データシートサーチシステム |
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LF400MH データシート(PDF) 10 Page - National Semiconductor (TI) |
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LF400MH データシート(HTML) 10 Page - National Semiconductor (TI) |
10 / 12 page Application Hints (Continued) TLH9414 – 21 FIGURE 1 Simplified Settling Time Test Circuit (see Text) CL s 49 pF tling time testing must be able to drive 50 X with a very clean g5V square wave For more information on measuring set- tling time see Application Note AN-428 Output Compensation When operating at very low temperatures a compensation network should be added to the LF400’s output The 100 X 22 pF network shown on the first page of this data sheet should be used when the junction temperature might reach 25 C (roughly 0 C ambient when the LF400 is ‘‘warmed up’’) In applications where the device will be operating with a junction temperature near 0 C the output RLC network in Figure 1 should be used This network will provide a small (about 20 ns) improvement in settling time at higher temper- atures as well Supply Bypassing Power supply bypassing is extremely important for good high-speed performance Ideally multiple bypass capacitors as in Figure 2 should be used A 10 mF tantalum a 22 mF ceramic and a 047 mF ceramic work well All bypass ca- pacitor leads should be very short For best results the ground leads of the capacitors should be separated to re- duce the inductance to ground A ground plane layout ap- proach will give the best results For simplicity bypass ca- pacitors have been omitted from some of the schematics in this data sheet but they should always be used TLH9414 – 22 FIGURE 2 Power Supply Bypassing (see Text) Output Drive and Current Limit The LF400 can drive heavier resistive loads than most oper- ational amplifiers The output at pin 6 is internally current- limited when the voltage drop across the 25 X output resis- tor reaches about 055V (IOUT e 22 mA) When more out- put current is needed pin 8 provides a means of increasing the maximum output current up to about 100 mA A resistor may be connected from pin 8 to pin 6 paralleling the inter- nal sense resistor and increasing the current limit threshold ( Figure 3 ) Pins 6 and 8 may be shorted together to com- pletely bypass the current limiting circuit To avoid damaging the LF400 observe the power dissipation limitations men- tioned in the Absolute Maximum Ratings and in Note 4 The effective load impedance (including feedback resist- ance) should be kept above 500 X for fastest settling Load capacitance should also be minimized if good settling time is to be optimized Large feedback resistors will make the circuit more susceptible to stray capacitance so in high- speed applications keep the feedback resistors in the 1 k X to2k X range wherever practical Avoid the use of inductive feedback resistors (some wirewounds for example) as these will degrade settling time ILimit 055V Rx 25X TLH9414 – 23 FIGURE 3 Increasing the current limit using pin 8 Current limit is now determined by RX in parallel with the internal 25 X sense resistor Vos Adjustment Offset voltage can be nulled using a 27k resistor and a 10k potentiometer connected to pins 1 and 5 as shown in Figure 4a Bypassing the Vos adjust pins with 01 mF capacitors will help to avoid noise pickup When not used for offset adjust- ment pins 1 and 5 can often be left open but to minimize the possibility of noise pickup the unused Vos trim pins should be connected to ground or V b 10 |
同様の部品番号 - LF400MH |
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同様の説明 - LF400MH |
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