Time (CL = 1.0 nF, TJ = 25°C) UNDERVOLTAGE LOCKOUT SECTION Startup Threshold UCX844 UCX845 Minimum Operating Voltage After Turn−On UCX844 UCX845 PWM SECTION Duty Cycle Maximum Minimum TOTAL DEVICE Power Supply Current (Note 4) Startup: (VCC = 6.5 V for UCX845A, (VCC 14 V for UCX844) Operating Power Supply Zener Voltage (ICC = 25 mA) ICC − − VZ 30 0.5 12 36 1.0 17 − − − 30 0.5 12 36 1.0 17 − V mA % DCmax DCmin 46 − 48 − 50 0 47 − 48 − 50 0 Vth V 15 7.8 9.0 7.0 16 8.4 10 7.6 17 9.0 11 8.2 14.5 7.8 8.5 7.0 16 8.4 10 7.6 17.5 9.0 V 11.5 8.2 V VOL VOH VOL(UVLO) tr tf − − 12 12 − − − 0.1 1.6 13.5 13.4 0.1 50 50 0.4 2.2 − − 1.1 150 150 − − 13 12 − − − 0.1 1.6 13.5 13.4 0.1 50 50 0.4 2.2 − − V 1.1 150 150 ns ns AV Vth PSRR − IIB tPLH(IN/OUT) − − 70 −2.0 150 − −10 300 − − − 70 −2.0 150 − −10 300 mA ns 2.85 0.9 3.0 1.0 3.15 1.1 2.85 0.9 3.0 1.0 3.15 1.1 V/V V dB BW PSRR ISink ISource VOH VOL 0.7 60 2.0 −0.5 5.0 − 1.0 70 12 −1.0 6.2 0.8 − − − − − 1.1 0.7 60 2.0 −0.5 5.0 − 1.0 70 12 −1.0 6.2 0.8 − − − − V − 1.1 MHz dB mA Symbol Min Typ Max Min UC384X Typ Max Unit VCC(min) 4. Adjust VCC above the Startup threshold before setting to 15 V. 5. Low duty cycle pulse techniques are used during test to maintain junction temperature as close to ambient as possible. Thigh = +70°C for UC3844, UC3845 Tlow = 0°C for UC3844, UC3845 −25°C for UC2844, UC2845 +85°C for UC2844, UC2845 6. This parameter is measured at the latch trip point with VFB = 0 V. 7. Comparator gain is defined as: AV DV Output Compensation DV Current Sense Input http://onsemi.com 3 UC3844, UC3845, UC2844, UC2845 % DT, PERCENT OUTPUT DEADTIME 10 0 50 20 10 5.0 2.0 75 VCC = 15 V TA = 25°C RT, TIMING RESISTOR (k Ω ) 70 65 CT = 10 nF 5.0 nF 1.0 nF 2.0 nF 60 55 50 10 k 500 pF NOTE: Output switches at one−half the oscillator frequency. 1.0 10 k 100 pF 200 pF 20 k 50 k 100 k 200 k 500 k 1.0 M 20 k 50 k 100 k 200 k 500 k 1.0 M fosc, OSCILLATOR FREQUENCY (Hz) fosc, OSCILLATOR FREQUENCY (Hz) Figure 2. Timing Resistor versus Oscillator Frequency Figure 3. Output Deadtime versus Oscillator Frequency 2.55 V VCC = 15 V AV = −1.0 TA = 25°C 3.0 V VCC = 15 V AV = −1.0 TA = 25°C 20 mV/DIV 2.5 V 2.5 V 2.45 V 0.5 ms/DIV 2.0 V 1.0 ms/DIV Figure 4. Error Amp Small Signal Transient Response Figure 5. Error Amp Large Signal Transient Response A VOL , OPEN LOOP VOLTAGE GAIN (dB) 100 80 Gain 60 40 Phase 20 0 VCC = 15 V VO = 2.0 V to 4.0 V RL = 100 K TA = 25°C Vth, CURRENT SENSE INPUT THRESHOLD (V) 0 30 60 90 120 150 φ EXCESS PHASE (DEGREES) , 1.2 VCC = 15 V 1.0 0.8 0.6 TA = 125°C 0.4 0.2 0 TA = −55°C TA = 25°C − 20 10 100 1.0 k 10 k 100 k 1.0 M 180 10 M 0 f, FREQUENCY (Hz) 2.0 4.0 6.0 VO, ERROR AMP OUTPUT VOLTAGE (V) 8.0 Figure 6. Error Amp Open Loop Gain and Phase versus Frequency Figure 7. Current Sense Input Threshold versus Error Amp Output Voltage http://onsemi.com 4 200 mV/DIV UC3844, UC3845, UC2844, UC2845 Δ V ref , REFERENCE VOLTAGE CHANGE (mV) 0 VCC = 15 V , REFERENCE SHORT CIRCUIT CURRENT (mA) SC 110 VCC = 15 V RL ≤ 0.1 W 90 −4.0 −8.0 −12 −16 −20 −24 TA = 125°C TA = 25°C 70 TA = −55°C 0 20 40 60 80 100 120 50 −55 −25 0 25 50 75 100 125 Iref, REFERENCE SOURCE CURRENT (mA) TA, AMBIENT TEMPERATURE (°C) Figure 8. Reference Voltage Change versus Source Current I Figure 9. Reference Short Circuit Current versus Temperature Δ V , OUTPUT VOLTAGE CHANGE (2.0 mV/DIV) VCC = 15 V IO = 1.0 mA to 20 mA TA = 25°C Δ V , OUTPUT VOLTAGE CHANGE (2.0 mV/DIV) VCC = 12 V to 25 V TA = 25°C O O 2.0 ms/DIV 2.0 ms/DIV Figure 10. Reference Load Regulation Figure 11. Reference Line Regulation V sat , OUTPUT SATURATION VOLTAGE (V) 0 VCC −1.0 −2.0 Source Saturation (Load to Ground) TA = 25°C TA = −55°C VCC = 15 V 80 ms Pulsed Load 120 Hz Rate 90% VCC = 15 V CL = 1.0 nF TA = 25°C 3.0 TA = −55°C 2.0 1.0 0 0 200 Sink Saturation (Load to VCC) TA = 25°C 10% GN D 400 600 800 50 ns/DIV IO, OUTPUT LOAD CURRENT (mA) Figure 12. Output Saturation Voltage versus Load Current Figure 13. Output Waveform http://onsemi.com 5 UC3844, UC3845, UC2844, UC2845 VCC, OUTPUT VOLTAGE 25 20 V/DIV ICC, SUPPLY CURRENT (mA) VCC = 30 V CL = 15 pF TA = 255C 20 15 10 UCX845 5 0 100 ns/DIV UCX844 RT = 10 k CT = 3.3 nF VFB = 0 V ISense = 0 V TA = 255C 40 ICC, SUPPLY CURRENT 100 mA/DIV 0 10 20 30 VCC, SUPPLY VOLTAGE (V) Figure 14. Output Cross Conduction Figure 15. Supply Current versus Supply Voltage PIN FUNCTION DESCRIPTION Pin 8−Pin 1 2 3 4 5 6 7 8 − 14−Pin 1 3 5 7 − 10 12 14 8 Function Compensation Voltage Feedback Current Sense RT/CT GND Output VCC Vref Power Ground Description This pin is Error Amplifier output and is made available for loop compensation. This is the inverting input of the Error Amplifier. It is normally connected to the switching power supply output through a resistor divider. A voltage proportional to inductor current is connected to this input. The PWM uses this information to terminate the output switch conduction. The Oscillator frequency and maximum Output duty cycle are programmed by connecting resistor RT to Vref and capacitor CT to ground. Operation to 1.0 MHz is possible. This pin is combined control circuitry and power ground (8−pin package only). This output directly drives the gate of a power MOSFET. Peak currents up to 1.0 A are sourced and sunk by this pin. The output switches at one−half the oscillator frequency. This pin is the positive supply of the control IC. This is the reference output. It provides charging current for capacitor CT through resistor RT. This pin is a separate power ground return (14−pin package only) that is connected back to the power source. It is used to reduce the effects of switching transient noise on the control circuitry. The Output high state (VOH) is set by the voltage applied to this pin (14−pin package only). With a separate power source connection, it can reduce the effects of switching transient noise on the control circuitry. This pin is the control circuitry ground return (14−pin package only) and is connected to back to the power source ground. No connection (14−pin package only). These pins are not internally connected. − 11 VC − − 9 2,4,6,13 GND NC http://onsemi.com 6 UC3844, UC3845, UC2844, UC2845 OPERATING DESCRIPTION The UC3844, UC3845 series are high performance, fixed frequency, current mode controllers. They are specifically designed for Off−Line and DC−to−DC converter applications offering the designer a cost effective solution with minimal external components. A representative block diagram is shown in Figure 16. Oscillator This occurs when the power supply is operating and the load is removed, or at the beginning of a soft−start interval (Figures 21, 22). The Error Amp minimum feedback resistance is limited by the amplifier’s source current (0.5 mA) and the required output voltage (VOH) to reach the comparator’s 1.0 V clamp level: Rf(min) ≈ 3.0 (1.0 V) + 1.4 V = 8800 W 0.5 mA The oscillator frequency is programmed by the values selected for the timing components RT and CT. Capacitor CT is charged from the 5.0 V reference through resistor RT to approximately 2.8 V and discharged to 1.2 V by an internal current sink. During the discharge of CT, the oscillator generates an internal blanking pulse that holds the center input of the NOR gate high. This causes the Output to be in a low state, thus producing a controlled amount of output deadtime. An internal flip−flop has been incorporated in the UCX844/5 which blanks the output off every other clock cycle by holding one of the inputs of the NOR gate high. This in combination with the CT discharge period yields output deadtimes programmable from 50% to 70%. Figure 2 shows RT versus Oscillator Frequency and Figure 3, Output Deadtime versus Frequency, both for given values of CT. Note that many values of RT and CT will give the same oscillator frequency but only one combination will yield a specific output deadtime at a given frequency. In many noise sensitive applications it may be desirable to frequency−lock the converter to an external system clock. This can be accomplished by applying a clock signal to the circuit shown in Figure 18. For reliable locking, the free−running oscillator frequency should be set about 10% less than the clock frequency. A method for multi unit synchronization is shown in Figure 19. By tailoring the clock waveform, accurate Output duty cycle clamping can be achieved to realize output deadtimes of greater than 70%. Error Amplifier Current Sense Comparator and PWM Latch The UC3844, UC3845 operate 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 the Error Amplifier Output/Compensation (Pin 1). Thus the error signal controls the inductor current on a cycle−by−cycle basis. The current Sense Comparator PWM Latch configuration used ensures that only a single pulse appears at the Output during any given oscillator cycle. The inductor current is converted to a voltage by inserting the ground referenced sense resistor RS in series with the source of output switch Q1. This voltage is monitored by the Current Sense Input (Pin 3) and compared a level derived from the Error Amp Output. The peak inductor current under normal operating conditions is controlled by the voltage at pin 1 where: Ipk = V(Pin 1) − 1.4 V 3 RS Abnormal operating conditions occur when the power supply output is overloaded or if output voltage sensing is lost. Under these conditions, the Current Sense Comparator threshold will be internally clamped to 1.0 V. Therefore the maximum peak switch current is: Ipk(max) = 1.0 V RS A fully compensated Error Amplifier with access to the inverting input and output is provided. It features a typical dc voltage gain of 90 dB, and a unity gain bandwidth of 1.0 MHz with 57 degrees of phase margin (Figure 6). The noninverting input is internally biased at 2.5 V and is not pinned out. The converter output voltage is typically divided down and monitored by the inverting input. The maximum input bias current is −2.0 mA which can cause an output voltage error that is equal to the product of the input bias current and the equivalent input divider source resistance. The Error Amp Output (Pin 1) is provide for external loop compensation (Figure 29). The output voltage is offset by two diode drops (≈ 1.4 V) and divided by three before it connects to the inverting input of the Current Sense Comparator. This guarantees that no drive pulses appear at the Output (Pin 6) when Pin 1 is at its lowest state (VOL). When designing a high power switching regulator it becomes desirable to reduce the internal clamp voltage in order to keep the power dissipation of RS to a reasonable level. A simple method to adjust this voltage is shown in Figure 20. The two external diodes are used to compensate the internal diodes yielding a constant clamp voltage over temperature. Erratic operation due to noise pickup can result if there is an excessive reduction of the Ipk(max) clamp voltage. A narrow spike on the leading edge of the current waveform can usually be observed and may cause the power supply to exhibit an instability when the output is lightly loaded. This spike is due to the power transformer interwinding capacitance and output rectifier recovery time. The addition of an RC filter on the Current Sense Input with a time constant that approximates the spike duration will usually eliminate the instability; refer to Figure 24. http://onsemi.com 7 UC3844, UC3845, UC2844, UC2845 VCC VCC 7(12) 36V + − VC Vref UVLO TQ 1.0mA S 2R R 1.0V Current Sense Comparator GND 5(9) + − = − + Q R PWM Latch 7(11) Output 6(10) Power Ground 5(8) Current Sense Input 3(5) RS Q1 Vin Vref 8(14) R 2.5V RT R 3.6V Oscillator 4(7) CT + − Error Amplifier + Internal Bias Reference Regulator + +− − + VCC UVLO − Voltage Feedback Input 2(3) Output Compensation 1(1) Sink Only Positive True Logic Pin numbers in parenthesis are for the D suffix SOIC−14 package. Figure 16. Representative Block Diagram Capacitor CT Latch ‘‘Set’’ Input Output/ Compensation Current Sense Input Latch ‘‘Reset’’ Input Output Large RT/Small CT Small RT/Large CT Figure 17. Timing Diagram http://onsemi.com 8 UC3844, UC3845, UC2844, UC2845 Undervoltage Lockout Two undervoltage lockout comparators have been incorporated to guarantee that the IC is fully functional before the output stage is enabled. The positive power supply terminal (VCC and the reference output (Vref) are each monitored by separate comparators. Each has built−in hysteresis to prevent erratic output behavior as their respective thresholds are crossed. The VCC comparator upper and lower thresholds are 16 V/10 V for the UCX844, and 8.4 V/7.6 V for the UCX845. The Vref comparator upper and lower thresholds are 3.6 V/3/4 V. The large hysteresis and low startup current of the UCX844 makes it ideally suited in off−line converter applications where efficient bootstrap startup techniques later required (Figure 30). The UCX845 is intended for lower voltage DC−to−DC converter applications. A 36 V zener is connected as a shunt regulator from VCC to ground. Its purpose is to protect the IC from excessive voltage that can occur during system startup. The minimum operating voltage for the UCX844 is 11 V and 8.2 V for the UCX845. Output designer added flexibility in tailoring the drive voltage independent of VCC. A zener clamp is typically connected to this input when driving power MOSFETs in systems where VCC is greater the 20 V. Figure 23 shows proper power and control ground connections in a current sensing power MOSFET application. Reference The 5.0 V bandgap reference is trimmed to ± 1.0% tolerance at TJ = 25°C on the UC284X, and ± 2.0% on the UC384X. Its primary purpose is to supply charging current to the oscillator timing capacitor. The reference has short circuit protection and is capable of providing in excess of 20 mA for powering additional control system circuitry. Design Considerations These devices contain a single totem pole output stage that was specifically designed for direct drive of power MOSFETs. It is capable of up to ± 1.0 A peak drive current and has a typical rise and fall time of 50 ns with a 1.0 nF load. Additional internal circuitry has been added to keep the Output in a sinking mode whenever and undervoltage lockout is active. This characteristic eliminates the need for an external pull−down resistor. The SOIC−14 surface mount package provides separate pins for VC (output supply) and Power Ground. Proper implementation will significantly reduce the level of switching transient noise imposed on the control circuitry. This becomes particularly useful when reducing the Ipk(max) clamp level. The separate VC supply input allows the Do not attempt to construct the converter on wire−wrap or plug−in prototype boards. High frequency circuit layout techniques are imperative to prevent pulsewidth jitter. This is usually caused by excessive noise pick−up imposed on the Current Sense or Voltage Feedback inputs. Noise immunity can be improved by lowering circuit impedances at these points. The printed circuit layout should contain a ground plane with low−current signal and high−current switch and output grounds returning on separate paths back to the input filter capacitor. Ceramic bypass capacitors (0.1 mF) connected directly to VCC, VC, and Vref may be required depending upon circuit layout. This provides a low impedance path for filtering the high frequency noise. All high current loops should be kept as short as possible using heavy copper runs to minimize radiated EMI. The Error Amp compensation circuitry and the converter output voltage divider should be located close to the IC and as far as possible from the power switch and other noise generating components. Vref 8(14) RT R Bias R OSC 0.01 CT 47 4(7) + − 2(3) 1(1) 5(9) The diode clamp is required if the Sync amplitude is large enough to cause the bottom side of CT to go more than 300 mV below ground. 1.44 f= (RA + 2RB)C Dmax = RB RA + 2RB EA + 5.0k 5 2 2R R C RA 8 RB 6 5.0k + − + − 4 8(14) R Bias R OSC Q S 3 7 2(3) 1(1) To Additional UCX84XA’s 5(9) 4(7) + − + 2R R External Sync Input R 5.0k MC1455 1 EA Figure 18. External Clock Synchronization Figure 19. External Duty Cycle Clamp and Multi−Unit Synchronization http://onsemi.com 9 UC3844, UC3845, UC2844, UC2845 VCC 7(12) + − Vin 5.0Vref 8(14) R Bias R OSC 4(7) R2 2(3) 1(1) 5(9) VClamp 1.67 R2 R1 +1 + 0.33 x 10−3 R1 R2 R1 + R2 + − + 1.0mA EA 2R R − + 1.0V R1 + − VClamp T + − + − 7(11) Q1 6(10) 5(8) 4(7) 3(5) 1.0M RS 2(3) 1(1) tSoft−Start  3600C in mF 5(9) + − + 1.0mA EA 2R R − + 1.0V C 8(14) R Bias R OSC + − T S R Q + − 5.0Vref Q R Comp/Latch S Ipk(max) ≈ VClamp RS Where: 0 ≤ VClamp ≤ 1.0 V Figure 20. Adjustable Reduction of Clamp Level VCC 7(12) + − Vin Figure 21. Soft−Start Circuit 5.0Vref 8(14) R Bias R OSC 4(7) + − 2(3) R2 1(1) C MPSA63 R1 VClamp 1.67 R2 R1 Ipk(max)≈ VClamp VCC + − 7(11) Q1 5.0Vref + 5(8) 3(5) RS − T S Q − R + Comp/Latch (10) G (8) (5) Control CIrcuitry Ground: To Pin (9) M + − + − + − (11) (12) Vin VPin 5 ≈ RS Ipk rDS(on) rDM(on) + RS + − VClamp 1.0mA 2R R + − + T 6(10) If: SENSEFET = MTP10N10M RS = 200 Then: Vpin 5 = 0.075 Ipk D SENSEFET S K EA S Q − R + Comp/Latch 1.0V 5(9) + 0.33 x 10−3 +1 R1 R2 R1 + R2 RS 1/4 W Power Ground To Input Source Return RS Where: 0 ≤ VClamp ≤ 1.0 V 1− VC 3VClamp C R1 R2 R1 + R2 tSoftstart = − In Virtually lossless current sensing can be achieved with the implement of a SENSEFET power switch. For proper operation during over current conditions, a reduction of the Ipk(max) clamp level must be implemented. Refer to Figures 20 and 22. Figure 22. Adjustable Buffered Reduction of Clamp Level with Soft−Start VCC 7(12) + − Figure 23. Current Sensing Power MOSFET Vin 5.0Vref + − + − 7(11) Q1 + − T − + Q R Comp/Latch S 6(10) 5(8) R 3(5) C RS The addition of the RC filter will eliminate instability caused by the leading edge spike on the current waveform. Figure 24. Current Waveform Spike Suppression http://onsemi.com 10 UC3844, UC3845, UC2844, UC2845 VCC 7(12) + − Vin + 0 + − 7(11) Rg T − + Q R Comp/Latch S 6(10) 5(8) 3(5) RS Series gate resistor Rg will damp any high frequency parasitic oscillations caused by the MOSFET input capacitance and any series wiring inductance in the gate−source circuit. Q1 Q1 6(1) 5(8) 3(5) RS The totem−pole output can furnish negative base current for enhanced transistor turn−off, with the addition of capacitor C1. − Base Charge Removal IB Vin 5.0Vref + − + − C1 Figure 25. MOSFET Parasitic Oscillations Figure 26. Bipolar Transistor Drive 8(14) R Bias R VCC 7(12) + − Isolation Boundary Vin 4(7) + − 2(3) VGS Waveforms + 0 − + OSC 1.0mA EA 2R R 5.0Vref + − + − 7(11) − T − + S Q R Comp/Latch 6(10) 5(8) R 3(5) C RS NS Ipk = Np Figure 27. Isolated MOSFET Drive From VO 2.5V Ri Rd CI 2(3) Rf 1(1) Rf ≥ 8.8 k 5(9) + − EA + 1.0mA 2R R Error Amp compensation circuit for stabilizing any current−mode topology except for boost and flyback converters operating with continuous inductor current. Figure 29. Error Amplifier Compensation ÉÉ É É ÉÉ É ÉÉ 50% DC + 0 − 25% DC NP NS V(pin 1) − 1.4 3 RS + Q1 1(1) MCR 101 2N 3905 2N 3903 5(9) The MCR101 SCR must be selected for a holding of less than 0.5 mA at TA(min). The simple two transistor circuit can be used in place of the SCR as shown. All resistors are 10 k. Figure 28. Latched Shutdown From VO Rp Cp Ri Rd CI 2(3) Rf 1(1) 2.5V + − + 1.0mA EA 2R R 5(9) Error Amp compensation circuit for stabilizing current−mode boost and flyback topologies operating with continuous inductor current. http://onsemi.com 11 UC3844, UC3845, UC2844, UC2845 4.7W 115VA C MDA 202 + 250 56k 4.7k 3300pF MBR1635 T1 2200 MUR110 1N4935 7(12) 8(14) 5.0Vref 0.01 Bias 33k 4(7) OSC 1.0nF 18k 2(3) 100pF 150k 4.7k + − EA − + + T S R Comp/Latch Q 6(10) 5(8) 3(5) 1.0k 470pF 5(9) T1 − Primary: 45 Turns # 26 AWG T1 − Secondary ± 12 V: 9 Turns # 30 AWG T1 − (2 strands) Bifiliar Wound T1 − Secondary 5.0 V: 4 Turns (six strands) T1 − #26 Hexfiliar Wound T1 − Secondary Feedback: 10 Turns #30 AWG T1 − (2 strands) Bifiliar Wound T1 − Core: Ferroxcube EC35−3C8 T1 − Bobbin: Ferroxcube EC35PCB1 T1 − Gap ≈ 0.01" for a primary inductance of 1.0 mH L1 − 15 mH at 5.0 A, Coilcraft Z7156. L2, L3 − 25 mH at 1.0 A, Coilcraft Z7157. 0.5W + + − + 100 + − + 1N4937 7(11) 22W 1N5819 MTP 4N50 MUR110 680pF 2.7k L3 68 1N4935 1000 + 47 1000 + 10 + + L2 10 + + L1 1000 + 5.0V/4.0A 5.0V RTN 12V/0.3A ±12V RTN −12V/0.3A 1N4937 1(1) Figure 30. 27 Watt Off−Line Flyback Regulator Test Line Regulation: Load Regulation: 5.0 V ± 12 V 5.0 V ± 12 V 5.0 V ± 12 V Conditions Vin = 95 VAC to 130 VAC Vin = 115 VAC, Iout = 1.0 A to 4.0 A Vin = 115 VAC, Iout = 100 mA to 300 mA Vin = 115 VAC Vin = 115 VAC Results D = 50 mV or ± 0.5% D = 24 mV or ± 0.1% D = 300 mV or ± 3.0% D = 60 mV or ± 0.25% 40 mVpp 80 mVpp 70% Output Ripple: Efficiency All outputs are at nominal load currents, unless otherwise noted. http://onsemi.com 12 UC3844, UC3845, UC2844, UC2845 Vin = 15V UC3845 7(12) 34V + − 7(11) Vref UVLO 6(10) Oscillator 1.0nF 2(3) + − Error Amplifier + T 0.5mA 2R S − + R 1.0V Current Sense Comparator 5(9) The capacitor’s equivalent series resistance must limit the Drive Output current to 1.0 A. An additional series resistor may be required when using tantalum or other low ESR capacitors. The converter’s output can provide excellent line and load regulation by connecting the R2/R1 resistor divider as shown. Q R PWM Latch 3(5) VO = 2.5 R2 +1 R2 R1 5(8) 1N5819 + 47 Output Load Regulation (open loop configuration) IO (mA) 0 2 9 18 36 VO (V) 29.9 28.8 28.3 27.4 24.4 8(14) R 2.5V 10k Reference Regulator Internal Bias 3.6V + +− − + VCC UVLO − R 4(7) 15 10 + 1N5819 + 47 R2 VO  2 (Vin) Connect to Pin 2 for closed loop operation. 1(1) Figure 31. Step−Up Charge Pump Converter Vin = 15V UC3845 7(12) 34V + − 7(11) Vref UVLO 6(10) Oscillator 1.0nF 2(3) + − Error Amplifier + T 0.5mA 2R S − + R 1.0V Current Sense Comparator 5(9) The capacitor’s equivalent series resistance must limit the Drive Output current to 1.0 A. An additional series resistor may be required when using tantalum or other low ESR capacitors. Q R PWM Latch 3(5) Output Load Regulation IO (mA) 0 2 9 18 32 VO (V) −14.4 −13.2 −12.5 −11.7 −10.6 + 5(8) + 47 8(14) R 2.5V 10k Reference Regulator Internal Bias 3.6V + +− − + VCC UVLO − R 4(7) 15 10 1N5819 1N5819 + 47 VO  − (Vin) 1(1) Figure 32. Voltage−Inverting Charge Pump Converter http://onsemi.com 13 UC3844, UC3845, UC2844, UC2845 ORDERING INFORMATION Device UC3844D UC3844DG UC3844DR2 UC3844DR2G UC3844N UC3844NG UC3845D UC3845DG UC3845DR2 UC3845DR2G UC3845N UC3845NG UC2844D UC2844DG UC2844DR2 UC2844DR2G UC2844N UC2844NG UC2845D UC2845DG UC2845DR2 UC2845DR2G UC2845N UC2845NG TA = −25° to +85°C TA = 0° to +70°C Operating Temperature Range Package SOIC−14 SOIC−14 (Pb−Free) SOIC−14 SOIC−14 (Pb−Free) PDIP−8 PDIP−8 (Pb−Free) SOIC−14 SOIC−14 (Pb−Free) SOIC−14 SOIC−14 (Pb−Free) PDIP−8 PDIP−8 (Pb−Free) SOIC−14 SOIC−14 (Pb−Free) SOIC−14 SOIC−14 (Pb−Free) PDIP−8 PDIP−8 (Pb−Free) SOIC−14 SOIC−14 (Pb−Free) SOIC−14 SOIC−14 (Pb−Free) PDIP−8 PDIP−8 (Pb−Free) Shipping† 55 Units/Rail 55 Units/Rail 2500 Tape & Reel 2500 Tape & Reel 50 Units/Rail 50 Units/Rail 55 Units/Rail 55 Units/Rail 2500 Tape & Reel 2500 Tape & Reel 50 Units/Rail 50 Units/Rail 55 Units/Rail 55 Units/Rail 2500 Tape & Reel 2500 Tape & Reel 50 Units/Rail 50 Units/Rail 55 Units/Rail 55 Units/Rail 2500 Tape & Reel 2500 Tape & Reel 50 Units/Rail 50 Units/Rail †For information on tape and reel specifications, including part orientation and tape sizes, please refer to our Tape and Reel Packaging Specifications Brochure, BRD8011/D. MARKING DIAGRAMS PDIP−8 N SUFFIX CASE 626 8 UC384xN AWL YYWWG 1 8 UC284xN AWL YYWWG 1 1 1 14 UC284xDG AWLYWW 14 UC384xDG AWLYWW 1 SOIC−14 D SUFFIX CASE 751A SOIC−8 D1 SUFFIX CASE 751 8 384x ALYW G x A WL, L YY, Y WW, W G or G = 4 or 5 = Assembly Location = Wafer Lot = Year = Work Week = Pb−Free Package http://onsemi.com 14 UC3844, UC3845, UC2844, UC2845 PACKAGE DIMENSIONS PDIP−8 N SUFFIX CASE 626−05 ISSUE L NOTES: 1. DIMENSION L TO CENTER OF LEAD WHEN FORMED PARALLEL. 2. PACKAGE CONTOUR OPTIONAL (ROUND OR SQUARE CORNERS). 3. DIMENSIONING AND TOLERANCING PER ANSI Y14.5M, 1982. DIM A B C D F G H J K L M N MILLIMETERS MIN MAX 9.40 10.16 6.10 6.60 3.94 4.45 0.38 0.51 1.02 1.78 2.54 BSC 0.76 1.27 0.20 0.30 2.92 3.43 7.62 BSC −−− 10_ 0.76 1.01 INCHES MIN MAX 0.370 0.400 0.240 0.260 0.155 0.175 0.015 0.020 0.040 0.070 0.100 BSC 0.030 0.050 0.008 0.012 0.115 0.135 0.300 BSC −−− 10_ 0.030 0.040 8 5 − B− 1 4 F NOTE 2 − A− L C −T− SEATING PLANE J N D K M M TA B H G 0.13 (0.005) M M SOIC−14 D SUFFIX CASE 751A−03 ISSUE G − A− 14 8 − B− P 7 PL 0.25 (0.010) M B M 1 7 G C R X 45 _ F NOTES: 1. DIMENSIONING AND TOLERANCING PER ANSI Y14.5M, 1982. 2. CONTROLLING DIMENSION: MILLIMETER. 3. DIMENSIONS A AND B DO NOT INCLUDE MOLD PROTRUSION. 4. MAXIMUM MOLD PROTRUSION 0.15 (0.006) PER SIDE. 5. DIMENSION D DOES NOT INCLUDE DAMBAR PROTRUSION. ALLOWABLE DAMBAR PROTRUSION SHALL BE 0.127 (0.005) TOTAL IN EXCESS OF THE D DIMENSION AT MAXIMUM MATERIAL CONDITION. DIM A B C D F G J K M P R MILLIMETERS MIN MAX 8.55 8.75 3.80 4.00 1.35 1.75 0.35 0.49 0.40 1.25 1.27 BSC 0.19 0.25 0.10 0.25 0_ 7_ 5.80 6.20 0.25 0.50 INCHES MIN MAX 0.337 0.344 0.150 0.157 0.054 0.068 0.014 0.019 0.016 0.049 0.050 BSC 0.008 0.009 0.004 0.009 0_ 7_ 0.228 0.244 0.010 0.019 −T− SEATING PLANE D 14 PL 0.25 (0.010) M K TB S M A S J http://onsemi.com 15 UC3844, UC3845, UC2844, UC2845 PACKAGE DIMENSIONS SOIC−8 D1 SUFFIX CASE 751−07 ISSUE AG − X− A 8 5 B 1 S 4 0.25 (0.010) M Y M − Y− G K NOTES: 1. DIMENSIONING AND TOLERANCING PER ANSI Y14.5M, 1982. 2. CONTROLLING DIMENSION: MILLIMETER. 3. DIMENSION A AND B DO NOT INCLUDE MOLD PROTRUSION. 4. MAXIMUM MOLD PROTRUSION 0.15 (0.006) PER SIDE. 5. DIMENSION D DOES NOT INCLUDE DAMBAR PROTRUSION. ALLOWABLE DAMBAR PROTRUSION SHALL BE 0.127 (0.005) TOTAL IN EXCESS OF THE D DIMENSION AT MAXIMUM MATERIAL CONDITION. 6. 751−01 THRU 751−06 ARE OBSOLETE. NEW STANDARD IS 751−07. MILLIMETERS MIN MAX 4.80 5.00 3.80 4.00 1.35 1.75 0.33 0.51 1.27 BSC 0.10 0.25 0.19 0.25 0.40 1.27 0_ 8_ 0.25 0.50 5.80 6.20 INCHES MIN MAX 0.189 0.197 0.150 0.157 0.053 0.069 0.013 0.020 0.050 BSC 0.004 0.010 0.007 0.010 0.016 0.050 0_ 8_ 0.010 0.020 0.228 0.244 C −Z− H D 0.25 (0.010) M SEATING PLANE N X 45 _ 0.10 (0.004) M J ZY S X S DIM A B C D G H J K M N S SOLDERING FOOTPRINT* 1.52 0.060 7.0 0.275 4.0 0.155 0.6 0.024 1.270 0.050 SCALE 6:1 mm inches *For additional information on our Pb−Free strategy and soldering details, please download the ON Semiconductor Soldering and Mounting Techniques Reference Manual, SOLDERRM/D. SENSEFET is a trademark of Semiconductor Components Industries, LLC. ON Semiconductor and are registered trademarks of Semiconductor Components Industries, LLC (SCILLC). SCILLC reserves the right to make changes without further notice to any products herein. SCILLC makes no warranty, representation or guarantee regarding the suitability of its products for any particular purpose, nor does SCILLC assume any liability arising out of the application or use of any product or circuit, and specifically disclaims any and all liability, including without limitation special, consequential or incidental damages. “Typical” parameters which may be provided in SCILLC data sheets and/or specifications can and do vary in different applications and actual performance may vary over time. All operating parameters, including “Typicals” must be validated for each customer application by customer’s technical experts. SCILLC does not convey any license under its patent rights nor the rights of others. SCILLC products are not designed, intended, or authorized for use as components in systems intended for surgical implant into the body, or other applications intended to support or sustain life, or for any other application in which the failure of the SCILLC product could create a situation where personal injury or death may occur. Should Buyer purchase or use SCILLC products for any such unintended or unauthorized application, Buyer shall indemnify and hold SCILLC and its officers, employees, subsidiaries, affiliates, and distributors harmless against all claims, costs, damages, and expenses, and reasonable attorney fees arising out of, directly or indirectly, any claim of personal injury or death associated with such unintended or unauthorized use, even if such claim alleges that SCILLC was negligent regarding the design or manufacture of the part. SCILLC is an Equal Opportunity/Affirmative Action Employer. This literature is subject to all applicable copyright laws and is not for resale in any manner. PUBLICATION ORDERING INFORMATION LITERATURE FULFILLMENT: Literature Distribution Center for ON Semiconductor P.O. Box 5163, Denver, Colorado 80217 USA Phone: 303−675−2175 or 800−344−3860 Toll Free USA/Canada Fax: 303−675−2176 or 800−344−3867 Toll Free USA/Canada Email: orderlit@onsemi.com N. American Technical Support: 800−282−9855 Toll Free USA/Canada Europe, Middle East and Africa Technical Support: Phone: 421 33 790 2910 Japan Customer Focus Center Phone: 81−3−5773−3850 ON Semiconductor Website: www.onsemi.com Order Literature: http://www.onsemi.com/orderlit For additional information, please contact your local Sales Representative http://onsemi.com 16 UC3844/D