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| STC494 Pulse Width Modulation Description The STC494 is a monolithic integrated circuit which includes all the necessary building blocks for the design of pulse width modulate(PWM) switching power supplies, including push-pull, bridge and series configuration. The device can operate at switching frequencies between 1KHz and 300KHz and output voltage up to 40V. The STC494 is specified over an operating temperature range of -40 to 85 . Features Uncommitted output transistors capable of 200mA source or sink Internal protection from double pulsing of out-puts with narrow pulse widths or with supply voltages bellows specified limits Easily synchronized to other circuits Dead time control comparator Output control selects single-ended or push-pull operation Ordering Information Type NO. STC494 Marking STC494 Package Code SOP-16 Outline Dimensions unit : mm PIN Connections 1. Non-INV Input 2. INV Input 3. Feed-Back 4. Dead-Time Control 5. CT 6. RT 7. GND 8. C1 9. E1 10. E2 11. C2 12. Vcc 13 Output Control 14. Ref Out 15. INV-Input 16. Non-INV Input 1 STC494 Absolute Maximum Ratings Characteristic supply voltage Voltage From Any Pin to Ground (except pin 8 and pin 11) Output Collector Voltage Peak Collector Current Power Dissipation Operating Temperature Storage Temperature S Ta=25 C Symbol VCC VIN VC1, VC2 IC1, IC2 PD Topr Tstg Ratings 42 VCC+0.3 42 250 1500 -40 ~ 85 -65 ~ 150 Unit V V V mA mW C C Recommended Operating Condition Characteristic supply voltage Voltage on Any Pin Except Pin 8 and 11(Referenced to Ground) Output Voltage Output Collector Current Timing Capacitor Timing Capacitor Timing Resistor Oscillator Frequency Symbol VCC VIN VC1, VC2 IC1, IC2 Ct Ct Rt fOSC Min. 7 -0.3 -0.3 470 1.8 1 Max. 40 VCC+0.3 40 200 10 500 300 Unit V V V mA PF KHz Electrical Characteristics Reference Section Characteristic Reference Voltage Line Regulation Load Regulation Temperature Coefficient Symbol Vref VLINE VLOAD - Test Condition Iref = 1.0mA 7V < Vcc < 40V Min. Typ. Max. 4.75 5.00 2 1 0.01 5.25 25 15 0.03 Unit V mV mV %/ C 1mA< IREF <10mA 0 C < Ta <70 C Oscillator Section Characteristic Oscillator Frequency Oscillator Frequency Change Over Operating Temperature Range Symbol fOSC fSOC Ct=0.01 Ct=0.01 Test Condition , Rt=12 , Rt=12 Min. Typ. Max. 10 2 Unit % 2 STC494 Dead Time Control Section Characteristic Input Bias Current (Pin4) Max. Duty cycle, Each Output Input Threshold Voltage Zero Duty Max Duty Symbol IIB(DT) DC(Max) VTH Test Condition Vcc = 15V, 0V < V4 < 5.25V Vcc = 15V, Pin4 = 0V, Output Control Pin = Vref - Min. Typ. Max. 43 0 -2 3 -10 45 3.3 - Unit % V Error Amplifier Section Characteristic Input Offset Voltage Input Offset Current Input Bias Current Input Common Mode voltage Range Large Signal Open Loop Voltage Range Unity Gain Band width Symbol VIOS IIOS IIB VICR GVO fC Test Condition V3 = 2.5V V3 = 2.5V V3 = 2.5V 7V 0.5V VCC V3 40V 3.5V Min. Typ. Max. -0.3 60 2 25 0.2 74 650 10 250 1 VCC - Unit mV nA V dB PWM Comparator Section (Pin3) Characteristic Inhibit Threshold Voltage Output Source Current Output Sink Current Symbol VTHI Io + - Test Condition Zero duty cycle 0.5V < V3 < 3.5V 0.5V< V3 < 3.5V Min. Typ. Max. 2 -0.2 4 -0.6 4.5 - Unit V mA mA Io Output Section Characteristic Output Saturation Voltage Common-Emitter Emitter-Follower Symbol VCE(SAT) IC(off) IE(off) Test Condition VE= 15V, IC = 200mA VC =15V, IE = 200mA VCC = VC = 40V, VE = 0 VCC = VC = 40V, VE = 0 Min. Typ. Max. 1.1 1.5 2 1.3 2.5 100 -100 Unit V Collector off-state Current Emitter off-state Current Output Control(Pin 13) Output Control Voltage Required for single-Ended or Parallel Output Operation Output Control Voltage Required for Push-pull operation VOCL VOCH 2.4 0.4 - V V Total Device Standby power Supply Current ICC 6 10 mA : These limits apply when the voltage measured at Pin 3 is with in the range specified. 3 STC494 Output AC Characteristic Characteristic Rise Time Common Emitter Emitter Follower Fall Time Common Emitter Emitter Follower Symbol tr - Test Condition Min. Typ. Max. 100 100 25 40 200 200 100 100 Unit ns tf - - Block Diagram KSI-K003-001 4 STC494 INFORMATION 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. 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 5V internal reference. See Figure7 for error amp sensing techniques. The second error amp is typically used to implement current limiting. The output control logic (Pin13) selects either push-pull or single-ended operation of the output transistors (see Figure6). The dead time control prevents on-state overlap of the output transistors as can be seen is Figure5. The dead time is approximately 3 to 5% of the total period if the dead time control(pin4) is grounded. This dead time can be increased by connecting the dead time control to a voltage up to 5 V. The frequency response of the error amps can be modified by using external resistors and capacitors. These components are typically connected between the compensation terminal (pin3) and the inverting input of the error amps(pin2 or pin15). The switching frequency of two or more S494 circuits can be synchronized. The timing capacitor, Ct is connected as shown in Figure8. 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. Operating Waveform 5 STC494 Test Circuit Fig.1Error Amplifier Test Circuit Fig.2 Current Limit sense Amplifier Test Circuit Fig. 3 Common-Emitter Configuration Test circuit and Waveform Fig. 5 Dead-Time and Feedback Control Test Circuit Fig. 4 Emitter-Follower Configuration Test circuit and waveform Voltage waveform 6 STC494 APPLICATION CIRCUIT Fig. 6 Output Connections for Single-Ended and Push-Pull Configurations Fig. 7 Error Amplifier Sensing Techniques Fig. 8 Slaving Tow or More Control Circuits Fig. 9Error Amplifier and Current Limit Sense Amplifier Output Circuits 7 STC494 Electrical Characteristic Curves Fig. 1 VCE(sat) -IC Fig. 2 VCE -IE Fig. 3 tOSC - RT Fig. 4 AVOL , Phase - f Fig. 5 ICC - VCC 8 |
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