LM494 Pulse Width Modulated Control Circuit General Description Features The LM494 is a monolithic integrated circuit which includes all the necessary building blocks for the design of pulse width modulated (PWM) switching power supplies, including push-pull, bridge and series configurations. The device can operate at switching frequencies between 1.0 kHz and 300 kHz and output voltages up to 40V. The operating temperature range specified for the LM494C is 0§ C to 70§ C and for the LM494V is b40§ C to a 85§ C. Y Y Y Y Y Y Y Uncommitted output transistors capable of 200 mA source or sink On-chip error amplifiers On-chip 5.0V reference Internal protection from double pulsing of outputs with narrow pulse widths or with supply voltages below specified limits Dead time control comparator Output control selects single ended or push-pull operation Easily synchronized (slaved) to other circuits Block Diagram TL/H/10056 – 2 Connection Diagram Ordering Information 16-Lead DIP Device Code Package Code Package Description LM494IN LM494CJ LM494CN N16A J16A N16A Molded DIP Ceramic DIP Molded DIP TL/H/10056 – 1 Top View C1995 National Semiconductor Corporation TL/H/10056 RRD-B30M115/Printed in U. S. A. LM494 Pulse Width Modulated Control Circuit June 1989 Absolute Maximum Ratings If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/Distributors for availability and specifications. Output Collector Voltage Storage Temperature Range Ceramic DIP Molded DIP ESD Susceptibility Operating Temperature Range Industrial (LM494I) Commercial (LM494C) b 65§ C to a 175§ C b 65§ C to a 150§ C Internal Power Dissipation (Notes 1, 2) 16L-Ceramic DIP 16L-Molded DIP Supply Voltage Voltage from Any Lead to Ground (except Lead 8 and Lead 11) 250 mA (to be determined) Recommended Operating Conditions b 40§ C to a 85§ C 0§ C to a 70§ C Lead Temperature Ceramic DIP (Soldering, 60 sec.) Molded DIP (Soldering, 10 sec.) 42V Peak Collector Current (IC1 and IC2) Power Supply Voltage (VCC) Voltage on Any Lead except Leads 8 and 11 (Referenced to Ground) (VI) 300§ C 265§ C 7.0V to 40V Output Voltage Collector (VC1, VC2) Output Collector Current (IC1, IC2) Timing Capacitor (CT) Timing Resistor (RT) Oscillator Frequency (fOSC) 1.50W 1.04W 42V VCC a 0.3V b 0.3V to VCC a 0.3V b 0.3V to 40V 200 mA 470 pF to 10 mF 1.8 kX to 500 kX 1.0 kHz to 300 kHz LM494 Electrical Characteristics TA e 0§ C to a 70§ C for the LM494C, TA e b40§ C to a 85§ C for the LM494I, VCC e 15V, fOSC e 10 kHz, unless otherwise specified Symbol Parameter Conditions Min Typ Max Units 4.75 REFERENCE SECTION VREF Reference Voltage (Note 3) IREF e 1.0 mA 5.0 5.25 V RegLINE Line Regulation of Reference Voltage 7.0V s VCC s 40V 2.0 25 mV TCVREF Temperature Coefficient of Reference Voltage 0§ C s TA s 70§ C 0.01 0.03 %/§ C RegLOAD Load Regulation of Reference Voltage 1.0 mA s IREF s 10 mA 1.0 15 mV IOS Output Short Circuit Current VREF e 0V 35 50 0§ C s TA s a 70§ C 10 b 40§ C s TA s a 85§ C mA 35 OSCILLATOR SECTION fOSC Oscillator Frequency (Figure 10) CT e 0.01 mF, RT e 12 kX DfOSC Oscillator Frequency Change CT e 0.01 mF, RT e 12 kX 10 kHz 0§ C s TA s a 70§ C 2.0 b 40§ C s TA s a 85§ C 2.0 % DEAD TIME CONTROL SECTION IIB (DT) Input Bias Current VCC e 15V, 0V s V4 s 5.25V DC(Max) Maximum Duty Cycle, Each Output VCC e 15V, Lead 4 e 0V, Output Control e VREF VTH(in) Input Threshold Voltage b 2.0 45 Zero Duty Cycle mA % 3.0 Maximum Duty Cycle b 10 3.3 V 0 ERROR AMPLIFIER SECTIONS VIO Input Offset Voltage V3 e 2.5V 2.0 10 IIO Input Offset Current V3 e 2.5V 25 250 nA IIB Input Bias Current V3 e 2.5V 0.2 1.0 mA VICR Input Common Mode Voltage Range 7.0V s VCC s 40V b 0.3 VCC V AVS Large Signal Voltage Gain 0.5V s V3 s 3.5V 60 BW Bandwidth 2 mV 74 dB 650 kHz LM494 Electrical Characteristics TA e 0§ C to a 70§ C for the LM494C, TA e b40§ C to a 85§ C for the LM494I, VCC e 15V, fOSC e 10 kHz, unless otherwise specified (Continued) Symbol Parameter Conditions Min Typ Max Units 4.0 4.5 V PWM COMPARATOR SECTION (Figure 9) VTHI Inhibit Threshold Voltage Zero Duty Cycle IO b Output Sink Current (Note 4) 0.5V s V3 s 3.5V IO a Output Source Current (Note 4) 0.5V s V3 s 3.5V b 0.2 b 0.6 mA 2.0 mA OUTPUT SECTION VCE(sat) Output Saturation Voltage Common Emitter Configuration (Figure 3) VE e 0V, IC e 200 mA 0§ C s TA s a 70§ C b 40§ C s TA s a 85§ C Emitter Follower Configuration (Figure 4) VC e 15V, IE e 200 mA 1.5 2.5 IC(off) Collector Off-State Current VCC e 40V, VCE e 40V 2.0 100 mA IE(off) Emitter Off-State Current VCC e VC e 40V, VE e 0 b 100 mA 0.4 V 1.1 1.3 V 0§ C s TA s a 70§ C, b 40§ C s TA s a 85§ C OUTPUT CONTROL (Figure 6) VOCL VOCH Output Control Voltage Required for Single Ended or Parallel Output Operation Output Control Voltage Required for Push-Pull Operation 2.4 V TOTAL DEVICE ICC Standby Power Supply Current 6.0 10 Rise Time of Output Voltage Common Emitter Configuration (Figure 3) 100 200 Emitter Follower Configuration (Figure 4) 100 200 Fall Time of Output Voltage Common Emitter Configuration (Figure 3) 25 100 Emitter Follower Configuration (Figure 4) 40 mA OUTPUT AC CHARACTERISTICS Use Recommended Operating Conditions with TA e 25§ C tr tf ns ns 100 Note 1: TJ Max e 150§ C for the Molded DIP, and 175§ C for the Ceramic DIP. Note 2: Ratings apply to ambient temperature at 25§ C. Above this temperature, derate the 16L-Ceramic DIP at 10 mW/§ C, and the 16L-Molded DIP at 8.3 mW/§ C. Note 3: Selected devices with tightened tolerance reference voltage available. Note 4: These limits apply when the voltage measured at Lead 3 is within the range specified. 3 Functional Description The basic oscillator (switching) frequency is controlled by an external resistor (RT) and capacitor (CT). The relationship between the values of RT, CT and frequency is shown in Figure 10 . The level of the sawtooth wave form is compared with an error voltage by the pulse width modulated comparator. The output of the PWM Comparator directs the pulse steering flip-flop and the output control logic. The error voltage is generated by the error amplifier. The error amplifier boosts the voltage difference between the output and the 5.0V internal reference. See Figure 7 for error amp sensing techniques. The second error amp is typically used to implement current-limiting. The output control logic selects either push-pull or singleended operation of the output transistors (see Figure 6 ). The dead time control prevents on-state overlap of the output transistors as can be seen in Figure 5 . The dead time is approximately 3.0% or 5.0% of the total period if the dead time control is grounded. This dead time can be increased by connecting the dead time control to a voltage up to 5.0V. The frequency response of the error amps (Figure 11) can be modified by using external resistors and capacitors. These components are typically connected between the compensation terminal and the inverting input of the error amps. The switching frequency of two or more LM494 circuits can be synchronized. The timing capacitor, CT, is connected as shown in Figure 8 . Charging current is provided by the master circuit. Discharging is through all the circuits slaved to the master. RT is required only for the master circuit. TL/H/10056 – 5 TL/H/10056 – 6 FIGURE 3. Common Emitter Configuration Test Circuit and Waveform TL/H/10056 – 7 Test Circuits TL/H/10056 – 8 FIGURE 4. Emitter Follower Configuration Test Circuit and Waveform TL/H/10056–3 FIGURE 1. Error Amplifier Test Circuit TL/H/10056–4 FIGURE 2. Current Limit Sense Amplifier Test Circuit TL/H/10056 – 9 FIGURE 5. Dead Time and Feedback Control Test Circuit 4 Typical Applications TL/H/10056 – 10 TL/H/10056 – 11 FIGURE 6. Output Connections for Single Ended and Push-Pull Configurations TL/H/10056 – 12 TL/H/10056 – 13 FIGURE 7. Error Amplifier Sensing Techniques TL/H/10056 – 14 FIGURE 8. Slaving Two or More Control Circuits 5 Typical Applications (Continued) TL/H/10056 – 15 FIGURE 9. Error Amplifier and Current Limit Sense Amplifier Output Circuits Typical Performance Characteristics TL/H/10056–16 TL/H/10056 – 17 FIGURE 10. Oscillator Frequency vs Timing Resistance FIGURE 11. Amplifier Voltage Gain vs Frequency 6 Voltage Waveforms TL/H/10056 – 18 Physical Dimensions inches (millimeters) 16-Lead Ceramic Dual-In-Line Package (J) Order Number LM494CJ NS Package Number J16A 7 LM494 Pulse Width Modulated Control Circuit Physical Dimensions inches (millimeters) (Continued) 16-Lead Molded Dual-In-Line Package (N) Order Number LM494CN or LM494IN NS Package Number N16A LIFE SUPPORT POLICY NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein: 1. Life support devices or systems are devices or systems which, (a) are intended for surgical implant into the body, or (b) support or sustain life, and whose failure to perform, when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a significant injury to the user. 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