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ISL6121HIBZA датащи(PDF) 4 Page - Intersil Corporation |
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ISL6121HIBZA датащи(HTML) 4 Page - Intersil Corporation |
4 / 11 page 4 FN9004.2 November 12, 2004 Introduction The ISL6121 is a single channel Overcurrent (OC) fault protection IC for the +2.5V to +5V environment. Each ISL6121 incorporates in a single 8 lead SOIC package a 50m Ω N channel MOSFET power switch for power control. See Figure 3 for switch resistance curves. With an enabling input and fault reporting output compatible with 3V and 5V logic allowing for external control and monitoring. See Figure 2 for IC operational waveforms. This device features internal current monitoring, consistent current limiting and an integrated power switch with a current limiting timed delay to latch-off feature for system protection. Key Feature Description and Operation UV Lock Out The ISL6121 undervoltage lockout feature prevents functionality of the device unless the correct ENABLE state and VIN > 2.5V are present. Soft Start A constant 500nA current source ramps up the switch’s gate causing a voltage follower effect on the output voltage. This provides a soft start turn-on and eliminates bus voltage drooping caused by inrush current charging heavy load capacitances. The rising and falling output is a current limited voltage ramp so that both the inrush current and voltage slew rate are limited, independent of load. This reduces supply droop due to surge and also eliminates the need for external EMI filters necessary on other IC products. See Figure 4 for turn-on wave forms. Fault Blanking On Start-Up During initial turn-on the ISL6121 prevents nuisance faults being reported to the system controller by blanking the fault signal for 12ms. This blanking eliminates the need for external RC filters necessary for other vendor products that assert a fault signal upon initial turn-on into a temporary high current condition. See Figures 11 through 13 for waveform examples. Current Regulation The ISL6121 has integrated current sensing on the power MOSFET that allows for rapid control of OC events. Once an OC is detected the ISL6121 goes into its Current Regulation (CR) control mode. The ISL6121 CR level is set to a nominal 2A. This current regulation is ±20% over the full operating temperature and voltage bias range. See Figures 5 and 6 for illustrative curves. The speed of this control is proportional to the magnitude of the OC fault. Thus a hard over current is more quickly controlled than a marginal condition. See Figure 7 for waveforms illustrating this and Figure 8 for an accompanying graph. Latch-Off Time Delay The primary function of any OC protection device is to quickly isolate the voltage bus from a faulty load. Unlike many other manufacturers’ IC products that sense the IC thermal condition (the monitored IC junction temperature depends on a number of factors the most important of which are power dissipation of the faulted switch and the package temp) to isolate a faulty load, the ISL6121 uses an internal 12ms timer that starts upon OC detection. Once an OC condition is detected the output is current limited for a nominal 12ms to allow transient conditions to pass before latch-off. The time to latch-off is independent of the device’s thermal condition. If, after the ISL6121 has latched off, and the fault has asserted and the enable is not deasserted but the OC condition still exists, the ISL6121 unlike other IC devices does not send to the controller a continuous string of fault pulses. The ISL6121’s single fault signal is sent at the time of latch off. Slow And Fast Shutdown The ISL6121 has two shutdown modes. When disabled with a Load Current less than the CR level the ISL6121 shuts down in a controlled manner using a 500nA constant current source controlled ramp. When latched-off during CR or if the timer has expired the ISL6121 quickly pulls down the output thereby quickly removing the faulted load from the voltage bus. See Figures 9 and 10 for waveforms of each mode. Temperature Shutdown Although the ISL6121 has a thermal shutdown feature, because of the 12ms timed shutdown this will only be invoked in extremely high ambient temperatures. Active Output Pulldown Another unique ISL6121 feature is the active pull down on the outputs to within 300mV of GND when the device is disabled. ISL6121 |
Аналогичный номер детали - ISL6121HIBZA |
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Аналогичное описание - ISL6121HIBZA |
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