參數(shù)資料
型號(hào)： MC10319DW
廠(chǎng)商： MOTOROLA INC
元件分類(lèi)： ADC
英文描述： Hex Inverter Buffers/Drivers With Open-Collector High-Voltage Outputs 14-CFP -55 to 125
中文描述： 8-BIT FLASH METHOD ADC, PARALLEL ACCESS, PDSO28
封裝： PLASTIC, SO-28
文件頁(yè)數(shù)： 10/20頁(yè)
文件大小： 338K
代理商： MC10319DW
MC10319
10
MOTOROLA ANALOG IC DEVICE DATA
APPLICATIONS INFORMATION
Power Supplies, Grounding
The PC board layout, and the quality of the power supplies
and the ground system
at the IC
are very important in order
to obtain proper operation. Noise, from any source, coming
into the device on VCC, VEE, or ground can cause an
incorrect output code due to interaction with the analog
portion of the circuit. At the same time, noise generated
within the MC10319 can cause incorrect operation if that
noise does not have a clear path to ac ground.
Both the VCC and VEE power supplies must be decoupled
to ground
at the IC
(within 1 max) with a 10
μ
F tantalum and
a 0.1
μ
F ceramic. Tantalum capacitors are recommended
since electrolytic capacitors simply have too much
inductance at the frequencies of interest. The quality of the
VCC and VEE supplies should then be checked at the IC with
a high frequency scope. Noise spikes (always present when
digital circuits are present) can easily exceed 400 mV peak,
and if they get into the analog portion of the IC, the operation
can be disrupted. Noise can be reduced by inserting resistors
and/or inductors between the supplies and the IC.
If switching power supplies are used, there will usually be
spikes of 0.5 V or greater at frequencies of 50 to 200 kHz.
These spikes are generally more difficult to reduce because
of their greater energy content. In extreme cases, 3–terminal
regulators (MC78L05ACP, MC7905.2CT), with appropriate
high frequency filtering, should be used and dedicated to
the MC10319.
The ripple content of the supplies should not allow their
magnitude to exceed the values in the Recommended
Operating Limits table.
The PC board tracks supplying VCC and VEE to the
MC10319 should preferably not be at the tail end of the bus
distribution, after passing through a maze of digital circuitry.
The MC10319 should be close to the power supply, or the
connector where the supply voltages enter the board. If the
VCC and VEE lines are supplying considerable current to
other parts of the boards, then it is preferable to have
dedicated lines from the supply or connector directly to
the MC10319.
The four ground pins (2, 12, 16, and 22) must be
connected directly together. Any long path between them can
cause stability problems due to the inductance (at 25 MHz) of
the PC tracks. The ground return for the signal source must
be noise free.
Reference Voltage Circuits
Since the accuracy of the conversion is directly related to
the quality of the references, it is imperative that accurate and
stable voltages be provided to VRT and VRB. If the reference
span is 2.0 V, then 1/2 LSB is only 3.9 mV, and it is desireable
that VRT and VRB be accurate to within this amount, and
furthermore, that they do not drift more than this amount once
set. Over the temperature range of 0
°
to 70
°
C, a maximum
temperature coefficient of 28 ppm/
°
C is required.
The voltage supplies used for digital circuits should
preferably
not
be used as a source for generating VRT and
VRB, due to the noise spikes (50 to 400 mV) present on the
supplies and on their ground lines. Generally
±
15 V, or
±
12 V, are available for analog circuits, and are usually
clean compared to supplies used for digital circuits,
although ripple may be present in varying amounts. Ripple
is easier to filter out than spikes, however, and so these
supplies are preferred.
Figure 21 depicts a circuit which can provide an
extremely stable voltage to VRT
at the current required
(the maximum reference current is 19.2 mA @ 2.0 V). The
MC1403 series of reference sources has very low
temperature coefficients, good noise rejection, and a high
initial accuracy, allowing the circuit to be built without an
adjustment pot if the VRT voltage is to remain fixed at one
value. Using 0.1% wirewound resistors for the divider
provides sufficient accuracy and stability in many cases.
Alternately, resistor networks provide high ratio accuracies,
and close temperature tracking. If the application requires
VRT to be changed periodically, the two resistors can be
replaced with a 20 turn, cermet potentiometer. Wirewound
potentiometers should not be used for this type of
application since the pot’s slider jumps from winding to
winding, and an exact setting can be difficult to obtain.
Cermet pots allow for a smooth continuous adjustment.
In Figure 21, R1 reduces the power dissipation in the
transistor, and can be carbon composition. The 0.1
μ
F
capacitor in the feedback path provides stability in the unity
gain configuration. Recommended op amps are: LM358,
MC34001 series, LM308A, LM324, and LM11C. Offset drift is
the key parameter to consider in choosing an op amp, and
the LM308A has the lowest drift of those mentioned. Bypass
capacitors are not shown in Figure 21, but should always be
provided at the input to the 2.5 V reference, and at the power
supply pins of the op amp.
Figure 22 shows a simpler and more economical circuit,
using the LM317LZ regulator, but with lower initial accuracy
and temperature stability. The op amp/current booster is not
needed since the LM317LZ can supply the current directly. In
a well controlled environment, this circuit will suffice for many
applications. Because of the lower initial accuracy, an
adjustment pot is a necessity.
Figure 23 shows two circuits for providing the voltage to
VRB. The circuits are similar to those of Figures 21 and 22,
and have similar accuracy and stability. The output
transistor is a PNP in this case since the circuit must sink the
reference current.
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