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LM2984C 数据表(PDF) 11 Page - National Semiconductor (TI) |
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LM2984C 数据表(HTML) 11 Page - National Semiconductor (TI) |
11 / 14 page Typical Performance Characteristics (Continued) Output Voltage TLH8821 – 8 Device Dissipation vs Ambient Temperature TLH8821 – 9 Output Capacitor ESR (Standby Output Pin 9) TLH8821 – 13 Output Capacitor ESR (Buffer Output Pin 10) TLH8821 – 14 Output Capacitor ESR (Main Output Pin 11) TLH8821 – 15 Application Hints OUTPUT CAPACITORS The LM2984C output capacitors are required for stability Without them the regulator outputs will oscillate sometimes by many volts Though the 10 mF shown are the minimum recommended values actual size and type may vary de- pending upon the application load and temperature range Capacitor effective series resistance (ESR) also affects the IC stability Since ESR varies from one brand to the next some bench work may be required to determine the mini- mum capacitor value to use in production Worst case is usually determined at the minimum ambient temperature and the maximum load expected Output capacitors can be increased in size to any desired value above the minimum One possible purpose of this would be to maintain the output voltages during brief condi- tions of negative input transients that might be characteris- tic of a particular system Capacitors must also be rated at all ambient temperatures expected in the system Many aluminum type electrolytics will freeze at temperatures less than b30 C reducing their effective capacitance to zero To maintain regulator stability down to b40 C capacitors rated at that temperature (such as tantalums) must be used Each output must be terminated by a capacitor even if it is not used STANDBY OUTPUT The standby output is intended for use in systems requiring standby memory circuits While the high current regulator outputs are controlled with the ONOFF pin described later the standby output remains on under all conditions as long as sufficient input voltage is supplied to the IC Thus memo- ry and other circuits powered by this output remain unaffect- ed by positive line transients thermal shutdown etc The standby regulator circuit is designed so that the quies- cent current to the IC is very low (k15 mA) when the other regulator outputs are off The capacitor on the output of this regulator can be in- creased without bound This will help maintain the output voltage during negative input transients and will also help to reduce the noise on all three outputs Because the other two track the standby output therefore any noise reduction here will also reduce the other two noise voltages BUFFER OUTPUT The buffer output is designed to drive peripheral sensor cir- cuitry in a mP system It will track the standby and main regulator within a few millivolts in normal operation There- fore a peripheral sensor can be powered off this supply and have the same operating voltage as the mP system This is important if a ratiometric sensor system is being used The buffer output can be short circuited while the other two outputs are in normal operation This protects the mP sys- tem from disruption of power when a sensor wire etc is temporarily shorted to ground ie only the sensor signal would be interrupted while the mP and memory circuits would remain operational The buffer output is similar to the main output in that it is controlled by the ONOFF switch in order to save power in 11 |
类似零件编号 - LM2984C |
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类似说明 - LM2984C |
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