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ADS7805P Schematic ( PDF Datasheet ) - Burr-Brown Corporation

Teilenummer ADS7805P
Beschreibung 16-Bit 10ms Sampling CMOS ANALOG-to-DIGITAL CONVERTER
Hersteller Burr-Brown Corporation
Logo Burr-Brown Corporation Logo 




Gesamt 12 Seiten
ADS7805P Datasheet, Funktion
® ADS7805
DEMO BOARD
AVAILABLE
See Appendix A
16-Bit 10µs Sampling CMOS
ANALOG-to-DIGITAL CONVERTER
FEATURES
q 100kHz min SAMPLING RATE
q STANDARD ±10V INPUT RANGE
q 86dB min SINAD WITH 20kHz INPUT
q ±3.0 LSB max INL
q DNL: 16-bits “No Missing Codes”
q SINGLE +5V SUPPLY OPERATION
q PIN-COMPATIBLE WITH 12-BIT ADS7804
q USES INTERNAL OR EXTERNAL
REFERENCE
q FULL PARALLEL DATA OUTPUT
q 100mW max POWER DISSIPATION
q 28-PIN 0.3" PLASTIC DIP AND SOIC
DESCRIPTION
The ADS7805 is a complete 16-bit sampling A/D
using state-of-the-art CMOS structures. It contains a
complete 16-bit, capacitor-based, SAR A/D with S/H,
reference, clock, interface for microprocessor use, and
three-state output drivers.
The ADS7805 is specified at a 100kHz sampling rate,
and guaranteed over the full temperature range. Laser-
trimmed scaling resistors provide an industry-
standard ±10V input range, while the innovative de-
sign allows operation from a single +5V supply, with
power dissipation under 100mW.
The 28-pin ADS7805 is available in a plastic 0.3" DIP
and in an SOIC, both fully specified for operation over
the industrial –25°C to +85°C range.
Clock
Successive Approximation Register and Control Logic
R/C
CS
BYTE
BUSY
±10V Input
20k
10k4k
CAP
REF
CDAC
Buffer
4k
Internal
+2.5V Ref
Comparator
Output
Latches
and
Three
State
Drivers
Three
State
Parallel
Data
Bus
International Airport Industrial Park • Mailing Address: PO Box 11400, Tucson, AZ 85734 • Street Address: 6730 S. Tucson Blvd., Tucson, AZ 85706 • Tel: (520) 746-1111 • Twx: 910-952-1111
Internet: http://www.burr-brown.com/ • FAXLine: (800) 548-6133 (US/Canada Only) • Cable: BBRCORP • Telex: 066-6491 • FAX: (520) 889-1510 • Immediate Product Info: (800) 548-6132
©1992 Burr-Brown Corporation
PDS-1157E
Printed in U.S.A. August, 1996






ADS7805P Datasheet, Funktion
TYPICAL PERFORMANCE CURVES (CONT)
TA = +25°C, fS = 100kHz, VDIG = VANA = +5V, using internal reference and fixed resistors shown in Figure 6b, unless otherwise specified.
INTERNAL REFERENCE VOLTAGE vs TEMPERATURE
2.520
2.515
2.510
2.505
2.500
2.495
2.490
2.485
2.480
–50 –25
0
25 50 75
Temperature (°C)
100 125 150
CONVERSION TIME vs TEMPERATURE
8.0
7.9
7.8
7.7
7.6
7.5
7.4
7.3
7.2
–50 –25 0 25 50 75 100 125 150
Temperature (°C)
8
4
0
–4
–8
0.2
0.1
0.0
–0.1
–0.2
BPZ ERROR (INTERNAL REFERNCE)
ENDPOINT ERRORS (EXTERNAL REFERNCE)
+FS Error
ENDPOINT ERRORS (EXTERNAL REFERNCE)
0.2
–FS Error
0.1
0.0
–0.1
–0.2
–50 –25 0 25 50 75 100 125
Temperature (°C)
150
®
ADS7805
6

6 Page









ADS7805P pdf, datenblatt
LAYOUT
POWER
For optimum performance, tie the analog and digital power
pins to the same +5V power supply and tie the analog and
digital grounds together. As noted in the electrical specifica-
tions, the ADS7805 uses 90% of its power for the analog
circuitry. The ADS7805 should be considered as an analog
component.
The +5V power for the A/D should be separate from the +5V
used for the system’s digital logic. Connecting VDIG (pin 28)
directly to a digital supply can reduce converter performance
due to switching noise from the digital logic. For best
performance, the +5V supply can be produced from what-
ever analog supply is used for the rest of the analog signal
conditioning. If +12V or +15V supplies are present, a simple
+5V regulator can be used. Although it is not suggested, if
the digital supply must be used to power the converter, be
sure to properly filter the supply. Either using a filtered
digital supply or a regulated analog supply, both VDIG and
VANA should be tied to the same +5V source.
GROUNDING
Three ground pins are present on the ADS7805. DGND is
the digital supply ground. AGND2 is the analog supply
ground. AGND1 is the ground which all analog signals
internal to the A/D are referenced. AGND1 is more suscep-
tible to current induced voltage drops and must have the path
of least resistance back to the power supply.
All the ground pins of the A/D should be tied to the analog
ground plane, separated from the system’s digital logic
ground, to achieve optimum performance. Both analog and
digital ground planes should be tied to the “system” ground
as near to the power supplies as possible. This helps to
prevent dynamic digital ground currents from modulating
the analog ground through a common impedance to power
ground.
SIGNAL CONDITIONING
The FET switches used for the sample hold on many CMOS
A/D converters release a significant amount of charge injec-
tion which can cause the driving op amp to oscillate. The
FET switch on the ADS7805, compared to the FET switches
on other CMOS A/D converters, releases 5%-10% of the
charge. There is also a resistive front end which attenuates
any charge which is released. The end result is a minimal
requirement for the anti-alias filter on the front end. Any op
amp sufficient for the signal in an application will be
sufficient to drive the ADS7805.
The resistive front end of the ADS7805 also provides a
guaranteed ±25V overvoltage protection. In most cases, this
eliminates the need for external input protection circuitry.
INTERMEDIATE LATCHES
The ADS7805 does have tri-state outputs for the parallel
port, but intermediate latches should be used if the bus will
be active during conversions. If the bus is not active during
conversion, the tri-state outputs can be used to isolate the
A/D from other peripherals on the same bus. Tri-state
outputs can also be used when the A/D is the only peripheral
on the data bus.
Intermediate latches are beneficial on any monolithic A/D
converter. The ADS7805 has an internal LSB size of 38µV.
Transients from fast switching signals on the parallel port,
even when the A/D is tri-stated, can be coupled through the
substrate to the analog circuitry causing degradation of
converter performance.
®
ADS7805
12

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