CONTENTS.
INTRODUCTION.
The TLO72 was first manufactured by Texas Instruments in 196?? in Bi-CMOS technology.
- The JFET input devices give their best noise performance at medium impedances, in the range 1K - 10K.
- Very high-impedance inputs, with effectively zero bias and offset currents.
- The common-mode range of the inputs does not extend all the way between the rails. If the common mode voltage gets to within a couple of volts of the V- rail, the op-amp phase inverts; the inputs swap their polarities. This must be guarded against as it causes dire troubles. There may be really horrible clipping, where the output hits the bottom rail and then shoots up to hit the top one, or the stage may simply latch up until the power is turned off. Cures for both problems will be described below.
- Not THD-free in the way the 5532 is. In audio usage, distortion depends primarily upon how heavily the outout is loaded. The maximum loading is a matter of opinion, usually being a tradeoff between quality and circuit economy. 2 KOhm would be my upper limit. This is not an opamp to use for quality audio unless the high input impedance, low price, or modest power consumption are important factors.
- Modest power consumption: typically 1.4mA per opamp section.
- Relatively relaxed about supply rail decoupling.
- Slew rate higher than 5532. (13 V/us against 9 V/us)
SPECS.
Here are the vital statistics. All typical values, for +/-15V supply rails.
| Supply voltage | +/-18V abs max
|
| Output range | +/-13V typ (2K load)
|
| CM range | +15 -12V
| en | 18 nV/rtHz typ 1 kHz
| | in | 0.01 pA/rtHz typ
| | Ibias | 65 pA typ
| | Slew rate: | 13 V/us
| | Supply current | 2.8 mA
| | Unity gain stable | YES
| | Cost | 45p RS Jan 2001
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Fig 3Distortion versus loading for the TL072, with various loads. Output level ** Vrms. Distortion always gets worse as the loading increases. This and the closed-loop NFB factor determine the THD.
(texas072.gif)
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TL072 opamps are not very critical in their decoupling
requirements, though they will sometimes show very visible
oscillation if they are at the end of very long and thin supply
tracks. One or two rail-to-rail decouplers (eg 100nF) per board
is usually sufficient to deal with this. A decoupler within six
inches of track length of the package is usually adequate. A
design with decoupling on every TL072 should be queried as it is
almost certainly wasting money.
TL072/71 opamps are prone to HF oscillation if faced with
significant capacitance to ground on the output pin; this is
particularly likely when they are used as unity-gain buffers. A
few inches of track can sometimes be enough. If this has been
foreseen by the designer, there will be a resistor (probably in
the 47 to 75 Ohm range) in series with the output. This must be
placed at the opamp end of the track to be effective.
| Fig 4Distortion of the TL072 on low and asymmetrical supply rails. The positive rail is fixed at +5V.
Linearity much improved on going from -5 to -8V on the -V rail.
Gain here 2.4x, non-inverting. (tlo72low.gif)
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