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PDF ADC0851CIV Data sheet ( Hoja de datos )
| Número de pieza | ADC0851CIV | |
| Descripción | 8-Bit Analog Data Acquisition and Monitoring Systems | |
| Fabricantes | National Semiconductor | |
| Logotipo |  |
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January 1995
ADC0851 and ADC0858 8-Bit Analog Data
Acquisition and Monitoring Systems
General Description
The ADC0851 and ADC0858 are 2 and 8 input analog data
acquisition systems They can function as conventional mul-
tiple input A D converters automatic scanning A D convert-
ers or programmable analog ‘‘watchdog’’ systems In
‘‘watchdog’’ mode they monitor analog inputs and deter-
mine whether these inputs are inside or outside user pro-
grammed window limits This monitoring process takes
place independent of the host processor When any input
falls outside of its programmed window limits an interrupt is
automatically generated which flags the processor the chip
can then be interrogated as to exactly which channels
crossed which limits
The advantage of this approach is that its frees the proces-
sor from having to frequently monitor analog variables It
can consequently save having to insert many A D subrou-
tine calls throughout real time application code In control
systems where many variables are continually being moni-
tored this can significantly free up the processor especially
if the variables are DC or slow varying signals
The Auto A D conversion feature allows the device to scan
through selected input channels performing an A D conver-
sion on each channel without the need to select a new
channel after each conversion
Applications
Y Instrumentation monitoring and process control
Y Digitizing automotive sensor signals
Y Embedded diagnostics
Key Specifications
Y Resolution
Y Total error
Y Low power
Y Conversion time
Y Limit comparison time
8 Bits
g LSB or g 1 LSB
50 mW
18 ms Channel
2 ms Limit
Features
Y Watchdog operation signals processor when any
channel is outside user programmed window limits
Y Frees microprocessor from continually monitoring
analog signals and simplifies applications software
Y 2 (ADC0851) or 8 (ADC0858) analog input channels
Y Single ended or differential input pairs
Y COM input for DC offsetting of input voltage
Y 4 (ADC0851) and 16 (ADC0858) 8-bit programmable
limits
Y NSC MICROWIRETM interface
Y Power fail detection
Y Auto A D conversion feature
Y Single 5V supply
Y Window limits are user programmable via serial inter-
face
Simplified Block Diagram
TRI-STATE is a registered trademark of National Semiconductor Corporation
MICROWIRETM is a trademark of National Semiconductor Corporation
C1995 National Semiconductor Corporation TL H 11021
FIGURE 1
TL H 11021 – 22
RRD-B30M75 Printed in U S A
1 page  
AC Electrical Characteristics (Continued)
The following specifications apply for VCC e a5 VDC VREF e a4 5 VDC AGND e DGND e 0V fCLK e 1 MHz tr e tf e
5 ns unless otherwise specified Boldface limits apply for TA e TJ e TMIN to TMAX all other limits apply at TA e TJ e 25 C
Symbol
Parameter
Conditions
Typical
(Note 5)
Limit
(Note 6)
Units
(Limits)
t1H t0H
Rising Edge of CS to
Data Output Hi-Z
C e 100 pF R e 2k
(See TRI-STATE
Test Circuits)
90
200
ns (Max)
fOSC
tEOC
Oscillator Clock Freq
(Analog Timing)
CS to End of
Conversion Delay
Rext e 3 16 kX
Cext e 170 pF
1
1 4 MHz (Max)
0 6 MHz (Min)
OSC Clock
Periods
1 Min
2 Max
tConv
Conversion Time
OSC Clock
Periods
17 (Min)
18 (Max)
tCS-INT
CIN
CS to Interrupt Delay
Capacitance of
Logic Input
60
120
ns (Max)
5 pF
COUT
Capacitance of
Logic Output
5 pF
Note 1 Absolute Maximum Ratings indicate limits beyond which damage to the device may occur Operating Ratings indicate conditions for which the device is
functional but do not guarantee specific performance limits For guaranteed specifications and test conditions see the Electrical Characteristics The guaranteed
specifications apply only for the test conditions listed Some performance characteristics may degrade when the device is not operated under the listed test
conditions
Note 2 All voltages are measured with respect to ground (AGND e DGND e 0V)
Note 3 All of the analog and digital input pins are internally diode clamped to the supply pins Should the applied voltage at any pin exceed the power supply
voltage the additional absolute value of current at that pin (caused by the forward biasing of the internal diodes) should be limited to 5 mA or less
Note 4 Human body model 100 pF discharged through a 1 5 kX resistor
Note 5 Typical specifications are at a25 C and represent the most likely parametric norm
Note 6 Tested limits are guaranteed to National’s AOQL (Average Outgoing Quality Level)
Note 7 Total unadjusted error includes comparator offset ADC linearity and multiplexer error and is expressed in LSBs
Note 8 Two on-chip diodes are tied to each analog input The diodes will forward conduct for analog input voltages one diode drop below ground or one diode drop
above VCC Care should be exercised when operating the device at low supply voltages (e g VCC e 4 5V) because high analog inputs (5V) can cause the input
diodes to conduct especially at elevated temperatures This will cause errors for analog inputs near full scale The specification allows 50 mV forward bias of either
clamp diode Thus as long as VIN or VREF does not exceed the supply voltage by more than 50 mV the output code will be correct To achieve an absolute 0 VDC
to 5 VDC input voltage range will therefore require a minimum supply voltage of 4 950 VDC
Note 9 Leakage current is measured with the oscillator clock disabled
Note 10 Measured supply current does not include the DAC ladder current
Note 11 A 40% to 60% clock duty cycle range ensures proper operation at all clock frequencies
5
5 Page 
Timing Diagrams for ADC0851 and ADC0858 (Continued)
11
11 Page | ||
| Páginas | Total 30 Páginas | |
| PDF Descargar | [ Datasheet ADC0851CIV.PDF ] | |
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