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LM359M 数据表(PDF) 10 Page - National Semiconductor (TI) |
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LM359M 数据表(HTML) 10 Page - National Semiconductor (TI) |
10 / 24 page Application Hints (Continued) gain in the non-inverting configuration) some external fre- quency compensation is required because the stray capaci- tance to ground from the (−) input and the feedback resistor add additional lagging phase within the feedback loop. The value of the input capacitance will typically be in the range of 6 pF to 10 pF for a reasonably constructed circuit board. When using a feedback resistance of 30 k Ω or less, the best method of compensation, without sacrificing slew rate, is to add a lead capacitor in parallel with the feedback resistor with a value on the order of 1 pF to 5 pF as shown in Figure 10 . Another method of compensation is to increase the effective value of the internal compensation capacitor by adding ca- pacitance from the COMP pin of an amplifier to ground. An external 20 pF capacitor will generally compensate for all gain settings but will also reduce the gain bandwidth product and the slew rate. These same results can also be obtained by reducing I SET(IN) if the full capabilities of the amplifier are not required. This method is termed over-compensation. Another area of concern from a stability standpoint is that of capacitive loading. The amplifier will generally drive capaci- tive loads up to 100 pF without oscillation problems. Any larger C loads can be isolated from the output as shown in Figure 11. Over-compensation of the amplifier can also be used if the corresponding reduction of the GBW product can be afforded. In most applications using the LM359, the input signal will be AC coupled so as not to affect the DC biasing of the ampli- fier. This gives rise to another subtlety of high frequency cir- cuits which is the effective series inductance (ESL) of the coupling capacitor which creates an increase in the imped- ance of the capacitor at high frequencies and can cause an unexpected gain reduction. Low ESL capacitors like solid tantalum for large values of C and ceramic for smaller values are recommended. A parallel combination of the two types is even better for gain accuracy over a wide frequency range. AMPLIFIER DESIGN EXAMPLES The ability of the LM359 to provide gain at frequencies higher than most monolithic amplifiers can provide makes it most useful as a basic broadband amplification stage. The design of standard inverting and non-inverting amplifiers, though different than standard op amp design due to the cur- rent differencing inputs, also entail subtle design differences between the two types of amplifiers. These differences will be best illustrated by design examples. For these examples a practical video amplifier with a passband of 8 Hz to 10 MHz and a gain of 20 dB will be used. It will be assumed that the input will come from a 75 Ω source and proper signal termi- nation will be considered. The supply voltage is 12 V DC and single resistor programming of the operating current, I SET, will be used for simplicity. AN INVERTING VIDEO AMPLIFIER 1. Basic circuit configuration: 2. Determine the required I SET from the characteristic curves for gain bandwidth product. GBW MIN= 10x10MHz = 100 MHz For a flat response to 10 MHz a closed loop response to two octaves above 10 MHz (40 MHz) will be sufficient. Actual GBW = 10x40MHz = 400 MHz I SET required = 0.5 mA DS007788-15 Cf = 1 pF to 5 pF for stability FIGURE 10. Best Method of Compensation DS007788-16 FIGURE 11. Isolating Large Capacitive Loads DS007788-17 www.national.com 10 |
类似零件编号 - LM359M |
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类似说明 - LM359M |
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