AD AD7677ASTRL 16-bit, 1 lsb inl, 1 msps differential adc Datasheet

a
FEATURES
Throughput: 1 MSPS
INL: ⴞ1 LSB Max (ⴞ0.0015% of Full-Scale)
16 Bits Resolution with No Missing Codes
S/(N+D): 94 dB Typ @ 45 kHz
THD: –110 dB Typ @ 45 kHz
Differential Input Range: ⴞ2.5 V
Both AC and DC Specifications
No Pipeline Delay
Parallel (8/16 Bits) and Serial 5 V/3 V Interface
Single 5 V Supply Operation
115 mW Typical Power Dissipation, 15 ␮W @ 100 SPS
Power-Down Mode: 7 ␮W Max
Package: 48-Lead Quad Flat Pack (LQFP)
Pin-to-Pin Compatible Upgrade of the AD7664/AD7675/
AD7676
16-Bit, 1 LSB INL, 1 MSPS
Differential ADC
AD7677*
FUNCTIONAL BLOCK DIAGRAM
AVDD AGND REF REFGND
DVDD
DGND
OVDD
AD7677
OGND
SERIAL
PORT
IN+
SWITCHED
CAP DAC
IN–
SER/PAR
BUSY
16
DATA[15:0]
CLOCK
PD
RESET
CONTROL LOGIC AND
CALIBRATION CIRCUITRY
PARALLEL
INTERFACE
CS
RD
OB/2C
BYTESWAP
WARP
IMPULSE
CNVST
APPLICATIONS
CT Scanners
Data Acquisition
Instrumentation
Spectrum Analysis
Medical Instruments
Battery-Powered Systems
Process Control
GENERAL DESCRIPTION
PRODUCT HIGHLIGHTS
The AD7677 is a 16-bit, 1 MSPS, charge redistribution SAR,
fully differential, analog-to-digital converter that operates from a
single 5 V power supply. The part contains a high-speed 16-bit
sampling ADC, an internal conversion clock, error correction
circuits, and both serial and parallel system interface ports.
1. Excellent INL
The AD7677 has a maximum integral nonlinearity of 1 LSB
with a no missing 16-bit code.
The AD7677 is hardware factory calibrated and comprehensively tested to ensure such ac parameters as signal-to-noise
ratio (SNR) and total harmonic distortion (THD), in addition
to the more traditional dc parameters of gain, offset, and linearity.
3. Fast Throughput
The AD7677 is a 1 MSPS, charge redistribution, 16-bit SAR
ADC with internal error correction circuitry.
It features a very high sampling rate mode (Warp) and, for
asynchronous conversion rate applications, a fast mode (Normal)
and, for low power applications, a reduced power mode (Impulse)
where the power is scaled with the throughput.
It is available in a 48-lead LQFP with operation specified from
–40°C to +85°C.
2. Superior AC Performances
The AD7677 has a minimum dynamic of 92 dB, 94 dB typical.
4. Single-Supply Operation
The AD7677 operates from a single 5 V supply and typically
dissipates only 115 mW. Its power dissipation decreases
with the throughput. It consumes 7 µW maximum when in
power-down.
5. Serial or Parallel Interface
Versatile parallel (8 or 16 bits) or 2-wire serial interface
arrangement compatible with both 3 V or 5 V logic.
*Patent pending
REV. 0
Information furnished by Analog Devices is believed to be accurate and
reliable. However, no responsibility is assumed by Analog Devices for its
use, nor for any infringements of patents or other rights of third parties that
may result from its use. No license is granted by implication or otherwise
under any patent or patent rights of Analog Devices.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781/329-4700
www.analog.com
Fax: 781/326-8703
© Analog Devices, Inc., 2001
AD7677–SPECIFICATIONS (–40ⴗC to +85ⴗC, AVDD = DVDD = 5 V, OVDD = 2.7 V to 5.25 V, unless otherwise stated.)
Parameter
Conditions
Min
RESOLUTION
ANALOG INPUT
Voltage Range
Operating Input Voltage
Analog Input CMRR
Input Current
Input Impedance
THROUGHPUT SPEED
Complete Cycle
Throughput Rate
Time Between Conversions
Complete Cycle
Throughput Rate
Complete Cycle
Throughput Rate
DC ACCURACY
Integral Linearity Error
Differential Linearity Error
No Missing Codes
Transition Noise
+Full-Scale Error3
–Full Scale Error3
Zero Error3
+Full-Scale Error3
–Full Scale Error3
Zero Error3
Power Supply Sensitivity
AC ACCURACY
Signal-to-Noise
Spurious Free Dynamic Range
Total Harmonic Distortion
Signal-to-(Noise+Distortion)
Max
16
VIN+ – VIN–
VIN+, VIN– to AGND
fIN = 10 kHz
1 MSPS Throughput
+VREF
+3
V
V
dB
µA
1
1
1
1.25
800
1.5
666
µs
MSPS
ms
µs
kSPS
µs
kSPS
+1
+1
LSB1, 2
LSB2
Bits
LSB
LSB
LSB
LSB
LSB
LSB
LSB
LSB
85
11
See Analog Input Section
In Warp Mode
In Warp Mode
In Warp Mode
In Normal Mode
In Normal Mode
In Impulse Mode
In Impulse Mode
0.001
0
0
–1
–1
16
0.35
In Warp Mode
In Warp Mode
In Warp Mode
In Impulse or Normal Mode
In Impulse or Normal Mode
In Impulse or Normal Mode
AVDD = 5 V ± 5%
–25
–20
–15
–40
–20
–23
fIN = 20 kHz
fIN = 45 kHz
fIN = 20 kHz
fIN = 45 kHz
fIN = 20 kHz
fIN = 45 kHz
fIN = 20 kHz
fIN = 45 kHz
fIN = 45 kHz, –60 dB Input
92
104.5
92
SAMPLING DYNAMICS
Aperture Delay
Aperture Jitter
Transient Response
Full-Scale Step
REFERENCE
External Reference Voltage Range
External Reference Current Drain
1 MSPS Throughput
± 1.4
94
94
110
110
–110
–110
94
94
34
15.8
+25
+20
+15
+40
+20
+23
–103.5
250
DIGITAL INPUTS
Logic Levels
VIL
VIH
IIL
IIH
–0.3
2.0
–1
–1
DIGITAL OUTPUTS
Data Format
Pipeline Delay
2.5
37
–2–
ns
ps rms
ns
AVDD – 1.85
V
µA
+0.8
DVDD + 0.3
+1
+1
V
V
µA
µA
Parallel or Serial 16-Bit Conversion
Results Available Immediately after
Completed Conversion
0.4
OVDD – 0.6
ISINK = 1.6 mA
ISOURCE = –100 µA
dB2, 4
dB
dB2
dB
dB2
dB
dB2
dB
MHz
2
5
2.3
Unit
Bits
–VREF
–0.1
–3 dB Input Bandwidth
VOL
VOH
Typ
V
V
REV. 0
AD7677
Parameter
POWER SUPPLIES
Specified Performance
AVDD
DVDD
OVDD
Operating Current2
AVDD
DVDD5
OVDD5
Power Dissipation5
Conditions
Min
Typ
Max
Unit
4.75
4.75
2.7
5
5
5.25
5.25
5.25
V
V
V
98
130
7
mA
mA
µA
mW
µW
mW
µW
+85
°C
1 MSPS Throughput
16.7
6.4
69
87
15
115
666 kSPS Throughput6
100 SPS Throughput6
1 MSPS Throughput2
In Power-Down Mode7
TEMPERATURE RANGE8
Specified Performance
TMIN to TMAX
–40
NOTES
1
LSB means Least Significant Bit. With the ± 2.5 V input range, one LSB is 76.3 µV.
2
In Warp Mode.
3
Tested with V REF = 2.5 V. See Definition of Specifications section. These specifications do not include the error contribution from the external reference.
4
All specifications in dB are referred to a full-scale input FS. Tested with an input signal at 0.5 dB below full scale unless otherwise specified.
5
Tested in parallel reading mode.
6
In Impulse Mode.
7
With all digital inputs forced to OVDD or OGND respectively.
8
Contact factory for extended temperature range.
Specifications subject to change without notice.
REV. 0
–3–
AD7677
TIMING SPECIFICATIONS (–40ⴗC to +85ⴗC, AVDD = DVDD = 5 V, OVDD = 2.7 V to 5.25 V, unless otherwise stated.)
Refer to Figures 11 and 12
Convert Pulsewidth
Time Between Conversions
(Warp Mode/Normal Mode/Impulse Mode)
CNVST LOW to BUSY HIGH Delay
BUSY HIGH All Modes Except in
Master Serial Read after Convert Mode
(Warp Mode/Normal Mode/Impulse Mode)
Aperture Delay
End of Conversion to BUSY LOW Delay
Conversion Time
(Warp Mode/Normal Mode/Impulse Mode)
Acquisition Time
RESET Pulsewidth
Symbol
Min
t1
t2
5
1/1.25/1.5
Typ
t3
t4
Refer to Figures 13, 14, and 15 (Parallel Interface Modes)
CNVST LOW to DATA Valid Delay
(Warp Mode/Normal Mode/Impulse Mode)
DATA Valid to BUSY LOW Delay
Bus Access Request to DATA Valid
Bus Relinquish Time
Unit
Note 1
ns
µs
30
0.75/1/1.25
ns
µs
0.75/1/1.25
ns
ns
µs
2
t5
t6
t7
10
t8
t9
250
10
ns
ns
t10
t11
t12
t13
Max
0.75/1/1.25
µs
40
15
ns
ns
ns
45
5
2
Refer to Figures 17 and 18 (Master Serial Interface Modes)
CS LOW to SYNC Valid Delay
CS LOW to Internal SCLK Valid Delay
CS LOW to SDOUT Delay
CNVST LOW to SYNC Delay (Read During Convert)
(Warp Mode/Normal Mode/Impulse Mode)
SYNC Asserted to SCLK First Edge Delay3
Internal SCLK Period3
Internal SCLK HIGH3
Internal SCLK LOW3
SDOUT Valid Setup Time3
SDOUT Valid Hold Time3
SCLK Last Edge to SYNC Delay3
CS HIGH to SYNC HI-Z
CS HIGH to Internal SCLK HI-Z
CS HIGH to SDOUT HI-Z
BUSY HIGH in Master Serial Read After Convert3
CNVST LOW to SYNC Asserted Delay
(Warp Mode/Normal Mode/Impulse Mode)
SYNC Deasserted to BUSY LOW Delay
Refer to Figures 19 and 20 (Slave Serial Interface Modes)
External SCLK Setup Time
External SCLK Active Edge to SDOUT Delay
SDIN Setup Time
SDIN Hold Time
External SCLK Period
External SCLK HIGH
External SCLK LOW
t14
t15
t16
t17
t18
t19
t20
t21
t22
t23
t24
t25
t26
t27
t28
t29
10
10
10
25/275/525
3
25
12
7
4
2
3
10
10
10
t30
t31
t32
t33
t34
t35
t36
t37
40
5
3
5
5
25
10
10
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
See Table I
0.75/1/1.25
µs
25
ns
18
ns
ns
ns
ns
ns
ns
ns
NOTES
1
In warp mode only, the maximum time between conversions is 1 ms, otherwise, there is no required maximum time.
2
In serial interface modes, the SYNC, SCLK, and SDOUT timings are defined with a maximum load C L of 10 pF; otherwise, the load is 60 pF maximum.
3
In serial master read during convert mode. See Table I for serial master read after convert mode.
Specifications subject to change without notice.
–4–
REV. 0
AD7677
Table I. Serial Clock Timings in Master Read after Convert
DIVSCLK[1]
DIVSCLK[0]
SYNC to SCLK First Edge Delay Minimum
Internal SCLK Period Minimum
Internal SCLK Period Maximum
Internal SCLK HIGH Minimum
Internal SCLK LOW Minimum
SDOUT Valid Setup Time Minimum
SDOUT Valid Hold Time Minimum
SCLK Last Edge to SYNC Delay Minimum
Busy High Width Maximum (Warp)
Busy High Width Maximum (Normal)
Busy High Width Maximum (Impulse)
t18
t19
t19
t20
t21
t22
t23
t24
t24
t24
t24
0
0
0
1
1
0
1
1
Unit
3
25
40
12
7
4
2
3
1.5
1.75
2
17
50
70
22
21
18
4
60
2
2.25
2.5
17
100
140
50
49
18
30
140
3
3.25
3.5
17
200
280
100
99
18
89
300
5.25
5.55
5.75
ns
ns
ns
ns
ns
ns
ns
ns
µs
µs
µs
ABSOLUTE MAXIMUM RATINGS 1
1.6mA
Analog Inputs
IN+2, IN–2, REF, REFGND . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . AVDD + 0.3 V to AGND – 0.3 V
Ground Voltage Differences
AGND, DGND, OGND . . . . . . . . . . . . . . . . . . . . . ± 0.3 V
Supply Voltages
AVDD, DVDD, OVDD . . . . . . . . . . . . . . . . . . . . . . . . . 7 V
AVDD to DVDD, AVDD to OVDD . . . . . . . . . . . . . . ± 7 V
DVDD to OVDD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ± 7 V
Digital Inputs . . . . . . . . . . . . . . . . . –0.3 V to DVDD + 0.3 V
Internal Power Dissipation3 . . . . . . . . . . . . . . . . . . . . 700 mW
Junction Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . 150°C
Storage Temperature Range . . . . . . . . . . . . –65°C to +150°C
Lead Temperature Range
(Soldering 10 sec) . . . . . . . . . . . . . . . . . . . . . . . . . . . 300°C
IOL
TO OUTPUT
PIN
1.4V
CL
60pF1
500␮A
IOH
NOTE
1 IN SERIAL INTERFACE MODES, THE SYNC, SCLK, AND
SDOUT TIMINGS ARE DEFINED WITH A MAXIMUM LOAD
CL OF 10pF; OTHERWISE, THE LOAD IS 60pF MAXIMUM.
Figure 1. Load Circuit for Digital Interface Timing,
SDOUT, SYNC, SCLK Outputs, CL = 10 pF
NOTES
1
Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; functional operation of the
device at these or any other conditions above those indicated in the operational
section of this specification is not implied. Exposure to absolute maximum rating
conditions for extended periods may affect device reliability.
2
See Analog Input section.
3
Specification is for device in free air: 48-Lead LQFP: ␪JA = 91°C/W, ␪JC = 30°C/W.
2V
0.8V
tDELAY
tDELAY
2V
0.8V
2V
0.8V
Figure 2. Voltage Reference Levels for Timings
ORDERING GUIDE
Model
Temperature Range
Package Description
Package Option
AD7677AST
AD7677ASTRL
EVAL-AD7677CB1
EVAL-CONTROL BRD22
–40°C to +85°C
–40°C to +85°C
Quad Flatpack (LQFP)
Quad Flatpack (LQFP)
Evaluation Board
Controller Board
ST-48
ST-48
NOTES
1
This board can be used as a stand-alone evaluation board or in conjunction with the EVAL-CONTROL BRD2 for evaluation/
demonstration purposes.
2
This board allows a PC to control and communicate with all Analog Devices evaluation boards ending in the CB designators.
CAUTION
ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily
accumulate on the human body and test equipment and can discharge without detection. Although
the AD7677 features proprietary ESD protection circuitry, permanent damage may occur on
devices subjected to high-energy electrostatic discharges. Therefore, proper ESD precautions are
recommended to avoid performance degradation or loss of functionality.
REV. 0
–5–
WARNING!
ESD SENSITIVE DEVICE
AD7677
PIN FUNCTION DESCRIPTIONS
Pin
No.
Mnemonic
Type
Description
1
2
3,
40–42,
44–48
4
AGND
AVDD
NC
P
P
Analog Power Ground Pin
Analog Power Pin. Nominally 5 V
No Connect
BYTESWAP
DI
5
OB/2C
DI
6
WARP
DI
7
IMPULSE
DI
8
SER/PAR
DI
9, 10
DATA[0:1]
DO
11, 12
DATA[2:3] or
DI/O
Parallel Mode Selection (8/16 bit). When LOW, the LSB is output on D[7:0] and the
MSB is output on D[15:8]. When HIGH, the LSB is output on D[15:8] and the MSB is
output on D[7:0].
Straight Binary/Binary Two’s Complement. When OB/2C is HIGH, the digital output is
straight binary; when LOW, the MSB is inverted resulting in a two’s complement output from
its internal shift register.
Mode Selection. When HIGH and IMPULSE LOW, this input selects the fastest mode, the
maximum throughput is achievable, and a minimum conversion rate must be applied in order to
guarantee full specified accuracy. When LOW, full accuracy is maintained independent of the
minimum conversion rate.
Mode Selection. When HIGH and WARP LOW, this input selects a reduced power mode.
In this mode, the power dissipation is approximately proportional to the sampling rate.
Serial/Parallel Selection Input. When LOW, the parallel port is selected; when HIGH, the
serial interface mode is selected and some bits of the DATA bus are used as a serial port.
Bit 0 and Bit 1 of the Parallel Port Data Output Bus. When SER/PAR is HIGH, these outputs
are in high impedance.
When SER/PAR is LOW, these outputs are used as Bit 2 and Bit 3 of the Parallel Port Data
Output Bus.
When SER/PAR is HIGH, EXT/INT is LOW and RDC/SDIN is LOW, which is the serial
master read after convert mode. These inputs, part of the serial port, are used to slow down if
desired the internal serial clock which clocks the data output. In the other serial modes, these
inputs are not used.
When SER/PAR is LOW, this output is used as the Bit 4 of the Parallel Port Data Output Bus.
When SER/PAR is HIGH, this input, part of the serial port, is used as a digital select input for
choosing the internal or an external data clock. With EXT/INT tied LOW, the internal clock
is selected on SCLK output. With EXT/INT set to a logic HIGH, output data is synchronized to an external clock signal connected to the SCLK input.
When SER/PAR is LOW, this output is used as the Bit 5 of the Parallel Port Data Output Bus.
When SER/PAR is HIGH, this input, part of the serial port, is used to select the active state
of the SYNC signal. When LOW, SYNC is active HIGH. When HIGH, SYNC is active LOW.
When SER/PAR is LOW, this output is used as the Bit 6 of the Parallel Port Data Output Bus.
When SER/PAR is HIGH, this input, part of the serial port, is used to invert the SCLK signal. It is active in both master and slave mode.
When SER/PAR is LOW, this output is used as the Bit 7 of the Parallel Port Data Output Bus.
When SER/PAR is HIGH, this input, part of the serial port, is used as either an external data
input or a read mode selection input depending on the state of EXT/INT. When EXT/INT is
HIGH, RDC/SDIN could be used as a data input to daisy chain the conversion results from
two or more ADCs onto a single SDOUT line. The digital data level on SDIN is output on
DATA with a delay of 16 SCLK periods after the initiation of the read sequence. When EXT/
INT is LOW, RDC/SDIN is used to select the read mode. When RDC/SDIN is HIGH, the
data is output on SDOUT during conversion. When RDC/SDIN is LOW, the data is output
on SDOUT only when the conversion is complete.
Input/Output Interface Digital Power Ground
Input/Output Interface Digital Power. Nominally at the same supply than the supply of the
host interface (5 V or 3 V).
DIVSCLK[0:1]
13
DATA[4]
or EXT/INT
DI/O
14
DATA[5]
or INVSYNC
DI/O
15
DATA[6]
or INVSCLK
DI/O
16
DATA[7]
or RDC/SDIN
DI/O
17
18
OGND
OVDD
P
P
–6–
REV. 0
AD7677
PIN FUNCTION DESCRIPTIONS (continued)
Pin
No.
Mnemonic
Type
Description
19
20
21
DVDD
DGND
DATA[8]
or SDOUT
P
P
DO
22
DATA[9]
or SCLK
DI/O
23
DATA[10]
or SYNC
DO
24
DATA[11]
or RDERROR
DO
25–28
DATA[12:15]
DO
29
BUSY
DO
30
31
32
DGND
RD
CS
P
DI
DI
33
34
RESET
PD
DI
DI
35
CNVST
DI
36
37
38
39
43
AGND
REF
REFGND
IN–
IN+
P
AI
AI
AI
AI
Digital Power. Nominally at 5 V.
Digital Power Ground
When SER/PAR is LOW, this output is used as the Bit 8 of the Parallel Port Data Output Bus.
When SER/PAR is HIGH, this output, part of the serial port, is used as a serial data output
synchronized to SCLK. Conversion results are stored in an on-chip register. The AD7677
provides the conversion result, MSB first, from its internal shift register. The DATA format is
determined by the logic level of OB/2C. In serial mode, when EXT/INT is LOW, SDOUT
is valid on both edges of SCLK. In serial mode, when EXT/INT is HIGH: If INVSCLK is
LOW, SDOUT is updated on SCLK rising edge and valid on the next falling edge. If INVSCLK
is HIGH, SDOUT is updated on SCLK falling edge and valid on the next rising edge.
When SER/PAR is LOW, this output is used as the Bit 9 of the Parallel Port Data Output Bus.
When SER/PAR is HIGH, this pin, part of the serial port, is used as a serial data clock input
or output, dependent upon the logic state of the EXT/INT pin. The active edge where the
data SDOUT is updated depends upon the logic state of the INVSCLK pin.
When SER/PAR is LOW, this output is used as the Bit 10 of the Parallel Port Data Output Bus.
When SER/PAR is HIGH, this output, part of the serial port, is used as a digital output frame
synchronization for use with the internal data clock (EXT/INT = Logic LOW). When a read
sequence is initiated and INVSYNC is LOW, SYNC is driven HIGH and remains HIGH
while SDOUT output is valid. When a read sequence is initiated and INVSYNC is HIGH,
SYNC is driven LOW and remains LOW while SDOUT output is valid.
When SER/PAR is LOW, this output is used as the Bit 11 of the Parallel Port Data Output Bus.
When SER/PAR is HIGH and EXT/INT is HIGH, this output, part of the serial port, is used
as an incomplete read error flag. In slave mode, when a data read is started and not complete
when the following conversion is complete, the current data is lost and RDERROR is pulsed high.
Bit 12 to Bit 15 of the Parallel Port Data Output Bus. These pins are always outputs regardless of the state of SER/PAR.
Busy Output. Transitions HIGH when a conversion is started, and remains HIGH until the
conversion is complete and the data is latched into the on-chip shift register. The falling edge
of BUSY could be used as a data ready clock signal.
Must be tied to digital ground.
Read Data. When CS and RD are both LOW, the interface parallel or serial output bus is enabled.
Chip Select. When CS and RD are both LOW, the interface parallel or serial output bus is
enabled. CS is also used to gate the external serial clock.
Reset Input. When set to a logic HIGH, reset the AD7677. Current conversion if any is aborted.
Power-Down Input. When set to a logic HIGH, power consumption is reduced and conversions are inhibited after the current one is completed.
Start Conversion. A falling edge on CNVST puts the internal sample/hold into the hold state and
initiates a conversion. In impulse mode (IMPULSE HIGH and WARP LOW), if CNVST is
held low when the acquisition phase (t8) is complete, the internal sample/hold is put into the
hold state and a conversion is immediately started.
Must be Tied to Analog Ground.
Reference Input Voltage
Reference Input Analog Ground
Differential Negative Analog Input
Differential Positive Analog Input
NOTES
AI = Analog Input
DI = Digital Input
DI/O = Bidirectional Digital
DO = Digital Output
P = Power
REV. 0
–7–
AD7677
REF
REFGND
IN–
NC
NC
NC
IN+
NC
NC
NC
NC
NC
PIN CONFIGURATION
48-Lead LQFP
(ST-48)
48 47 46 45 44 43 42 41 40 39 38 37
AGND 1
AVDD 2
PIN 1
IDENTIFIER
36
AGND
35
NC 3
34
CNVST
PD
BYTESWAP 4
33
RESET
OB/2C 5
WARP 6
32
CS
31
30
RD
DGND
SER/PAR 8
D0 9
29
BUSY
28
D15
D1 10
27
D14
D2/DIVSCLK[0] 11
26
D13
D3/DIVSCLK[1] 12
25
D12
AD7677
TOP VIEW
(Not to Scale)
IMPULSE 7
D11/RDERROR
D10/SYNC
D9/SCLK
D8/SDOUT
DGND
DVDD
OVDD
OGND
D7/RDC/SDIN
D6/INVSCLK
13 14 15 16 17 18 19 20 21 22 23 24
D4/EXT/INT
D5/INVSYNC
NC = NO CONNECT
DEFINITION OF SPECIFICATIONS
EFFECTIVE NUMBER OF BITS (ENOB)
INTEGRAL NONLINEARITY ERROR (INL)
ENOB is a measurement of the resolution with a sine wave
input. It is related to S/(N+D) by the following formula:
Linearity error refers to the deviation of each individual code from
a best-fit line drawn from “negative full scale” through “positive
full scale.” The point used as “negative full scale” occurs 1/2 LSB
before the first code transition. “Positive full scale” is defined as a
level 1 1/2 LSB beyond the last code transition.
( [
ENOB = S / N + D
]
) / 6.02
dB – 1.76
and is expressed in bits.
TOTAL HARMONIC DISTORTION (THD)
DIFFERENTIAL NONLINEARITY ERROR (DNL)
THD is the ratio of the rms sum of the first five harmonic
components to the rms value of a full-scale input signal and is
expressed in decibels.
In an ideal ADC, code transitions are 1 LSB apart. Differential
nonlinearity is the maximum deviation from this ideal value. It
is often specified in terms of resolution for which no missing
codes are guaranteed.
SIGNAL-TO-NOISE RATIO (SNR)
SNR is the ratio of the rms value of the actual input signal to
the rms sum of all other spectral components below the Nyquist
frequency, excluding harmonics and dc. The value for SNR is
expressed in decibels.
+FULL-SCALE ERROR
The last transition (from 011 . . . 10 to 011 . . . 11 in two’s
complement coding) should occur for an analog voltage 1 1/2 LSB
below the nominal +full scale (2.499886 V for the ± 2.5 V range).
The +full-scale error is the deviation of the actual level of the
last transition from the ideal level.
SIGNAL-TO-(NOISE + DISTORTION) RATIO (S/[N+D])
S/(N+D) is the ratio of the rms value of the actual input signal
to the rms sum of all other spectral components below the
Nyquist frequency, including harmonics but excluding dc. The
value for S/(N+D) is expressed in decibels.
–FULL-SCALE ERROR
The first transition (from 100 . . . 00 to 100 . . . 01 in two’s
complement coding) should occur for an analog voltage 1/2 LSB
above the nominal –full scale (–2.499962 V for the ± 2.5 V range).
The –full-scale error is the deviation of the actual level of the
first transition from the ideal level.
APERTURE DELAY
Aperture delay is a measure of the acquisition performance and
is measured from the falling edge of the CNVST input to when
the input signal is held for a conversion.
ZERO ERROR
The zero error is the difference between the ideal midscale input
voltage (0 V) and the actual voltage producing the midscale
output code.
TRANSIENT RESPONSE
The time required for the AD7677 to achieve its rated accuracy
after a full-scale step function is applied to its input.
SPURIOUS FREE DYNAMIC RANGE (SFDR)
The difference, in decibels (dB), between the rms amplitude of
the input signal and the peak spurious signal.
–8–
REV. 0
1.00
1.00
0.75
0.75
0.50
0.50
0.25
0.25
DNL – LSB
INL – LSB
Typical Performance Characteristics–AD7677
0.00
0.00
–0.25
–0.25
–0.50
–0.50
–0.75
–0.75
–1.00
0
16384
32768
CODE
49152
–1.00
65536
TPC 1. Integral Nonlinearity vs. Code
0
16384
32768
CODE
49152
65536
TPC 4. Differential Nonlinearity vs. Code
9000
16000
8287
14352
8066
8000
14000
7000
12000
6000
COUNTS
COUNTS
10000
5000
4000
8000
6000
3000
4000
2000
2000
1000
0000
994
0
0
0
10
21
0
0
0
0000
7FFB 7FFC 7FFD 7FFE 7FFF 8000 8001 8002 8003 8004
CODE IN HEXA
20
20
16
16
12
8
4
0
0.0
0
1
1037
0
0
0
0
7FFA 7FFB 7FFC 7FFD 7FFE 7FFF 8000 8001 8002 8003 8004
CODE IN HEXA
12
8
4
0.1
0.2
0.3
0.4 0.5 0.6 0.7
POSITIVE INL – LSB
0.8
0.9
1.0
0
–1.0 –0.9 –0.8 –0.7 –0.6 –0.5 –0.4 –0.3 –0.2 –0.1
NEGATIVE INL – LSB
1.1
TPC 3. Typical Positive INL Distribution (199 Units)
REV. 0
0
TPC 5. Histogram of 16,384 Conversions of a
DC Input at the Code Center
NUMBER OF UNITS
NUMBER OF UNITS
TPC 2. Histogram of 16,384 Conversions of a
DC Input at the Code Transition
0
0.0
1.0
TPC 6. Typical Negative INL Distribution (199 Units)
–9–
AD7677
SNR = 93.5dB
THD = –109.5dB
SFDR = 109dB
SINAD = 93dB
–40
–60
SNR
SNR – dB
AMPLITUDE – dB of Full Scale
–20
–104
96
fS = 1MSPS
fIN = 45.01kHz
–80
–100
93
–106
90
–108
87
–110
THD – dB
0
–120
–140
–160
THD
–180
0
100
200
300
FREQUENCY – kHz
400
84
–55
500
TPC 7. FFT Plot
5
25
45
65
TEMPERATURE – ⴗC
85
–112
125
105
50
16.0
OVDD = 2.7V @ 85ⴗC
15.5
SNR
15.0
SINAD
14.5
85
ENOB
80
14.0
75
13.5
t12 DELAY – ns
90
40
ENOB – Bits
SNR AND S/[N+D] – dB
–15
TPC 10. SNR, THD vs. Temperature
100
95
–35
OVDD = 2.7V @ 25ⴗC
30
OVDD = 5.0V @ 85ⴗC
20
OVDD = 5.0V @ 25ⴗC
10
70
1
0
13.0
1000
10
100
FREQUENCY – kHz
TPC 8. SNR, S/(N+D), and ENOB vs. Frequency
0
50
100
CL – pF
150
200
TPC 11. Typical Delay vs. Load Capacitance CL
1M
96
SNR
94
OPERATING CURRENTS – ␮A
SNR (REFERRED TO FULL SCALE) – dB
AVDD, WARP/NORMAL
10k
SINAD
92
90
DVDD, WARP/NORMAL
1k
100
AVDD, IMPULSE
10
DVDD, IMPULSE
1
0.1
OVDD, ALL MODES
0.01
88
–60
–50
–40
–30
–20
INPUT LEVEL – dB
–10
0.001
10
0
TPC 9. SNR and S/(N+D) vs. Input Level
100
1k
10k
SAMPLING RATE – SPS
100k
1M
TPC 12. Operating Currents vs. Sample Rate
–10–
REV. 0
AD7677
During the acquisition phase, terminals of the array tied to the
comparator’s input are connected to AGND via SW+ and SW–.
All independent switches are connected to the analog inputs.
Thus, the capacitor arrays are used as sampling capacitors and
acquire the analog signal on IN+ and IN– inputs. When the
acquisition phase is complete and the CNVST input goes
low, a conversion phase is initiated. When the conversion phase
begins, SW+ and SW– are opened first. The two capacitor arrays
are then disconnected from the inputs and connected to the
REFGND input. Therefore, the differential voltage between the
inputs IN+ and IN– captured at the end of the acquisition phase
is applied to the comparator inputs, causing the comparator to
become unbalanced. By switching each element of the capacitor
array between REFGND or REF, the comparator input varies
by binary weighted voltage steps (VREF/2, VREF/4 . . . VREF/65536).
The control logic toggles these switches, starting with the MSB
first, in order to bring the comparator back into a balanced
condition. After the completion of this process, the control logic
generates the ADC output code and brings BUSY output low.
POWER-DOWN OPERATING CURRENTS – nA
250
DVDD
200
150
100
50
0
–55
AVDD
OVDD
–35
–15
5
25
45
65
85
105
TEMPERATURE – ⴗC
TPC 13. Power-Down Operating Currents vs. Temperature
CIRCUIT INFORMATION
The AD7677 is a very fast, low-power, single-supply, precise,
16-bit analog-to-digital converter (ADC). The AD7677 features
different modes to optimize performances according to the
applications.
Modes of Operation
The AD7677 features three modes of operations, Warp, Normal,
and Impulse. Each of these modes is more suitable for specific
applications.
In Warp mode, the AD7677 is capable of converting 1,000,000
samples per second (1 MSPS).
The Warp mode allows the fastest conversion rate up to 1 MSPS.
However, in this mode, and this mode only, the full specified accuracy is guaranteed only when the time between conversion does
not exceed 1 ms. If the time between two consecutive conversions
is longer than 1 ms, for instance, after power-up, the first conversion result should be ignored. This mode makes the AD7677
ideal for applications where fast sample rates are required.
The AD7677 provides the user with an on-chip track/hold,
successive approximation ADC that does not exhibit any pipeline or latency, making it ideal for multiple multiplexed channel
applications.
The AD7677 can be operated from a single 5 V supply and
be interfaced to either 5 V or 3 V digital logic. It is housed in a
48-lead LQFP package that combines space savings and flexible
configurations as either serial or parallel interface. The AD7677
is a pin-to-pin-compatible upgrade of the AD7664, AD7675,
and AD7676.
The Normal mode is the fastest mode (800 kSPS) without any
limitation about the time between conversions. This mode makes
the AD7677 ideal for asynchronous applications such as data
acquisition systems, where both high accuracy and fast sample
rate are required.
CONVERTER OPERATION
The AD7677 is a successive approximation analog-to-digital
converter based on a charge redistribution DAC. Figure 3 shows
the simplified schematic of the ADC. The capacitive DAC consists of two identical arrays of 16 binary weighted capacitors
that are connected to the two comparator inputs.
The Impulse mode, the lowest power dissipation mode, allows
power saving between conversions. The maximum throughput
in this mode is 666 kSPS. When operating at 100 SPS, for
example, it typically consumes only 15 µW. This feature makes
the AD7677 ideal for battery-powered applications.
IN+
MSB
32,768C 16,384C
LSB
4C
2C
C
SW+
SWITCHES
CONTROL
C
BUSY
REF
COMP
CONTROL
LOGIC
OUTPUT
CODE
REFGND
32,768C 16,384C
4C
2C
C
C
LSB
MSB
IN–
Figure 3. ADC Simplified Schematic
REV. 0
–11–
SW–
CNVST
AD7677
Transfer Functions
Analog Inputs
Figure 6 shows a simplified analog input section of AD7677.
Using the OB/2C digital input, the AD7677 offers two output
codings: straight binary and two’s complement. The ideal transfer characteristic for the AD7677 is shown in Figure 4.
AVDD
R+ = 168⍀
ADC CODE – Straight Binary
IN+
CS
111...111
111...110
111...101
CS
IN–
R– = 168⍀
AGND
Figure 6. Simplified Analog Input
000...010
The diodes shown in Figure 6 provide ESD protection for the
inputs. Care must be taken to ensure that the analog input signal never exceeds the absolute ratings on these inputs. This will
cause these diodes to become forward-biased and start conducting current. These diodes can handle a forward-biased current
of 120 mA maximum. This condition could eventually occur
when the input buffer’s (U1) or (U2) supplies are different from
AVDD. In such case, an input buffer with a short-circuit current
limitation can be used to protect the part.
000...001
000...000
–FS
–FS + 1 LSB
+FS – 1 LSB
–FS + 0.5 LSB
+FS – 1.5 LSB
ANALOG INPUT
Figure 4. ADC Ideal Transfer Function
TYPICAL CONNECTION DIAGRAM
Figure 5 shows a typical connection diagram for the AD7677.
Different circuitry shown on this diagram are optional and are
discussed below.
This analog input structure is a true differential structure. By
using these differential inputs, signals common to both inputs
are rejected as shown in Figure 7, which represents the typical
CMRR over frequency.
DVDD
ANALOG
SUPPLY
(5V)
100⍀
DIGITAL SUPPLY
(3.3V OR 5V)
NOTE 5
+
+
100nF
10␮F
ADR421
AVDD
AGND
10␮F
100nF
DGND
DVDD
100nF
OVDD
1M⍀
C
50k⍀ + REF
NOTE 1
100nF
10␮F
OGND
REF
2.5V REF
+
SERIAL PORT
SCLK
1␮F
SDOUT
NOTE 2
REFGND
NOTE 3
50⍀
NOTE 4
ANALOG INPUT+
BUSY
–
U1
+
AD8021
15⍀
CC
CNVST
IN+
␮C/␮P/DSP
50⍀
D
NOTE 7
2.7nF
AD7677
NOTE 5
OB/2C
SER/PAR
DVDD
50⍀
NOTE 4
ANALOG INPUT–
–
U2
+
AD8021
CS
15⍀
CC
IN–
CLOCK
RD
BYTESWAP
2.7nF
RESET
NOTE 5
PD
NOTES
1. SEE VOLTAGE REFERENCE INPUT SECTION.
2. WITH THE RECOMMENDED VOLTAGE REFERENCES, CREF IS 47␮F. SEE CHAPTER VOLTAGE REFERENCE INPUT SECTION.
3. OPTIONAL CIRCUITRY FOR HARDWARE GAIN CALIBRATION.
4. THE AD8021 IS RECOMMENDED. SEE DRIVER AMPLIFIER CHOICE SECTION.
5. SEE ANALOG INPUT SECTION.
6. OPTION, SEE POWER SUPPLY SECTION.
7. OPTIONAL LOW JITTER CNVST, SEE CONVERSION CONTROL SECTION.
Figure 5. Typical Connection Diagram
–12–
REV. 0
AD7677
90
Driver Amplifier Choice
85
Although the AD7677 is easy to drive, the driver amplifier needs
to meet at least the following requirements:
80
• The driver amplifier and the AD7677 analog input circuit
have to be able together to settle for a full-scale step of the
capacitor array at a 16-bit level (0.0015%). In the amplifier’s
data sheet, the settling at 0.1% or 0.01% is more commonly
specified. It could significantly differ from the settling time at
a 16-bit level and, therefore, it should be verified prior to the
driver selection. The tiny op-amp, AD8021, which combines
ultralow noise and a high gain bandwidth, meets this settling
time requirement even when used with a high gain up to 13.
CMRR – dB
75
70
65
60
55
50
45
1k
10k
100k
1M
10M
FREQUENCY – Hz
Figure 7. Analog Input CMRR vs. Frequency
During the acquisition phase, for ac signals, the AD7677 behaves
like a one-pole RC filter consisting of the equivalent resistance R+ , R–, and CS. The resistors R+ and R– are typically
168 V and are lumped components made up of some serial
resistors and the on resistance of the switches. The capacitor CS is
typically 60 pF and is mainly the ADC sampling capacitor. This
one-pole filter with a typical –3 dB cutoff frequency of 15.8 MHz
reduces undesirable aliasing effect and limits the noise coming from the inputs.
Because the input impedance of the AD7677 is very high, the
AD7677 can be driven directly by a low impedance source
without gain error. That allows the user to input, as shown in
Figure 5, an external one-pole RC filter between the output of
the amplifier output and the ADC analog inputs to even further
improve the noise filtering done by the AD7677 analog input
circuit. However, the source impedance has to be kept low
because it affects the ac performances, especially the total harmonic distortion. The maximum source impedance depends
on the amount of total harmonic distortion (THD) that can
be tolerated. The THD degrades proportionally to the source
impedance.
Single to Differential Driver
For applications using unipolar analog signals, a single-endedto-differential driver will allow for a differential input into the
part. The schematic is shown in Figure 8.
ANALOG INPUT
(UNIPOLAR)
U1
AD8021
IN+
590⍀
2.5V REF
AD7677
IN–
REF
AD8021
590⍀
CC
2.5V REF
Figure 8. Single-Ended-to-Differential Driver Circuit
where
f–3 dB is the –3 dB input bandwidth in MHz of the AD7677
(15.8 MHz) or the cutoff frequency of the input filter if
any used.
N is the noise factor of the amplifiers (1 if in buffer configuration).
eN is the equivalent input noise voltage of each opamp in
nV/(Hz)1/2.
For instance, a driver with an equivalent input noise of 2 nV/√Hz
(like the AD8021) and configured as a buffer, thus with a noise
gain of +1, the SNR degrades by only 0.07 dB with the filter in
Figure 5, and 0.27 dB without.
• The driver needs to have a THD performance suitable to
that of the AD7677.
The AD8021 meets these requirements and is usually appropriate for almost all applications. The AD8021 needs an external
compensation capacitor of 10 pF. This capacitor should have
good linearity as an NPO ceramic or mica type.
The AD829 is another alternative where high-frequency (above
1 MHz) performance is not required. In gain of 1, it requires an
82 pF compensation capacitor.
The AD8610 is also another option where low bias current is
needed in low-frequency applications.
This configuration, when provided an input signal of 0 to VREF,
will produce a differential ± 2.5 V with midscale at 1.25 V.
If the application can tolerate more noise, the AD8138 can
be used.
REV. 0






The AD8132 or the AD8138 could also be used to generate a
differential signal from a single-ended signal.
590⍀
U2
SNRLOSS


28
= 20 LOG 
2
π

 784 + f –3 dB ( N eN )

4
The AD8022 could also be used where a dual version is needed
and gain of 1 is used.
CC
590⍀
• The noise generated by the driver amplifier needs to be kept
as low as possible in order to preserve the SNR and transition noise performance of the AD7677. The noise coming
from the driver is filtered by the AD7677 analog input circuit
one-pole, low-pass filter made by R+, R–, and CS. The SNR
degradation due to the amplifier is:
–13–
AD7677
Voltage Reference Input
The AD7677 uses an external 2.5 V voltage reference. The
voltage reference input REF of the AD7677 has a dynamic
input impedance. Therefore, it should be driven by a low
impedance source with an efficient decoupling between REF
and REFGND inputs. This decoupling depends on the choice
of the voltage reference, but usually consists of a 1 µF ceramic
capacitor and a low ESR tantalum capacitor connected to the
REF and REFGND inputs with minimum parasitic inductance.
47 µF is an appropriate value for the tantalum capacitor when
used with one of the recommended reference voltages:
digital input/output interface supply OVDD. The OVDD supply
allows direct interface with any logic working between 2.7 V and
5.25 V. To reduce the number of supplies needed, the digital
core (DVDD) can be supplied through a simple RC filter from
the analog supply as shown in Figure 5. The AD7677 is independent of power supply sequencing and thus free from supply
voltage induced latchup. Additionally, it is very insensitive to
power supply variations over a wide frequency range as shown
in Figure 9.
POWER DISSIPATION
In Impulse mode, the AD7677 automatically reduces its power
consumption at the end of each conversion phase. During the
acquisition phase, the operating currents are very low which
allows a significant power saving when the conversion rate is
reduced as shown in Figure 10. This feature makes the AD7677
ideal for very low-power battery applications.
• The lownoise, low temperature drift ADR421 and AD780
voltage references
• The lowpower ADR291 voltage reference
• The lowcost AD1582 voltage reference
For applications using multiple AD7677s, it is more effective
to buffer the reference voltage with a lownoise, very stable op
amp like the AD8031.
Care should also be taken with the reference temperature coefficient of the voltage reference which directly affects the full-scale
accuracy if this parameter matters. For instance, a ± 15 ppm/°C
tempco of the reference changes the full scale by ± 1 LSB/°C.
It should be noted that the digital interface remains active even
during the acquisition phase. To reduce the operating digital
supply currents even further, the digital inputs need to be driven
close to the power rails (i.e., DVDD and DGND) and OVDD
should not exceed DVDD by more than 0.3 V.
1M
Note that VREF , as mentioned in the specification table, could be
increased to AVDD – 1.85 V. Since the input range is defined
in terms of VREF, this would essentially increase the range to
make it a ± 3 V input range with a reference voltage of 3 V. One
of the benefits here is the increased SNR obtained as a result of
this increase. The theoretical improvement as a result of this
increase in reference is 1.58 dB (20 log [3/2.5]). Due to the
theoretical quantization noise however, the observed improvement is approximately 1 dB. The AD780 can be selected with a
3 V reference voltage.
WARP/NORMAL
POWER DISSIPATION – ␮W
100k
10k
1k
IMPULSE
100
10
1
75
0.1
10
70
100
1k
10k
100k
1M
SAMPLING RATE – SPS
65
PSRR – dB
Figure 10. Power Dissipation vs. Sample Rate
60
CONVERSION CONTROL
55
Figure 11 shows the detailed timing diagrams of the conversion
process. The AD7677 is controlled by the signal CNVST which
initiates conversion. Once initiated, it cannot be restarted or
aborted, even by the power-down input PD, until the conversion is complete. The CNVST signal operates independently of
CS and RD signals.
50
45
40
35
1k
10k
100k
1M
10M
FREQUENCY – Hz
Figure 9. PSRR vs. Frequency
Power Supply
The AD7677 uses three sets of power supply pins: an analog
5 V supply AVDD, a digital 5 V core supply DVDD, and a
In Impulse mode, conversions can be automatically initiated. If
CNVST is held low when BUSY is low, the AD7677 controls
the acquisition phase and then automatically initiates a new
conversion. By keeping CNVST low, the AD7677 keeps the
conversion process running by itself. It should be noted that the
–14–
REV. 0
AD7677
analog input has to be settled when BUSY goes low. Also, at
power-up, CNVST should be brought low once to initiate the
conversion process. In this mode, the AD7677 could sometimes
run slightly faster than the guaranteed limits in the impulse
mode of 666 kSPS. This feature does not exist in warp or
Normal modes.
CS = RD = 0
t1
CNVST
t10
t4
BUSY
t3
t2
t11
t1
DATA
BUS
CNVST
t4
t3
t6
t5
ACQUIRE
NEW DATA
Figure 13. Master Parallel Data Timing for Reading
(Continuous Read)
BUSY
MODE
PREVIOUS CONVERSION DATA
PARALLEL INTERFACE
CONVERT
ACQUIRE
t7
t8
CONVERT
Figure 11. Basic Conversion Timing
Although CNVST is a digital signal, it should be designed with
this special care with fast, clean edges and levels, with minimum
overshoot and undershoot or ringing.
The AD7677 is configured to use the parallel interface (Figure 13)
when the SER/PAR is held low. The data eithercan be read
after each conversion, which is during the next acquisition phase,
or during the following conversion as shown, respectively, in
Figure 14 and Figure 15. When the data is read during the conversion however, it is recommended that it is a read-only during
the first half of the conversion phase. This avoids any potential
feedthrough between voltage transients on the digital interface
and the most critical analog conversion circuitry.
For applications where the SNR is critical, the CNVST signal
should have a very low jitter. Some solutions to achieve that are to
use a dedicated oscillator for CNVST generation or, at least, to
clock it with a high frequency low jitter clock as shown in Figure 5.
CS
RD
t9
RESET
BUSY
DATA
BUS
BUSY
CURRENT
CONVERSION
t12
t13
Figure 14. Slave Parallel Data Timing for Reading (Read
After Convert)
DATA
CS = 0
t8
t1
CNVST,
RD
CNVST
BUSY
Figure 12. RESET Timing
t4
t3
DIGITAL INTERFACE
The AD7677 has a versatile digital interface; it can be interfaced
with the host system by using either a serial or parallel interface.
The serial interface is multiplexed on the parallel data bus. The
AD7677 digital interface also accommodates both 3 V or 5 V
logic by simply connecting the OVDD supply pin of the AD7677
to the host system interface digital supply. Finally, by using the
OB/2C input pin, both two’s complement or straight binary
coding can be used.
The two signals, CS and RD, control the interface. When at least
one of these signals is high, the interface outputs are in high
impedance. Usually, CS allows the selection of each AD7677 in
multicircuits applications and is held low in a single AD7677
design. RD is generally used to enable the conversion result on
the data bus.
REV. 0
PREVIOUS
CONVERSION
DATA
BUS
t12
t13
Figure 15. Slave Parallel Data Timing for Reading (Read
During Convert)
The BYTESWAP pin allows a glueless interface to an 8-bit bus.
As shown in Figure 16, the LSB byte is output on D[7:0] and
the MSB is output on D[15:8] when BYTESWAP is low. When
BYTESWAP is high, the LSB and MSB bytes are swapped and
the LSB is output on D[15:8] and the MSB is output on D[7:0].
By connecting BYTESWAP to an address line, the 16 bits of
data can be read in 2 bytes on either D[15:8] or D[7:0].
–15–
AD7677
SERIAL INTERFACE
The AD7677 is configured to use the serial interface when the
SER/PAR is held high. The AD7677 outputs 16 bits of data,
MSB first, on the SDOUT pin. This data is synchronized with
the 16 clock pulses provided on the SCLK pin.
CS
RD
MASTER SERIAL INTERFACE
Internal Clock
BYTE
PINS D[15:8]
HI-Z
HIGH BYTE
t12
PINS D[7:0]
HI-Z
t12
LOW BYTE
The AD7677 is configured to generate and provide the serial
data clock SCLK when the EXT/INT pin is held low. The AD7677
also generates a SYNC signal to indicate to the host when the
serial data is valid. The serial clock SCLK and the SYNC signal
can be inverted if desired. The output data is valid on both the
HI-Z
LOW BYTE
t13
HI-Z
HIGH BYTE
Figure 16. 8-Bit Parallel Interface
RDC/SDIN = 0
EXT/INT = 0
CS, RD
INVSCLK = INVSYNC = 0
t3
CNVST
t28
BUSY
t30
t29
t25
SYNC
t18
t19
t14
t20
t24
t21
t26
1
SCLK
2
3
14
15
16
t15
t27
X
SDOUT
t16
D15
D14
D2
D1
D0
t23
t22
Figure 17. Master Serial Data Timing for Reading (Read After Convert)
RDC/SDIN = 1
EXT/INT = 0
CS, RD
INVSCLK = INVSYNC = 0
t1
CNVST
t3
BUSY
t17
t25
SYNC
t14
t19
t20 t21
t15
SCLK
1
t24
2
3
14
15
t18
X
SDOUT
t16
t27
D15
t22
t26
16
D14
D2
D1
D0
t23
Figure 18. Master Serial Data Timing for Reading (Read Previous Conversion During Convert)
–16–
REV. 0
AD7677
rising and falling edge of the data clock. Depending on RDC/
SDIN input, the data can be read after each conversion, or during
the following conversion.
SLAVE SERIAL INTERFACE
External Clock
Figure 17 and Figure 18 show the detailed timing diagrams of
these two modes.
Usually, because the AD7677 is used with a fast throughput, the
mode master, read during conversion, is the most recommended
serial mode when it can be used.
In read-after-conversion mode, it should be noted that, unlike in
other modes, the signal BUSY returns low after the 16 data bits
are pulsed out and not at the end of the conversion phase which
results in a longer BUSY width.
The AD7677 is configured to accept an externally supplied serial
data clock on the SCLK pin when the EXT/INT pin is held
high. In this mode, several methods can be used to read the
data. The external serial clock is gated by CS and the data are
output when both CS and RD are low. Thus, depending on CS,
the data can be read after each conversion or during the following conversion. The external clock can be either a continuous
or discontinuous clock. A discontinuous clock can be either
normally high or normally low when inactive. Figure 19 and
Figure 20 show the detailed timing diagrams of these methods.
While the AD7677 is performing a bit decision, it is important that
voltage transients not occur on digital input/output pins or degradation of the conversion result could occur. This is particularly
important during the second half of the conversion phase because
the AD7677 provides error correction circuitry that can correct for
In read-during-conversion mode, the serial clock and data toggle at
appropriate instances minimizes potential feedthrough between
digital activity and the critical conversion decisions.
To accommodate slow digital hosts, the serial clock can be
slowed down by using DIVSCLK.
RD = 0
INVSCLK = 0
EXT/INT = 1
CS
BUSY
t36
SCLK
t35
t37
1
2
t31
3
14
15
16
17
18
t32
SDOUT
X
D15
t16
D14
D13
D1
D0
X15
X14
X14
X13
X1
X0
Y15
Y14
t34
SDIN
X15
t33
Figure 19. Slave Serial Data Timing for Reading (Read After Convert)
RD = 0
INVSCLK = 0
EXT/INT = 1
CS
CNVST
BUSY
t3
t35
t36
SCLK
t37
1
2
t31
SDOUT
3
14
15
16
t32
X
D15
D14
D13
D1
D0
t16
Figure 20. Slave Serial Data Timing for Reading (Read Previous Conversion During Convert)
REV. 0
–17–
AD7677
an improper bit decision made during the first half of the conversion phase. For this reason, it is recommended that when an
external clock is being provided, it is a discontinuous clock that is
toggling only when BUSY is low or, more importantly, that it does
not transition during the latter half of BUSY high.
External Discontinuous Clock Data Read after Conversion
This mode is the most recommended of the serial slave modes.
Figure 19 shows the detailed timing diagrams of this method.
After a conversion is complete, indicated by BUSY returning
low, the result of this conversion can be read while both CS and
RD are low. The data is shifted out, MSB first, with 16 clock
pulses and is valid on both rising and falling edge of the clock.
Among the advantages of this method, the conversion performance is not degraded because there is no voltage transients on
the digital interface during the conversion process.
Another advantage is to be able to read the data at any speed up
to 40 MHz which accommodates both slow digital host interface
and the fastest serial reading.
Finally, in this mode only, the AD7677 provides a “daisy chain”
feature using the RDC/SDIN input pin for cascading multiple
converters together. This feature is useful for reducing component count and wiring connections when it is desired as it is, for
instance, in isolated multiconverters applications.
An example of the concatenation of two devices is shown in
Figure 21. Simultaneous sampling is possible by using a common
CNVST signal. It should be noted that the RDC/SDIN input is
latched on the opposite edge of SCLK of the one used to shift
out the data on SDOUT. Hence, the MSB of the “upstream”
converter just follows the LSB of the “downstream” converter
on the next SCLK cycle.
BUSY
OUT
BUSY
BUSY
AD7677
AD7677
#2 (UPSTREAM)
#1 (DOWNSTREAM)
To reduce performance degradation due to digital activity, a fast
discontinuous clock of at least 25 MHz, when impulse mode is
used, 32 MHz when normal, or 40 MHz when warp mode is
used, 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 like 18 MHz in impulse mode,
21 MHz in normal mode, and 26 MHz in warp mode.
MICROPROCESSOR INTERFACING
The AD7677 is ideally suited for traditional dc measurement
applications supporting a microprocessor and ac signal processing applications interfacing to a digital signal processor. The
AD7677 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 AD7677 to prevent digital noise from coupling into
the ADC. The following sections illustrate the use of the AD7677
with an SPI equipped microcontroller, the ADSP-21065L and
ADSP-218x signal processors.
SPI Interface (MC68HC11)
Figure 22 shows an interface diagram between the AD7677 and
an SPI-equipped microcontroller like the MC68HC11. To
accommodate the slower speed of the microcontroller, the
AD7677 acts as a slave device and data must be read after
conversion. This mode also allows the “daisy chain” feature. The
convert command could be initiated in response to an internal
timer interrupt. The reading of output data, one byte at a time, if
necessary, could be initiated in response to the end-of-conversion
signal (BUSY going low) using an interrupt line of the microcontroller. The Serial Peripheral Interface (SPI) on the MC68HC11
is configured for master mode (MSTR) = 1, Clock Polarity Bit
(CPOL) = 0, Clock Phase Bit (CPHA) = 1, and SPI interrupt
enable (SPIE) = 1 by writing to the SPI Control Register (SPCR).
The IRQ is configured for edge-sensitive-only operation (IRQE = 1
in OPTION register).
DVDD
MC68HC11*
AD7677*
RDC/SDIN
SDOUT
RDC/SDIN
CNVST
SDOUT
DATA
OUT
SER/PAR
CNVST
EXT/INT
CS
CS
CS
BUSY
SCLK
SCLK
RD
SDOUT
INVSCLK
CNVST
SCLK
SCLK IN
CS IN
CNVST IN
Figure 21. Two AD7677s in a “Daisy Chain” Configuration
SCK
I/O PORT
*ADDITIONAL PINS OMITTED FOR CLARITY
External Clock Data Read During Conversion
Figure 20 shows the detailed timing diagrams 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 rising and
falling edges of the clock. The 16 bits have to be read before the
current conversion is complete. If that is not done, 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.
IRQ
MISO/SDI
Figure 22. Interfacing the AD7677 to SPI Interface
ADSP-21065L in Master Serial Interface
As shown in Figure 23, the AD7677 can be interfaced to the
ADSP-21065L using the serial interface in master mode without any glue logic required. This mode combines the advantages
of reducing the wire connections and the ability to read the data
during or after conversion maximum speed transfer (DIVSCLK
[0:1] both low).
–18–
REV. 0
AD7677
The AD7677 is configured for the internal clock mode (EXT/INT
low) and acts, therefore, as the master device. The convert command can be generated by either an external low jitter oscillator
or, as shown, by a FLAG output of the ADSP-21065L, or by a
frame output TFS of one serial port of the ADSP-21065L which
can be used like a timer. The serial port on the ADSP-21065L is
configured for external clock (IRFS = 0), rising edge active
(CKRE = 1), external late framed sync signals (IRFS = 0, LAFS
= 1, RFSR = 1), and active high (LRFS = 0). The serial port of
the ADSP-21065L is configured by writing to its receive control
register (SRCTL)—see ADSP-2106x SHARC User’s Manual.
Because the serial port within the ADSP-21065L will be seeing
a discontinuous clock, an initial word reading has to be done
after the ADSP-21065L has been reset to ensure that the serial
port is properly synchronized to this clock during each following
data read operation.
DVDD
ADSP-21065L*
AD7677*
SHARC
SER/PAR
RDC/SDIN
RD
EXT/INT
CS
INVSYNC
SYNC
SDOUT
SCLK
CNVST
RFS
DR
RCLK
FLAG OR TFS
INVSCLK
*ADDITIONAL PINS OMITTED FOR CLARITY
Figure 23. Interfacing to the ADSP-21065L Using the
Serial Master Mode
APPLICATION HINTS
Layout
The AD7677 has very good immunity to noise on the power
supplies as can be seen in Figure 9. However, care should still
be taken with regard to grounding layout.
The printed circuit board that houses the AD7677 should be
designed so the analog and digital sections are separated and
confined to certain areas of the board. This facilitates the use of
ground planes that can be easily separated. Digital and analog
ground planes should be joined in only one place, preferably
underneath the AD7677, or at least as close as possible to the
AD7677. If the AD7677 is in a system where multiple devices
require analog to digital ground connections, the connection
should still be made at one point only, a star ground point,
which should be established as close as possible to the AD7677.
It is recommended to avoid running digital lines under the device
as these will couple noise onto the die. The analog ground
REV. 0
plane should be allowed to run under the AD7677 to avoid
noise coupling. Fast switching signals like CNVST or clocks
should be shielded with digital ground to avoid radiating noise
to other sections of the board, and should never run near analog
signal paths. Crossover of digital and analog signals should be
avoided. Traces on different but close layers of the board should
run at right angles to each other. This will reduce the effect of
feedthrough through the board. The power supply lines to the
AD7677 should use as large a trace as possible to provide low
impedance paths and reduce the effect of glitches on the power
supply lines. Good decoupling is also important to lower the
supplies impedance presented to the AD7677 and reduce the
magnitude of the supply spikes. Decoupling ceramic capacitors,
typically 100 nF, should be placed on each power supplies pins
AVDD, DVDD, and OVDD close to, and ideally right up against
these pins and their corresponding ground pins. Additionally,
low ESR 10 µF capacitors should be located in the vicinity of
the ADC to further reduce low frequency ripple.
The DVDD supply of the AD7677 can be either a separate
supply or come from the analog supply, AVDD, or from the
digital interface supply, OVDD. When the system digital supply
is noisy, or fast switching digital signals are present, it is recommended if no separate supply available, to connect the DVDD
digital supply to the analog supply AVDD through an RC filter
as shown in Figure 5, and connect the system supply to the interface digital supply OVDD and the remaining digital circuitry.
When DVDD is powered from the system supply, it is useful to
insert a bead to further reduce high-frequency spikes.
The AD7677 has four different ground pins; REFGND, AGND,
DGND, and OGND. REFGND senses the reference voltage
and should be a low impedance return to the reference because
it carries pulsed currents. AGND is the ground to which most
internal ADC analog signals are referenced. This ground must
be connected with the least resistance to the analog ground
plane. DGND must be tied to the analog or digital ground
plane depending on the configuration. OGND is connected to
the digital system ground.
The layout of the decoupling of the reference voltage is important. The decoupling capacitor should be close to the ADC and
connected with short and large traces to minimize parasitic
inductances.
Evaluating the AD7677 Performance
A recommended layout for the AD7677 is outlined in the evaluation board for the AD7677. The evaluation board package
includes a fully assembled and tested evaluation board, documentation, and software for controlling the board from a PC
via the Eval-Control BRD2.
–19–
AD7677
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
0.067 (1.70)
0.059 (1.50)
0.055 (1.40)
0.021 (0.53)
0.020 (0.50)
0.019 (0.48)
0.362 (9.19)
0.354 (9.00) SQ
0.346 (8.79)
37
36
48
1
SEATING
PLANE
0.280 (7.10)
0.276 (7.0) SQ
0.272 (6.90)
TOP VIEW
(PINS DOWN)
0ⴗ
MIN
12
25
13
24
0.023 (0.58) 0.010 (0.26)
0.020 (0.50) 0.007 (0.18)
0.017 (0.42) 0.006 (0.15)
0.007 (0.18)
0.005 (0.127)
0.004 (0.09)
7ⴗ
3.5ⴗ
0ⴗ
0.057 (1.45)
0.055 (1.40)
0.053 (1.35)
PRINTED IN U.S.A.
0.006 (0.15)
0.004 (0.10)
0.002 (0.05)
C02632–.8–12/01(0)
48-Lead Quad Flatpack (LQFP)
(ST-48)
–20–
REV. 0