HI5800-EV(1999) Просмотр технического описания (PDF) - Intersil
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HI5800-EV Datasheet PDF : 15 Pages
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HI5800
Description
The HI5800 is a 12-bit, two-step, sampling analog-to-digital
converter which uses a subranging technique with digital
error correction. As illustrated in the block diagram, it uses a
sample and hold front end, 7-bit, R-2R D/A converter which
is laser trimmed to 14 bits accuracy, a 7-bit BiCMOS flash
converter, precision bandgap reference, digital controller and
timing generator, error correction logic, output latches and
BiCMOS output drivers.
The falling edge of the convert command signal puts the
sample and hold (S/H) in the hold mode and the conversion
process begins. At this point the Interrupt Request (IRQ) line is
set high indicating that a conversion is in progress. The output
of the S/H circuit drives the input of the 7-bit flash converter
through a switch. After allowing the flash to settle, the
intermediate output of the flash is stored in the latches which
feed the D/A and error correction logic. The D/A reconstructs
the analog signal and feeds the gain amplifier whose summing
node subtracts the held signal of the S/H and amplifies the
residue by 32. This signal is then switched to the flash for a
second pass using the input switch. The output of the second
flash conversion is fed directly to the error correction which
reconstructs the twelve bit word from the fourteen bit input. The
logic also decodes the overflow bit and the polarity of the
overflow. The output of the error correction is then gated
through the read controller to the output drivers. The data is
ready on the bus as soon as the IRQ line goes low.
I/O Control Inputs
The converter has four active low inputs (CS, CONV, OE and
A0) and fourteen outputs (D0 - D11, IRQ and OVF). All
inputs and outputs are TTL compatible and will also interface
to the newer TTL compatible families. All four inputs are
CMOS high input impedance stages and all outputs are
BiMOS drivers capable of driving 100pF loads.
In order to initiate a conversion or read the data bus, CS should
be held low. The conversion is initiated by the falling edge of the
CONV command. The OE input controls the output bus directly
and is independent of the conversion process. The data on the
bus changes just before the IRQ goes low. Therefore if the OE
line is held low all the time, the data on the bus will change just
before the IRQ line goes low. The byte control signal A0 is also
independent of the conversion process and the byte can be
manipulated anytime. When A0 is low the 12-bits and overflow
word is read on the bus. The bus can also be hooked up such
that the upper byte (D11 - D4) is read when A0 is low. When A0
is high, the lower byte (D3 - D0) is output on the same eight
pins with trailing zeros.
In order to minimize switching noise during a conversion,
byte manipulations done using the A0 signal should be done
in the single shot mode and A0 should be changed during
the acquisition phase. For accuracy, allow sufficient time for
settling from any glitches before the next conversion.
Once a conversion is started, the converter will complete the
conversion and acquisition periods irrespective of the input
states. If during these cycles another convert command is
issued, it will be ignored until the acquire phase is complete.
Stand Alone Operation
The converter can be operated in a stand alone configuration
with bus inputs controlling the converter. The conversion will be
started on the negative edge of the convert (CONV) pulse as
long as this pulse is less than the converter throughput rate. If
the converter is given multiple convert commands, it will ignore
all but the first command until such time when the acquisition
period of the next cycle is complete. At this point it will start a
new conversion on the first negative edge of the input
command. This allows the converter to be synchronized to a
multiple of a faster external clock. The new output data of the
conversion is available on the same cycle at the negative edge
of the IRQ pulse and is valid until the next negative edge of the
IRQ pulse. Data may be accessed at any time during these
cycles. It should be noted that if the data bus is kept enabled all
the time (OE is low), then the data will be updating just before
the IRQ goes low. During this time, the data may not be valid for
a few nanoseconds.
Continuous Convert Mode
The converter can be operated at its maximum rate by taking
the CONV line low (supplying the first negative edge) and
holding it low. This enables the continuous convert mode.
During this time, at the end of the internal acquisition period,
the converter automatically starts a new conversion. The
data will be valid between the IRQ negative edges.
Note that there is no pipeline delay on the data. The output data
is available during the same cycle as the conversion and is valid
until the next conversion ends. This allows data access to both
previous and present conversions in the same cycle.
When initiating a conversion or a series of conversions, the
last signal (CS and CONV) to arrive dominates the function.
The same condition holds true for enabling the bus to read
the data (CS and OE). To terminate the bus operations, the
first signal (CS and OE) to arrive dominates the function.
Interrupt Request Output
The interrupt request line (IRQ) goes high at the start of each
conversion and goes low to indicate the start of the acquisition.
During the time that IRQ is high, the internal sample and hold is
in hold mode. At the termination of IRQ, the sample and hold
switches to acquire mode which lasts approximately 100ns. If
no convert command is issued for a period of time, the sample
and hold simply remains in acquire mode tracking the analog
input signal until the next conversion cycle is initiated. The IRQ
line is the only output that is not three-stateable.
Analog Input, VIN
The analog input of the HI5800 is coupled into the input
stage of the Sample and Hold amplifier. The input is a high
impedance bipolar differential pair complete with an ESD
protection circuit. Typically it has >3MΩ input impedance.
With this high input impedance circuit, the HI5800 is easily
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