Datasheet LM146, LM346 (Texas Instruments) - 9

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LM146, LM346 www.ti.com
SNOSBH5B – MAY 2004 – REVISED SEPTEMBER 2004
APPLICATION HINTS
Avoid reversing the power supply polarity; the device will fail.
COMMON-MODE INPUT VOLTAGE
The negative common-mode voltage limit is one diode drop above the negative supply voltage. Exceeding this limit on either input will result in an output phase reversal. The positive common-mode limit is typically 1V below the positive supply voltage. No output phase reversal will occur if this limit is exceeded by either input.
OUTPUT VOLTAGE SWING VS ISET
For a desired output voltage swing the value of the minimum load depends on the positive and negative output current capability of the op amp. The maximum available positive output current, (ICL+), of the device increases with ISET whereas the negative output current (ICL−) is independent of ISET. Figure 26 illustrates the above.
Figure 26. Output Current Limit vs ISET INPUT CAPACITANCE
The input capacitance, CIN, of the LM146 is approximately 2 pF; any stray capacitance, CS, (due to external circuit circuit layout) will add to CIN. When resistive or active feedback is applied, an additional pole is added to the open loop frequency response of the device. For instance with resistive feedback (Figure 27), this pole occurs at ½π (R1||R2) (CIN + CS). Make sure that this pole occurs at least 2 octaves beyond the expected −3 dB frequency corner of the closed loop gain of the amplifier; if not, place a lead capacitor in the feedback such that the time constant of this capacitor and the resistance it parallels is equal to the RI(CS + CIN), where RI is the input resistance of the circuit.
Figure 27. Resistive Feedback Circuit Example TEMPERATURE EFFECT ON THE GBW
The GBW (gain bandwidth product), of the LM146 is directly proportional to ISET and inversely proportional to the absolute temperature. When using resistors to set the bias current, ISET, of the device, the GBW product will decrease with increasing temperature. Compensation can be provided by creating an ISET current directly proportional to temperature (see Typical Applications).
ISOLATION BETWEEN AMPLIFIERS
The LM146 die is isothermally layed out such that crosstalk between all 4 amplifiers is in excess of −105 dB (DC). Optimum isolation (better than −110 dB) occurs between amplifiers A and D, B and C; that is, if amplifier A dissipates power on its output stage, amplifier D is the one which will be affected the least, and vice versa. Same argument holds for amplifiers B and C. Copyright © 2004, Texas Instruments Incorporated Submit Documentation Feedback 9 Product Folder Links: LM146 LM346 Document Outline FEATURES DESCRIPTION Connection Diagram Capacitorless Active Filters (Basic Circuit) ABSOLUTE MAXIMUM RATINGS DC ELECTRICAL CHARACTERISTICS DC ELECTRICAL CHARACTERISTIC DC ELECTRICAL CHARACTERISTICS TYPICAL PERFORMANCE CHARACTERISTICS APPLICATION HINTS COMMON-MODE INPUT VOLTAGE OUTPUT VOLTAGE SWING VS ISET INPUT CAPACITANCE TEMPERATURE EFFECT ON THE GBW ISOLATION BETWEEN AMPLIFIERS LM146 TYPICAL PERFORMANCE SUMMARY SPEED VS POWER CONSUMPTION Typical Applications Active Filters Applications Circuit Synthesis Equations Circuit Synthesis Equations Miscellaneous Applications Schematic Diagram