基于TL2845的电流模式 PWM 控制器

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基于TL2845的电流模式 PWM 控制器

　　1 Features

　　Optimized for Off-Line and DC-to-DC Converters

　　Low Start-Up Current (< 1 mA)

　　Automatic Feed-forward compensation

　　Pulse-by-Pulse Current Limiting

　　Enhanced Load-Response Characteristics

　　Undervoltage Lockout With Hysteresis

　　Double-Pulse Suppression

　　High-Current Totem-Pole Output

　　Internally Trimmed Bandgap Reference

　　500-kHz Operation

　　Error Amplifier With Low Output Resistance

　　Designed to be Interchangeable with UC2842 and UC3842 Series

　　2 Applications

　　Switching regulators of any polarity

Transformer-coupled DC/DC convertors

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　　3 Description

　　The TL284x and TL384x series of control integrated circuits provide the features that are necessary to implement off-line or DC-to-DC fixed-frequency current-mode control schemes, with a minimum number of external components. Some of the internally implemented circuits are an undervoltage lockout (UVLO), featuring a start-up current of less than 1 mA, and a precision reference trimmed for accuracy at the error amplifier input. Other internal circuits include logic to ensure latched operation, a pulse-width modulation (PWM) comparator (that also provides current-limit control), and a totem-pole output stage designed to source or sink high-peak current. The output stage, suitable for driving N-channel MOSFETs, is low when it is in the off state.

　　The TL284x and TL384x series of control integrated circuits provide the features that are necessary to implement off-line or DC-to-DC fixed-frequency current-mode control schemes, with a minimum number of external components. Some of the internally implemented circuits are an undervoltage lockout (UVLO), featuring a start-up current of less than 1 mA, and a precision reference trimmed for accuracy at the error amplifier input. Other internal circuits include logic to ensure latched operation, a pulse-width modulation (PWM) comparator (that also provides current-limit control), and a totem-pole output stage designed to source or sink high-peak current. The output stage, suitable for driving N-channel MOSFETs, is low when it is in the off state.

　　Major differences between members of these series are the UVLO thresholds and maximum duty-cycle ranges. Typical UVLO thresholds of 16 V (on) and 10 V (off) on the TLx842 and TLx844 devices make them ideally suited to off-line applications. The corresponding typical thresholds for the TLx843 and TLx845 devices are 8.4 V (on) and 7.6 V (off). The TLx842 and TLx843 devices can operate to duty cycles approaching 100%. A duty-cycle range of 0 to 50% is obtained by the TLx844 and TLx845 by the addition of an internal toggle flip-flop, which blanks the output off every other clock cycle.

　　The TL284x-series devices are characterized for operation from −40°C to +85°C. The TL384x devices are characterized for operation from 0°C to 70°C.