Low Power, 16-Bit, 500-kHz, Single/Dual Unipolar Input, ADC w

Low Power, 16-Bit, 500-kHz, Single/Dual Unipolar Input, ADC w
ADS8327
ADS8328
SLAS415E – APRIL 2006 – REVISED JANUARY 2011
www.ti.com
LOW POWER, 16-BIT, 500-kHz, SINGLE/DUAL UNIPOLAR INPUT, ANALOG-TO-DIGITAL
CONVERTERS WITH SERIAL INTERFACE
Check for Samples: ADS8327, ADS8328
FEATURES
APPLICATIONS
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2.7-V to 5.5-V Analog Supply, Low Power:
– 10.6 mW (500 kHz, +VA = 2.7 V,
+VBD = 1.8 V)
500-kHz Sampling Rate
Excellent DC Performance
– ±1.5 LSB Typ, ±2 LSB Max INL
– ±0.6 LSB Typ, ±1 LSB Max DNL
– 16-Bit NMC Over Temperature
– ±0.5 mV Max Offset Error at 2.7 V
– ±1 mV Max Offset Error at 5 V
Excellent AC Performance at fI = 10 kHz with
91 dB SNR, 100 dB SFDR, –96 dB THD
Built-In Conversion Clock (CCLK)
1.65 V to 1.5×(+VA) I/O Supply
– SPI/DSP Compatible Serial
– SCLK up to 50 MHz
Comprehensive Power-Down Modes:
– Deep Power-Down
– Nap Power-Down
– Auto Nap Power-Down
Unipolar Input Range: 0 V to VREF
Software Reset
Global CONVST (Independent of CS)
Programmable Status/Polarity EOC/INT
16-Pin 4×4 QFN or 16-Pin TSSOP Packages
Multi-Chip Daisy Chain Mode
Programmable TAG Bit Output
Auto/Manual Channel Select Mode
ADS8328
ADS8327
+IN1
NC
+IN0
COM
+IN
−IN
REF+
REF−
Communications
Transducer Interface
Medical Instruments
Magnetometers
Industrial Process Control
Data Acquisition Systems
Automatic Test Equipment
DESCRIPTION
The ADS8327 is a low power, 16-bit, 500-kSPS
analog-to-digital converter with a unipolar input. The
device includes a 16-bit capacitor-based SAR A/D
converter with inherent sample and hold.
The ADS8328 is based on the same core and
includes a 2-to-1 input MUX with programmable
option of TAG bit output. Both the ADS8327 and
ADS8328 offer a high-speed, wide voltage serial
interface and are capable of chain mode operation
when multiple converters are used.
These converters are available in a 16-lead TSSOP
or 4x4 QFN packages and are fully specified for
operation over the industrial –40°C to +85°C
temperature range.
Table 1. Low Power, High-Speed SAR Converter
Family
Type/Speed
16 Bit Pseudo-Diff
1 MHz
ADS8327
ADS8329
Dual
ADS8328
ADS8330
OUTPUT
LATCH
and
3−STATE
DRIVER
SAR
+
_
500 kHz
Single
SDO
CDAC
COMPARATOR
OSC
CONVERSION
and
CONTROL
LOGIC
FS/CS
SCLK
SDI
CONVST
EOC/INT/CDI
1
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of Texas
Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
© 2006–2011, Texas Instruments Incorporated
ADS8327
ADS8328
SLAS415E – APRIL 2006 – REVISED JANUARY 2011
www.ti.com
This integrated circuit can be damaged by ESD. Texas Instruments recommends that all integrated circuits be handled with
appropriate precautions. Failure to observe proper handling and installation procedures can cause damage.
ESD damage can range from subtle performance degradation to complete device failure. Precision integrated circuits may be more
susceptible to damage because very small parametric changes could cause the device not to meet its published specifications.
ORDERING INFORMATION (1)
MODEL
ADS8327I
MAXIMUM
INTEGRAL
LINEARITY
(LSB)
±3
MAXIMUM
DIFFERENTIAL
LINEARITY
(LSB)
–1/+2
MAXIMUM
OFFSET
ERROR
(mV)
PACKAGE
TYPE
PACKAGE
DESIGNATOR
TSSOP-16
PW
±1.25
TSSOP-16
±2
±1
±3
–1/+2
±1
2
ADS8327IRSAT
Small tape and
reel 250
ADS8327IRSAR
Tape and reel
3000
ADS8327IBPW
Tube 90
ADS8327IBPWR
Tape and reel
2000
ADS8327IBRSAT
Small tape and
reel 250
ADS8327IBRSAR
Tape and reel
3000
RSA
ADS8328IPW
Tube 90
ADS8328IPWR
Tape and reel
2000
ADS8328IRSAT
Small tape and
reel 250
ADS8328IRSAR
Tape and reel
3000
PW
RSA
ADS8328IBPW
Tube 90
ADS8328IBPWR
Tape and reel
2000
ADS8328IBRSAT
Small tape and
reel 250
ADS8328IBRSAR
Tape and reel
3000
PW
±1
–40°C to +85°C
4×4 QFN-16
(1)
ADS8327IPWR
–40°C to +85°C
TSSOP-16
±2
Tube 90
Tape and reel
2000
PW
±1.25
4×4 QFN-16
ADS8328IB
ADS8327IPW
–40°C to +85°C
TSSOP-16
TRANSPORT
MEDIA
QUANTITY
RSA
±1
4×4 QFN-16
ADS8328I
ORDERING
INFORMATION
–40°C to +85°C
4×4 QFN-16
ADS8327IB
TEMPERATURE
RANGE
RSA
For the most current package and ordering information, see the Package Option Addendum at the end of this document, or visit the
device product folder at www.ti.com.
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© 2006–2011, Texas Instruments Incorporated
Product Folder Link(s): ADS8327 ADS8328
ADS8327
ADS8328
SLAS415E – APRIL 2006 – REVISED JANUARY 2011
www.ti.com
ABSOLUTE MAXIMUM RATINGS
Over operating free-air temperature range, unless otherwise noted. (1)
UNIT
Voltage
+IN to AGND
–0.3 V to +VA + 0.3 V
–IN to AGND
–0.3 V to +VA + 0.3 V
–0.3 V to 7 V
+VA to AGND
Voltage range
+REF to AGND
–0.3 V to +VA + 0.3 V
–REF to AGND
–0.3 V to +0.3 V
+VBD to BDGND
–0.3 V to 7 V
AGND to BDGND
–0.3 V to 0.3 V
Digital input voltage to BDGND
–0.3 V to +VBD + 0.3 V
Digital output voltage to BDGND
–0.3 V to +VBD + 0.3 V
TA
Operating free-air temperature range
–40°C to +85°C
Tstg
Storage temperature range
–65°C to +150°C
Junction temperature (TJ max)
(1)
TSSOP-16
Package
Power dissipation
4×4 QFN-16
Package
Power dissipation
+150°C
(TJMax - TA)/qJA
qJA thermal impedance
86°C/W
(TJMax – TA)/qJA
qJA thermal impedance
47°C/W
Stresses beyond those listed under absolute maximum ratings may cause permanent damage to the device. These are stress ratings
only, and functional operation of the device at these or any other conditions beyond those indicated under recommended operating
conditions is not implied. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
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© 2006–2011, Texas Instruments Incorporated
Product Folder Link(s): ADS8327 ADS8328
3
ADS8327
ADS8328
SLAS415E – APRIL 2006 – REVISED JANUARY 2011
www.ti.com
SPECIFICATIONS
TA = –40°C to 85°C, +VA = 2.7 V to 3.6 V, +VBD = 1.65 V to 1.5 × (+VA), VREF = 2.5 V, and fSAMPLE = 500 kHz, unless
otherwise noted.
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
V
ANALOG INPUT
Full-scale input voltage
(1)
+IN – (–IN) or (+INx – COM)
Absolute input voltage
0
+VREF
+IN, +IN0, +IN1
AGND – 0.2
+VA + 0.2
–IN or COM
AGND – 0.2
AGND + 0.2
Input capacitance
40
No ongoing conversion,
DC Input
Input leakage current
Input channel isolation, ADS8328 only
–1
At dc
108
VI = ±1.25 VPP at 50 kHz
101
V
45
pF
1
nA
dB
SYSTEM PERFORMANCE
Resolution
16
No missing codes
INL
Integral linearity
Differential
linearity
DNL
Offset error (3)
EO
–2
±1.2
2
ADS8327I, ADS8328I
–3
±2
3
ADS8327IB,
ADS8328IB
–1
±0.6
1
ADS8327I, ADS8328I
–1
±1
2
ADS8327IB,
ADS8328IB
–0.5
±0.1
0.5
ADS8327I, ADS8328I
–0.8
±0.1
0.8
–0.25
–0.07
0.2
Gain error
Gain error drift
CMRR
Common-mode rejection ratio
At dc
70
VI = 0.4 VPP at 1 MHz
50
Power-supply rejection ratio
At FFFFh output code (3)
LSB (2)
LSB (2)
mV
ppm/°C
0.25
0.3
Noise
PSRR
Bits
ADS8327IB,
ADS8328IB
Offset error drift
EG
Bits
16
%FSR
ppm/°C
dB
33
mV RMS
78
dB
18
CCLK
SAMPLING DYNAMICS
tCONV
tSAMPLE1
tSAMPLE2
Conversion time
Acquisition time
Manual trigger
Auto trigger
3
Throughput rate
(1)
(2)
(3)
4
CCLK
3
500
kHz
Aperture delay
5
ns
Aperture jitter
10
ps
Step response
100
ns
Overvoltage recovery
100
ns
Ideal input span, does not include gain or offset error.
LSB means least significant bit.
Measured relative to an ideal full-scale input [+IN – (–IN)] of 2.5 V when +VA = 2.7 V.
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Product Folder Link(s): ADS8327 ADS8328
ADS8327
ADS8328
SLAS415E – APRIL 2006 – REVISED JANUARY 2011
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SPECIFICATIONS (continued)
TA = –40°C to 85°C, +VA = 2.7 V to 3.6 V, +VBD = 1.65 V to 1.5 × (+VA), VREF = 2.5 V, and fSAMPLE = 500 kHz, unless
otherwise noted.
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
DYNAMIC CHARACTERISTICS
(4)
THD
Total harmonic distortion
SNR
Signal-to-noise ratio
SINAD
Signal-to-noise + distortion
SFDR
Spurious-free dynamic range
–98
VIN = 2.5 VPP at 10 kHz
VIN = 2.5 VPP at 100 kHz
–83.5
VIN = 2.5 VPP at 10 kHz
88.5
VIN = 2.5 VPP at 100 kHz
dB
dB
85
VIN = 2.5 VPP at 10 kHz
88.5
VIN = 2.5 VPP at 100 kHz
81
VIN = 2.5 VPP at 10 kHz
101
VIN = 2.5 VPP at 100 kHz
84
–3dB small-signal bandwidth
dB
dB
30
MHz
CLOCK
Internal conversion clock frequency
SCLK External serial clock
10.5
11
Used as I/O clock only
12.2
33
As I/O clock and conversion clock
1
21
0.3
2.525
–0.1
0.1
MHz
MHz
EXTERNAL VOLTAGE REFERENCE INPUT
VREF
Input reference
range
Resistance
VREF(REF+ – REF–)
3.6 V ≥ +VA ≥ 2.7 V
(REF–) – AGND
(5)
Reference input
80
V
kΩ
DIGITAL INPUT/OUTPUT
Logic family—CMOS
VIH
High-level input voltage
(+VA × 1.5) V ≥ +VBD ≥ 1.65 V
0.65 × (+VBD)
+VBD + 0.3
VIL
Low-level input voltage
(+VA × 1.5) V ≥ +VBD ≥ 1.65 V
–0.3
0.35 × (+VBD)
V
II
Input current
VI = +VBD or BDGND
–50
50
nA
CI
Input capacitance
5
VOH
High-level output voltage
(+VA × 1.5) V ≥ +VBD ≥ 1.65 V,
IO = 100 mA
VOL
Low-level output voltage
(+VA × 1.5) V ≥ +VBD ≥ 1.65 V,
IO = 100 mA
CO
Output capacitance
CL
Load capacitance
V
pF
+VBD – 0.6
+VBD
V
0
0.4
V
5
pF
30
pF
1.5 × (+VA)
V
3.6
V
Data format—straight binary
POWER-SUPPLY REQUIREMENTS
Power-supply
voltage
+VBD
1.65
+VA
Supply current
+VA
2.7
500-kHz Sample rate
3.8
5
NAP/Auto-NAP mode
0.2
0.4
2
50
nA
14
mW
+85
°C
Deep power-down mode
Buffer I/O supply current
500 kSPS
Power dissipation
+VA = 2.7 V, +VBD = 1.8 V
0.2
10.6
mA
mA
TEMPERATURE RANGE
TA
(4)
(5)
–40
Operating free-air temperature
Calculated on the first nine harmonics of the input frequency.
Can vary ±30%.
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Product Folder Link(s): ADS8327 ADS8328
5
ADS8327
ADS8328
SLAS415E – APRIL 2006 – REVISED JANUARY 2011
www.ti.com
SPECIFICATIONS
TA = –40°C to 85°C, +VA = 4.5 V to 5.5 V, +VBD = 1.65 V to 5.5 V, VREF = 4.096 V, and fSAMPLE = 500 kHz, unless otherwise
noted.
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
V
ANALOG INPUT
Full-scale input voltage
(1)
Absolute input voltage
+IN – (–IN) or (+INx – COM)
0
+VREF
+IN, +IN0, +IN1
AGND – 0.2
+VA + 0.2
–IN or COM
AGND – 0.2
AGND + 0.2
Input capacitance
40
Input leakage current
Input channel isolation, ADS8328 only
No ongoing conversion,
DC Input
–1
At dc
109
VI = ±1.25 VPP at 50 kHz
101
V
45
pF
1
nA
dB
SYSTEM PERFORMANCE
Resolution
16
No missing codes
ADS8327IB,
Integral linearity ADS8328IB
ADS8327I, ADS8328I
INL
Differential
linearity
DNL
Offset error (3)
EO
±1.5
2
–3
±2
3
ADS8327IB,
ADS8328IB
–1
±0.7
1
ADS8327I, ADS8328I
–1
±1
2
ADS8327IB,
ADS8328IB
–1
±0.4
1
–1.25
±0.4
1.25
–0.25
–0.07
Offset error drift
0.5
Gain error
Gain error drift
CMRR
Common-mode rejection ratio
At dc
70
VI = 1 VPP at 1 MHz
50
Power-supply rejection ratio
At FFFFh output code (3)
LSB (2)
LSB (2)
mV
ppm/°C
0.25
0.3
Noise
PSRR
Bits
–2
ADS8327I, ADS8328I
EG
Bits
16
%FSR
ppm/°C
dB
33
mV RMS
78
dB
18
CCLK
SAMPLING DYNAMICS
tCONV
Conversion time
tSAMPLE
1
tSAMPLE
Manual trigger
3
Acquisition time
CCLK
Auto trigger
3
2
Throughput rate
(1)
(2)
(3)
6
500
kHz
Aperture delay
5
ns
Aperture jitter
10
ps
Step response
100
ns
Overvoltage recovery
100
ns
Ideal input span, does not include gain or offset error.
LSB means least significant bit.
Measured relative to an ideal full-scale input [+IN – (–IN)] of 4.096 V when +VA = 5 V.
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Product Folder Link(s): ADS8327 ADS8328
ADS8327
ADS8328
SLAS415E – APRIL 2006 – REVISED JANUARY 2011
www.ti.com
SPECIFICATIONS (continued)
TA = –40°C to 85°C, +VA = 4.5 V to 5.5 V, +VBD = 1.65 V to 5.5 V, VREF = 4.096 V, and fSAMPLE = 500 kHz, unless otherwise
noted.
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
DYNAMIC CHARACTERISTICS
VIN = 4.096 VPP at 10 kHz
THD
Total harmonic distortion
(4)
SNR
Signal-to-noise ratio
SINAD
Signal-to-noise + distortion
SFDR
Spurious-free dynamic range
-96
VIN = 4.096 VPP at 100 kHz,
ADS8327/28IB
–95.7
VIN = 4.096 VPP at 100 kHz,
ADS8327/28I
–95.7
VIN = 4.096 VPP at 10 kHz
91
VIN = 4.096 VPP at 100 kHz
89
VIN = 4.096 VPP at 10 kHz
91
VIN = 4.096 VPP at 100 kHz
88
VIN = 4.096 VPP at 10 kHz
dB
dB
dB
100
VIN = 4.096 VPP at 100 kHz,
ADS8327/28IB
98.8
VIN = 4.096 VPP at 100 kHz,
ADS8327/28I
98.8
–3dB Small-signal bandwidth
dB
30
MHz
CLOCK
Internal conversion clock frequency
SCLK External serial clock
10.9
12
Used as I/O clock only
12.6
50
As I/O clock and conversion clock
1
21
MHz
MHz
EXTERNAL VOLTAGE REFERENCE INPUT
VREF
Input reference
range
Resistance
VREF (REF+ – REF–)
5.5 V ≥ +VA ≥ 4.5 V
0.3
(REF–) – AGND
(5)
4.096
–0.1
Reference input
4.2
0.1
80
V
kΩ
DIGITAL INPUT/OUTPUT
Logic family—CMOS
VIH
High-level input voltage
5.5 V ≥ +VBD ≥ 4.5 V
0.65 × (+VBD)
+VBD + 0.3
VIL
Low-level input voltage
5.5 V ≥ +VBD ≥ 4.5 V
–0.3
0.35 × (+VBD)
V
II
Input current
VI = +VBD or BDGND
-50
50
nA
CI
Input capacitance
5
VOH
High-level output voltage
5.5 V ≥ +VBD ≥ 4.5 V,
IO = 100 mA
VOL
Low-level output voltage
5.5 V ≥ +VBD ≥ 4.5 V,
IO = 100 mA
CO
Output capacitance
CL
Load capacitance
V
pF
+VBD – 0.6
+VBD
V
0
0.4
V
5
pF
30
pF
Data format—straight binary
POWER-SUPPLY REQUIREMENTS
Power supply
voltage
+VBD
1.65
3.3
5.5
V
4.5
5
5.5
V
500-kHz Sample rate
5
6.2
NAP/Auto-NAP mode
0.3
0.5
Deep power-down mode
6
50
500 kSPS
1
+VA
Supply current
Buffer I/O supply current
Power dissipation
+VA = 5 V, +VBD = 5 V
+VA = 5 V, +VBD = 1.8 V
mA
nA
mA
30
38.5
25.4
32
mW
TEMPERATURE RANGE
TA
(4)
(5)
–40
Operating free-air temperature
+85
°C
Calculated on the first nine harmonics of the input frequency.
Can vary ±30%
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ADS8328
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TIMING CHARACTERISTICS
All specifications typical at –40°C to 85°C, +VA = 2.7 v, +VBD = 1.8 V (1)
(2)
PARAMETER
fCCLK
Frequency, conversion clock, CCLK
MIN
External,
fCCLK = 1/2 fSCLK
0.5
Internal
fCCLK = 1/2 fSCLK
10.5
TYP
MAX
UNIT
10.5
MHz
11
12.2
tsu(CSF-EOC)
Setup time, falling edge of CS to EOC
1
CCLK
th(CSF-EOC)
Hold time, falling edge of CS to EOC
0
ns
twL(CONVST)
Pulse duration, CONVST low
40
ns
tsu(CSF-EOS)
Setup time, falling edge of CS to EOS
20
ns
th(CSF-EOS)
Hold time, falling edge of CS to EOS
20
ns
tsu(CSR-EOS)
Setup time, rising edge of CS to EOS
20
ns
th(CSR-EOS)
Hold time, rising edge of CS to EOS
20
ns
tsu(CSF-SCLK1F)
Setup time, falling edge of CS to first falling
SCLK
5
ns
twL(SCLK)
Pulse duration, SCLK low
8
tc(SCLK) – 8
ns
twH(SCLK)
Pulse duration, SCLK high
8
tc(SCLK) – 8
ns
I/O Clock only
I/O and conversion clock
tc(SCLK)
Cycle time, SCLK
I/O Clock, chain mode
I/O and conversion clock,
chain mode
30
47.6
2000
ns
30
47.6
2000
td(SCLKF-SDOINVALID)
Delay time, falling edge of SCLK to SDO
invalid
10-pF Load
td(SCLKF-SDOVALID)
Delay time, falling edge of SCLK to SDO
valid
10-pF Load
16
ns
td(CSF-SDOVALID)
Delay time, falling edge of CS to SDO valid,
SDO MSB output
10-pF Load
13
ns
tsu(SDI-SCLKF)
Setup time, SDI to falling edge of SCLK
8
ns
th(SDI-SCLKF)
Hold time, SDI to falling edge of SCLK
4
ns
td(CSR-SDOZ)
Delay time, rising edge of CS/FS to SDO
3-state
tsu(16th SCLKF-CSR)
Setup time, 16th falling edge of SCLK
before rising edge of CS/FS
td(SDO-CDI)
Delay time, CDI high to SDO high in daisy
chain mode
(1)
(2)
8
7.5
ns
8
10
10-pF Load, chain mode
ns
ns
25
ns
All input signals are specified with tr = tf = 1.5 ns (10% to 90% of VDD) and timed from a voltage level of (VIL + VIH)/2.
See timing diagrams.
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Product Folder Link(s): ADS8327 ADS8328
ADS8327
ADS8328
SLAS415E – APRIL 2006 – REVISED JANUARY 2011
www.ti.com
TIMING CHARACTERISTICS
All specifications typical at –40°C to 85°C, +VA = +VBD = 5 V
(1) (2)
PARAMETER
fCCLK
Frequency, conversion clock, CCLK
MIN
External,
fCCLK = 1/2 fSCLK
0.5
Internal
fCCLK = 1/2 fSCLK
10.9
TYP
MAX
UNIT
10.5
MHz
12
12.6
tsu(CSF-EOC)
Setup time, falling edge of CS to EOC
1
CCLK
th(CSF-EOC)
Hold time, falling edge of CS to EOC
0
ns
twL(CONVST)
Pulse duration, CONVST low
40
ns
tsu(CSF-EOS)
Setup time, falling edge of CS to EOS
20
ns
th(CSF-EOS)
Hold time, falling edge of CS to EOS
20
ns
tsu(CSR-EOS)
Setup time, rising edge of CS to EOS
20
ns
th(CSR-EOS)
Hold time, rising edge of CS to EOS
20
ns
tsu(CSF-SCLK1F)
Setup time, falling edge of CS to first falling
SCLK
5
ns
twL(SCLK)
Pulse duration, SCLK low
8
tc(SCLK) – 8
ns
twH(SCLK)
Pulse duration, SCLK high
8
tc(SCLK) – 8
ns
I/O Clock only
I/O and conversion clock
tc(SCLK)
Cycle time, SCLK
I/O Clock, chain mode
I/O and conversion clock,
chain mode
20
47.6
2000
ns
20
47.6
2000
td(SCLKF-SDOINVALID)
Delay time, falling edge of SCLK to SDO
invalid
10-pF Load
td(SCLKF-SDOVALID)
Delay time, falling edge of SCLK to SDO
valid
10-pF Load
10
ns
td(CSF-SDOVALID)
Delay time, falling edge of CS to SDO
valid, SDO MSB output
10-pF Load
8.5
ns
tsu(SDI-SCLKF)
Setup time, SDI to falling edge of SCLK
8
ns
th(SDI-SCLKF)
Hold time, SDI to falling edge of SCLK
4
ns
td(CSR-SDOZ)
Delay time, rising edge of CS/FS to SDO
3-state
tsu(16th SCLKF-CSR)
Setup time, 16th falling edge of SCLK
before rising edge of CS/FS
td(SDO-CDI)
Delay time, CDI high to SDO high in
daisy-chain mode
(1)
(2)
2
ns
5
10
10-pF Load, chain mode
ns
ns
16
ns
All input signals are specified with tr = tf = 1.5 ns (10% to 90% of VDD) and timed from a voltage level of (VIL + VIH)/2.
See timing diagrams.
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PIN ASSIGNMENTS
ADS8327
ADS8328
PW PACKAGE
(TOP VIEW)
PW PACKAGE
(TOP VIEW)
16
15
14
13
12
11
10
9
1
2
3
4
5
6
7
8
+VA
RESERVED
+IN
−IN
AGND
REF−
REF+ (REFIN)
NC
+VBD
SCLK
BDGND
SDO
SDI
FS/CS
EOC/INT
CONVST
16
15
14
13
12
11
10
9
1
2
3
4
5
6
7
8
+VA
+IN1
+IN0
COM
AGND
REF−
REF+ (REFIN)
NC
+VBD
SCLK
BDGND
SDO
SDI
FS/CS
EOC/INT
CONVST
NC − No internal connection
REF−
AGND
COM
+IN0
13
16
15
14
13
11
+VA
CONVST
3
10
EOC/INT/CDI
4
9
6
7
8
1
12
+IN1
NC
2
11
+VA
+VBD
CONVST
3
10
+VBD
SCLK
EOC/INT/CDI
4
9
SCLK
5
6
7
8
BDGND
2
5
REF+(REFIN)
SDO
NC
BDGND
RESERVED
SDO
12
SDI
1
FS/CS
REF+(REFIN)
SDI
14
FS/CS
15
+IN
16
−IN
AGND
ADS8328
RSA PACKAGE
(TOP VIEW)
REF−
ADS8327
RSA PACKAGE
(TOP VIEW)
NC − No internal connection
CAUTION: The thermal pad is internally connected to the substrate. This pad can be connected to the analog ground or left
floating. Keep the thermal pad separate from the digital ground, if possible.
10
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ADS8327 Terminal Functions
NAME
NO.
I/O
DESCRIPTION
TSSOP
QFN
AGND
5
15
–
Analog ground
BDGND
14
8
–
Interface ground
CONVST
9
3
I
Freezes sample and hold, starts conversion with next rising edge of internal clock
O
Status output. If programmed as EOC, this pin is low (default) when a conversion is in
progress. If programmed as an interrupt (INT), this pin is low for a preprogrammed
duration after the end of conversion and valid data are to be output. The polarity of EOC
or INT is programmable. This pin can also be used as a chain data input when the device
is operated in chain mode.
EOC/ INT/ CDI
10
4
FS/CS
11
5
+IN
3
–IN
4
NC
8
2
REF+
7
1
I
External reference input.
REF–
6
16
I
Connect to AGND through individual via.
RESERVED
2
12
–
Reserved, connect to AGND or +VA
SCLK
15
9
I
Clock for serial interface
SDI
12
6
I
Serial data in
SDO
13
7
O
Serial data out
+VA
1
11
Analog supply, +2.7 V to +5.5 VDC.
+VBD
16
10
Interface supply
I
Frame sync signal for TMS320 DSP serial interface or chip select input for SPI interface
slave select (SS–).
13
I
Noninverting input
14
I
Inverting input, usually connected to ground
No connection
ADS8328 Terminal Functions
NAME
NO.
I/O
DESCRIPTION
TSSOP
QFN
AGND
5
15
–
Analog ground
BDGND
14
8
–
Interface ground
COM
4
14
I
Common inverting input, usually connected to ground
CONVST
9
3
I
Freezes sample and hold, starts conversion with next rising edge of internal clock
EOC/ INT/
CDI
10
4
O
Status output. If programmed as EOC, this pin is low (default) when a conversion is in
progress. If programmed as an interrupt (INT), this pin is low for a preprogrammed
duration after the end of conversion and valid data are to be output. The polarity of EOC
or INT is programmable. This pin can also be used as a chain data input when the device
is operated in chain mode.
FS/CS
11
5
I
Frame sync signal for TMS320 DSP serial interface or chip select input for SPI interface
+IN1
2
12
I
Second noninverting input.
+IN0
3
13
I
First noninverting input
NC
8
2
–
No connection.
REF+
7
1
I
External reference input.
REF–
6
16
I
Connect to AGND through individual via.
SCLK
15
9
I
Clock for serial interface
SDI
12
6
I
Serial data in (conversion start and reset possible)
SDO
13
7
O
Serial data out
+VA
1
11
Analog supply, +2.7 V to +5.5 VDC.
+VBD
16
10
Interface supply
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MANUAL TRIGGER / READ While Sampling
(use internal CCLK, EOC and INT polarity programmed as active low)
Nth
Nth
tCONV = 18 CCLKs
tSAMPLE1 = 3 CCLKs min
INT
(active low)
tSAMPLE1 = 3 CCLKs min
th(CSR-EOS)
th(CSF-EOC)
th(CSF-EOS)
EOS
twL(CONVST)
EOC
EOC
(active low)
EOS
EOC
CONVST
th(CSF-EOC)
tsu(CSF-EOC)
tsu(CSF-EOS)
CS/FS
1
SCLK
1 . . . . . . . . . . . . . . . . . . . . 16
SDO
td(CSR-EOS) = 20 ns min
Nth
Nth−1st
SDI
1101b
1101b
READ Result
READ Result
Figure 1. Timing for Conversion and Acquisition Cycles for Manual Trigger (Read While Sampling)
AUTO TRIGGER / READ While Sampling
(use internal CCLK, EOC and INT polarity programmed as active low)
tCONV = 18 CCLKs
tSAMPLE2 = 3 CCLKs
Nth
tSAMPLE2 = 3 CCLKs
tCONV = 18 CCLKs
INT
(active low)
EOS
EOC
(active low)
EOC
EOS
EOS
EOC
CONVST = 1
th(CSF-EOS)
th(CSF-EOC)
tsu(CSF-EOS)
tsu(CSF-EOS)
CS/FS
SCLK
SDO
SDI
1 . . . . . . . . . . . . . . . . . . .16
1 . . . . . . . . . . . . . . . . . . .16
N − 2nd
N − 1st
1110b. . . . . . . . . . . . . .
CONFIGURE
1101b
READ Result
th(CSF-EOC)
1
Nth
1101b
READ Result
Figure 2. Timing for Conversion and Acquisition Cycles for Autotrigger (Read While Sampling)
12
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MANUAL TRIGGER / READ While Converting
(use internal CCLK, EOC and INT polarity programmed as active low)
N + 1st
Nth
Nth
EOC
(active low)
EOS
EOC
twL(CONVST)
EOS
CONVST
tCONV = 18 CCLKs
N + 1st
tSAMPLE1 = 3 CCLKs min
INT
(active low)
th(CSF-EOS)
tsu(CSR-EOS)
tsu(CSF-EOS)
CS/FS
tsu(CSF-EOC)
th(CSF-EOC)
SCLK
1
1 . . . . . . . . . . . . . . . . . . . .16
SDO
N th
N − 1st
1101b
SDI
1101b
READ Result
READ Result
Figure 3. Timing for Conversion and Acquisition Cycles for Manual Trigger (Read While Converting)
AUTO TRIGGER / READ While Converting
(use internal CCLK, EOC and INT polarity programmed as active low)
th(CSF-EOS)
tsu(CSF-EOS)
tSAMPLE2 = 3 CCLKs min
tSAMPLE2 = 3 CCLKs min
Nth
EOS
tCONV = 18 CCLKs
tCONV = 18 CCLKs
INT
(active low)
N + 1st
EOC
EOC
(active low)
EOS
EOS
EOC
CONVST = 1
th(CSR-EOS)
tsu(CSR-EOS)
th(CSF-EOS)
CS/FS
1 . . . . . . . . . . . . . . . . . . 16
SCLK
SDO
SDI
1 . . . . . . . . . . . . . . . . . . .16
N − 2nd
1 . . . . . . . . . . . . . . . . . . 16
??
1110b . . . . . . . . . . . . . . .
CONFIGURE
tsu(CSR-EOS)
Nth
N − 1st
1101b
READ Result
1101b
READ Result
Figure 4. Timing for Conversion and Acquisition Cycles for Autotrigger (Read While Converting)
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2
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3
4
5
6
14
7
15
16
SCLK
tsu(CSF−SCLK1F)
tc(SCLK)
twH(SCLK)
twL(SCLK)
CS/FS
tsu(16thSCLK−CSR)
td(SCLKF−SDOINVALID)
td(CSR−SDOZ)
td(SCLKF−SDOVALID)
td(CSF−SDOVALID)
SDO
Hi−Z
MSB−1 MSB−2 MSB−3 MSB−4
MSB
MSB−5 MSB−6
LSB+2
LSB+1
LSB
th(SDI−SCLKF)
MSB
SDI
MSB−1 MSB−2 MSB−3 MSB−4 MSB−5
MSB−6
LSB+2
LSB+1
LSB
tsu(SDI−SCLKF)
Figure 5. Detailed SPI Transfer Timing
MANUAL TRIGGER / READ While Sampling
(use internal CCLK active high, EOC and INT active low, TAG enabled, auto channel select)
Nth CH1
Nth CH0
CONVST
twL(CONVST)
EOS
EOC
(active low)
EOC
twL(CONVST)
Nth CH0
Nth CH1
tCONV = 18 CCLKs
tCONV = 18 CCLKs
tSAMPLE1 = 3 CCLKs min
INT
(active low)
tsu(CSF-EOS)
th(CSF-EOC)
CS/FS
SCLK
1 . . . . . . . . . . . . . . . . . . . . . . . 16
17
1 . . . . . . . . . . . . . . . . . . . . . . . 16
17
td(CSR-EOS) = 20 ns MIN
SDO
Hi−Z
Nth CH0
N−1th CH1
TAG = 0
TAG = 1
SDI
1101b
Hi−Z
1101b
READ Result
READ Result
Figure 6. Simplified Dual Channel Timing
14
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TYPICAL CHARACTERISTICS
At –40°C to 85°C, VREF (REF+ – REF–) = 4.096 V when +VA = +VBD = 5 V or VREF (REF+ – REF–) = 2.5 V
when +VA = +VBD = 2.7 V, fSCLK = 21 MHz, fI = DC for DC curves, and fI = 100 kHz for AC curves, unless
otherwise noted.
CROSSTALK
vs
FREQUENCY
DIFFERENTIAL NONLINEARITY
vs
FREE-AIR TEMPERATURE
INTEGRAL NONLINEARITY
vs
FREE-AIR TEMPERATURE
0.9
110
1.8
105
1.7
+VA = 5 V
+VA = 5 V
INL - LSB
95
DNL - LSB
Crosstalk - dB
0.8
100
0.7
1.6
+VA = 5 V
+VA = 2.7
90
1.5
0.6
85
+VA = 2.7 V
+VA = 2.7
80
0
50
100
150
F -Frequency - kHz
0.5
-40 -25 -10
200
5
20
35
50
65
1.4
5
20 35 50 65
-40 -25 -10
TA - Free-Air Temperature - °C
80
TA - Free-Air Temperature - °C
80
Figure 7.
Figure 8.
Figure 9.
DIFFERENTIAL NONLINEARITY
vs
EXTERNAL CLOCK FREQUENCY
INTEGRAL NONLINEARITY
vs
EXTERNAL CLOCK FREQUENCY
DIFFERENTIAL NONLINEARITY
vs
EXTERNAL CLOCK FREQUENCY
2
2
2
+VA = 5 V
+VA = 5 V
+VA = 2.7 V
1.5
1.5
1.5
Max
MAX
1
1
1
0.5
0.5
0
MIN
DNL - LSB
INL - LSB
DNL - LSB
Max
0.5
0
-0.5
-0.5
-1
-1
-1.5
-1.5
0
Min
-0.5
-1
Min
-1.5
-2
-2
0
-2
External Clock Frequency - MHz
5
10
15
External Clock Frequency - MHz
Figure 10.
Figure 11.
5
10
15
20
0
20
0
10
15
5
External Clock Frequency - MHz
Figure 12.
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TYPICAL CHARACTERISTICS (continued)
INTEGRAL NONLINEARITY
vs
EXTERNAL CLOCK FREQUENCY
OFFSET VOLTAGE
vs
FREE-AIR TEMPERATURE
2
OFFSET VOLTAGE
vs
SUPPLY VOLTAGE
1
1
0.8
0.8
+VA = 2.7 V
1.5
Max
0.5
0
-0.5
-1
0.6
+VA = 5 V
0.4
0.2
5
10
15
20
External Clock Frequency - MHz
25
3.2
3.7
4.2
4.7
+VA - Supply Voltage - V
5.2
Figure 14.
Figure 15.
GAIN ERROR
vs
FREE-AIR TEMPERATURE
GAIN ERROR
vs
SUPPLY VOLTAGE
POWER-SUPPLY REJECTION
RATIO
vs
SUPPLY RIPPLE FREQUENCY
+VA = 5 V
-0.070
+VA = 2.7
-0.075
-40 -25 -10
5
20
35
50
65
-0.068
-0.070
-0.073
-0.075
2.7
80
PSRR - Power Supply Rejection Ratio - dB
Offset Voltage Change - mV
-0.065
-0.068
TA - Free-Air Temperature - °C
3.2
3.7
4.2
4.7
+VA - Supply Voltage - V
-80
-78
-76
+VA = 5 V
+VA = 2.7 V
-74
-72
-70
5.2
0
20
40
60
80
Supply Ripple Frequency - kHz
100
Figure 17.
Figure 18.
SIGNAL-TO-NOISE RATIO
vs
INPUT FREQUENCY
SIGNAL-TO-NOISE AND
DISTORTION
vs
INPUT FREQUENCY
TOTAL HARMONIC DISTORTION
vs
INPUT FREQUENCY
+VA = 5 V
90
88
+VA = 2.7 V
86
20
40
60
80
fi - Input Frequency - kHz
100
Figure 19.
SINAD - Signal-To-Noise and Distortion - dB
Figure 16.
92
84
0
0
2.7
80
Figure 13.
-0.065
-0.073
-10 5
20 35 50 65
TA - Free-Air Temperature - °C
-150
92
THD - Total Harmonic Distortion - dB
0
Gain Error - % FSR
0.4
0.2
+VA = 2.7
0
-40 -25
-2
SNR - Signal-To-Noise Ratio - dB
0.6
Min
-1.5
16
Offset Voltage - mV
Offset Voltage - mV
INL - LSB
1
+VA = 5 V
90
88
+VA = 2.7 V
86
84
82
80
0
20
40
60
80
fi - Input Frequency - kHz
100
Figure 20.
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-100
+VA = 5 V
-95
-90
+VA = 2.7 V
-85
-80
0
20
40
60
80
fi - Input Frequency - kHz
100
Figure 21.
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TYPICAL CHARACTERISTICS (continued)
SPURIOUS-FREE DYNAMIC RANGE
vs
INPUT FREQUENCY
SNR - Signal-To-Noise Ratio - dB
100
+VA = 5 V
95
+VA = 2.7 V
90
85
5V
84
80
76
72
0
60
80
20
40
fi - Input Frequency - kHz
0
100
1
2
3
Full Scale Range - V
4
2.7 V
5V
84
80
76
72
5
0
1
2
3
Full Scale Range - V
4
5
Figure 22.
Figure 23.
Figure 24.
TOTAL HARMONIC DISTORTION
vs
FULL-SCALE RANGE
SPURIOUS-FREE DYNAMIC RANGE
vs
FULL-SCALE RANGE
TOTAL HARMONIC DISTORTION
vs
FREE-AIR TEMPERATURE
SFDR - Spurious Free Dynamic Range - dB
-100
10 kHz Input
2.7 V
-96
5V
-92
-88
0
1
2
3
Full Scale Range - V
4
102
-100
10 KHz
100
2.7 V
98
5V
96
94
92
+VA = 2.7 V, 10 kHz Input
-98
+VA = 5 V, 100 kHz Input
-96
90
5
0
1
2
3
4
Full Scale Range - V
-94
20 35 50 65
-40 -25 -10
5
TA - Free-Air Temperature - °C
5
Figure 25.
Figure 26.
Figure 27.
SPURIOUS-FREE DYNAMIC RANGE
vs
FREE-AIR TEMPERATURE
SIGNAL-TO-NOISE RATIO
vs
FREE-AIR TEMPERATURE
SIGNAL-TO-NOISE AND
DISTORTION
vs
FREE-AIR TEMPERATURE
92
102
+VA = 5 V, 100 kHz Input
SNR - Signal-To-Noise Ratio - dB
THD - Total Harmonic Distortion -dB
2.7 V
10 kHz Input
88
THD - Total Harmonic Distortion - dB
80
88
SINAD - Signal-To-Noise and Distortion - dB
SFDR - Spurious Free Dynamic Range - dB
10 kHz Input
105
92
SINAD - Signal-To-Noise and Distortion - dB
92
110
SFDR - Spurious Free Dynamic Range - dB
SIGNAL-TO-NOISE AND
DISTORTION
vs
FULL-SCALE RANGE
SIGNAL-TO-NOISE RATIO
vs
FULL-SCALE RANGE
+VA = 2.7 V, 10 kHz Input
100
+VA = 5 V, 100 kHz Input
98
96
94
-40 -25 -10 5
20 35 50 65
TA - Free-Air Temperature - °C
Figure 28.
80
91
90
89
+VA = 2.7 V, 10 kHz Input
88
87
-40 -25
-10
5
20 35 50 65
TA - Free-Air Temperature - °C
80
Figure 29.
92
91
+VA =5 V, 100 kHz Input
90
89
+VA = 2.7 V, 10 kHz Input
88
87
-40 -25 -10
5
20 35 50 65
TA - Free-Air Temperature - °C
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Figure 30.
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TYPICAL CHARACTERISTICS (continued)
EFFECTIVE NUMBER OF BITS
vs
FREE-AIR TEMPERATURE
INTERNAL CLOCK FREQUENCY
vs
SUPPLY VOLTAGE
INTERNAL CLOCK FREQUENCY
vs
FREE-AIR TEMPERATURE
14.7
+VA = 5 V, 100 kHz Input
14.5
12
Internal Clock Frequency - MHz
14.9
Internal Clock Frequency - MHz
11.8
11.6
11.4
11.2
11.0
2.7
14.3
-40 -25 -10
5 20 35 50 65
TA - Free-Air Temperature - °C
80
3.2
11.2
3.7
4.2
4.7
5.2
+VA - Supply Voltage - V
11
-40
5.7
80
ANALOG SUPPLY CURRENT
vs
SUPPLY VOLTAGE
ANALOG SUPPLY CURRENT
vs
SUPPLY VOLTAGE
12
NAP Mode
4.6
4.1
PD Mode
300
Analog Supply Current - nA
5.1
280
260
240
220
3.2
3.7
4.2
4.7
+VA - Supply Voltage - V
200
2.7
5.2
3.2
3.7
4.2
4.7
+VA - Supply Voltage - V
10
8
6
4
2
0
2.7
5.2
3.2
3.7
4.2
4.7
+VA - Supply Voltage - V
5.2
Figure 34.
Figure 35.
Figure 36.
ANALOG SUPPLY CURRENT
vs
SAMPLE RATE
ANALOG SUPPLY CURRENT
vs
SAMPLE RATE
ANALOG SUPPLY CURRENT
vs
FREE-AIR TEMPERATURE
6
5.5
400
Analog Supply Current - mA
5
4
+VA = 5 V
3
+VA = 2.7 V
2
1
300
+VA = 5 V
200
+VA = 2.7 V
100
200
300
400
Sample Rate - kSPS
500
600
Figure 37.
5
+VA = 5 V
4.5
4
+VA = 2.7 V
3.5
3
0
0
100
500 kSPS Sample Rate
PD Mode
Autonap Mode
0
-10 5 20
35 50 65
TA - Free-Air Temperature - °C
ANALOG SUPPLY CURRENT
vs
SUPPLY VOLTAGE
320
3.6
2.7
-25
Figure 33.
Analog Supply Current - mA
Analog Supply Current - mA
+VA = 2.7 V
11.4
Figure 32.
500 kSPS
Analog Supply Current - mA
11.6
Figure 31.
5.6
18
+VA = 5 V
11.8
+VA = 2.7 V, 10 kHz Input
Analog Supply Current - mA
ENOB - Effective Number of Bits - bits
12
0
5
10
15
Sample Rate - kSPS
20
25
Figure 38.
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-40
-25 -10 5
20 35 50 65
TA - Free-Air Temperature - °C
80
Figure 39.
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TYPICAL CHARACTERISTICS (continued)
ANALOG SUPPLY CURRENT
vs
FREE-AIR TEMPERATURE
0.4
Analog Supply Current - mA
NAP Mode
+VA = 5 V
0.3
+VA = 2.7
0.2
0.1
0
-40 -25 -10 5
20 35 50 65
TA - Free-Air Temperature - °C
80
Figure 40.
INL
DNL
2
3
fi = 500 kSPS,
+VA = 5 V,
Vref = 4.096 V
2.5
2
fi = 500 kSPS,
+VA = 5 V,
Vref = 4.096 V
1.5
1.5
1
1
DNL - Bits
INL - Bits
0.5
0.5
0
-0.5
0
-0.5
-1
-1
-1.5
-2
-1.5
-2.5
-3
-2
0
10000
20000
30000
40000
Code
50000
60000
70000
0
10000
20000
30000
40000
50000
60000
70000
Code
Figure 41.
Figure 42.
INL
DNL
2
3
fi = 500 kSPS,
+VA = 2.7 V,
Vref = 2.5 V
2.5
2
fi = 500 kSPS,
+VA = 2.7 V,
Vref = 2.5 V
1.5
1.5
1
1
DNL - Bits
INL - Bits
0.5
0.5
0
0
-0.5
-0.5
-1
-1.5
-1
-2
-1.5
-2.5
3
-2
0
10000
20000
30000
40000
50000
60000
70000
0
10000
Code
Figure 43.
20000
30000
40000
Code
50000
60000
70000
Figure 44.
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TYPICAL CHARACTERISTICS (continued)
FFT
FFT
0
0
1 kHz Input,+VA = 2.7 V,
Vref = 2.5 V, fs = 500 kSPS
-20
-40
-40
Amplitude - dB
Amplitude - dB
10 kHz Input,+VA = 2.7 V,
Vref = 2.5 V, fs = 500 kSPS
-20
-60
-80
-100
-60
-80
-100
-120
-120
-140
-140
-160
-160
0
50
100
150
f - Frequency - kHz
200
250
0
50
Figure 45.
100
150
f - Frequency - kHz
FFT
200
250
FFT
0
100 kHz Input,
+VA = 2.7 V, Vref = 2.5 V,
fs = 500 kSPS
-20
1 kHz Input,+VA = 5 V,
Vref = 4.096 V, fs = 500 kSPS
-20
-40
Amplitude - dB
-40
Amplitude - dB
250
Figure 46.
0
-60
-80
-100
-60
-80
-100
-120
-120
-140
-140
-160
-160
0
50
100
150
200
250
0
50
100
150
f - Frequency - kHz
f - Frequency - kHz
Figure 47.
20
200
Figure 48.
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TYPICAL CHARACTERISTICS (continued)
FFT
FFT
0
0
10 kHz Input,+VA = 5 V,
Vref = 4.096 V, fs = 500 kSPS
100 kHz Input,+VA = 5 V,
Vref = 4.096 V, fs = 500 kSPS
-20
-40
-40
-60
-60
Amplitude - dB
Amplitude - dB
-20
-80
-100
-80
-100
-120
-120
-140
-140
-160
-160
0
50
100
150
f - Frequency - kHz
200
250
0
50
Figure 49.
100
150
f - Frequency - kHz
200
250
Figure 50.
THEORY OF OPERATION
The ADS8327/28 is a high-speed, low power, successive approximation register (SAR) analog-to-digital
converter (ADC) that uses an external reference. The architecture is based on charge redistribution, which
inherently includes a sample/hold function.
The ADS8327/28 has an internal clock that is used to run the conversion but can also be programmed to run the
conversion based on the external serial clock, SCLK.
The ADS8327 has one analog input. The analog input is provided to two input pins: +IN and –IN. When a
conversion is initiated, the differential input on these pins is sampled on the internal capacitor array. While a
conversion is in progress, both +IN and –IN inputs are disconnected from any internal function.
The ADS8328 has two inputs. Both inputs share the same common pin—COM. The negative input is the same
as the –IN pin for the ADS8327. The ADS8328 can be programmed to select a channel manually or can be
programmed into the auto channel select mode to sweep between channel 0 and 1 automatically.
ANALOG INPUT
When the converter enters hold mode, the voltage difference between the +IN and –IN inputs is captured on the
internal capacitor array. The voltage on the –IN input is limited between AGND – 0.2 V and AGND + 0.2 V,
allowing the input to reject small signals which are common to both the +IN and –IN inputs. The +IN input has a
range of –0.2 V to VREF + 0.2 V. The input span (+IN – (–IN)) is limited to 0 V to VREF.
The (peak) input current through the analog inputs depends upon a number of factors: sample rate, input
voltage, and source impedance. The current into the ADS8327/28 charges the internal capacitor array during the
sample period. After this capacitance has been fully charged, there is no further input current. The source of the
analog input voltage must be able to charge the input capacitance (45 pF) to a 16-bit settling level within the
minimum acquisition time (238 ns). When the converter goes into hold mode, the input impedance is greater than
1 GΩ.
Care must be taken regarding the absolute analog input voltage. To maintain linearity of the converter, the +IN
and –IN inputs and the span (+IN – (–IN)) should be within the limits specified. Outside of these ranges,
converter linearity may not meet specifications. To minimize noise, low bandwidth input signals with low-pass
filters should be used. Care should be taken to ensure that the output impedance of the sources driving the +IN
and –IN inputs are matched. If this is not observed, the two inputs could have different settling times. This may
result in an offset error, gain error, and linearity error which change with temperature and input voltage.
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Device in Hold Mode
40 pF
150 W
+IN
4 pF
+VA
AGND
4 pF
40 pF
150 W
−IN
AGND
Figure 51. Input Equivalent Circuit
Driver Amplifier Choice
The analog input to the converter needs to be driven with a low noise, op-amp like the THS4031 or
OPA365
. An RC filter is recommended at the input pins to low-pass filter the noise from the source. Two
resistors of 20Ω and a capacitor of 470 pF is recommended. The input to the converter is a unipolar input voltage
in the range 0 V to VREF. The minimum -3dB bandwidth of the driving operational amplifier can be calculated to:
f3db = (ln(2) ×(n+1))/(2p × tACQ)
where n is equal to 16, the resolution of the ADC (in the case of the ADS8327/28). When tACQ = 238 ns
(minimum acquisition time), the minimum bandwidth of the driving amplifier is 7.9 MHz. The bandwidth can be
relaxed if the acquisition time is increased by the application. The OPA365, OPA827, or THS4031 from Texas
Instruments are recommended. The THS4031 used in the source follower configuration to drive the converter is
shown in the typical input drive configuration, Figure 52. For the ADS8330, a series resistor of 0Ω should be
used on the COM input (or no resistor at all).
Bipolar to Unipolar Driver
In systems where the input is bipolar, the THS4031 can be used in the inverting configuration with an additional
DC bias applied to its + input so as to keep the input to the ADS8327/28 within its rated operating voltage range.
This configuration is also recommended when the ADS8327/28 is used in signal processing applications where
good SNR and THD performance is required. The DC bias can be derived from the REF3225 or the REF3240
reference voltage ICs. The input configuration shown in Figure 53 is capable of delivering better than 91-dB SNR
and –96-dB THD at an input frequency of 10 kHz. In case bandpass filters are used to filter the input, care
should be taken to ensure that the signal swing at the input of the bandpass filter is small so as to keep the
distortion introduced by the filter minimal. In such cases, the gain of the circuit shown in Figure 53 can be
increased to keep the input to the ADS8327/28 large to keep the SNR of the system high. Note that the gain of
the system from the + input to the output of the THS4031 in such a configuration is a function of the gain of the
AC signal. A resistor divider can be used to scale the output of the REF3225 or REF3240 to reduce the voltage
at the DC input to THS4031 to keep the voltage at the input of the converter within its rated operating range.
5V
ADS8327
+VA
Input Signal
(0 V to 4 V)
20 W
THS4031
+IN
470 pF
-IN
50 W
20 W
Figure 52. Unipolar Input Drive Configuration
22
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5V
ADS8327
+VA
1 VDC
20 W
THS4031
Input Signal
(-2V to 2 V)
+IN
600 W
470 pF
-IN
600 W
20 W
Figure 53. Bipolar Input Drive Configuration
REFERENCE
The ADS8327/28 can operate with an external reference with a range from 0.3 V to 4.2 V. A clean, low noise,
well-decoupled reference voltage on this pin is required to ensure good performance of the converter. A low
noise band-gap reference like the REF3240 can be used to drive this pin. A 10-mF ceramic decoupling capacitor
is required between the REF+ and REF– pins of the converter. These capacitors should be placed as close as
possible to the pins of the device. REF– should be connected to its own via to the analog ground plane with the
shortest possible distance.
CONVERTER OPERATION
The ADS8327/28 has an oscillator that is used as an internal clock which controls the conversion rate. The
frequency of this clock is 10.5 MHz minimum. The oscillator is always on unless the device is in the deep
power-down state or the device is programmed for using SCLK as the conversion clock (CCLK). The minimum
acquisition (sampling) time takes 3 CCLKs (this is equivalent to 238 ns at 12.6 MHz) and the conversion time
takes 18 conversion clocks (CCLK) (~1500 ns) to complete one conversion.
The conversion can also be programmed to run based on the external serial clock, SCLK, if is so desired. This
allows a system designer to achieve system synchronization. The serial clock SCLK, is first reduced to 1/2 of its
frequency before it is used as the conversion clock (CCLK). For example, with a 21-MHz SCLK this provides a
10.5-MHz clock for conversions. If it is desired to start a conversion at a specific rising edge of the SCLK when
the external SCLK is programmed as the source of the conversion clock (CCLK) (and manual start of conversion
is selected), the setup time between CONVST and that rising SCLK edge should be observed. This ensures the
conversion is complete in 18 CCLKs (or 36 SCLKs). The minimum setup time is 20 ns to ensure synchronization
between CONVST and SCLK. In many cases the conversion can start one SCLK period (or CCLK) later which
results in a 19 CCLK (or 37 SCLK) conversion. The 20 ns setup time is not required once synchronization is
relaxed.
The duty cycle of SCLK is not critical as long as it meets the minimum high and low time requirements of 8 ns.
Since the ADS8327/28 is designed for high-speed applications, a higher serial clock (SCLK) must be supplied to
be able to sustain the high throughput with the serial interface and so the clock period of SCLK must be at most
1 ms (when used as conversion clock (CCLK). The minimum clock frequency is also governed by the parasitic
leakage of the capacitive digital-to-analog (CDAC) capacitors internal to the ADS8327/28.
CFR_D10
Conversion Clock
(CCLK)
=1
OSC
=0
Divider
1/2
SPI Serial
Clock (SCLK)
Figure 54. Converter Clock
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Manual Channel Select Mode
The conversion cycle starts with selecting an acquisition channel by writing a channel number to the command
register (CMR). This cycle time can be as short as 4 serial clocks (SCLK).
Auto Channel Select Mode
Channel selection can also be done automatically if auto channel select mode is enabled. This is the default
channel select mode. The dual channel converter, ADS8328, has a built-in 2-to-1 MUX. If the device is
programmed for auto channel select mode then signals from channel 0 and channel 1 are acquired with a fixed
order. Channel 0 is accessed first in the next cycle after the command cycle that configured CFR_D11 to 1 for
auto channel select mode. This automatic access stops the cycle after the command cycle that sets CFR_D11 to
'0'.
Start of a Conversion
The end of acquisition or sampling instance (EOS) is the same as the start of a conversion. This is initiated by
bringing the CONVST pin low for a minimum of 40 ns. After the minimum requirement has been met, the
CONVST pin can be brought high. CONVST acts independent of FS/CS so it is possible to use one common
CONVST for applications requiring simultaneous sample/hold with multiple converters. The ADS8327/28
switches from sample to hold mode on the falling edge of the CONVST signal. The ADS8327/28 requires 18
conversion clock (CCLK) edges to complete a conversion. The conversion time is equivalent to 1500 ns with a
12-MHz internal clock. The minimum time between two consecutive CONVST signals is 21 CCLKs.
A conversion can also be initiated without using CONVST if it is so programmed (CFR_D9 = 0). When the
converter is configured as auto trigger, the next conversion is automatically started three conversion clocks
(CCLK) after the end of a conversion. These three conversion clocks (CCLK) are used as the acquisition time. In
this case the time to complete one acquisition and conversion cycle is 21 CCLKs.
Table 2. Different Types of Conversion
MODE
SELECT CHANNEL
Auto Channel Select (1)
Automatic No need to write channel number to the CMR. Use internal sequencer for the
ADS8328.
Manual
(1)
Manual Channel Select
Write the channel number to the CMR.
START CONVERSION
Auto Trigger
Start a conversion based on the conversion
clock CCLK.
Manual Trigger
Start a conversion with CONVST.
Auto channel select should be used with auto trigger and also with the TAG bit enabled.
Status Output EOC/INT
When the status pin is programmed as EOC and the polarity is set as active low, the pin works in the following
manner: The EOC output goes LOW immediately following CONVST going LOW when manual trigger is
programmed. EOC stays LOW throughout the conversion process and returns to HIGH when the conversion has
ended. The EOC output goes low for three conversion clocks (CCLK) after the previous rising edge of EOC, if
auto trigger is programmed.
This status pin is programmable. It can be used as an EOC output (CFR.D[7:6] = 1, 1) where the low time is
equal to the conversion time. This status pin can be used as INT. (CFR.D[7:6] = 1, 0) which is set LOW at the
end of a conversion is brought to HIGH (cleared) by the next read cycle. The polarity of this pin, used as either
function (EOC or INT), is programmable through CFR_D7.
24
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Power-Down Modes
The ADS8327/28 has a comprehensive built-in power-down feature. There are three power-down modes: Deep
power-down mode, Nap power-down mode, and auto nap power-down mode. All three power-down modes are
enabled by setting the related CFR bits. The first two power-down modes are activated when enabled. A wakeup
command, 1011b, can resume device operation from a power-down mode. Auto nap power-down mode works
slightly different. When the converter is enabled in auto nap power-down mode, an end of conversion instance
(EOC) puts the device into auto nap power-down. The beginning of sampling resumes operation of the converter.
The contents of the configuration register is not affected by any of the power-down modes. Any ongoing
conversion when nap or deep power-down is activated is aborted.
+VA − Supply Current − mA
100
10
1
0.1
20
10020
20020
30020
40020
Settling Time − ns
Figure 55. Typical Analog Supply Current Drop versus Time After Power-Down
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Deep Power-Down Mode
Deep power-down mode can be activated by writing to configuration register bit CFR_D2. When the device is in
deep power-down mode, all blocks except the interface are in power-down. The external SCLK is blocked to the
analog block. The analog blocks no longer have bias currents and the internal oscillator is turned off. In this
mode, supply current falls from 5 mA to 6 nA in 100 ns. The wake-up time after a power-down is 1 ms. When bit
D2 in the configuration register is set to 0, the device is in deep power-down. Setting this bit to '1' or sending a
wake-up command can resume the converter from the deep power-down state.
Nap Mode
In nap mode the ADS8327/28 turns off biasing of the comparator and the mid-volt buffer. In this mode supply
current falls from 5 mA in normal mode to about 0.3 mA in 200 ns after the configuration cycle. The wake-up
(resume) time from nap power-down mode is 3 CCLKs (238 ns with a 12.6-MHz conversion clock). As soon as
the CFR_D3 bit in the control register is set to '0', the device goes into nap power-down mode, regardless of the
conversion state. Setting this bit to '1' or sending a wake-up command can resume the converter from the nap
power-down state.
Auto Nap Mode
Auto nap mode is almost identical to nap mode. The only difference is the time when the device is actually
powered down and the method to wake up the device. Configuration register bit D4 is only used to
enable/disable auto nap mode. If auto nap mode is enabled, the device turns off biasing after the conversion has
finished, which means the end of conversion activates auto nap power-down mode. The supply current falls from
5 mA in normal mode to about 0.3 mA in 200 ns. A CONVST resumes the device and turns biasing on again in 3
CCLKs (238 ns with a 12.6-MHz conversion clock). The device can also be woken up by disabling auto nap
mode when bit D4 of the configuration register is set to '1'. Any channel select command 0XXXb, wake-up
command, or the set default mode command 1111b can also wake up the device from auto nap power-down.
NOTE
1. This wake-up command is the word 1011b in the command word. This command sets bits D2
and D3 to 1 in the configuration register but not D4. But a wake-up command does remove the
device from either one of these power-down states, deep/nap/auto nap power-down.
2. Wake-up time is defined as the time between when the host processor tries to wake up the
converter and when a convert start can occur.
Table 3. Power-Down Mode Comparisons
TYPE OF
POWER-DOWN
POWER
CONSUMPTION
Normal operation
5 mA/3.8 mA
Deep power-down
6 nA/2 nA
Nap power-down
Auto nap power-down
26
0.3 mA/0.2 mA
ACTIVATED BY
Setting CFR
Setting CFR
EOC (end of
conversion)
ACTIVATION TIME
RESUME POWER BY
RESUME TIME
ENABLE
100 ns
Woken up by command 1011b
1 ms
Set CFR
200 ns
Woken up by command 1011b to achieve 6.6 mA
since (1.3 + 12)/2 = 6.6
3 CCLKs
Set CFR
200 ns
Woken up by CONVST, any channel select
command, default command 1111b, or wake up
command 1011b.
3 CCLKs
Set CFR
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EOS
EOC
EOS
Converter
State
N+1
Converter State
EOC
N
CONVST
N+1 −th Sampling
N −th Conversion
N+1 −th Conversion
Read While Converting
20 ns MIN
1 CCLK MIN
CS
(For Read Result)
Read N−1 −th Result
Read While Sampling
0 ns MIN
20 ns MIN
CS
(For Read Result)
Read N −th Result
Figure 56. Read While Converting versus Read While Sampling (Manual trigger)
Manual Trigger
Converter
State
Resume
N −th Sampling
>=3CCLK
N −th Conversion
Activation
Resume
=18 CCLK
N+1 −th Sampling
>=3CCLK
EOC
EOC
EOS
N+1
EOS
N
CONVST
N+1 −th Conversion
Activation
=18 CCLK
20 ns MIN
20 ns MIN
1 CCLK MIN
Read While Converting
Read N−1 −th
CS
Read N −th
Result
Result
20 ns MIN
20 ns MIN
Read While Sampling
Read N−1 −th
CS
20 ns MIN
0 ns MIN
20 ns MIN
Read N −th
Result
Result
20 ns MIN
20 ns MIN
Figure 57. Read While Converting versus Read While Sampling with Deep or Nap Power-Down
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40 ns MIN
Manual Trigger Case 1
N
N+1
Converter
State
Resume
N −th Sampling
EOS
POWERDOWN
N −th Conversion
>=3CCLK
Resume
=18 CCLK
EOC
EOS
EOC
(programmed
Active Low)
EOC
CONVST
N+1 −th Sampling
N+1 −th Conversion
>=3CCLK
=18 CCLK
6 CCLKs
POWERDOWN
6 CCLKs
Read While Converting
20 ns MIN
20 ns MIN
Read N −th
Result
Read N−1 −th
Result
CS
20 ns MIN
20 ns MIN
1 CCLK MIN
Read While Sampling
1 CCLK MIN
0 ns MIN
Read N −th
Result
Read N−1 −th
Result
CS
20 ns MIN
20 ns MIN
40 ns MIN
Manual Trigger Case 2 (wake up by CONVST)
N+1
Converter
State
N −th Sampling
>=3CCLK
N −th Conversion
POWER
DOWN
Resume
N+1 −th Sampling
>=3CCLK
=18 CCLK
EOC
EOS
Resume
EOS
N
EOC
(programmed
Active Low)
EOC
CONVST
N+1 −th Conversion
POWER
DOWN
=18 CCLK
Read While Converting
20 ns MIN
CS
20 ns MIN
Read While Sampling
20 ns MIN
20 ns MIN
CS
20 ns MIN
Read N −th
Result
Read N−1 −th
Result
0 ns MIN
20 ns MIN
Read N −th
Result
Read N−1 −th
Result
20 ns MIN
20 ns MIN
Figure 58. Read While Converting versus Read While Sampling with Auto Nap Power-Down
28
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Total Acquisition + Conversion Cycle Time:
Automatic:
= 21 CCLKs
Manual:
≥ 21 CCLKs
Manual + deep
power-down:
≥ 4SCLK + 100 ms + 3 CCLK + 18 CCLK +16 SCLK + 1 ms
Manual + nap power-down: ≥ 4 SCLK + 3 CCLK + 3 CCLK + 18 CCLK +16 SCLK
Manual + auto nap
power-down:
≥ 4 SCLK + 3 CCLK + 3 CCLK + 18 CCLK +16 SCLK (use wakeup to resume)
Manual + auto nap
power-down:
≥ 1 CCLK + 3 CCLK + 3 CCLK + 18 CCLK +16 SCLK (use CONVST to resume)
DIGITAL INTERFACE
The serial clock is designed to accommodate the latest high-speed processors with an SCLK frequency up to 50
MHz. Each cycle is started with the falling edge of FS/CS. The internal data register content which is made
available to the output register at the EOC is presented on the SDO output pin at the falling edge of FS/CS. This
is the MSB. Output data are valid at the falling edge of SCLK with td(SCLKF–SDOVALID) delay so that the host
processor can read it at the falling edge. Serial data input is also read with the falling edge of SCLK.
The complete serial I/O cycle starts with the first falling edge of SCLK after the falling edge of FS/CS and ends
16 (see NOTE) falling edges of SCLK later. The serial interface is very flexible. It works with CPOL = 0, CPHA =
1 or CPOL = 1, CPHA = 0. This means the falling edge of FS/CS may fall while SCLK is high. The same
relaxation applies to the rising edge of FS/CS where SCLK may be high or low as long as the last SCLK falling
edge happens before the rising edge of FS/CS.
NOTE
There are cases where a cycle is four SCLKs or up to 24 SCLKs depending on the read
mode combination. See Table 4 for details.
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Internal Register
The internal register consists of two parts, 4 bits for the command register (CMR) and 12 bits for configuration
data register (CFR).
Table 4. Command Set Defined by Command Register (CMR) (1)
D[15:12]
HEX
COMMAND
D[11:0]
(2)
WAKE UP FROM
AUTO NAP
MINIMUM SCLKs
REQUIRED
R/W
0000b
0h
Select analog input channel 0
Don't care
Y
4
W
0001b
1h
Select analog input channel 1 (2)
Don't care
Y
4
W
0010b
2h
Reserved
Reserved
–
–
–
0011b
3h
Reserved
Reserved
–
–
–
0100b
4h
Reserved
Reserved
–
–
–
0101b
5h
Reserved
Reserved
–
–
–
0110b
6h
Reserved
Reserved
–
–
–
0111b
7h
Reserved
Reserved
–
–
–
1000b
8h
Reserved
Reserved
–
–
–
1001b
9h
Reserved
Reserved
–
–
–
1010b
Ah
Reserved
Reserved
–
–
–
1011b
Bh
Wake up
Don't care
Y
4
W
1100b
Ch
Read CFR
Don't care
–
16
R
1101b
Dh
Read data
Don't care
–
16
R
1110
Eh
Write CFR
CFR Value
–
16
W
1111b
Fh
Default mode (load CFR with default value)
Don't care
Y
4
W
(1)
(2)
When SDO is not in 3-state (FS/CS low and SCLK running), the bits from SDO are always part (depending on how many SCLKs are
supplied) of the previous conversion result.
These two commands apply to the ADS8328 only.
WRITING TO THE CONVERTER
There are two different types of writes to the register, a 4-bit write to the CMR and a full 16-bit write to the CMR
plus CFR. The command set is listed in Table 4. A simple command requires only 4 SCLKs and the write takes
effect at the 4th falling edge of SCLK. A 16-bit write or read takes at least 16 SCLKs (see Table 7 for exceptions
that require more than 16 SCLKs).
Configuring the Converter and Default Mode
The converter can be configuring with command 1110b (write to the CFR) or command 1111b (default mode). A
write to the CFR requires a 4-bit command followed by 12-bits of data. A 4-bit command takes effect at the fourth
falling edge of SCLK. A CFR write takes effect at the 16th falling edge of SCLK.
A default mode command can be achieved by simply tying SDI to +VBD. As soon as the chip is selected at least
four 1s are clocked in by SCLK. The default value of the CFR is loaded into the CFR at the 4th falling edge of
SCLK.
CFR default values are all 1s (except for CFR_D1, this bit is ignored by the ADS8327 and is always read as a 0).
The same default values apply for the CFR after a power-on reset (POR) and SW reset.
30
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READING THE CONFIGURATION REGISTER
The host processor can read back the value programmed in the CFR by issuing command 1100b. The timing is
similar to reading a conversion result except CONVST is not used and there is no activity on the EOC/INT pin.
The CFR value read back contains the first four MSBs of conversion data plus valid 12-bit CFR contents.
Table 5. Configuration Register (CFR) Map
SDI BIT
DEFINITION
CFR – D[11 – 0]
Channel select mode
D11 Default = 1
D10 Default = 1
D9 Default = 1
D8 Default = 0
D7 Default = 1
D6 Default = 1
D5 Default = 1
D4 Default = 1
D3 Default = 1
D2 Default = 1
D1 Default =
0: ADS8327
1: ADS8328
D0 Default = 1
0: Manual channel select enabled. Use channel select commands to
access a different channel.
1: Auto channel select enabled. All channels are sampled and
converted sequentially until the cycle after this bit is set to 0.
Conversion clock (CCLK) source select
0: Conversion clock (CCLK) = SCLK/2
1: Conversion clock (CCLK) = Internal OSC
Trigger (conversion start) select: start conversion at the end of sampling (EOS). If D9 = 0, the D4 setting is ignored.
0: Auto trigger automatically starts (4 internal clocks after EOC inactive)
1: Manual trigger manually started by falling edge of CONVST
Don't care
Don't care
Pin 10 polarity select when used as an output (EOC/INT)
0: EOC Active high/INT active high
1: EOC Active low/INT active low
Pin 10 function select when used as an output (EOC/INT)
0: Pin used as INT
1: Pin used as EOC
Pin 10 I/O select for chain mode operation
0: Pin 10 is used as CDI input (chain mode enabled)
1: Pin 10 is used as EOC/INT output
Auto nap power-down enable/disable (mid voltage and comparator shut down between cycles). This bit setting is ignored if D9 = 0.
0: Auto nap power-down enabled (not activated)
1: Auto nap power-down disabled
Nap power-down (mid voltage and comparator shut down between cycles). This bit is set to 1 automatically by wake-up command.
0: Enable/activate device in nap power-down
1: Remove device from nap power-down (resume)
Deep power-down. This bit is set to 1 automatically by wake-up command.
0: Enable/activate device in deep power-down
1: Remove device from deep power-down (resume)
TAG bit enable. This bit is ignored by the ADS8327 and is always read 0.
0: TAG bit disabled.
1: TAG bit output enabled. TAG bit appears at the 17th SCLK.
Reset
0: System reset
1: Normal operation
READING CONVERSION RESULT
The conversion result is available to the input of the output data register (ODR) at EOC and presented to the
output of the output register at the next falling edge of CS or FS. The host processor can then shift the data out
via the SDO pin any time except during the quiet zone. This is 20 ns before and 20 ns after the end of sampling
(EOS) period. End of sampling (EOS) is defined as the falling edge of CONVST when manual trigger is used or
the end of the 3rd conversion clock (CCLK) after EOC if auto trigger is used.
The falling edge of FS/CS should not be placed at the precise moment (minimum of at least one conversion
clock (CCLK) delay) at the end of a conversion (by default when EOC goes high), otherwise the data are corrupt.
If FS/CS is placed before the end of a conversion, the previous conversion result is read. If FS/CS is placed after
the end of a conversion, the current conversion result is read.
The conversion result is 16-bit data in straight binary format as shown in Table 5. Generally 16 SCLKs are
necessary, but there are exceptions where more than 16 SCLKS are required (see Table 7). Data output from
the serial output (SDO) is left adjusted MSB first. The trailing bits are filled with the TAG bit first (if enabled) plus
all zeros. SDO remains low until FS/CS is brought high again.
SDO is active when FS/CS is low. The rising edge of FS/CS 3-states the SDO output.
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NOTE
Whenever SDO is not in 3-state (when FS/CS is low and SCLK is running), a portion of
the conversion result is output at the SDO pin. The number of bits depends on how many
SCLKs are supplied. For example, a manual select channel command cycle requires 4
SCLKs, therefore 4 MSBs of the conversion result are output at SDO. The exception is
SDO outputs all 1s during the cycle immediately after any reset (POR or software reset).
If SCLK is used as the conversion clock (CCLK) and a continuous SCLK is used, it is not possible to clock out all
16 SDO bits during the sampling time (6 SCLKs) because of the quiet zone requirement. In this case it is better
to read the conversion result during the conversion time (36 SCLKs or 48 SCLKs in auto nap mode).
Table 6. Ideal Input Voltages and Output Codes
DESCRIPTION
ANALOG VALUE
DIGITAL OUTPUT
Full scale range
VREF
STRAIGHT BINARY
Least significant bit (LSB)
VREF/65536
Full scale
+VREF – 1 LSB
1111 1111 1111 1111
FFFF
Midscale
VREF/2
1000 0000 0000 0000
8000
Midscale – 1 LSB
VREF/2– 1 LSB
0111 1111 1111 1111
7FFF
Zero
0V
0000 0000 0000 0000
0000
BINARY CODE
HEX CODE
TAG Mode
The ADS8328 includes a feature, TAG, that can be used as a tag to indicate which channel sourced the
converted result. An address bit is added after the LSB read out from SDO indicating which channel the result
came from if TAG mode is enabled. This address bit is 0 for channel 0 and 1 for channel 1. The converter
requires more than the 16 SCLKs that are required for a 4 bit command plus 12 bit CFR or 16 data bits because
of the additional TAG bit.
Chain Mode
The ADS8327/28 can operate as a single converter or in a system with multiple converters. System designers
can take advantage of the simple high-speed SPI compatible serial interface by cascading them in a single chain
when multiple converters are used. A bit in the CFR is used to reconfigure the EOC/INT status pin as a
secondary serial data input, chain data input (CDI), for the conversion result from an upstream converter. This is
chain mode operation. A typical connection of three converters is shown in Figure 59.
Micro Controller
INT
GPIO1
GPIO2
SDI SCLK CONVST
CS
ADS8327
#1
SDO
EOC/INT
Program Device #1 CFR_D5 = 1
GPIO3
SDI SCLK CONVST
CS
ADS8327
#2
SDO
CDI
SDOSCLK
SDI
SDI SCLK CONVST
CS
ADS8327
#3
CDI
SDO
Program Devices #2 and #3 CFR_D5 = 0
Figure 59. Multiple Converters Connected Using Chain Mode
32
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When multiple converters are used in chain mode, the first converter is configured in regular mode while the rest
of the converters downstream are configured in chain mode. When a converter is configured in chain mode, the
CDI input data goes straight to the output register, therefore the serial input data passes through the converter
with a 16 SCLK (if the TAG feature is disabled) or a 24 SCLK delay, as long as CS is active. See Figure 60 for
detailed timing. In this timing the conversion in each converters are done simultaneously.
INT #3
(active low)
Nth
EOS
EOC #1
(active low)
EOC
CONVST #1,
CONVST #2,
CONVST #3
EOS
Cascaded Manual Trigger/Read While Sampling
(Use internal CCLK, EOC active low, and INT active low) CS held
low during the N times 16 bits transfer cycle.
tSAMPLE1 = 3 CCLKs min
tCONV = 18 CCLKs
td(CSR-EOS) = 20 ns min
CS/FS #1
SCLK #1,
SCLK #2,
SCLK #3
SDO #1,
CDI #2
1 . . . . . . . . . . . . . . . . . . 16
1 . . . . . . . . . . . . . . . . . . 16
Hi-Z
Nth from #1
td(CSR-EOS) = 20 ns min
CS/FS #2,
CS/FS #3
SDO #2,
CDI #3
SDO #3
1 . . . . . . . . . . . . . . . . . . 16
Hi-Z
Hi-Z
td(SDO-CDI)
Hi-Z
Nth from #2
Hi-Z
Nth from #1
Hi-Z
Nth from #3
SDI #1,
SDI #2,
SDI #3
Nth from #1
td(SDO-CDI)
1110............
CONFIGURE
Nth from #2
1101b
READ Result
Nth from #1
1101b
READ Result
Figure 60. Simplified Cascade Mode Timing with Shared CONVST and Continuous CS
Care must be given to handle the multiple CS signals when the converters are operating in chain mode. The
different chip select signals must be low for the entire data transfer (in this example 48 bits for three converters).
The first 16-bit word after the falling chip select is always the data from the chip that received the chip select
signal.
Case 1: If chip select is not toggled (CS stays low), the next 16 bits are data from the upstream converter, and so
on. This is shown in Figure 60. If there is no upstream converter in the chain, as converter #1 in the example, the
same data from the converter is going to be shown repeatedly.
Case 2: If the chip select is toggled during a chain mode data transfer cycle, as illustrated in Figure 61, the same
data from the converter is read out again and again in all three discrete 16-bit cycles. This is not a desired result.
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INT #1
(active low)
Nth
EOS
EOC #1
(active low)
EOC
CONVST #1,
CONVST #2,
CONVST #3
EOS
Cascaded Manual Trigger/Read While Sampling
(Use internal CCLK, EOC, and INT polarity programmed as active low)
CS held low during the N times 16 bits transfer cycle.
tSAMPLE1 = 3 CCLKs min
td(EOS-CSF) = 20 ns min
tCONV = 18 CCLKs
td(CSR-EOS) = 20 ns min
CS/FS #1
SCLK #1,
SCLK #2,
SCLK #3
16
1
SDO #1,
CDI #2
1
16
Nth from #1
CS/FS #2
SCLK #2,
SDO #2,
CDI #3
Nth from #2
CS/FS #3
1
16
Nth from #1
Nth from #1
td(EOS-CSF) =
td(CSR-EOS) =
20 ns min
20 ns min
Nth from #1
td(EOS-CSF) =
20 ns min
Nth from #1
td(CSR-EOS) =
20 ns min
SDO #3
SDI #1,
SDI #2,
SDI #3
Nth from #2
Nth from #3
1110............
CONFIGURE
1101b
READ Result
Nth from #1
1101b
READ Result
Figure 61. Simplified Cascade Mode Timing with Shared CONVST and Discrete CS
Figure 62 shows a slightly different scenario where CONVST is not shared by the second converter. Converters
#1 and #3 have the same CONVST signal. In this case, converter #2 simply passes previous conversion data
downstream.
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Cascaded Manual Trigger/Read While Sampling
(Use internal CCLK, EOC active low and INT active low)
CS held low during the N times 16 bits transfer cycle.
Note : old data shown.
INT #1
(active low)
Nth
EOS
EOC #1
(active low)
EOC
CONVST #2 = 1
EOS
CONVST #1,
CONVST #3
tSAMPLE1 = 3 CCLKs min
tCONV = 18 CCLKs
td(CSR-EOS) = 20 ns min
CS/FS #1
SCLK #1,
SCLK #2,
SCLK #3
1 . . . . . . . . . . . . . . . . . .16
1 . . . . . . . . . . . . . . . . . .16
1 . . . . . . . . . . . . . . . . . .16
Hi-Z
SDO #1,
CDI #2
Hi-Z
Nth from #1
td(CSR-EOS) = 20 ns min
CS/FS #2,
CS/FS #3
td(SDO-CDI)
SDO #2,
CDI #3
Hi-Z
SDO #3
Hi-Z
Hi-Z
Nth from #1
N − 1th from #2
SDI #1,
SDI #2,
SDI #3
td(SDO-CDI)
Hi-Z
N − 1th from #2
Nth from #3
1110............
CONFIGURE
Nth from #1
1101b
1101b
READ Result
READ Result
Figure 62. Simplified Cascade Timing (Separate CONVST)
The number of SCLKs required for a serial read cycle depends on the combination of different read modes, TAG
bit, chain mode, and the way a channel is selected, i.e., auto channel select. This is listed in Table 7.
Table 7. Required SCLKs For Different Read Out Mode Combinations
CHAIN MODE
AUTO CHANNEL
ENABLED CFR.D5 SELECT CFR.D11
TAG ENABLED CFR.D1
NUMBER OF SCLK PER SPI
READ
TRAILING BITS
0
0
0
16
None
0
0
1
≥17
MSB is TAG bit plus zero(s)
0
1
0
16
None
0
1
1
≥17
TAG bit plus 7 zeros
1
0
0
16
None
1
0
1
24
TAG bit plus 7 zeros
1
1
0
16
None
1
1
1
24
TAG bit plus 7 zeros
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SCLK skew between converters and data path delay through the converters configured in chain mode can affect
the maximum frequency of SCLK. The delay can also be affected by supply voltage and loading. It may be
necessary to slow down the SCLK when the devices are configured in chain mode.
ADS 8327 # 3
CDI
SDO
Logic
D
Delay
< = 8 .3 ns
Logic
Delay
Plus PAD
2.7 ns
Serial data
output
Logic
Delay
Plus PAD
8.3 ns
Q
CLK
ADS 8327 # 2
SDO
CDI
Logic
D
Delay
< = 8 .3 ns
Logic
Delay
Plus PAD
2.7 ns
Logic
Delay
Plus PAD
8.3 ns
Q
CLK
ADS 8327 # 1
CDI
Serial data
input
SDO
Logic
D
Delay
< = 8 .3 ns
Logic
Delay
Plus PAD
2.7 ns
Logic
Delay
Plus PAD
8.3 ns
Q
CLK
SCLK input
Figure 63. Typical Delay Through Converters Configured in Chain Mode
RESET
The converter has two reset mechanisms, a power-on reset (POR) and a software reset using CFR_D0. These
two mechanisms are NOR-ed internally. When a reset (software or POR) is issued, all register data are set to the
default values (all 1s) and the SDO output (during the cycle immediately after reset) is set to all 1s. The state
machine is reset to the power-on state.
SW RESET
CDI
POR
SET
SAR Shift
Register
Intermediate
Latch
Output
Register
Conversion Clock
Latched by End Of
Conversion
SDO
SCLK
Latched by Falling Edge of CS
CS
EOC
EOC
Figure 64. Digital Output Under Reset Condition
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When the device is powered up, the POR sets the device in default mode when AVDD reaches 1.5 V. When the
device is powered down, the POR circuit requires AVDD to remain below 125 mV for a duration of at least 350
ms to ensure proper discharging of internal capacitors and to correct the behavior of the device when powered
up again. If AVDD drops below 400 mV but remains above 125 mV, the internal POR capacitor does not
discharge fully and the device requires a software reset to perform correctly after the recovery of AVDD (this is
shown as the undefined zone in Figure 65).
AVDD (V)
5.500
5.000
Specified Supply
Voltage Range
4.000
3.000
2.700
2.000
POR
Trigger Level
1.500
1.000
0.400
0.125
Undefined Zone
0
0.350
t (s)
Figure 65. Relevant Voltage Levels for POR
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APPLICATION INFORMATION
TYPICAL CONNECTION
Analog +5 V
4.7 mF
AGND
Ext Ref Input
10 mF
Analog Input
AGND
+VA REF+ REF− AGND IN+ IN−
Host
Processor
FS/CS
SDO
SDI
SCLK
Interface
Supply
+1.8 V
ADS8327
BDGND
CONVST
4.7 mF
EOC/INT
+VBD
Figure 66. Typical Circuit Configuration
Part Change Notification # 20071101000
The ADS8327 and ADS8328 devices underwent a silicon change under Texas Instruments Part Change
Notification (PCN) number 20071101000. Details on this part change can be obtained from the Product
Information Center at Texas Instruments or by contacting your local sales/distribution office. Devices with a date
code of 82xx and higher are covered by this PCN.
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REVISION HISTORY
NOTE: Page numbers for previous revisions may differ from page numbers in the current version.
Changes from Revision D (June 2009) to Revision E
Page
•
Updated Figure 60 .............................................................................................................................................................. 33
•
Updated Figure 61 .............................................................................................................................................................. 34
Changes from Revision C (March 2008) to Revision D
Page
•
Added +REF to AGND and –REF to AGND specifications to Absolute Maximum Ratings table ........................................ 3
•
Revised conditions of 2.7 V to 3.6 V Specifications table to +VA = 2.7 V to 3.6 V and +VDB = 1.65 V to 1.5 × (+VA) ...... 4
•
Revised conditions of 2.7 V to 3.6 V Specifications table to +VA = 2.7 V to 3.6 V and +VDB = 1.65 V to 1.5 × (+VA) ...... 5
•
Changed test condition of Supply current, Nap mode row to NAP/Auto-NAP mode in 2.7 V to 3.6 V Specifications
table ...................................................................................................................................................................................... 5
•
Changed test condition of Supply current, PD Mode row to Deep power-down mode in Specifications table .................... 5
•
Revised conditions of 4.5 V to 5.5 V Specifications table to read +VA = 4.5 V to 5.5 V and +VDB = 1.65 V to 5.5 V ........ 6
•
Revised conditions of 4.5 V to 5.5 V Specifications table to read +VA = 4.5 V to 5.5 V and +VDB = 1.65 V to 5.5 V ........ 7
•
Changed test condition of Supply current, Nap mode row to NAP/Auto-NAP mode in 4.5 V to 5.5 V Specifications
table ...................................................................................................................................................................................... 7
•
Changed test condition of Supply current, PD Mode row to Deep power-down mode in 4.5 V to 5.5 V Specifications
table ...................................................................................................................................................................................... 7
•
Corrected typo in Figure 1 .................................................................................................................................................. 12
•
Updated SDO trace in Figure 2 .......................................................................................................................................... 12
•
Changed N – 1th to N + 1st in CONVST trace of Figure 3 ................................................................................................ 13
•
Corrected EOC and SDO traces in Figure 4 ...................................................................................................................... 13
•
Added last sentence to Driver Amplifier Choice section ..................................................................................................... 22
•
Updated Figure 52 .............................................................................................................................................................. 22
•
Updated Figure 53 .............................................................................................................................................................. 23
•
Changed fifth sentence of the Deep Power-Down Mode section ....................................................................................... 26
•
Changed second sentence of Nap Mode section ............................................................................................................... 26
•
Changed fifth sentence of Auto Nap Mode section ............................................................................................................ 26
•
Changed ms to ns in Activation Time column of Table 3 .................................................................................................... 26
•
Added Figure 65 and corresponding paragraph to the RESET section ............................................................................. 37
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PACKAGE OPTION ADDENDUM
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25-Oct-2016
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
Lead/Ball Finish
MSL Peak Temp
(2)
(6)
(3)
Op Temp (°C)
Device Marking
(4/5)
ADS8327IBPW
ACTIVE
TSSOP
PW
16
90
Green (RoHS
& no Sb/Br)
CU NIPDAU
Level-2-260C-1 YEAR
-40 to 85
ADS
8327I A
B
ADS8327IBPWG4
ACTIVE
TSSOP
PW
16
90
Green (RoHS
& no Sb/Br)
CU NIPDAU
Level-2-260C-1 YEAR
-40 to 85
ADS
8327I A
B
ADS8327IBPWR
ACTIVE
TSSOP
PW
16
2000
Green (RoHS
& no Sb/Br)
CU NIPDAU
Level-2-260C-1 YEAR
-40 to 85
ADS
8327I A
B
ADS8327IBRSAR
ACTIVE
QFN
RSA
16
3000
Green (RoHS
& no Sb/Br)
CU NIPDAU
Level-2-260C-1 YEAR
-40 to 85
ADS
8327I A
ADS8327IBRSARG4
ACTIVE
QFN
RSA
16
3000
Green (RoHS
& no Sb/Br)
CU NIPDAU
Level-2-260C-1 YEAR
-40 to 85
ADS
8327I A
ADS8327IBRSAT
ACTIVE
QFN
RSA
16
250
Green (RoHS
& no Sb/Br)
CU NIPDAU
Level-2-260C-1 YEAR
-40 to 85
ADS
8327I A
ADS8327IBRSATG4
ACTIVE
QFN
RSA
16
250
Green (RoHS
& no Sb/Br)
CU NIPDAU
Level-2-260C-1 YEAR
-40 to 85
ADS
8327I A
ADS8327IPW
ACTIVE
TSSOP
PW
16
90
Green (RoHS
& no Sb/Br)
CU NIPDAU
Level-2-260C-1 YEAR
-40 to 85
ADS
8327I A
ADS8327IPWR
ACTIVE
TSSOP
PW
16
2000
Green (RoHS
& no Sb/Br)
CU NIPDAU
Level-2-260C-1 YEAR
-40 to 85
ADS
8327I A
ADS8327IRSAT
ACTIVE
QFN
RSA
16
250
Green (RoHS
& no Sb/Br)
CU NIPDAU
Level-2-260C-1 YEAR
-40 to 85
ADS
(8327I ~ 8327I A)
ADS8328IBPW
ACTIVE
TSSOP
PW
16
90
Green (RoHS
& no Sb/Br)
CU NIPDAU
Level-2-260C-1 YEAR
-40 to 85
ADS
8328I A
B
ADS8328IBPWG4
ACTIVE
TSSOP
PW
16
90
Green (RoHS
& no Sb/Br)
CU NIPDAU
Level-2-260C-1 YEAR
-40 to 85
ADS
8328I A
B
ADS8328IBRSAT
ACTIVE
QFN
RSA
16
250
Green (RoHS
& no Sb/Br)
CU NIPDAU
Level-2-260C-1 YEAR
-40 to 85
ADS
8328I A
ADS8328IPW
ACTIVE
TSSOP
PW
16
90
Green (RoHS
& no Sb/Br)
CU NIPDAU
Level-2-260C-1 YEAR
-40 to 85
ADS
(8328I ~ 8328I A)
ADS8328IPWG4
ACTIVE
TSSOP
PW
16
90
Green (RoHS
& no Sb/Br)
CU NIPDAU
Level-2-260C-1 YEAR
-40 to 85
ADS
(8328I ~ 8328I A)
Addendum-Page 1
Samples
PACKAGE OPTION ADDENDUM
www.ti.com
Orderable Device
25-Oct-2016
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
Lead/Ball Finish
MSL Peak Temp
(2)
(6)
(3)
Op Temp (°C)
Device Marking
(4/5)
ADS8328IPWR
ACTIVE
TSSOP
PW
16
2000
Green (RoHS
& no Sb/Br)
CU NIPDAU
Level-2-260C-1 YEAR
-40 to 85
ADS
(8328I ~ 8328I A)
ADS8328IRSAT
ACTIVE
QFN
RSA
16
250
Green (RoHS
& no Sb/Br)
CU NIPDAU
Level-2-260C-1 YEAR
-40 to 85
ADS
8328I A
(1)
The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2)
Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check http://www.ti.com/productcontent for the latest availability
information and additional product content details.
TBD: The Pb-Free/Green conversion plan has not been defined.
Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement that
lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes.
Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used between
the die and leadframe. The component is otherwise considered Pb-Free (RoHS compatible) as defined above.
Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weight
in homogeneous material)
(3)
MSL, Peak Temp. - The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature.
(4)
There may be additional marking, which relates to the logo, the lot trace code information, or the environmental category on the device.
(5)
Multiple Device Markings will be inside parentheses. Only one Device Marking contained in parentheses and separated by a "~" will appear on a device. If a line is indented then it is a continuation
of the previous line and the two combined represent the entire Device Marking for that device.
(6)
Lead/Ball Finish - Orderable Devices may have multiple material finish options. Finish options are separated by a vertical ruled line. Lead/Ball Finish values may wrap to two lines if the finish
value exceeds the maximum column width.
Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information
provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and
continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals.
TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release.
In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis.
Addendum-Page 2
Samples
PACKAGE OPTION ADDENDUM
www.ti.com
25-Oct-2016
Addendum-Page 3
PACKAGE MATERIALS INFORMATION
www.ti.com
1-Nov-2016
TAPE AND REEL INFORMATION
*All dimensions are nominal
Device
Package Package Pins
Type Drawing
SPQ
Reel
Reel
A0
Diameter Width (mm)
(mm) W1 (mm)
B0
(mm)
K0
(mm)
P1
(mm)
W
Pin1
(mm) Quadrant
ADS8327IBPWR
TSSOP
PW
16
2000
330.0
12.4
6.9
5.6
1.6
8.0
12.0
Q1
ADS8327IBRSAR
QFN
RSA
16
3000
330.0
12.4
4.3
4.3
1.5
8.0
12.0
Q2
ADS8327IBRSAT
QFN
RSA
16
250
180.0
12.4
4.3
4.3
1.5
8.0
12.0
Q2
ADS8327IPWR
TSSOP
PW
16
2000
330.0
12.4
6.9
5.6
1.6
8.0
12.0
Q1
ADS8327IRSAT
QFN
RSA
16
250
180.0
12.4
4.3
4.3
1.5
8.0
12.0
Q2
ADS8328IBRSAT
QFN
RSA
16
250
180.0
12.4
4.3
4.3
1.5
8.0
12.0
Q2
ADS8328IPWR
TSSOP
PW
16
2000
330.0
12.4
6.9
5.6
1.6
8.0
12.0
Q1
ADS8328IRSAT
QFN
RSA
16
250
180.0
12.4
4.3
4.3
1.5
8.0
12.0
Q2
Pack Materials-Page 1
PACKAGE MATERIALS INFORMATION
www.ti.com
1-Nov-2016
*All dimensions are nominal
Device
Package Type
Package Drawing
Pins
SPQ
Length (mm)
Width (mm)
Height (mm)
ADS8327IBPWR
ADS8327IBRSAR
TSSOP
PW
16
2000
367.0
367.0
38.0
QFN
RSA
16
3000
336.6
336.6
28.6
ADS8327IBRSAT
QFN
RSA
16
250
210.0
185.0
35.0
ADS8327IPWR
TSSOP
PW
16
2000
367.0
367.0
38.0
ADS8327IRSAT
QFN
RSA
16
250
210.0
185.0
35.0
ADS8328IBRSAT
QFN
RSA
16
250
210.0
185.0
35.0
ADS8328IPWR
TSSOP
PW
16
2000
367.0
367.0
38.0
ADS8328IRSAT
QFN
RSA
16
250
210.0
185.0
35.0
Pack Materials-Page 2
IMPORTANT NOTICE
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