AD73311LAR Analog Devices Inc, AD73311LAR Datasheet - Page 26

• Manufacturer Part Number: AD73311LAR
• Description: IC ANALOG FRONT END 20-SOIC
• Manufacturer: Analog Devices Inc

Specifications of AD73311LAR

• Rohs Status: RoHS non-compliant
• Number Of Bits: 16
• Number Of Channels: 2
• Power (watts): 50mW
• Voltage - Supply, Analog: 3V
• Voltage - Supply, Digital: 3V
• Package / Case: 20-SOIC (7.5mm Width)
• Single Supply Voltage (min): 2.7V
• Single Supply Voltage (max): 3.3V
• Package Type: SOIC W
• Lead Free Status / RoHS Status: Not Compliant

AD73311L
Avoid running digital lines under the device for they will couple
noise onto the die. The analog ground plane should be allowed
to run under the AD73311L to avoid noise coupling. The power
supply lines to the AD73311L should use as large a trace as
possible to provide low impedance paths and reduce the effects
of glitches on the power supply lines. Fast switching signals such
as clocks should be shielded with digital ground to avoid radiat-
ing noise to other sections of the board, and clock signals should
never be run near the analog inputs. Traces on opposite sides of
the board should run at right angles to each other. This will
reduce the effects of feedthrough through the board. A microstrip
technique is by far the best but is not always possible with a
double-sided board. In this technique, the component side of
the board is dedicated to ground planes while signals are placed
on the other side.
Good decoupling is important when using high speed devices.
All analog and digital supplies should be decoupled to AGND
and DGND respectively, with 0.1 µF ceramic capacitors in
parallel with 10 µF tantalum capacitors. To achieve the best
from these decoupling capacitors, they should be placed as close
as possible to the device, ideally right up against it. In systems
where a common supply voltage is used to drive both the AVDD
and DVDD of the AD73311, it is recommended that the system’s
AVDD supply be used. This supply should have the recom-
mended analog supply decoupling between the AVDD pins of
the AD73311L and AGND and the recommended digital sup-
ply decoupling capacitors between the DVDD pin and DGND.
DSP Programming Considerations
This section discusses some aspects of how the serial port of the
DSP should be configured and the implications of whether Rx
and Tx interrupts should be enabled.
DSP SPORT Configuration
Following are the key settings of the DSP SPORT required for
the successful operation with the AD73311L:
• Configure for external SCLK.
• Serial Word Length = 16 bits.
• Transmit and Receive Frame Syncs required with every word.
• Receive Frame Sync is an input to the DSP.
• Transmit Frame Sync is an:
• Frame Syncs occur one SCLK cycle before the MSB of the
•
• Frame Syncs are active high.
DSP SPORT Interrupts
If SPORT interrupts are enabled, it is important to note that the
active signals on the frame sync pins do not necessarily corre-
spond with the positions in time of where SPORT interrupts are
generated.
Input—in Frame Sync Loop-Back Mode
Output—in Nonframe Sync Loop-Back Mode.
serial word.
DIGITAL GROUND
ANALOG GROUND
On ADSP-218x processors, it is necessary to enable SPORT
interrupts and use Interrupt Service Routines (ISRs) to handle
Tx/Rx activity, while on the TMS320C5x processors it is pos-
sible to poll the status of the Rx and Tx registers, which means
that Rx/Tx activity can be monitored using a single ISR that
would ideally be the Tx ISR as the Tx interrupt will typically
occur before the Rx ISR.
DSP SOFTWARE CONSIDERATIONS WHEN
INTERFACING TO THE AD73311L
It is important when choosing the operating mode and hardware
configuration of the AD73311L to be aware of their implications
for DSP software operation. The user has the flexibility of choosing
from either FSLB or nonFSLB when deciding on DSP to AFE
connectivity. There is also a choice to be made between using
autobuffering of input and output samples or simply choosing to
accept them as individual interrupts. As most modern DSP engines
support these modes, this appendix will attempt to discuss these
topics in a generic DSP sense.
Operating Mode
The AD73311L supports two basic operating modes: Frame Sync
Loop Back (FSLB) and nonFSLB (see Interfacing section). As
described previously, FSLB has some limitations when used in
Mixed Mode but is very suitable for use with the autobuffering
feature that is offered on many modern DSPs. Autobuffering
allows the user to specify the number of input or output words
(samples) that are transferred before a specific Tx or Rx SPORT
interrupt is generated. Given that the AD73311L outputs two
sample words per sample period, it is possible using autobuffering
to have the DSP’s SPORT generate a single interrupt on receipt
of the second of the two sample words. Additionally, both samples
could be stored in a data buffer within the data memory store.
This technique has the advantage of reducing the number of both
Tx and Rx SPORT interrupts to a single one at each sample
interval. The user also knows where each sample is stored. The
alternative is to handle a larger number of SPORT interrupts
(twice as many in the case of a single AD73311L) while also
having some status flags to indicate where each new sample
comes from (or is destined for).
Mixed-Mode Operation
To take full advantage of Mixed-Mode operation, it is necessary
to configure the DSP/Codec interface in nonFSLB and to disable
autobuffering. This allows a variable numbers of words to be sent
to the AD73311L in each sample period—the extra words being
control words which are typically used to update gain settings in
adaptive control applications. The recommended sequence for
updating control registers in mixed-mode is to send the control
word(s) first before the DAC update word.
It is possible to use Mixed-Mode operation when configured in
FSLB, but it is necessary to replace the DAC update with a control
word write in each sample period which may cause some discon-
tinuity in the output signal due to a sample point being missed
and the previous sample being repeated. This however may be
acceptable in some cases as the effect may be masked by gain
changes, etc.