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MIC2293 Datasheet(PDF) 5 Page - Micrel Semiconductor |
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MIC2293 Datasheet(HTML) 5 Page - Micrel Semiconductor |
5 / 9 page July 2005 5 M9999-070105 MIC2292/93 Micrel, Inc. Functional Description The MIC2292/93 is a constant frequency, PWM current mode boost regulator. The block diagram is shown above. The MIC2292/93iscomposedofanoscillator,slopecompensation ramp generator, current amplifier, gm error amplifier, PWM generator, 500mA bipolar output transistor, and Schottky rectifier diode.The oscillator generates a 1.6MHz clock for the MIC2292 and a 2.0MHz clock for the MIC2293. The clocks' two functions are to trigger the PWM generator that turns on the output transistor and to reset the slope compensation ramp generator. The current amplifier is used to measure the switch current by amplifying the voltage signal from the internal sense resistor. The output of the current amplifier is summed with the output of the slope compensation ramp generator. This summed current-loop signal is fed to one of the inputs of the PWM generator. Functional Diagram MIC2292/93 Block Diagram The gm error amplifier measures the LED current through the external sense resistor and amplifies the error between the detected signal and the 95mV reference voltage. The output of the gm error amplifier provides the voltage-loop signal that is fed to the other input of the PWM generator. When the current-loop signal exceeds the voltage-loop signal, the PWM generator turns off the bipolar output transistor. The next clock period initiates the next switching cycle, maintain- ing the constant frequency current-mode PWM control. The LED is set by the feedback resistor: ILED = 95mv RFB The Enable pin shuts down the output switching and disables control circuitry to reduce input current to leakage levels. Enable pin input current is zero at zero volts. GND VREF PWM Generator Ramp Generator 2.0MHz Oscillator SW EN FB OUT VIN 95mV gm OVP* S 1.6MHz or |
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Similar Description - MIC2293 |
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