AD7664AST Analog Devices Inc, AD7664AST Datasheet - Page 18

• Manufacturer Part Number: AD7664AST
• Description: IC ADC 16BIT UNIPOLAR 48-LQFP
• Manufacturer: Analog Devices Inc
• Series: PulSAR®r

Specifications of AD7664AST

• Rohs Status: RoHS non-compliant
• Number Of Bits: 16
• Sampling Rate (per Second): 570k
• Data Interface: Serial, Parallel
• Number Of Converters: 1
• Power Dissipation (max): 115mW
• Voltage Supply Source: Analog and Digital
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 48-LQFP
• For Use With: EVAL-AD7664CBZ - BOARD EVALUATION FOR AD7664

AD7664
External Clock Data Read during Conversion
Figure 20 shows the detailed timing diagram of this method.
During a conversion, while both CS and RD are LOW, the result
of the previous conversion can be read. The data is shifted out
MSB first with 16 clock pulses, and is valid on both the rising and
falling edge of the clock. The 16 bits have to be read before the
current conversion is complete; otherwise, RDERROR is pulsed
HIGH and can be used to interrupt the host interface to
prevent incomplete data reading. There is no daisy-chain
feature in this mode and RDC/SDIN input should always be tied
either HIGH or LOW.
To reduce performance degradation due to digital activity, a fast
discontinuous clock of at least 18 MHz when in Impulse Mode,
25 MHz when in Normal Mode, or 40 MHz when in Warp
Mode is recommended to ensure that all the bits are read during
the first half of the conversion phase. It is also possible to begin
to read the data after conversion and continue to read the last bits
even after a new conversion has been initiated. That allows the use of
a slower clock speed such as 14 MHz in Impulse Mode, 18 MHz
in Normal Mode, and 25 MHz in Warp Mode.
MICROPROCESSOR INTERFACING
The AD7664 is ideally suited for traditional dc measurement
applications supporting a microprocessor and ac signal processing
applications interfacing to a digital signal processor. The AD7664
is designed to interface either with a parallel 8-bit or 16-bit wide
interface, or with a general-purpose serial port or I/O ports on
a microcontroller. A variety of external buffers can be used
with the AD7664 to prevent digital noise from coupling into the
ADC. The following section discusses the use of an AD7664
with an ADSP-219x SPI equipped DSP.
Figure 20. Slave Serial Data Timing for Reading (Read Previous Conversion during Convert)
SDOUT
CNVST
BUSY
SCLK
CS
t
16
t
3
t
31
X
t
36
1
t
35
D15
t
37
2
D14
t
EXT/INT = 1
32
3
D13
–18–
SPI Interface (ADSP-219x)
Figure 21 shows an interface diagram between the AD7664 and
an SPI-equipped ADSP-219x. To accommodate the slower speed
of the DSP, the AD7664 acts as a slave device and data must be
read after conversion. This mode also allows the daisy-chain
feature. The convert command can be initiated in response to
an internal timer interrupt. The reading process can be initi-
ated in response to the end-of-conversion signal (BUSY going
LOW) using an interrupt line of the DSP. The serial interface
(SPI) on the ADSP-219x is configured for master mode—
(MSTR) = 1, Clock Polarity bit (CPOL) = 0, Clock Phase bit
(CPHA) = 1, and SPI Interrupt Enable (TIMOD) = 00— by
writing to the SPI control register (SPICLTx). To meet all
timing requirements, the SPI clock should be limited to 17
Mbps, which allows it to read an ADC result in less than 1
When a higher sampling rate is desired, use of one of the
parallel interface modes is recommended.
Figure 21. Interfacing the AD7664 to an SPI Interface
DVDD
INVSCLK = 0
14
INVSCLK
RD
SER/PAR
EXT/INT
15
AD7664*
*ADDITIONAL PINS OMITTED FOR CLARITY
D1
16
SDOUT
CNVST
RD = 0
BUSY
SCLK
CS
D0
PFx
SPIxSEL (PFx)
MISOx
SCKx
PFx or TFSx
ADSP-219x*
REV. E
µ
s.