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LM139JAN Datasheet(PDF) 9 Page - National Semiconductor (TI) |
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LM139JAN Datasheet(HTML) 9 Page - National Semiconductor (TI) |
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9 / 20 page  Application Hints The LM139 is a high gain, wide bandwidth device which, like most comparators, can easily oscillate if the output lead is inadvertently allowed to capacitively couple to the inputs via stray capacitance. This shows up only during the output voltage transition intervals as the comparator changes states. Power supply bypassing is not required to solve this problem. Standard PC board layout is helpful as it reduces stray input-output coupling. Reducing the input resistors to < 10 k Ω reduces the feedback signal levels and finally, adding even a small amount (1 to 10 mV) of positive feedback (hysteresis) causes such a rapid transition that oscillations due to stray feedback are not possible. Simply socketing the IC and attaching resistors to the pins will cause input-output oscillations during the small transition intervals unless hys- teresis is used. If the input signal is a pulse waveform, with relatively fast rise and fall times, hysteresis is not required. All pins of any unused comparators should be tied to the negative supply. The bias network of the LM139 establishes a drain current which is independent of the magnitude of the power supply voltage over the range of from 5 V DC to 30 VDC. It is usually unnecessary to use a bypass capacitor across the power supply line. The differential input voltage may be larger than V + without damaging the device. Protection should be provided to pre- vent the input voltages from going negative more than −0.3 V DC (at 25˚C). An input clamp diode can be used as shown in the applications section. The output of the LM139 is the uncommitted collector of a grounded-emitter NPN output transistor. Many collectors can be tied together to provide an output OR’ing function. An output pull-up resistor can be connected to any available power supply voltage within the permitted supply voltage range and there is no restriction on this voltage due to the magnitude of the voltage which is applied to the V + terminal of the LM139 package. The output can also be used as a simple SPST switch to ground (when a pull-up resistor is not used). The amount of current which the output device can sink is limited by the drive available (which is independent of V +) and the β of this device. When the maximum current limit is reached (approximately 16 mA), the output transistor will come out of saturation and the output voltage will rise very rapidly. The output saturation voltage is limited by the ap- proximately 60 Ω R SAT of the output transistor. The low offset voltage of the output transistor (1 mV) allows the output to clamp essentially to ground level for small load currents. Typical Applications (V+ = 5.0 V DC) Basic Comparator 20129503 Driving CMOS 20129504 Driving TTL 20129505 AND Gate 20129508 OR Gate 20129509 www.national.com 9 |
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