EVAL-AD7441CBZ Analog Devices Inc, EVAL-AD7441CBZ Datasheet - Page 20

• Manufacturer Part Number: EVAL-AD7441CBZ
• Manufacturer: Analog Devices Inc

Specifications of EVAL-AD7441CBZ

• Lead Free Status / Rohs Status: Supplier Unconfirmed

AD7441/AD7451
POWER VS. THROUGHPUT RATE
By using the power-down mode on the device when not con-
verting, the average power consumption of the ADC decreases
at lower throughput rates. Figure 32 shows how, as the through-
put rate is reduced, the device remains in its power-down state
longer and the average power consumption reduces accordingly.
For example, if the AD7441/AD7451 are operated in continuous
sampling mode with a throughput rate of 100 kSPS and an SCLK
of 18 MHz, and the device is placed in the power-down mode
between conversions, then the power consumption during
normal operation equals 9.25 mW maximum (for V
If the power-up time is one dummy cycle (1 μs) and the remain-
ing conversion time is another cycle (1 μs), then the AD7441/
AD7451 can be said to dissipate 9.25 mW for 2 μs during each
conversion cycle. (This power consumption figure assumes a
very short time to enter power-down mode. This power figure
increases as the burst of clocks used to enter power-down mode
is increased). The AD7441/AD7451 consume just 5 μW for the
remaining 8 μs.
Calculate the power numbers in Figure 32 as follows:
If the throughput rate = 100 kSPS, then the cycle time = 10 μs,
and the average power dissipated during each cycle is
For the same scenario, if V
during normal operation is 4 mW maximum.
The AD7441/AD7451 can now be said to dissipate 4 mW for
2 μs during each conversion cycle.
The average power dissipated during each cycle with a
throughput rate of 100 kSPS is, therefore,
(2/10) × 9.25 mW = 1.85 mW
(2/10) × 4 mW = 0.8 mW
0.01
100
0.1
10
Figure 32. Power vs. Throughput Rate for Power-Down Mode
1
0
50
100
THROUGHPUT (kSPS)
DD
150
= 3 V, the power dissipation
V
DD
200
= 5V
V
DD
= 3V
250
300
DD
= 5 V).
350
Rev. C | Page 20 of 24
For optimum power performance in throughput rates above
320 kSPS, it is recommended that the serial clock frequency be
reduced.
MICROPROCESSOR AND DSP INTERFACING
The serial interface on the AD7441/AD7451 allows the part to
be connected directly to a range of different microprocessors.
This section explains how to interface the AD7441/AD7451
with some of the more common microcontroller and DSP serial
interface protocols.
AD7441/AD7451 to ADSP-21xx
The ADSP-21xx family of DSPs is interfaced directly to the
AD7441/AD7451 without any glue logic required. The SPORT
control register is set up as follows:
TFSW = RFSW = 1
INVRFS = INVTFS = 1
DTYPE = 00
SLEN = 1111
ISCLK = 1
TFSR = RFSR = 1
IRFS = 0
ITFS = 1
To implement power-down mode, SLEN is set to 1001 to issue
an 8-bit SCLK burst.
The connection diagram is shown in Figure 33. ADSP-21xx has
the TFS and RFS of the SPORT tied together, with TFS set as an
output and RFS set as an input. The DSP operates in alternate
framing mode, and the SPORT control register is set up as
described. The frame synchronization signal generated on the
TFS is tied to CS , and, as with all signal processing applications,
equidistant sampling is necessary. However, in this example,
the timer interrupt is used to control the sampling rate of the
ADC, and, under certain conditions, equidistant sampling
cannot be achieved.
*ADDITIONAL PINS REMOVED FOR CLARITY.
AD7451*
AD7441/
SDATA
SCLK
CS
Figure 33. Interfacing to the ADSP-21xx
Alternate framing
Active low frame signal
Right justify data
16-bit data-words
Internal serial clock
Frame every word
SCLK
DR
RFS
TFS
ADSP-21xx*