MC34071,2,4,A MC33071,2,4,A
Since the input capacitance associated with the small
geometry input device is substantially lower (2.5 pF) than the
typical JFET input gate capacitance (5.0 pF), better
frequency response for a given input source resistance can
be achieved using the MC34071 series of amplifiers. This
performance feature becomes evident, for example, in fast
settling D–to–A current to voltage conversion applications
where the feedback resistance can form an input pole with
the input capacitance of the op amp. This input pole creates
a 2nd order system with the single pole op amp and is
therefore detrimental to its settling time. In this context, lower
input capacitance is desirable especially for higher values of
feedback resistances (lower current DACs). This input pole
can be compensated for by creating a feedback zero with a
capacitance across the feedback resistance, if necessary, to
reduce overshoot. For 2.0 kΩ of feedback resistance, the
MC34071 series can settle to within 1/2 LSB of 8 bits in 1.0
µs,
and within 1/2 LSB of 12–bits in 2.2
µs
for a 10 V step. In
a inverting unity gain fast settling configuration, the
symmetrical slew rate is
±13
V/µs. In the classic noninverting
unity gain configuration, the output positive slew rate is +10
V/µs, and the corresponding negative slew rate will exceed
the positive slew rate as a function of the fall time of the input
waveform.
Since the bipolar input device matching characteristics are
superior to that of JFETs, a low untrimmed maximum offset
voltage of 3.0 mV prime and 5.0 mV downgrade can be
economically offered with high frequency performance
characteristics. This combination is ideal for low cost
precision, high speed quad op amp applications.
The all NPN output stage, shown in its basic form on the
equivalent circuit schematic, offers unique advantages over
the more conventional NPN/PNP transistor Class AB
output stage. A 10 kΩ load resistance can swing within 1.0 V
of the positive rail (VCC), and within 0.3 V of the negative
rail (VEE), providing a 28.7 Vpp swing from
±15
V supplies.
This large output swing becomes most noticeable at lower
supply voltages.
The positive swing is limited by the saturation voltage of
the current source transistor Q7, and VBE of the NPN pull up
transistor Q17, and the voltage drop associated with the short
circuit resistance, R7. The negative swing is limited by the
saturation voltage of the pull–down transistor Q16, the
voltage drop ILR6, and the voltage drop associated with
resistance R7, where IL is the sink load current. For small
valued sink currents, the above voltage drops are negligible,
allowing the negative swing voltage to approach within
millivolts of VEE. For large valued sink currents (>5.0 mA),
diode D3 clamps the voltage across R6, thus limiting the
negative swing to the saturation voltage of Q16, plus the
forward diode drop of D3 (≈VEE +1.0 V). Thus for a given
supply voltage, unprecedented peak–to–peak output voltage
swing is possible as indicated by the output swing
specifications.
If the load resistance is referenced to VCC instead of
ground for single supply applications, the maximum possible
output swing can be achieved for a given supply voltage. For
light load currents, the load resistance will pull the output to
VCC during the positive swing and the output will pull the load
resistance near ground during the negative swing. The load
resistance value should be much less than that of the
feedback resistance to maximize pull up capability.
Because the PNP output emitter–follower transistor has
been eliminated, the MC34071 series offers a 20 mA
minimum current sink capability, typically to an output voltage
of (VEE +1.8 V). In single supply applications the output can
directly source or sink base current from a common emitter
NPN transistor for fast high current switching applications.
In addition, the all NPN transistor output stage is inherently
fast, contributing to the bipolar amplifier’s high gain
bandwidth product and fast settling capability. The
associated high frequency low output impedance (30
Ω
typ
@ 1.0 MHz) allows capacitive drive capability from 0 pF to
10,000 pF without oscillation in the unity closed loop gain
configuration. The 60° phase margin and 12 dB gain margin
as well as the general gain and phase characteristics are
virtually independent of the source/sink output swing
conditions. This allows easier system phase compensation,
since output swing will not be a phase consideration. The
high frequency characteristics of the MC34071 series also
allow excellent high frequency active filter capability,
especially for low voltage single supply applications.
Although the single supply specifications is defined at
5.0 V, these amplifiers are functional to 3.0 V @ 25°C
although slight changes in parametrics such as bandwidth,
slew rate, and DC gain may occur.
If power to this integrated circuit is applied in reverse
polarity or if the IC is installed backwards in a socket, large
unlimited current surges will occur through the device that
may result in device destruction.
Special static precautions are not necessary for these
bipolar amplifiers since there are no MOS transistors on
the die.
As with most high frequency amplifiers, proper lead dress,
component placement, and PC board layout should
be exercised for optimum frequency performance. For
example, long unshielded input or output leads may result in
unwanted input–output coupling. In order to preserve the
relatively low input capacitance associated with these
amplifiers, resistors connected to the inputs should be
immediately adjacent to the input pin to minimize additional
stray input capacitance. This not only minimizes the input
pole for optimum frequency response, but also minimizes
extraneous “pick up” at this node. Supply decoupling with
adequate capacitance immediately adjacent to the supply pin
is also important, particularly over temperature, since many
types of decoupling capacitors exhibit great impedance
changes over temperature.
The output of any one amplifier is current limited and thus
protected from a direct short to ground. However, under such
conditions, it is important not to allow the device to exceed
the maximum junction temperature rating. Typically for
±15
V
supplies, any one output can be shorted continuously to
ground without exceeding the maximum temperature rating.
MOTOROLA ANALOG IC DEVICE DATA
11
MOTOROLA [ MOTOROLA, INC ]
