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L4990 Datasheet(PDF) 4 Page - STMicroelectronics |
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L4990 Datasheet(HTML) 4 Page - STMicroelectronics |
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4 / 24 page  FUNCTIONAL DESCRIPTION The I.C. contains a standard PWM current mode control section with improved performance with respect to the UC384X family. Enhanced features include start-up bias current reduced to < 270 µA (typ), improved E/A perform- ance (4MHz B/W, 1.3mA Source Current, high- slew rate) accurate 1MHz oscillator, and also re- duced propagation delays in the critical path from Current Sense to Output. ADDITIONAL FEATURES Soft Start (SS) An external capacitor is charged by an internal constant current source (20 µA) to generate a SS signal which clamps the E/A output The SS pin doubles as a Fault Reset Delay func- tion as described below. Current Limit / Reset Delay An internal high-speed current limit comparator ELECTRICAL CHARACTERISTICS (continued.) Symbol Parameter Test Condition Min. Typ. Max. Unit OUTPUT SECTION VOL Output Low Voltage IO = 250mA 1.0 V VOH Output High Voltage IO = 20mA; VCC = 12V 10 10.5 V IO = 200mA; VCC = 12V 9 10 V VOUT CLAMP Output Clamp Voltage IO = 5mA; VCC = 20V 13 V Collector Leakage VCC = 20V VC = 24V 100 200 µA Fall Time CO = 1nF CO = 2.5nF 20 35 60 ns ns Rise Time CO = 1nF CO = 2.5nF 50 70 100 ns ns UVLO Saturation VCC =0V to VCCON;Isink = 10mA 1.0 V SUPPLY SECTION VCCON Startup voltage L4990 L4990A 15 7.8 16 8.4 17 9 V V VCCOFF Minimum Operating Voltage L4990 L4990A 9 7 10 7.6 11 8.2 V v Vhys Voltage After Turn-on Hysteresis L4990 L4990A 5.5 0.5 6 0.8 V v IS Start Up Current Before Turn-on at: VCC =VCCON - 0.5V 100 270 450 µA Iop Operating Current CT = 1nF, RT = 4.42k Ω,CO =1nF 12 18 mA Iq Quiescent Current (After turn on), Co =0nF CT = 1nF, RT = 4.42k Ω, 7.0 10 mA ISH Shutdown Current 100 270 450 µA VZ Zener Voltage I8 = 20mA 21 25 30 V SYNCHRONIZATION SECTION Master Operation V1 Clock Amplitude ISOURCE = 0.8mA 4 V I1 Clock Source Current Vclock = 3.5V 7 mA Slave Operation V1 Sync Pulse Low Level 1 V High Level 3.5 V I1 Sync Pulse Current VSYNC = 3.5V 0.8 mA OVER CURRENT PROTECTION Vt Fault Threshold Voltage 1.1 1.2 1.3 V DISABLE SECTION Shutdown threshold 2.4 2.5 2.6 V L4990 - L4990A 4/24 |
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