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PDF ADS7810U Data sheet ( Hoja de datos )
| Número de pieza | ADS7810U | |
| Descripción | 12-Bit 800kHz Sampling CMOS ANALOG-to-DIGITAL CONVERTER | |
| Fabricantes | Burr-Brown Corporation | |
| Logotipo |  |
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ADS7810
ADS7810
12-Bit 800kHz Sampling CMOS
ANALOG-to-DIGITAL CONVERTER
FEATURES
q 1.25µs THROUGHPUT TIME
q STANDARD ±10V INPUT RANGE
q 69dB min SINAD WITH 250kHz INPUT
q ±3/4 LSB max INL AND ±1 LSB max DNL
q INTERNAL REFERENCE
q COMPLETE WITH S/H, REF, CLOCK, ETC.
q PARALLEL DATA w/LATCHES
q 28-PIN SOIC
DESCRIPTION
The ADS7810 is a complete 12-bit sampling A/D
using state-of-the-art CMOS structures. It contains a
complete 12-bit capacitor-based SAR A/D with inher-
ent S/H, reference, clock, interface for microprocessor
use, and three-state output drivers.
The ADS7810 is specified at an 800kHz sampling
rate, and guaranteed over the full temperature range.
Laser-trimmed scaling resistors provide the industry-
standard ±10V input range, while an innovative design
allows operation from ±5V supplies.
The 28-pin ADS7810 is available in a plastic SOIC
fully specified for operation over the industrial –40°C
to +85°C range.
Clock
Successive Approximation Register and Control Logic
2450Ω
±10V Input
625Ω
Cap
CDAC
Comparator
Output
Latches
and
Three
State
Drivers
BUSY
Three
State
Parallel
Data
Bus
18kΩ
Buffer
2.5V Ref Out/In
4.8kΩ
8.6kΩ
Internal
Ref
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-1138E
Printed in U.S.A. March, 1998
1 page  
TYPICAL PERFORMANCE CURVES
T = +25°C, fS =800kHz, +VDIG = +VANA = +5V, –VANA = –5V, using internal reference and the input 50Ω resistors as shown in Figure 4b, unless otherwise specified.
0
–20
–40
–60
–80
–100
–120
0
FREQUENCY SPECTRUM
(4096 Point FFT; fIN = 252kHz, –0.5dB)
100 200 300
Frequency (kHz)
400
0
–20
–40
–60
–80
–100
–120
0
FREQUENCY SPECTRUM
(4096 Point FFT; fIN = 502kHz, –0.5dB)
100 200 300
Frequency (kHz)
400
0
–20
–40
–60
–80
–100
–120
0
FREQUENCY SPECTRUM
(4096 Point FFT; fIN = 1.002MHz, –0.5dB)
100 200 300
Frequency (kHz)
400
0
–20
–40
–60
–80
–100
–120
0
FREQUENCY SPECTRUM
(4096 Point FFT; f1IN = 232kHz, –6.5dB;
f2IN = 272kHz, –6.5dB)
100 200 300
Frequency (kHz)
400
90
80
70
60
50
40
30
20
10
1k
SIGNAL-TO-(NOISE + DISTORTION)
vs INPUT FREQUENCY (fIN = –0.5dB)
10k 100k 1M
Input Signal Frequency (Hz)
10M
100
95
90
85
80
75
70
65
60
–50
A.C. PARAMETERS vs TEMPERATURE
(fIN = 250kHz, –0.5dB)
SFDR
THD
SNR
SINAD
–25 0
25 50 75
Temperature (°C)
–100
–95
–90
–85
–80
–75
–70
–65
–60
100
®
5 ADS7810
5 Page 
CAP
CAP (pin 4) is the output of the internal reference buffer. A
10µF tantalum capacitor should be placed as close to the
CAP as possible to provide optimum switching currents for
the CDAC throughout the conversion cycle and compensa-
tion for the output of the buffer. Using a capacitor any
smaller than 1µF can cause the output buffer to oscillate and
may not have sufficient charge for the CDAC. Capacitor
values larger than 10µF will have little effect on improving
performance. The voltage on the CAP pin is approximately
2V when using the internal reference, or 80% of an exter-
nally supplied reference.
LAYOUT
POWER
The ADS7810 uses the majority of its power for analog and
static circuitry, and it should be considered as an analog
component. For optimum performance, tie the analog and
digital +5V power pins to the same +5V power supply and
tie the analog and digital grounds together.
For best performance, the ±5V supplies can be produced
from whatever analog supply is used for the rest of the
analog signal conditioning. If ±12V or ±15V supplies are
present, simple regulators can be used. The +5V power for
the A/D should be separate from the +5V used for the
system’s digital logic. Connecting +VDIG (pin 27) directly to
a digital supply can reduce converter performance due to
switching noise from the digital logic.
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 ADS7810. DGND
(pin 22) is the digital supply ground. AGND2 (pin 5) is the
analog supply ground. AGND1 (pin 2) is the ground which all
analog signals internal to the A/D are referenced. AGND1 is
more susceptible to current induced voltage drops and must
have the path of least resistance back to the power supply.
All the ground pins of the ADS should be tied to the
analog ground plane, separated from the system’s digital
logic ground, to achieve optimum performance. Both ana-
log and digital ground planes should be tied to the “sys-
tem” 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
resistive front end of the ADS7810 attenuates this charge
and reduces its magnitude significantly—reducing the bur-
den on the external input amplifier or buffer.
However, keep in mind that maintaining signal integrity at
voltage swings of ±10V and frequencies of several hundred
kilohertz is extremely challenging. In addition, the external
input amplifier must drive the ADS7810 mainly during its
sample period—roughly 200ns. This will require a high-
speed, precision amplifier which can swing to greater than
±10V.
For signals where the predominant frequencies are below
200kHz, the OPA671 operational amplifier should be ad-
equate for most applications. In some cases or where input
frequencies are higher, a composite configuration of the
OPA671 and BUF634 (in its wide bandwidth mode) may be
the best choice. See the BUF634 data sheet for more infor-
mation.
The resistive front end of the ADS7810 also provides a
guaranteed ±25V over voltage protection. In most cases, this
eliminates the need for external input protection circuitry.
INTERMEDIATE LATCHES
The ADS7810 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
conversions, the tri-state outputs can be used to isolate the
A/D from other peripherals on the same bus.
Intermediate latches are beneficial on any monolithic A/D
converter. The ADS7810 has an internal LSB size of 610µV.
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.
®
11 ADS7810
11 Page | ||
| Páginas | Total 11 Páginas | |
| PDF Descargar | [ Datasheet ADS7810U.PDF ] | |
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