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MIC2070-1PCQS Datasheet(PDF) 7 Page - Micrel Semiconductor |
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MIC2070-1PCQS Datasheet(HTML) 7 Page - Micrel Semiconductor |
7 / 13 page January 2005 7 M9999-101104 MIC2010/2070 Micrel Functional Description The MIC2010/2070 are designed to support the power distri- bution requirements for USB wakeup from the ACPI S3 state. It integrates two independent channels under control of input S3#. When S3# is asserted LOW (ACPI S3 state) the MIC2010/ 2070 will switch a 500mΩ MOSFET switch from the AUX input to each of its two outputs. In addition the current-limit threshold will be set to a value specified by a resistor connected to the RSET inputs. Conversely when the S3# input is HIGH the MIC2010/2070 will switch a 100mΩ MOSFET switch from the MAIN inputs to each of its two outputs. The current-limit threshold is preset to 500mA in this state. The lower current limit during the ACPI S3 state helps to ensure that the standby supply maintains regulation even during fault conditions. Thermal Shutdown Thermal shutdown is employed to protect the device from damage should the die temperature exceed safe margins due mainly to short circuit faults. Thermal shutdown shuts off the output MOSFET and asserts the FAULT output if the die temperature reaches 140°C and the overheated channel is in current limit. The other channel is not affected. If however, the die temperature exceeds 160°C, both channels will be shut off even if neither channel is in current limit. Power Dissipation The device’s junction temperature depends on several fac- tors such as the load, PCB layout, ambient temperature and package type. The power dissipated in each channel is P D = RDS(on) × IOUT 2 where R DS(on) is the on-resistance of the internal MOSFETs and I OUT is the continuous output current. Total power dissipation of the device will be the summation of P D for both channels. To relate this to junction temperature, the following equation can be used: Functional Diagram Current Limit 10ms Timer Charge Pump + Gate Control S3# EN Current Limit MAIN OUT AUX RSET /FAULT AUX Latch To Other Channel * MAIN FET AUX FET *MIC2070-1/2 Only Thermal Sense * 'P' options only TJ = P D × θJA + TA where: T J = junction temperature T A = ambient temperature θJA = is the thermal resistance of the package Current Sensing and Limiting The current-limit threshold of each channel is preset inter- nally at 500mA when S3# is deasserted. When S3# is asserted the current-limit threshold is specified by a resistor connected to the RSET input. The value of the current-limit threshold is determined by the equation 18/R SET ohms where R SET is the resistance connected between the RSET pin and ground. The current-limit threshold should be set at 1.2X of the applications continous output current requirement. When an overcurrent condition lasts longer than t DLY the MIC2070 will activate an internal circuit breaker that will latch the output off and assert FAULT. The output will remain off until either the load is removed or EN is toggled. When the MIC2070 enters a latched output condition a 1mA pull-up current source is activated. This provides a way to automati- cally reset the output once the load is removed without the need to toggle the enable input. Please refer to Figure 7 for timing details. The MIC2010 will automatically reset its output when the die temperature cools down to 120°C. The MIC2010 output and FAULT signal will continue to cycle on and off until the device is disabled or the fault is removed. Figure 6 depicts typical timing. Depending on PCB layout, package, ambient tem- perature, etc., it may take several hundred milliseconds from the incidence of the fault to the output MOSFET being shut |
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