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LM3900N датащи(PDF) 3 Page - National Semiconductor (TI) |
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LM3900N датащи(HTML) 3 Page - National Semiconductor (TI) |
3 / 20 page Electrical Characteristics (Note 6) Va e 15 VDC unless otherwise stated (Continued) Parameter Conditions LM2900 LM3900 LM3301 Units Min Typ Max Min Typ Max Min Typ Max Power Supply Rejection TA e 25 C f e 100 Hz 70 70 70 dB Mirror Gain 20 mA (Note 3) 090 10 11 090 10 11 090 1 110 m A mA 200 mA (Note 3) 090 10 11 090 10 11 090 1 110 D Mirror Gain 20 mAto200 mA (Note 3) 2 5 2 5 2 5 % Mirror Current (Note 4) 10 500 10 500 10 500 m ADC Negative Input Current TA e 25 C (Note 5) 10 10 10 mADC Input Bias Current Inverting Input 300 300 nA Note 1 For operating at high temperatures the device must be derated based on a 125 C maximum junction temperature and a thermal resistance of 92 CW which applies for the device soldered in a printed circuit board operating in a still air ambient Thermal resistance for the SO package is 131 CW Note 2 The output current sink capability can be increased for large signal conditions by overdriving the inverting input This is shown in the section on Typical Characteristics Note 3 This spec indicates the current gain of the current mirror which is used as the non-inverting input Note 4 Input VBE match between the non-inverting and the inverting inputs occurs for a mirror current (non-inverting input current) of approximately 10 mA This is therefore a typical design center for many of the application circuits Note 5 Clamp transistors are included on the IC to prevent the input voltages from swinging below ground more than approximately b03 VDC The negative input currents which may result from large signal overdrive with capacitance input coupling need to be externally limited to values of approximately 1 mA Negative input currents in excess of 4 mA will cause the output voltage to drop to a low voltage This maximum current applies to any one of the input terminals If more than one of the input terminals are simultaneously driven negative smaller maximum currents are allowed Common-mode current biasing can be used to prevent negative input voltages see for example the ‘‘Differentiator Circuit’’ in the applications section Note 6 These specs apply for b40 C s TA s a85 C unless otherwise stated Note 7 Human body model 15 kX in series with 100 pF Application Hints When driving either input from a low-impedance source a limiting resistor should be placed in series with the input lead to limit the peak input current Currents as large as 20 mA will not damage the device but the current mirror on the non-inverting input will saturate and cause a loss of mir- ror gain at mA current levelsespecially at high operating temperatures Precautions should be taken to insure that the power supply for the integrated circuit never becomes reversed in polarity or that the unit is not inadvertently installed backwards in a test socket as an unlimited current surge through the result- ing forward diode within the IC could cause fusing of the internal conductors and result in a destroyed unit Output short circuits either to ground or to the positive pow- er supply should be of short time duration Units can be destroyed not as a result of the short circuit current causing metal fusing but rather due to the large increase in IC chip dissipation which will cause eventual failure due to exces- sive junction temperatures For example when operating from a well-regulated a5VDC power supply at TA e 25 C with a 100 kX shunt-feedback resistor (from the output to the inverting input) a short directly to the power supply will not cause catastrophic failure but the current magnitude will be approximately 50 mA and the junction temperature will be above TJ max Larger feedback resistors will reduce the current 11 MX provides approximately 30 mA an open cir- cuit provides 13 mA and a direct connection from the out- put to the non-inverting input will result in catastrophic fail- ure when the output is shorted to V a as this then places the base-emitter junction of the input transistor directly across the power supply Short-circuits to ground will have magni- tudes of approximately 30 mA and will not cause cata- strophic failure at TA e 25 C Unintentional signal coupling from the output to the non-in- verting input can cause oscillations This is likely only in breadboard hook-ups with long component leads and can be prevented by a more careful lead dress or by locating the non-inverting input biasing resistor close to the IC A quick check of this condition is to bypass the non-inverting input to ground with a capacitor High impedance biasing resis- tors used in the non-inverting input circuit make this input lead highly susceptible to unintentional AC signal pickup Operation of this amplifier can be best understood by notic- ing that input currents are differenced at the inverting-input terminal and this difference current then flows through the external feedback resistor to produce the output voltage Common-mode current biasing is generally useful to allow operating with signal levels near ground or even negative as this maintains the inputs biased at aVBE Internal clamp transistors (see note 5) catch-negative input voltages at ap- proximately b03 VDC but the magnitude of current flow has to be limited by the external input network For operation at high temperature this limit should be approximately 100 mA This new ‘‘Norton’’ current-differencing amplifier can be used in most of the applications of a standard IC op amp Performance as a DC amplifier using only a single supply is not as precise as a standard IC op amp operating with split supplies but is adequate in many less critical applications New functions are made possible with this amplifier which are useful in single power supply systems For example biasing can be designed separately from the AC gain as was shown in the ‘‘inverting amplifier’’ the ‘‘difference integra- tor’’ allows controlling the charging and the discharging of the integrating capacitor with positive voltages and the ‘‘fre- quency doubling tachometer’’ provides a simple circuit which reduces the ripple voltage on a tachometer output DC voltage 3 |
Аналогичный номер детали - LM3900N |
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Аналогичное описание - LM3900N |
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