AD976A Analog Devices, AD976A Datasheet - Page 14

• Manufacturer Part Number: AD976A
• Description: 16-Bit, 200 kSPS, Parallel I/O A/D Converter
• Manufacturer: Analog Devices

Specifications of AD976A

• Resolution (bits): 16bit
• # Chan: 1
• Sample Rate: 200kSPS
• Interface: Par
• Analog Input Type: SE-Bip,SE-Uni
• Ain Range: Bip 10V
• Adc Architecture: SAR
• Pkg Type: DIP,SOIC,SOP

AD976/AD976A
8051 Interface
Figure 21 illustrates the use of the AD976/AD976A with an
8051 microcontroller.
TMS320C25 Interface
Figure 22 shows an interface between the AD976/AD976A and
the TMS320C25.
ADSP-2111 Interface
Figure 23 shows an interface to the ADSP-2111 signal processor.
In this example, CS is being used to control conversions and is
generated by an external timer. A conversion is initiated each
time the timer output goes low as long as you are not reading
from the AD976/AD976A and while the Flag Output (FO) pin
of the ADSP-2111 is low. When a conversion is complete, the
BUSY line will return high. With the IRQn pin programmed to
generate an interrupt on a high-to-low transition, an interrupt
will occur at the end of each conversion. The 16-bit result of the
conversion can be read from within the interrupt service routine
by first forcing FO high, then performing a read operation with
the AD976/AD976A.
Figure 22. AD976/AD976A to TMS320C25 Interface
8051
TMS320C25
P0
P2
AD7
AD0
A15
WR
INT
Figure 21. AD976/AD976A to 8051 Interface
RD
A8
READY
STRB
BUS
NSC
R/W
A15
D15
INT
A0
D0
IS
*ADDITIONAL PINS OMITTED FOR CLARITY
DECODE
LATCH
*ADDITIONAL PINS OMITTED FOR CLARITY
ADDR
BUS
BUS
ADDRESS BUS
DATA BUS
EN
DECODE
A0
ADDR
TIMER
DB15
CS
BUSY
DB0
R/C
AD976A
AD976/
DB0
BYTE
DB7
R/C
CS
BUSY
AD976A
AD976/
–14–
POWER SUPPLIES AND DECOUPLING
The AD976/AD976A has two power supply input pins. V
and V
portions, respectively. V
analog circuitry, and V
digital circuitry. The AD976/AD976A is designed to be inde-
pendent of power supply sequencing and, thus, free from supply
voltage induced latch-up.
With high performance linear circuits, changes in the power
supplies can result in undesired circuit performance. Optimally,
well regulated power supplies should be chosen with less than
1% ripple. The ac output impedance of a power supply is a
complex function of frequency and it will generally increase with
frequency. Thus, high frequency switching, such as that encoun-
tered with digital circuitry, requires the fast transient currents
that most power supplies can not adequately provide. Such a
situation results in large voltage spikes on the supplies. To com-
pensate for the finite ac output impedance of most supplies,
charge “reserves” should be stored in bypass capacitors. This
will effectively lower the supplies impedance presented to the
AD976/AD976A V
of these spikes. Decoupling capacitors, typically 0.1 F, should
be placed close to the power supply pins of the AD976/AD976A
to minimize any inductance between the capacitors and the
V
The AD976/AD976A may be operated from a single +5 V sup-
ply. When separate supplies are used, however, it is beneficial to
have larger capacitors, 10 F, placed between the logic supply
(V
supply (V
10 F capacitors should be located in the vicinity of the ADC to
further reduce low frequency ripple. In systems where the device
will be subjected to harsh environmental noise, additional de-
coupling may be required.
ANA
DIG
Figure 23. AD976/AD976A to ADSP-2111 Interface
ADSP-2111
) and digital common (DGND) and between the analog
and V
DIG
ANA
provide the supply voltages to the analog and digital
DIG
IRQn
DMS
A13
D15
) and the analog common (AGND2). Additionally,
RD
FO
A0
D0
pins.
*ADDITIONAL PINS OMITTED FOR CLARITY
ANA
ADDRESS BUS
EN
DECODE
ADDR
DATA BUS
DIG
and V
ANA
is the +5 V supply for the on-chip
is the +5 V supply for the on-chip
DIG
pins and reduce the magnitude
TIMER
CS
BUSY
DB15
R/C
DB0
AD976A
AD976/
REV. C
ANA