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MIC2007YML Datasheet(PDF) 11 Page - Micrel Semiconductor |
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MIC2007YML Datasheet(HTML) 11 Page - Micrel Semiconductor |
11 / 17 page Micrel MIC2007/MIC2017 October 2005 11 M9999-102805 Functional Description Input and Output VIN is both the power supply connection for the internal circuitry driving the switch and the input (Source connection) of the power MOSFET switch. VOUT is the Drain connection of the power MOSFET and supplies power to the load. In a typical circuit, current flows from VIN to VOUT toward the load. Since the switch is bi- directional when enabled, if VOUT is greater than VIN, current will flow from VOUT to VIN. When the switch is disabled, current will not flow to the load, except for a small unavoidable leakage current of a few microamps. However, should VOUT exceed VIN by more than a diode drop (~0.6V), while the switch is disabled, current will flow from output to input via the power MOSFET’s body diode. While this effect can be used to advantage when large bypass capacitors are placed on MIC2007/2017’s’s output, it can not be relied upon to fully or reliably discharge the load capacitance, because discharging depends upon the characteristics of the circuitry at VIN. To ensure proper discharge of any output capacitance, MIC2007/2017 is equipped with a discharge FET which is ON any time the device is not Enabled. Current Sensing and Limiting The MIC2007/2017 protects the system power supply and load from damage by continuously monitoring current through the on-chip power MOSFET. Load current is monitored, by means of a current mirror, in parallel with the power MOSFET switch. Current limiting is invoked when the load exceeds an externally set over-current threshold. When current limiting is activated the output current is constrained to the limit value, and remains at this level until either the load/fault is removed, the load’s current requirement drops below the limiting value, or the MIC2007/2017 goes into thermal shutdown. Kickstart (MIC2017 only) The MIC2017 is designed to allow momentary current surges (Kickstart) before the onset of current limiting, which permits dynamic loads, such as small disk drives or portable printers to draw the energy needed to overcome inertial loads without sacrificing system safety. In this respect, the MIC2017 differs markedly from MIC2007 and its peers, which immediately limit load current, potentially starving the motor and causing the appliance to stall or stutter. During this delay period, typically 128 ms, a secondary current limit is in effect. If the load demands a current in excess of the secondary limit, the MIC2017 acts immediately to restrict output current to the secondary limit for the duration of the Kickstart period. After this time, the MIC2017 reverts to its normal current limit. An example of Kickstart operation is shown below. T U O T U O Figure 3. Kickstart Operation Picture Key: A) MIC2017 is enabled into an excessive load (slew rate limiting not visible at this time scale) The initial current surge is limited by either the overall circuit resistance and power supply compliance, or the secondary current limit, whichever is less. B) RON of the power FET increases due to internal heating (effect exaggerated for emphasis). C) Kickstart period. D) Current limiting initiated. FAULT/ goes LOW. (Note: MIC2007/2017 does not provide a FAULT/ output.) E) VOUT is non-zero (load is heavy, but not a dead short where VOUT = 0. Limiting response will be the same for dead shorts). F) Thermal shutdown followed by thermal cycling. G) Excessive load released, normal load remains. MIC2017 drops out of current limiting. H) FAULT/ delay period followed by FAULT/ going HIGH. (Note: MIC2007/2017 does not provide a FAULT/ output.) Under Voltage Lock Out Under voltage lock-out insures no anomalous operation occurs before the device’s minimum input voltage of 2.5V had been achieved. Prior to reaching this voltage, the output switch (power MOSFET) is OFF and no circuit functions, such as ENABLE, are considered to be valid or operative. |
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