LM6142, LM6144
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SNOS726D –JUNE 2000–REVISED MARCH 2013
LM6142/LM6144 APPLICATION IDEAS
The LM6142 brings a new level of ease of use to op amp system design.
With greater than rail-to-rail input voltage range concern over exceeding the common-mode voltage range is
eliminated.
Rail-to-rail output swing provides the maximum possible dynamic range at the output. This is particularly
important when operating on low supply voltages.
The high gain-bandwidth with low supply current opens new battery powered applications, where high power
consumption, previously reduced battery life to unacceptable levels.
To take advantage of these features, some ideas should be kept in mind.
ENHANCED SLEW RATE
Unlike most bipolar op amps, the unique phase reversal prevention/speed-up circuit in the input stage causes the
slew rate to be very much a function of the input signal amplitude.
Figure 36 shows how excess input signal, is routed around the input collector-base junctions, directly to the
current mirrors.
The LM6142/LM6144 input stage converts the input voltage change to a current change. This current change
drives the current mirrors through the collectors of Q1–Q2, Q3–Q4 when the input levels are normal.
Figure 36.
If the input signal exceeds the slew rate of the input stage, the differential input voltage rises above two diode
drops. This excess signal bypasses the normal input transistors, (Q1–Q4), and is routed in correct phase through
the two additional transistors, (Q5, Q6), directly into the current mirrors.
This rerouting of excess signal allows the slew-rate to increase by a factor of 10 to 1 or more. (See Figure 37.)
As the overdrive increases, the op amp reacts better than a conventional op amp. Large fast pulses will raise the
slew- rate to around 30V to 60V/μs.
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