UC3842B, UC3843B, UC2842B, UC2843B, NCV3843BV High Performance Current Mode Controllers The UC3842B, UC3843B series are high performance fixed frequency current mode controllers. They are specifically designed for Off-Line and DC-DC converter applications offering the designer a cost-effective solution with minimal external components. These integrated circuits feature a trimmed oscillator for precise duty cycle control, 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, programmable output deadtime, and a latch for single pulse metering. These devices are available in an 8-pin dual-in-line and surface mount (SOIC-8) 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 UCX842B has UVLO thresholds of 16 V (on) and 10 V (off), ideally suited for off-line converters. The UCX843B is tailored for lower voltage applications having UVLO thresholds of 8.5 V (on) and 7.6 V (off). Trimmed Oscillator for Precise Frequency Control Oscillator Frequency Guaranteed at 250 kHz Current Mode Operation to 500 kHz Automatic Feed Forward Compensation Latching PWM for Cycle-By-Cycle Current Limiting Internally Trimmed Reference with Undervoltage Lockout High Current Totem Pole Output Undervoltage Lockout with Hysteresis Low Startup and Operating Current Pb-Free Packages are Available VCC Vref 5.0V Reference 8(14) R RT/CT 1 SOIC-14 D SUFFIX CASE 751A 14 1 SOIC-8 D1 SUFFIX CASE 751 8 1 1 8 2 7 3 6 4 5 Vref VCC Output GND (Top View) Compensation NC Voltage Feedback NC Current Sense NC RT/CT VCC Undervoltage Lockout 1 14 2 13 3 12 4 11 5 10 6 9 7 8 Vref NC VCC VC Output GND Power Ground (Top View) VC ORDERING INFORMATION 7(11) See detailed ordering and shipping information in the package dimensions section on page 17 of this data sheet. Output Oscillator 4(7) 2(3) Output Compensation 1(1) 8 Compensation Voltage Feedback Current Sense RT/CT 7(12) Vref Undervoltage Lockout R Voltage Feedback Input PDIP-8 N SUFFIX CASE 626 PIN CONNECTIONS Features * * * * * * * * * * http://onsemi.com 6(10) Power Ground 5(8) Latching PWM + - Error Amplifier DEVICE MARKING INFORMATION See general marking information in the device marking section on page 19 of this data sheet. Current Sense 3(5) Input GND 5(9) Pin numbers in parenthesis are for the D suffix SOIC-14 package. Figure 1. Simplified Block Diagram (c) Semiconductor Components Industries, LLC, 2008 September, 2008 - Rev. 12 1 Publication Order Number: UC3842B/D UC3842B, UC3843B, UC2842B, UC2843B, NCV3843BV MAXIMUM RATINGS Rating Symbol Value Unit Bias and Driver Voltages (Zero Series Impedance, see also Total Device spec) VCC, VC 30 V Total Power Supply and Zener Current (ICC + IZ) 30 mA IO 1.0 A Output Current, Source or Sink Output Energy (Capacitive Load per Cycle) W 5.0 mJ Current Sense and Voltage Feedback Inputs Vin - 0.3 to + 5.5 V Error Amp Output Sink Current IO 10 mA PD RqJA 862 145 mW C/W PD RqJA 702 178 mW C/W PD RqJA 1.25 100 W C/W TJ +150 C Power Dissipation and Thermal Characteristics D Suffix, Plastic Package, SOIC-14 Case 751A Maximum Power Dissipation @ TA = 25C Thermal Resistance, Junction-to-Air D1 Suffix, Plastic Package, SOIC-8 Case 751 Maximum Power Dissipation @ TA = 25C Thermal Resistance, Junction-to-Air N Suffix, Plastic Package, Case 626 Maximum Power Dissipation @ TA = 25C Thermal Resistance, Junction-to-Air Operating Junction Temperature Operating Ambient Temperature UC3842B, UC3843B UC2842B, UC2843B UC3842BV, UC3843BV NCV3843BV Storage Temperature Range TA Tstg 0 to 70 - 25 to + 85 -40 to +105 -40 to +125 - 65 to +150 C 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. This device series contains ESD protection and exceeds the following tests: Human Body Model 4000 V per JEDEC Standard JESD22-A114B Machine Model Method 200 V per JEDEC Standard JESD22-A115-A 2. This device contains latch-up protection and exceeds 100 mA per JEDEC Standard JESD78 http://onsemi.com 2 UC3842B, UC3843B, UC2842B, UC2843B, NCV3843BV ELECTRICAL CHARACTERISTICS (VCC = 15 V [Note 3], RT = 10 k, CT = 3.3 nF. For typical values TA = 25C, for min/max values TA is the operating ambient temperature range that applies [Note 4], unless otherwise noted.) UC284XB Characteristics UC384XB, XBV Symbol Min Typ Max Min Typ Max Unit REFERENCE SECTION Reference Output Voltage (IO = 1.0 mA, TJ = 25C) Vref 4.95 5.0 5.05 4.9 5.0 5.1 V Line Regulation (VCC = 12 V to 25 V) Regline - 2.0 20 - 2.0 20 mV Load Regulation (IO = 1.0 mA to 20 mA) Regload - 3.0 25 - 3.0 25 mV Temperature Stability TS - 0.2 - - 0.2 - mV/C Total Output Variation over Line, Load, and Temperature Vref 4.9 - 5.1 4.82 - 5.18 V Output Noise Voltage (f = 10 Hz to 10 kHz, TJ = 25C) Vn - 50 - - 50 - mV Long Term Stability (TA = 125C for 1000 Hours) S - 5.0 - - 5.0 - mV ISC - 30 - 85 -180 - 30 - 85 -180 mA 49 48 225 52 - 250 55 56 275 49 48 225 52 - 250 55 56 275 Output Short Circuit Current OSCILLATOR SECTION Frequency TJ = 25C TA = Tlow to Thigh TJ = 25C (RT = 6.2 k, CT = 1.0 nF) fOSC kHz Frequency Change with Voltage (VCC = 12 V to 25 V) DfOSC/DV - 0.2 1.0 - 0.2 1.0 % Frequency Change with Temperature, TA = Tlow to Thigh DfOSC/DT - 1.0 - - 0.5 - % Oscillator Voltage Swing (Peak-to-Peak) VOSC - 1.6 - - 1.6 - V Discharge Current (VOSC = 2.0 V) TJ = 25C, TA = Tlow to Thigh Idischg 7.8 7.5 - 8.3 - - 8.8 8.8 - 7.8 7.6 7.2 8.3 - - 8.8 8.8 8.8 UC284XB, UC384XB TA = Tlow to Thigh UC384XBV mA ERROR AMPLIFIER SECTION Voltage Feedback Input (VO = 2.5 V) Input Bias Current (VFB = 5.0 V) Open Loop Voltage Gain (VO = 2.0 V to 4.0 V) Unity Gain Bandwidth (TJ = 25C) 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) VFB 2.45 2.5 2.55 2.42 2.5 2.58 V IIB - - 0.1 -1.0 - - 0.1 - 2.0 mA AVOL 65 90 - 65 90 - dB BW 0.7 1.0 - 0.7 1.0 - MHz PSRR 60 70 - 60 70 - dB ISink 2.0 - 0.5 12 -1.0 - - 2.0 - 0.5 12 -1.0 - - VOH VOL 5.0 6.2 - 5.0 6.2 - - - 0.8 - 1.1 - - - 0.8 0.8 1.1 1.2 2.85 - 3.0 - 3.15 - 2.85 2.85 3.0 3.0 3.15 3.25 0.9 - 1.0 - 1.1 - 0.9 0.85 1.0 1.0 1.1 1.1 PSRR - 70 - - 70 - dB IIB - - 2.0 -10 - - 2.0 -10 mA tPLH(In/Out) - 150 300 - 150 300 ns ISource 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) UC284XB, UC384XB UC384XBV mA V CURRENT SENSE SECTION Current Sense Input Voltage Gain (Notes 5 and 6) UC284XB, UC384XB UC384XBV AV Maximum Current Sense Input Threshold (Note 5) UC284XB, UC384XB UC384XBV Vth Power Supply Rejection Ratio (VCC = 12 V to 25 V, Note 5) Input Bias Current Propagation Delay (Current Sense Input to Output) V/V V 3. Adjust VCC above the Startup threshold before setting to 15 V. 4. Low duty cycle pulse techniques are used during test to maintain junction temperature as close to ambient as possible. Tlow = 0C for UC3842B, UC3843B; -25C for UC2842B, UC2843B; -40C for UC3842BV, UC3843BV Thigh = +70C for UC3842B, UC3843B; +85C for UC2842B, UC2843B; +105C for UC3842BV, UC3843BV NCV3843BV: Tlow = -40C, Thigh = +125C. Guaranteed by design. NCV prefix is for automotive and other applications requiring site and change control. 5. This parameter is measured at the latch trip point with VFB = 0 V. 6. Comparator gain is defined as: AV DV Output Compensation DV Current Sense Input http://onsemi.com 3 UC3842B, UC3843B, UC2842B, UC2843B, NCV3843BV ELECTRICAL CHARACTERISTICS (VCC = 15 V [Note 7], RT = 10 k, CT = 3.3 nF. For typical values TA = 25C, for min/max values TA is the operating ambient temperature range that applies [Note 8], unless otherwise noted.) UC284XB Characteristics UC384XB, XBV Symbol Min Typ Max Min Typ Max Unit VOL - - - 13 - 12 0.1 1.6 - 13.5 - 13.4 0.4 2.2 - - - - - - - 13 12.9 12 0.1 1.6 1.6 13.5 13.5 13.4 0.4 2.2 2.3 - - - VOL(UVLO) - 0.1 1.1 - 0.1 1.1 V Output Voltage Rise Time (CL = 1.0 nF, TJ = 25C) tr - 50 150 - 50 150 ns Output Voltage Fall Time (CL = 1.0 nF, TJ = 25C) tf - 50 150 - 50 150 ns 15 7.8 16 8.4 17 9.0 14.5 7.8 16 8.4 17.5 9.0 9.0 7.0 10 7.6 11 8.2 8.5 7.0 10 7.6 11.5 8.2 94 - - 96 - - - - 0 94 93 - 96 96 - - - 0 - 0.3 0.5 - 0.3 0.5 - 12 17 - 12 17 30 36 - 30 36 - OUTPUT SECTION Output Voltage Low State (ISink = 20 mA) (ISink = 200 mA) High State (ISource = 20 mA) UC284XB, UC384XB UC384XBV UC284XB, UC384XB UC384XBV VOH (ISource = 200 mA) Output Voltage with UVLO Activated (VCC = 6.0 V, ISink = 1.0 mA) V UNDERVOLTAGE LOCKOUT SECTION Startup Threshold (VCC) Minimum Operating Voltage After Turn-On (VCC) Vth UCX842B, BV UCX843B, BV UCX842B, BV UCX843B, BV VCC(min) V V PWM SECTION Duty Cycle Maximum UC284XB, UC384XB Maximum UC384XBV Minimum DC(max) DC(min) % TOTAL DEVICE Power Supply Current Startup (VCC = 6.5 V for UCX843B, Startup VCC 14 V for UCX842B, BV) (Note 7) ICC + IC Power Supply Zener Voltage (ICC = 25 mA) VZ mA V 7. Adjust VCC above the Startup threshold before setting to 15 V. 8. Low duty cycle pulse techniques are used during test to maintain junction temperature as close to ambient as possible. Tlow = 0C for UC3842B, UC3843B; -25C for UC2842B, UC2843B; -40C for UC3842BV, UC3843BV Thigh = +70C for UC3842B, UC3843B; +85C for UC2842B, UC2843B; +105C for UC3842BV, UC3843BV NCV3843BV: Tlow = -40C, Thigh = +125C. Guaranteed by design. NCV prefix is for automotive and other applications requiring site and change control. http://onsemi.com 4 UC3842B, UC3843B, UC2842B, UC2843B, NCV3843BV 80 100 % DT, PERCENT OUTPUT DEADTIME 20 8.0 5.0 VCC = 15 V TA = 25C 2.0 0.8 10 k 20 k Freq + 50 k 100 k 200 k 500 k fOSC, OSCILLATOR FREQUENCY (kHz) 1 Vosc Ct Vosc ) Ct Idis*I IRt Rt 1. CT = 10 nF 50 2. CT = 5.0 nF 3. CT = 2.0 nF 4. CT = 1.0 nF 20 5. CT = 500 pF 6. CT = 200 pF 10 7. CT = 100 pF D max , MAXIMUM OUTPUT DUTY CYCLE (%) I dischg , DISCHARGE CURRENT (mA) 7 VCC = 15 V TA = 25C 2.0 20 k 50 k 100 k 200 k 500 k fOSC, OSCILLATOR FREQUENCY (kHz) 1.0 M Figure 3. Output Deadtime versus Oscillator Frequency VCC = 15 V VOSC = 2.0 V 8.5 8.0 7.5 0 25 50 75 TA, AMBIENT TEMPERATURE (C) 100 125 100 90 80 60 Idischg = 8.8 mA 50 40 0.8 1.0 2.0 3.0 4.0 RT, TIMING RESISTOR (kW) VCC = 15 V CT = 3.3 nF TA = 25C 5.0 6.0 7.0 8.0 Figure 5. Maximum Output Duty Cycle versus Timing Resistor VCC = 15 V AV = -1.0 TA = 25C VCC = 15 V AV = -1.0 TA = 25C 3.0 V 20 mV/DIV 2.50 V Idischg = 7.5 mA 70 Figure 4. Oscillator Discharge Current versus Temperature 2.55 V 6 Where: Vosc = 1.7 V IRt = Vref/Rt Idis = 8.3 mA 9.0 -25 1 5 Figure 2. Timing Resistor versus Oscillator Frequency 7.0 -55 3 2 5.0 1.0 10 k 1.0 M 4 20 mV/DIV R T, TIMING RESISTOR (k ) 50 2.5 V 2.45 V 2.0 V 0.5 ms/DIV 1.0 ms/DIV Figure 6. Error Amp Small Signal Transient Response Figure 7. Error Amp Large Signal Transient Response http://onsemi.com 5 UC3842B, UC3843B, UC2842B, UC2843B, NCV3843BV http://onsemi.com 6 Gain 60 0 30 60 40 90 Phase 20 120 0 150 100 1.0 k 10 k 100 k 180 10 M 1.0 M 0.8 TA = 25C 0.6 TA = 125C 0.4 TA = -55C 0.2 0 0 Figure 8. Error Amp Open Loop Gain and Phase versus Frequency Figure 9. Current Sense Input Threshold versus Error Amp Output Voltage AAAA -4.0 -8.0 -12 AAAA AAAA AAAA TA = 125C -16 -20 AAA AAA TA = -55C TA = 25C 20 40 60 80 100 120 8.0 AAA AAA 110 VCC = 15 V RL 0.1 W 90 70 50 -55 -25 0 25 50 75 100 Iref, REFERENCE SOURCE CURRENT (mA) TA, AMBIENT TEMPERATURE (C) Figure 10. Reference Voltage Change versus Source Current Figure 11. Reference Short Circuit Current versus Temperature V O , OUTPUT VOLTAGE CHANGE (2.0 mV/DIV) V O , OUTPUT VOLTAGE CHANGE (2.0 mV/DIV) VCC = 15 V 1.0 2.0 4.0 6.0 VO, ERROR AMP OUTPUT VOLTAGE (V) VCC = 15 V 0 1.2 f, FREQUENCY (Hz) 0 -24 Vth, CURRENT SENSE INPUT THRESHOLD (V) 80 -20 10 Vref , REFERENCE VOLTAGE CHANGE (mV) VCC = 15 V VO = 2.0 V to 4.0 V RL = 100 K TA = 25C , EXCESS PHASE (DEGREES) 100 I SC , REFERENCE SHORT CIRCUIT CURRENT (mA) A VOL , OPEN LOOP VOLTAGE GAIN (dB) UC3842B, UC3843B, UC2842B, UC2843B, NCV3843BV VCC = 15 V IO = 1.0 mA to 20 mA TA = 25C 2.0 ms/DIV Figure 12. Reference Load Regulation VCC = 12 V to 25 TA = 25C 2.0 ms/DIV Figure 13. Reference Line Regulation http://onsemi.com 7 125 0 -1.0 -2.0 Source Saturation (Load to Ground) VCC = 15 V 80 ms Pulsed Load 120 Hz Rate VCC = 15 V CL = 1.0 nF TA = 25C 90% TA = -55C 3.0 TA = -55C 2.0 TA = 25C GND 400 600 200 10% 800 IO, OUTPUT LOAD CURRENT (mA) 50 ns/DIV Figure 14. Output Saturation Voltage versus Load Current Figure 15. Output Waveform 25 20 V/DIV 100 mA/DIV I CC , SUPPLY CURRENT 20 15 10 5 0 0 10 100 ns/DIV AAAA AAAA AAAA AAAA RT = 10 k CT = 3.3 nF VFB = 0 V ISense = 0 V TA = 25C UCX842B VCC = 30 V CL = 15 pF TA = 25C UCX843B 0 Sink Saturation (Load to VCC) I CC , SUPPLY CURRENT (mA) 1.0 0 AAAAAAAAAA AAA AAAAAAAAAAAAAA AAAAA AAAA AAAA AAAA AAA AAA AAA AAAA AAA AAAA AA VCC TA = 25C V O , OUTPUT VOLTAGE Vsat, OUTPUT SATURATION VOLTAGE (V) UC3842B, UC3843B, UC2842B, UC2843B, NCV3843BV 20 30 40 VCC, SUPPLY VOLTAGE (V) Figure 16. Output Cross Conduction Figure 17. Supply Current versus Supply Voltage PIN FUNCTION DESCRIPTION 8-Pin 14-Pin Function 1 1 Compensation 2 3 Voltage Feedback 3 5 Current Sense 4 7 RT/CT The Oscillator frequency and maximum Output duty cycle are programmed by connecting resistor RT to Vref and capacitor CT to ground. Operation to 500 kHz is possible. GND This pin is the combined control circuitry and power ground. 6 10 Output 7 12 VCC This pin is the positive supply of the control IC. 8 14 Vref This is the reference output. It provides charging current for capacitor CT through resistor RT. 8 Power Ground 11 VC The Output high state (VOH) is set by the voltage applied to this pin. With a separate power source connection, it can reduce the effects of switching transient noise on the control circuitry. 9 GND This pin is the control circuitry ground return and is connected back to the power source ground. 2,4,6,1 3 NC 5 Description This pin is the 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. This output directly drives the gate of a power MOSFET. Peak currents up to 1.0 A are sourced and sunk by this pin. This pin is a separate power ground return that is connected back to the power source. It is used to reduce the effects of switching transient noise on the control circuitry. No connection. These pins are not internally connected. http://onsemi.com 8 UC3842B, UC3843B, UC2842B, UC2843B, NCV3843BV OPERATING DESCRIPTION The UC3842B, UC3843B 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 18. This occurs when the power supply is operating and the load is removed, or at the beginning of a soft-start interval (Figures 24, 25). 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) Oscillator 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. 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. The oscillator thresholds are temperature compensated to within 6% at 50 kHz. Also because of industry trends moving the UC384X into higher and higher frequency applications, the UC384XB is guaranteed to within 10% at 250 kHz. These internal circuit refinements minimize variations of oscillator frequency and maximum output duty cycle. The results are shown in Figures 4 and 5. 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 21. 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 22. By tailoring the clock waveform, accurate Output duty cycle clamping can be achieved. 3.0 (1.0 V) + 1.4 V = 8800 W 0.5 mA Current Sense Comparator and PWM Latch The UC3842B, UC3843B 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 peak 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 to 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 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 23. 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 27). Error Amplifier 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 8). The non-inverting 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 provided for external loop compensation (Figure 32). The output voltage is offset by two diode drops (1.4 V) and divided by three before it connects to the non-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). http://onsemi.com 9 UC3842B, UC3843B, UC2842B, UC2843B, NCV3843BV VCC VCC 7(12) 36V Vref Reference Regulator 8(14) R 2.5V RT Vin + - VCC UVLO Internal Bias R + - 3.6V (See Text) VC 7(11) Vref UVLO Output Q1 Oscillator CT 4(7) 6(10) + 1.0mA S Voltage Feedback Input 2(3) Output/ Compensation 1(1) 2R Q R R Error Amplifier Power Ground PWM Latch 1.0V Current Sense Comparator GND 5(8) Current Sense Input 3(5) 5(9) Pin numbers adjacent to terminals are for the 8-pin dual-in-line package. Pin numbers in parenthesis are for the D suffix SOIC-14 package. = Sink Only Positive True Logic Figure 18. Representative Block Diagram Capacitor CT Latch "Set" Input Output/ Compensation Current Sense Input Latch "Reset" Input Output Small RT/Large CT Large RT/Small CT Figure 19. Timing Diagram http://onsemi.com 10 RS UC3842B, UC3843B, UC2842B, UC2843B, NCV3843BV Undervoltage Lockout Design Considerations 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 UCX842B, and 8.4 V/7.6 V for the UCX843B. The Vref comparator upper and lower thresholds are 3.6 V/3.4 V. The large hysteresis and low startup current of the UCX842B makes it ideally suited in off-line converter applications where efficient bootstrap startup techniques are required (Figure 34). The UCX843B 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 (VCC) for the UCX842B is 11 V and 8.2 V for the UCX843B. 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 an 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 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 than 20 V. Figure 26 shows proper power and control ground connections in a current-sensing power MOSFET application. Do not attempt to construct the converter on wire-wrap or plug-in prototype boards. High frequency circuit layout techniques are imperative to prevent pulse-width 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. Current mode converters can exhibit subharmonic oscillations when operating at a duty cycle greater than 50% with continuous inductor current. This instability is independent of the regulator's closed loop characteristics and is caused by the simultaneous operating conditions of fixed frequency and peak current detecting. Figure 20A shows the phenomenon graphically. At t0, switch conduction begins, causing the inductor current to rise at a slope of m1. This slope is a function of the input voltage divided by the inductance. At t1, the Current Sense Input reaches the threshold established by the control voltage. This causes the switch to turn off and the current to decay at a slope of m2, until the next oscillator cycle. The unstable condition can be shown if a perturbation is added to the control voltage, resulting in a small DI (dashed line). With a fixed oscillator period, the current decay time is reduced, and the minimum current at switch turn-on (t2) is increased by DI + DI m2/m1. The minimum current at the next cycle (t3) decreases to (DI + DI m2/m1) (m2/m1). This perturbation is multiplied by m2/m1 on each succeeding cycle, alternately increasing and decreasing the inductor current at switch turn-on. Several oscillator cycles may be required before the inductor current reaches zero causing the process to commence again. If m2/m1 is greater than 1, the converter will be unstable. Figure 20B shows that by adding an artificial ramp that is synchronized with the PWM clock to the control voltage, the DI perturbation will decrease to zero on succeeding cycles. This compensating ramp (m3) must have a slope equal to or slightly greater than m2/2 for stability. With m2/2 slope compensation, the average inductor current follows the control voltage, yielding true current mode operation. The compensating ramp can be derived from the oscillator and added to either the Voltage Feedback or Current Sense inputs (Figure 33). Reference The 5.0 V bandgap reference is trimmed to 1.0% tolerance at TJ = 25C on the UC284XB, and 2.0% on the UC384XB. 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. http://onsemi.com 11 UC3842B, UC3843B, UC2842B, UC2843B, NCV3843BV (A) DI Control Voltage m2 m1 Inductor Current Dl ) Dl m2 m1 Dl ) Dl m2 m2 m1 m1 Vref 8(14) Oscillator Period t0 t1 t2 External Sync Input m3 DI Bias RT t3 (B) Control Voltage R R Osc 4(7) CT + 0.01 2R m1 2(3) 47 m2 Inductor Current R EA 1(1) 5(9) Oscillator Period t4 t5 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. t6 Figure 20. Continuous Current Waveforms Figure 21. External Clock Synchronization VCC Vin 7(12) 5.0V Ref 8(14) 8(14) 6 Q1 Osc 5.0k 3 5.0k 2 7(11) + - R 4 4(7) Osc R 5 R Bias 8 + - Bias R RA RB R 4(7) Q Q 2R S S 1.0 mA + 7 R 2R R EA 2(3) 1.0V C 5.0k MC1455 2(3) EA 6(10) VClamp + R2 5(8) Comp/Latch R 3(5) 1(1) 1 R1 5(9) 1(1) f + 1.44 (RA ) 2RB)C D(max) + RB RA ) 2RB 5(9) To Additional UCX84XBs Figure 22. External Duty Cycle Clamp and Multi-Unit Synchronization VClamp 1.67 R2 )1 R1 + 0.33x10-3 R1R)1R2R2 Where: 0 VClamp 1.0 V Ipk(max) [ VClamp RS Figure 23. Adjustable Reduction of Clamp Level http://onsemi.com 12 RS UC3842B, UC3843B, UC2842B, UC2843B, NCV3843BV VCC Vin 7(12) 5.0V Ref 8(14) + - R Bias 5.0V Ref 8(14) R 7(11) + - R Bias Q1 Osc R 4(7) Q Q EA C 1.0V R1 3(5) MPSA63 VClamp [ tSoftStart + * In 1 * Figure 24. Soft-Start Circuit VCC 1.67 RR21 ) 1 C 5(9) Where: 0 VClamp 1.0 V R1R2 VC C R1 ) R2 3VClamp Ipk(max) [ VClamp RS Figure 25. Adjustable Buffered Reduction of Clamp Level with Soft-Start Vin VPin 5 [ (12) RS Ipk rDS(on) rDM(on) ) RS VCC If: SENSEFET = MTP10N10M RS = 200 5.0V Ref Vin 7(12) Then : VPin5 [ 0.075Ipk + - 5.0V Ref D (11) + - RS 5(9) 1(1) tSoft-Start 3600C in mF 5(8) Comp/Latch 1(1) R 2R R 1.0V R2 S 1.0mA 2(3) R 2R R EA 2(3) + 1.0M S 1.0 mA Osc 4(7) 6(10) VClamp + + - + - SENSEFET S K (10) 7(11) + - G Q1 M 6(10) S Q R S (8) Q 5(8) R Comp/Latch (5) RS 1/4 W Power Ground: To Input Source Return Comp/Latch 3(5) R C RS Control Circuitry Ground: To Pin (9) Virtually lossless current sensing can be achieved with the implementation 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 23 and 25. The addition of the RC filter will eliminate instability caused by the leading edge spike on the current waveform. Figure 26. Current Sensing Power MOSFET Figure 27. Current Waveform Spike Suppression http://onsemi.com 13 UC3842B, UC3843B, UC2842B, UC2843B, NCV3843BV VCC Vin IB 7(12) Vin + 0 5.0V Ref + - Base Charge Removal 7(11) + - C1 Rg Q1 Q1 6(10) 6(10) S Q R 5(8) 5(8) Comp/Latch 3(5) RS 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. The totem pole output can furnish negative base current for enhanced transistor turn-off, with the addition of capacitor C1. Figure 28. MOSFET Parasitic Oscillations Figure 29. Bipolar Transistor Drive Vin VCC 8(14) R Bias 7(12) R Isolation Boundary Osc 5.0V Ref 4(7) + 7(11) + - Q1 + 50% DC Q 5(8) Ipk + R Comp/Latch 2(3) 0 - 6(10) 25% DC V(Pin1) * 1.4 NS Np 3RS R 3(5) C RS NS 1.0 mA 2R + 0 S + VGS Waveforms EA R 1(1) MCR 101 2N 3905 5(9) 2N 3903 NP The MCR101 SCR must be selected for a holding of < 0.5 mA @ TA(min). The simple two transistor circuit can be used in place of the SCR as shown. All resistors are 10 k. Figure 30. Isolated MOSFET Drive Figure 31. Latched Shutdown http://onsemi.com 14 UC3842B, UC3843B, UC2842B, UC2843B, NCV3843BV From VO 2.5V + Ri 1.0mA 2R 2(3) Cf Rd EA Rf R 1(1) Rf 8.8 k 5(9) Error Amp compensation circuit for stabilizing any current mode topology except for boost and flyback converters operating with continuous inductor current. From VO 2.5V + Rp Cp 1.0mA Ri 2(3) Cf Rd 2R R EA Rf 1(1) 5(9) Error Amp compensation circuit for stabilizing current mode boost and flyback topologies operating with continuous inductor current. Figure 32. Error Amplifier Compensation VCC Vin 7(12) 36V 8(14) RT RSlope CT Rd + + 2(3) Cf Rf 1(1) 7(11) Osc 4(7) 1.0mA Ri + - Bias R MPS3904 From VO 5.0V Ref R -m R EA R 1.0V 6(10) S 2R Q m - 3.0m 5(9) The buffered oscillator ramp can be resistively summed with either the voltage feedback or current sense inputs to provide slope compensation. Figure 33. Slope Compensation http://onsemi.com 15 5(8) Comp/Latch 3(5) RS UC3842B, UC3843B, UC2842B, UC2843B, NCV3843BV L1 MBR1635 4.7W + MDA 202 4.7k 250 3300 pF 56k 115 Vac T1 2200 + 1000 + 5.0V RTN MUR110 1N4935 7(12) + 1N4935 68 1000 + 1000 8(14) 0.01 R R 10 + 10 + -12V/0.3A + - Bias 10k 12V/0.3A + 12V RTN 1N4937 5.0V Ref + L2 47 100 5.0V/4.0A MUR110 680pF L3 7(11) + - 2.7k 22 1N4937 Osc 4(7) 4700pF 1N5819 S 2(3) 4.7k 100 pF MTP 4N50 6(10) + 18k Q R EA 150k 5(8) 1.0k Comp/Latch 3(5) 1(1) 0.5 470pF 5(9) Figure 34. 27 W Off-Line Flyback Regulator Test Conditions Results Line Regulation: 5.0 V 12 V Vin = 95 to 130 Vac D = 50 mV or 0.5% D = 24 mV or 0.1% Load Regulation: 5.0 V Vin = 115 Vac, Iout = 1.0 A to 4.0 A Vin = 115 Vac, Iout = 100 mA to 300 mA D = 300 mV or 3.0% 12 V Output Ripple: Efficiency 5.0 V 12 V L1 - 15 mH at 5.0 A, Coilcraft Z7156 L2, L3 - 25 mH at 5.0 A, Coilcraft Z7157 D = 60 mV or 0.25% Vin = 115 Vac 40 mVpp 80 mVpp Vin = 115 Vac 70% All outputs are at nominal load currents, unless otherwise noted http://onsemi.com 16 T1 - Primary: 45 Turns #26 AWG Secondary 12 V: 9 Turns #30 AWG (2 Strands) Bifiliar Wound Secondary 5.0 V: 4 Turns (six strands) #26 Hexfiliar Wound Secondary Feedback: 10 Turns #30 AWG (2 strands) Bifiliar Wound Core: Ferroxcube EC35-3C8 Bobbin: Ferroxcube EC35PCB1 Gap: 0.10" for a primary inductance of 1.0 mH UC3842B, UC3843B, UC2842B, UC2843B, NCV3843BV ORDERING INFORMATION Package Shipping UC2842BD SOIC-14 55 Units/Rail UC2842BDG SOIC-14 (Pb-Free) 55 Units/Rail UC2842BD1 SOIC-8 98 Units/Rail SOIC-8 (Pb-Free) 98 Units/Rail SOIC-8 2500 Tape & Reel SOIC-8 (Pb-Free) 2500 Tape & Reel Device Operating Temperature Range UC2842BD1G UC2842BD1R2 TA = -25 to +85C UC2842BD1R2G PDIP-8 UC2842BN PDIP-8 (Pb-Free) UC2842BNG PDIP-8 UC3842BN 1000 Units/Rail UC3842BNG PDIP-8 (Pb-Free) UC3842BD SOIC-14 55 Units/Rail UC3842BDG SOIC-14 (Pb-Free) 55 Units/Rail SOIC-14 2500 Tape & Reel SOIC-14 (Pb-Free) 2500 Tape & Reel UC3842BDR2 UC3842BDR2G TA = 0 to +70C SOIC-8 98 Units/Rail UC3842BD1G SOIC-8 (Pb-Free) 98 Units/Rail UC3842BD1R2 SOIC-8 UC3842BD1 UC3842BD1R2G SOIC-8 (Pb-Free) UC3842BVDR2 SOIC-14 UC3842BVDR2G SOIC-14 (Pb-Free) UC3842BVD1 UC3842BVD1G TA = -40 to +105C 2500 Tape & Reel SOIC-8 98 Units/Rail SOIC-8 (Pb-Free) 98 Units/Rail SOIC-8 2500 Tape & Reel UC3842BVD1R2G SOIC-8 (Pb-Free) 2500 Tape & Reel UC2843BD SOIC-14 55 Units/Rail UC2843BDG SOIC-14 (Pb-Free) 55 Units/Rail SOIC-14 2500 Tape & Reel SOIC-14 (Pb-Free) 2500 Tape & Reel UC3842BVD1R2 UC2843BDR2 UC2843BDR2G TA = -25 to +85C SOIC-8 98 Units/Rail UC2843BD1G SOIC-8 (Pb-Free) 98 Units/Rail UC2843BD1R2 SOIC-8 2500 Tape & Reel SOIC-8 (Pb-Free) 2500 Tape & Reel PDIP-8 1000 Units/Rail PDIP-8 (Pb-Free) 1000 Units/Rail UC2843BD1 UC2843BD1R2G UC2843BN TA = -25 to +85C UC2843BNG 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. http://onsemi.com 17 UC3842B, UC3843B, UC2842B, UC2843B, NCV3843BV ORDERING INFORMATION Package Shipping UC3843BD SOIC-14 55 Units/Rail UC3843BDG SOIC-14 (Pb-Free) 55 Units/Rail UC3843BDR2 SOIC-14 2500 Tape & Reel UC3843BDR2G SOIC-14 (Pb-Free) 2500 Tape & Reel SOIC-8 98 Units/Rail SOIC-8 (Pb-Free) 98 Units/Rail Device Operating Temperature Range UC3843BD1 UC3843BD1G UC3843BD1R2 TA = 0 to +70C SOIC-8 UC3843BD1R2G SOIC-8 (Pb-Free) UC3843BDR2 SOIC-14 UC3843BDR2G SOIC-14 (Pb-Free) UC3843BN 2500 Tape & Reel PDIP-8 1000 Units/Rail UC3843BNG PDIP-8 (Pb-Free) 1000 Units/Rail UC3843BVD SOIC-14 55 Units/Rail UC3843BVDG SOIC-14 (Pb-Free) 55 Units/Rail UC3843BVDR2 SOIC-14 2500 Tape & Reel UC3843BVDR2G SOIC-14 (Pb-Free) 2500 Tape & Reel SOIC-8 98 Units/Rail SOIC-8 (Pb-Free) 98 Units/Rail SOIC-8 2500 Tape & Reel SOIC-8 (Pb-Free) 2500 Tape & Reel PDIP-8 1000 Units/Rail PDIP-8 (Pb-Free) 1000 Units/Rail SOIC-14 2500 Tape & Reel SOIC-14 (Pb-Free) 2500 Tape & Reel UC3843BVD1 UC3843BVD1G TA = -40 to +105C UC3843BVD1R2 UC3843BVD1R2G UC3843BVN UC3843BVNG NCV3843BVDR2 NCV3843BVDR2G TA = -40 to +125C 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. http://onsemi.com 18 UC3842B, UC3843B, UC2842B, UC2843B, NCV3843BV MARKING DIAGRAMS PDIP-8 N SUFFIX CASE 626 8 8 UC384xBN AWL YYWWG 8 UC3843BVN AWL YYWWG 1 UC284xBN AWL YYWWG 1 1 SOIC-14 D SUFFIX CASE 751A 14 14 UC384xBDG AWLYWW 1 14 * UC384xBVDG AWLYWW UC284xBDG AWLYWW 1 1 SOIC-8 D1 SUFFIX CASE 751 8 8 8 384xB ALYW G 1 384xB ALYWV G 1 284xB ALYW G 1 x A WL, L YY, Y WW, W G or G = 2 or 3 = Assembly Location = Wafer Lot = Year = Work Week = Pb-Free Package *This marking diagram also applies to NCV3843BV. http://onsemi.com 19 UC3842B, UC3843B, UC2842B, UC2843B, NCV3843BV PACKAGE DIMENSIONS PDIP-8 N SUFFIX CASE 626-05 ISSUE L 8 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. 5 -B- 1 4 DIM A B C D F G H J K L M N F -A- NOTE 2 L C J -T- N SEATING PLANE D 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 M K G H 0.13 (0.005) M T A M B M SOIC-14 D SUFFIX CASE 751A-03 ISSUE G -A- 14 8 -B- P 7 PL 0.25 (0.010) B M 7 1 G 0.25 (0.010) M T B J M K D 14 PL F R X 45 _ C -T- SEATING PLANE M S A S http://onsemi.com 20 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 UC3842B, UC3843B, UC2842B, UC2843B, NCV3843BV PACKAGE DIMENSIONS SOIC-8 D1 SUFFIX CASE 751-07 ISSUE AJ -X- 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. A 8 5 S B 0.25 (0.010) M Y M 1 4 -Y- K G C N DIM A B C D G H J K M N S X 45 _ SEATING PLANE -Z- 0.10 (0.004) H D 0.25 (0.010) M Z Y S X M J S 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 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. 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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 http://onsemi.com 21 ON Semiconductor Website: www.onsemi.com Order Literature: http://www.onsemi.com/orderlit For additional information, please contact your local Sales Representative UC3842B/D