ADS8504
SLAS434A – JUNE 2005 – REVISED JUNE 2007
12-BIT 250-KSPS SAMPLING CMOS ANALOG-TO-DIGITAL CONVERTER
FEATURES
APPLICATIONS
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250-kHz Sampling Rate
Standard ±10-V Input Range
73-dB SINAD With 45-kHz Input
±0.45 LSB Max INL
±0.45 LSB Max DNL
12 Bit No Missing Code
±1 LSB Bipolar Zero Errors
±0.4 PPM/°C Bipolar Zero Error Drift
Single 5-V Supply Operation
Pin-Compatible With ADS7804/05 (Low Speed)
and 16-Bit ADS8505
Uses Internal or External Reference
Full Parallel Data Output
70-mW Typ Power Dissipation at 250 KSPS
28-Pin SOIC Package
Industrial Process Control
Data Acquisition Systems
Digital Signal Processing
Medical Equipment
Instrumentation
DESCRIPTION
The ADS8504 is a complete 12-bit sampling A/D
converter using state-of-the-art CMOS structures. It
contains a complete 12-bit, capacitor-based, SAR
A/D with S/H, reference, clock, interface for
microprocessor use, and 3-state output drivers.
The ADS8504 is specified at a 250-kHz sampling
rate over the full temperature range. Precision
resistors provide an industry standard ±10-V input
range, while the innovative design allows operation
from a single +5-V supply, with power dissipation
under 100 mW.
The ADS8504 is available in a 28-pin SOIC package
and is fully specified for operation over the industrial
-40°C to 85°C temperature range.
Clock
Successive Approximation Register and Control Logic
R/C
CS
BYTE
BUSY
CDAC
9.8 kΩ
± 10 V Input
5 kΩ
2 kΩ
Comparator
Output
Latches
and
Three
State
Drivers
Three
State
Parallel
Data
Bus
CAP
Buffer
Internal
+2.5 V Ref
4 kΩ
REF
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.
Copyright © 2005–2007, Texas Instruments Incorporated
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SLAS434A – JUNE 2005 – REVISED JUNE 2007
These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam
during storage or handling to prevent electrostatic damage to the MOS gates.
PACKAGE/ORDERING INFORMATION (1)
PRODUCT
MINIMUM
RELATIVE
ACCURACY
(LSB)
NO
MISSING
CODE
MINIMUM
SINAD
(dB)
SPECIFICATION
TEMPERATURE
RANGE
PACKAGE
LEAD
PACKAGE
DESIGNATOR
ADS8504IB
±0.45
12
72
-40°C to 85°C
SO-28
DW
(1)
ORDERING
NUMBER
ADS8504IBDW
ADS8504IBDWR
TRANSPORT
MEDIA, QTY
Tube, 20
Tape and Reel, 1000
For the most current package and ordering information, see the Package Option Addendum at the end of this document, or see the TI
web site at www.ti.com.
ABSOLUTE MAXIMUM RATINGS (1)
over operating free-air temperature range (unless otherwise noted) (2)
ADS8504
Analog inputs
±25V
VIN
Ground voltage differences
CAP
+VANA + 0.3 V to AGND2 - 0.3 V
REF
Indefinite short to AGND2, momentary short to VANA
±0.3 V
DGND, AGND1, AGND2
VANA
6V
VDIG to VANA
0.3 V
VDIG
6V
Digital inputs
-0.3 V to +VDIG + 0.3 V
Maximum junction temperature
165°C
Internal power dissipation
825 mW
Lead temperature (soldering, 1,6mm from case, 10 seconds)
(1)
(2)
260°C
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.
All voltage values are with respect to network ground terminal.
ELECTRICAL CHARACTERISTICS
TA = -40°C to 85°C, fs = 250 kHz, VDIG = VANA = 5 V, using internal reference (unless otherwise noted)
PARAMETER
TEST CONDITIONS
MIN
TYP
Resolution
MAX
12
UNIT
Bits
ANALOG INPUT
Voltage range
±10
V
Impedance
11.5
kΩ
50
pF
Capacitance
THROUGHPUT SPEED
Conversion cycle
Acquire and convert
Throughput rate
4
250
µs
kHz
DC ACCURACY
INL
Integral linearity error
-0.45
0.45
LSB (1)
DNL
Differentiall linearity error
-0.45
0.45
LSB (1)
No missing codes
Transition
(1)
(2)
2
12
noise (2)
Bits
0.1
LSB means least significant bit. For the 12-bit, ±10-V input ADS8504, one LSB is 4.88 mV.
Typical rms noise at worst case transitions and temperatures.
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ELECTRICAL CHARACTERISTICS (continued)
TA = -40°C to 85°C, fs = 250 kHz, VDIG = VANA = 5 V, using internal reference (unless otherwise noted)
PARAMETER
TEST CONDITIONS
error (3) (4)
Int. Ref.
Full-scale error drift
Int. Ref.
Full-scale error (3) (4)
Ext. 2.5-V Ref.
Full-scale error drift
Ext. 2.5-V Ref.
Full-scale
Bipolar zero error (3)
MIN
TYP
-0.25
MAX
0.25
±7
-0.25
±2
Power supply sensitivity
(VDIG = VANA = VD)
+4.75 V < VD < +5.25 V
-0.5
%FSR
ppm/°C
1
±0.4
Bipolar zero error drift
%FSR
ppm/°C
0.25
-1
UNIT
LSB
ppm/°C
0.5
LSB
AC ACCURACY
SFDR
Spurious-free dynamic range
fI = 45 kHz
THD
Total harmonic distortion
fI = 45 kHz
SINAD
Signal-to-(noise+distortion)
SNR
Signal-to-noise ratio
fI = 45 kHz
86
-95
72
–60-dB Input
fI = 45 kHz
72
Full-power bandwidth (6)
dB (5)
94
-86
dB
73
dB
32
dB
73
dB
500
kHz
SAMPLING DYNAMICS
Aperture delay
5
Transient response
FS Step
ns
2
Overvoltage recovery (7)
150
µs
ns
REFERENCE
Internal reference voltage
2.48
2.5
2.52
V
Internal reference source current (must use
external buffer)
1
µA
Internal reference drift
8
ppm/°C
External reference voltage range for specified
linearity
External reference current drain
2.3
Ext. 2.5-V Ref.
2.5
2.7
V
100
µA
V
DIGITAL INPUTS
Logic levels
VIL
Low-level input voltage
-0.3
0.8
VIH
High-level input voltage
2.0
VDIG +0.3 V
V
IIL
Low-level input current
±10
µA
IIH
High-level input current
±10
µA
0.4
V
DIGITAL OUTPUTS
Data format (Parallel 12-bits)
Data coding (Binary 2's complement)
VOL
Low-level output voltage
ISINK = 1.6 mA
VOH
High-level output voltage
ISOURCE = 500 µA
Leakage current
Hi-Z state, VOUT = 0 V to VDIG
±5
µA
Output capacitance
Hi-Z state
15
pF
83
ns
4
V
DIGITAL TIMING
Bus access timing
(3)
(4)
(5)
(6)
(7)
As measured with fixed resistors shown in Figure 24. Adjustable to zero with external potentiometer.
Full-scale error is the worst case of -full-scale or +full-scale deviation from ideal first and last code transitions, divided by the transition
voltage (not divided by the full-scale range) and includes the effect of offset error.
All specifications in dB are referred to a full-scale ±10-V input.
Full-power bandwidth is defined as the full-scale input frequency at which signal-to-(noise + distortion) degrades to 60 dB, or 10 bits of
accuracy.
Recovers to specified performance after 2 x FS input overvoltage.
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ELECTRICAL CHARACTERISTICS (continued)
TA = -40°C to 85°C, fs = 250 kHz, VDIG = VANA = 5 V, using internal reference (unless otherwise noted)
PARAMETER
TEST CONDITIONS
MIN
TYP
Bus relinquish timing
MAX
UNIT
83
ns
V
POWER SUPPLIES
VDIG
Digital input voltage
VANA
Analog input voltage
IDIG
Digital input current
IANA
Analog input current
Power dissipation
Must be ≤ VANA
4.75
5
5.25
4.75
5
5.25
fS = 250 kHz
V
4
mA
10
mA
70
100
mW
TEMPERATURE RANGE
Specified performance
-40
85
°C
Derated performance (8)
-55
125
°C
Storage
-65
150
°C
THERMAL RESISTANCE (ΘJA)
SO
(8)
46
The internal reference may not be started correctly beyond the industrial temperature range (-40°C to 85°C), therefore use of an
external reference is recommended.
DEVICE INFORMATION
DW PACKAGE
(TOP VIEW)
VIN 1
AGND1 2
28 VDIG
27 VANA
REF 3
26 BUSY
CAP 4
25 CS
AGND2 5
D11 (MSB) 6
4
°C/W
24 R/C
23 BYTE
D10 7
22 DZ
D9 8
21 DZ
D8 9
20 DZ
D7 10
19 DZ
D6 11
18 D0 (LSB)
D5 12
17 D1
D4 13
16 D2
DGND 14
15 D3
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DEVICE INFORMATION (continued)
Terminal Functions
TERMINAL
NAME
DW NO.
DIGITAL
I/O
DESCRIPTION
AGND1
2
Analog ground. Used internally as ground reference point.
AGND2
5
Analog ground.
BUSY
26
O
At the start of a conversion, BUSY goes low and stays low until the conversion is
completed and the digital outputs have been updated.
BYTE
23
I
Selects 8 most significant bits (low) or 8 least significant bits (high).
CAP
4
CS
25
Reference buffer capacitor. 2.2-µF tantalum capacitor to ground.
DGND
14
D11 (MSB)
6
O
Data bit 11. Most significant bit (MSB) of conversion results. Hi-Z state when CS is
high, or when R/C is low.
D10
7
O
Data bit 10. Hi-Z state when CS is high, or when R/C is low.
D9
8
O
Data bit 9. Hi-Z state when CS is high, or when R/C is low.
D8
9
O
Data bit 8. Hi-Z state when CS is high, or when R/C is low.
D7
10
O
Data bit 7. Hi-Z state when CS is high, or when R/C is low.
D6
11
O
Data bit 6. Hi-Z state when CS is high, or when R/C is low.
D5
12
O
Data bit 5. Hi-Z state when CS is high, or when R/C is low.
D4
13
O
Data bit 4. Hi-Z state when CS is high, or when R/C is low.
D3
15
O
Data bit 3. Hi-Z state when CS is high, or when R/C is low.
D2
16
O
Data bit 2. Hi-Z state when CS is high, or when R/C is low.
D1
17
O
Data bit 1. Hi-Z state when CS is high, or when R/C is low.
D0 (LSB)
18
O
Data bit 0. Least significant bit (LSB) of conversion results. Hi-Z state when CS is high,
or when R/C is low.
DZ
19
O
Low when CS low, R/C high. Hi-Z state when CS is high, or when R/C is low.
DZ
20
O
Low when CS low, R/C high. Hi-Z state when CS is high, or when R/C is low.
DZ
21
O
Low when CS low, R/C high. Hi-Z state when CS is high, or when R/C is low.
DZ
22
O
Low when CS low, R/C high. Hi-Z state when CS is high, or when R/C is low.
R/C
24
I
With CS low and BUSY high, a falling edge on R/C initiates a new conversion. With CS
low, a rising edge on R/C enables the parallel output.
REF
3
Reference input/output. 2.2-µF tantalum capacitor to ground.
VANA
27
Analog supply input. Nominally +5 V. Decouple to ground with 0.1-µF ceramic and
10-µF tantalum capacitors.
VDIG
28
Digital supply input. Nominally +5 V. Connect directly to pin 27. Must be ≤ VANA.
VIN
1
Analog input.
I
Internally ORed with R/C. If R/C low, a falling edge on CS initiates a new conversion.
Digital ground.
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Typical Characteristics
TOTAL HARMONIC DISTORTION
vs
FREE-AIR TEMPERATURE
110
90
80
70
−20
0
20
40
60
−95
−90
−85
−80
−70
−40
80
50
fi = 45 kHz
−20
0
20
40
60
40
−40
80
−20
0
20
40
60
Figure 2.
Figure 3.
SIGNAL-TO-NOISE
AND DISTORTION
vs
FREE-AIR TEMPERATURE
SIGNAL-TO-NOISE RATIO
vs
INPUT FREQUENCY
SIGNAL-TO-NOISE
AND DISTORTION
vs
INPUT FREQUENCY
60
50
SINAD − Signal-to-Noise and Distortion − dB
80
70
75
70
65
60
55
fi = 45 kHz
50
−20
0
20
40
60
80
1
10
100
1000
80
75
70
65
60
55
50
1
fi − Input Frequency − kHz
TA − Free-Air-Temperature − 5C
10
100
1000
fi − Input Frequency − kHz
Figure 4.
Figure 5.
Figure 6.
SPURIOUS FREE DYNAMIC RANGE
vs
INPUT FREQUENCY
TOTAL HARMONIC DISTORTION
vs
INPUT FREQUENCY
BIPOLAR ZERO ERROR
vs
FREE-AIR TEMPERATURE
90
80
70
60
50
−100
5
−90
4
BPZ − Bipolar Zero Error −mV
THD − Total Harmonic Distortion − dB
100
−80
−70
−60
−50
−40
−30
−20
−10
10
100
fi − Input Frequency − kHz
Figure 7.
1000
3
2
1
0
−1
−2
−3
−4
0
1
80
TA − Free-Air-Temperature − 5C
Figure 1.
SNR − Signal-to-Noise − dB
SINAD − Signal-to-Noise and Distortion − dB
60
TA − Free-Air-Temperature − 5C
80
40
−40
70
−75
TA − Free-Air-Temperature − 5C
SFDR − Spurious Free Dynamic Range − dB
80
SNR − Signal-to-Noise − dB
100
−40
6
SIGNAL-TO-NOISE RATIO
vs
FREE-AIR TEMPERATURE
−100
fi = 45 kHz
THD − Total Harmonic Distortion − dB
SFDR − Spurious Free Dynamic Range − dB
SPURIOUS FREE DYNAMIC RANGE
vs
FREE-AIR TEMPERATURE
1
10
100
fi − Input Frequency − kHz
Figure 8.
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−5
−40
−20
0
20
40
60
TA− Free-Air Temperature − 5 C
Figure 9.
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Typical Characteristics (continued)
POSITIVE FULL-SCALE ERROR
vs
FREE-AIR TEMPERATURE
SUPPLY CURRENT
vs
FREE-AIR TEMPERATURE
20
0.2
19
0.15
0.1
0.05
0
−0.05
−0.1
−0.15
0.15
0.1
0.05
0
−0.05
−0.1
−20
0
20
40
60
80
17
16
15
14
13
11
−0.25
−40
TA− Free-Air Temperature − 5 C
10
−20
0
20
40
60
−40
80
−20
0
20
40
60
80
TA− Free-Air Temperature − 5 C
TA − Free-Air Temperature − 5 C
Figure 10.
Figure 11.
Figure 12.
INL
0.5
fs = 250 KSPS
0.4
0.3
0.2
INL − LSBs
−40
18
12
−0.15
−0.2
−0.2
−0.25
I DD − Supply Current − mA
0.25
0.2
Positive Full−Scale Error − %FSR
0.25
0.1
0
−0.1
−0.2
−0.3
−0.4
−0.5
0
512
1024
1536
2048
2560
3072
3584
4096
3072
3584
4096
Code
(Binary 2’s Complement in Decimal)
Figure 13.
DNL
0.5
fs = 250 KSPS
0.4
0.3
0.2
DNL − LSBs
Negative Full−Scale Error − FSR%
NEGATIVE FULL-SCALE ERROR
vs
FREE-AIR TEMPERATURE
0.1
0
−0.1
−0.2
−0.3
−0.4
−0.5
0
512
1024
1536
2048
2560
Code
(Binary 2’s Complement in Decimal)
Figure 14.
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Typical Characteristics (continued)
FFT
20
8192 Points
fs = 250 KSPS
fi = 1 kHz, 0dB
SINAD = 73.47 dB
THD = −94.03 dB
0
Amplitude − dB
−20
−40
−60
−80
−100
−120
−140
−160
0
25
50
75
100
125
75
100
125
f − Frequency − Hz
Figure 15.
FFT
20
8192 Points
fs = 250 KSPS
fi = 45 kHz, 0dB
SINAD = 73.62 dB
THD = −94.03 dB
0
Amplitude − dB
−20
−40
−60
−80
−100
−120
−140
−160
0
25
50
f − Frequency − Hz
Figure 16.
BASIC OPERATION
Figure 17 shows a basic circuit to operate the ADS8504 with a full parallel data output. Taking R/C (pin 24) low
for a minimum of 40 ns (1.75 µs max if BUSY is used to latch the data) initiates a conversion. BUSY (pin 26)
goes low and stays low until the conversion is completed and the output registers are updated. Data is output in
binary 2's complement with the MSB on pin 6. BUSY going high can be used to latch the data.
The ADS8504 begins tracking the input signal at the end of the conversion. Allowing 4 µs between convert
commands assures accurate acquisition of a new signal.
The offset and gain are adjusted internally to allow external trimming with a single supply. The external resistors
compensate for this adjustment and can be left out if the offset and gain are corrected in software (refer to the
Calibration section).
STARTING A CONVERSION
The combination of CS (pin 25) and R/C (pin 24) low for a minimum of 40 ns immediately puts the sample/hold
of the ADS8504 in the hold state and starts conversion n. BUSY (pin 26) goes low and stays low until
conversion n is completed and the internal output register has been updated. All new convert commands during
BUSY low will abort the conversion in progress and reset the ADC (see Figure 22).
The ADS8504 begins tracking the input signal at the end of the conversion. Allowing 4 µs between convert
commands assures accurate acquisition of a new signal. Refer to Table 1 for a summary of CS, R/C, and BUSY
states and Figure 19, Figure 20, and Figure 21 for the timing diagrams.
8
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BASIC OPERATION (continued)
CS and R/C are internally ORed and level triggered. There is not a requirement which input goes low first when
initiating a conversion. If, however, it is critical that CS or R/C initiates conversion n, be sure the less critical
input is low at least 10 ns prior to the initiating input.
To reduce the number of control pins, CS can be tied low using R/C to control the read and convert modes. The
parallel output becomes active whenever R/C goes high. Refer to the READING DATA section.
Table 1. Control Line Functions for Read and Convert
(1)
(2)
CS
R/C
BUSY
1
X
X
None. Databus is in Hi-Z state.
OPERATION
↓
0
1
Initiates conversion n. Databus remains in Hi-Z state.
0
↓
1
Initiates conversion n. Databus enters Hi-Z state.
0
1
↑
Conversion n completed. Valid data from conversion n on the databus.
↓
1
1
Enables databus with valid data from conversion n.
↓
1
0
Enables databus with valid data from conversion n-1 (1). Conversion n in progress.
0
↑
0
Enables databus with valid data from conversion n-1 (1). Conversion n in progress.
0
0
↑
Data is invalid. CS and/or R/C must be high when BUSY goes high.
X
↓
0
Conversion n is halted. Causes ADC to reset. (2)
See Figure 19 and Figure 20 for constraints on data valid from conversion n-1.
See Figure 22 for details on ADC reset.
200 Ω
1
28
2
27
3
26
4
25
5
24
D11 (MSB)
6
23
D10
7
D9
33.2 kΩ
+
2.2 µF
2.2 µF
+
+
0.1 µF
+5V
+
10 µF
BUSY
Convert Pulse
R/C
22
DZ Low
8
21
DZ Low
D8
9
20
DZ Low
D7
10
19
DZ Low
D6
11
18
D0 (LSB)
D5
12
17
D1
D4
13
16
D2
14
15
D3
ADS8504
40 ns Min
Figure 17. Basic Operation
READING DATA
The ADS8504 outputs full or byte-reading parallel data in binary 2's complement data output format. The parallel
output is active when R/C (pin 24) is high and CS (pin 25) is low. Any other combination of CS and R/C 3-states
the parallel output. Valid conversion data can be read in a full parallel, 12-bit word or two 8-bit bytes on pins
6-13 and pins 15-22. BYTE (pin 23) can be toggled to read both bytes within one conversion cycle. Refer to
Table 2 for ideal output codes and Figure 18 for bit locations relative to the state of BYTE.
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Table 2. Ideal Input Voltages and Output Codes
DESCRIPTION
ANALOG INPUT
Full-scale range
±10 V
DIGITAL OUTPUT BINARY 2's COMPLEMENT
BINARY CODE
HEX CODE
7FF
Least significant bit (LSB)
4.88 mV
Full scale (10 V-1 LSB)
9.99512 V
0111 1111 1111
Midscale
0V
0000 0000 0000
000
One LSB below midscale
-4.88 mV
1111 1111 1111
FFF
-Full scale
-10 V
1000 0000 0000
800
PARALLEL OUTPUT (After a Conversion)
After conversion n is completed and the output registers have been updated, BUSY (pin 26) goes high. Valid
data from conversion n is available on D11-D0 (pins 6-13 and 15-18). BUSY going high can be used to latch the
data. Refer to Table 3 and Figure 19, Figure 20, and Figure 21 for timing specifications.
PARALLEL OUTPUT (During a Conversion)
After conversion n has been initiated, valid data from conversion n-1 can be read and is valid up to t2 (2.2 µs
typ) after the start of conversion n. Do not attempt to read data from t2 (2.2 µs typ) after the start of conversion n
until BUSY (pin 26) goes high; this may result in reading invalid data. Refer to Table 3 and Figure 19, Figure 20,
and Figure 21 for timing specifications.
Note: For the best possible performance, data should not be read during a conversion. The switching noise of
the asynchronous data transfer can cause digital feedthrough degrading the converter's performance.
The number of control lines can be reduced by tying CS low while using the falling edge of R/C to initiate
conversions and the rising edge of R/C to activate the output mode of the converter. See Figure 19.
Table 3. Conversion Timing
SYMBOL
MIN
TYP
40
MAX
UNITS
tw1
Pulse duration, convert
1750
ns
ta
Access time, data valid after R/C low
2.2
3.2
µs
tpd
Propagation delay time, BUSY from R/C low
15
25
ns
tw2
Pulse duration, BUSY low
2.2
µs
td1
Delay time, BUSY after end of conversion
5
td2
Delay time, aperture
5
tconv
Conversion time
tacq
Acquisition time
1.8
tdis
Disable time, bus
10
30
td3
Delay time, BUSY after data valid
35
50
tv
Valid time, previous data remains valid after R/C low
1.5
2
tconv + tacq
10
DESCRIPTION
Setup time, R/C to CS
ns
2.2
µs
µs
Throughput time
tsu
ns
83
ns
ns
µs
4
10
µs
ns
µs
tc
Cycle time between conversions
4
ten
Enable time, bus
10
30
83
ns
td4
Delay time, BYTE
5
10
30
ns
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BYTE LOW
BYTE HIGH
+5 V
Bit 11 (MSB) 6
23
Bit 3 6
22 Low
Bit 2 7
Bit 9 8
21 Low
Bit 1 8
21 Bit 5
Bit 8 9
20 Low
Bit 0 9
20 Bit 6
Bit 7 10
19 Low
Low 10
19 Bit 7
Bit 6 11
18 Bit 0 (LSB)
Low 11
18 Bit 8
Bit 5 12
17 Bit 1
Low 12
17 Bit 9
Bit 4 13
16 Bit 2
Low 13
16 Bit 10
14
15 Bit 3
14
Bit 10 7
ADS8504
23
22 Bit 4
ADS8504
15 Bit 11 (MSB)
Figure 18. Bit Locations Relative to State of BYTE (Pin 23)
tw1
R/C
tc
ta1
tw2
BUSY
tpd
td2
td1
Acquire
MODE
Convert
Acquire
tconv
DATA BUS
Previous
Data Valid
Previous
Data Valid
Hi−Z
Convert
tacq
Not Valid
Data Valid
Hi−Z
Data Valid
td3
tdis
tv
Figure 19. Conversion Timing with Outputs Enabled after Conversion (CS Tied Low)
tsu
tsu
tsu
tsu
R/C
tw1
CS
tpd
tw2
BUSY
td2
MODE Acquire
Convert
Acquire
tconv
DATA BUS
Hi−Z State
Data Valid
ten
Hi−Z State
tdis
Figure 20. Using CS to Control Conversion and Read Timing
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tsu
tsu
R/C
CS
BYTE
Pins 6 − 13 Hi−Z
High Byte
Low Byte
ten
td4
Low Byte
High Byte
Pins 15 − 18 Hi−Z
Hi−Z
tdis
Hi−Z
Figure 21. Using CS and BYTE to Control Data Bus
tc
tw1
tw1
R/C
tpd
tpd
BUSY
0 ns MIN
4.75V
VANA
VDIG
DATA BUS
Unknown
Hi-Z
Not Valid
Hi-Z
Not Valid
Data Valid
td3
Figure 22. ADC Reset
ADC RESET
The ADC reset function of the ADS8504 can be used to terminate the current conversion cycle. Bringing R/C low
for at least 40 ns while BUSY is low will initiate the ADC reset. To initiate a new conversion, R/C must return to
the high state and remain high long enough to acquire a new sample (see Table 3, tc) before going low to initiate
the next conversion sequence. In applications that do not monitor the BUSY signal, it is recommended that the
ADC reset function be implemented as part of a system initialization sequence.
INPUT RANGES
The ADS8504 offers a standard ±10-V input range. Figure 24 shows the necessary circuit connections for the
ADS8504 with and without hardware trim. Offset and full-scale error specifications are tested and specified with
the fixed resistors shown in Figure 24(b). Full-scale error includes offset and gain errors measured at both +FS
and -FS. Adjustments for offset and gain are described in the Calibration section of this data sheet.
The offset and gain are adjusted internally to allow external trimming with a single supply. The external resistors
compensate for this adjustment and can be left out if the offset and gain are corrected in software (refer to the
Calibration section).
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The nominal input impedance of 11.5 kΩ results from the combination of the internal resistor network shown on
the front page of the product data sheet and the external resistors. The input resistor divider network provides
inherent overvoltage protection assured to at least ±25 V. The 1% resistors used for the external circuitry do not
compromise the accuracy or drift of the converter. They have little influence relative to the internal resistors, and
tighter tolerances are not required.
The input signal must be referenced to AGND1. This will minimize the ground loop problem typical to analog
designs. The analog input should be driven by a low impedance source. A typical driving circuit using OPA627
or OPA132 is shown in Figure 23.
+15V
2.2 mF
22 pF
ADS8504
200 W
100 nF
GND
VIN
2 kW
Pin 7
2 kW
Vin
Pin 2
22 pF
Pin3
Pin 1
−
OPA 627
or
OPA 132
+
REF
2.2 mF
33.2 kW
Pin 6
AGND1
Pin4
GND
CAP
2.2 mF
GND
100 nF
2.2 mF
DGND
GND
AGND2
GND
−15 V
GND
Figure 23. Typical Driving Circuitry (±10 V, No Trim)
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APPLICATION INFORMATION
CALIBRATION
The ADS8504 can be trimmed in hardware or software. The offset should be trimmed before the gain since the
offset directly affects the gain. To achieve optimum performance, several iterations may be required.
Hardware Calibration
To calibrate the offset and gain of the ADS8504, install the proper resistors and potentiometers as shown in
Figure 24(a).
Software Calibration
To calibrate the offset and gain of the ADS8504 in software, no external resistors are required. See the No
Calibration section for details on the effects of the external resistors. Refer to Table 4 for range of offset and
gain errors with and without external resistors.
No Calibration
See Figure 24(b) for circuit connections. The external resistors shown in Figure 24(b) may not be necessary in
some applications. These resistors provide compensation for an internal adjustment of the offset and gain which
allows calibration with a single supply. Refer to Table 4 for range of offset and gain errors with and without
external resistors.
Table 4. Typical Offset (Bipolar Zero Error, BPZ) and Gain Errors With and Without External Resistors
WITH EXTERNAL RESISTORS
WITHOUT EXTERNAL RESISTORS
-4.88 < BPZ < 4.88
-56.6 < BPZ < -32.2
mV
-1 < BPZ < 1
-11.6 < BPZ < -6.6
LSBs
+Full scale
-0.25 < Error < 0.25
-2.5 < Error < -1.25
–Full scale
-0.25 < Error < 0.25
-3.5 < Error < -2.25
BPZ
Gain error
200 Ω
1
±10 V
2
33.2 kΩ
+5 V
2.2 µF +
50 kΩ
Offset
50 kΩ
Gain
576 kΩ
3
4
+
2.2 µF
5
VIN
±10 V
% of FSR
200 Ω
1
2
AGND1
33.2 kΩ
2.2 µF +
REF
2.2 µF
AGND2
(a) ±10 V With Hardware Trim
3
4
CAP
UNITS
VIN
AGND1
REF
CAP
+
5
AGND2
(b) ±10 V Without Hardware Trim
Note: Use 1% metal film resistors.
Figure 24. Circuit Diagram With and Without External Trim Hardware
REFERENCE
The ADS8504 can operate with its internal 2.5-V reference or an external reference. By applying an external
reference to pin 5, the internal reference can be bypassed. The reference voltage at REF is buffered internally
with the output on CAP (pin 4).
The internal reference has an 8 ppm/°C drift (typical) and accounts for approximately 20% of the full-scale error
(FSE = ±0.5%).
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REF
REF (pin 3) is an input for an external reference or the output for the internal 2.5-V reference. A 2.2-µF capacitor
should be connected as close to the REF pin as possible. The capacitor and the output resistance of REF create
a low-pass filter to bandlimit noise on the reference. Using a smaller value capacitor introduces more noise to
the reference degrading the SNR and SINAD. The REF pin should not be used to drive external ac or dc loads.
The range for the external reference is 2.3 V to 2.7 V and determines the actual LSB size. Increasing the
reference voltage increases the full-scale range and the LSB size of the converter which can improve the SNR.
CAP
CAP (pin 4) is the output of the internal reference buffer. A 2.2-µF capacitor should be placed as close to the
CAP pin as possible to provide optimum switching currents for the CDAC throughout the conversion cycle and
compensation for the output of the internal buffer. Using a capacitor any smaller than 1 µF can cause the output
buffer to oscillate and may not have sufficient charge for the CDAC. Capacitor values larger than 2.2 µF have
little affect on improving performance. The ESR (equivalent series resistance) of these compensation capacitors
is also critical. Keep the total ESR under 3 Ω. See the TYPICAL CHARACTERISTICS section for how
performance is affected by ESR.
The output of the buffer is capable of driving up to 2 mA of current to a dc load. A dc load requiring more than 2
mA of current from the CAP pin begins to degrade the linearity of the ADS8504. Using an external buffer allows
the internal reference to be used for larger dc loads and ac loads. Do not attempt to directly drive an ac load
with the output voltage on CAP. This causes performance degradation of the converter.
LAYOUT
POWER
For optimum performance, tie the analog and digital power pins to the same +5-V power supply and tie the
analog and digital grounds together. As noted in the electrical specifications, the ADS8504 uses 90% of its
power for the analog circuitry. The ADS8504 should be considered as an analog component.
The +5-V power for the A/D should be separate from the +5 V used for the system's digital logic. Connecting
VDIG (pin 28) directly to a digital supply can reduce converter performance due to switching noise from the digital
logic. For best performance, the +5-V supply can be produced from whatever analog supply is used for the rest
of the analog signal conditioning. If +12-V or +15-V supplies are present, a simple +5-V regulator can be used.
Although it is not suggested, if the digital supply must be used to power the converter, be sure to properly filter
the supply. Either using a filtered digital supply or a regulated analog supply, both VDIG and VANA should be tied
to the same +5-V source.
GROUNDING
Three ground pins are present on the ADS8504. DGND is the digital supply ground. AGND2 is the analog
supply ground. AGND1 is the ground which all analog signals internal to the A/D are referenced. AGND1 is more
susceptible to current induced voltage drops and must have the path of least resistance back to the power
supply.
All the ground pins of the A/D should be tied to the analog ground plane, separated from the system's digital
logic ground, to achieve optimum performance. Both analog and digital ground planes should be tied to the
system ground as near to the power supplies as possible. This helps to prevent dynamic digital ground currents
from modulating the analog ground through a common impedance to power ground.
SIGNAL CONDITIONING
The FET switches used for the sample hold on many CMOS A/D converters release a significant amount of
charge injection which can cause the driving op amp to oscillate. The FET switch on the ADS8504, compared to
the FET switches on other CMOS A/D converters, releases 5%-10% of the charge. There is also a resistive front
end which attenuates any charge which is released. The end result is a minimal requirement for the anti-alias
filter on the front end. Any op amp sufficient for the signal in an application is sufficient to drive the ADS8504.
The resistive front end of the ADS8504 also provides an assured ±25-V overvoltage protection. In most cases,
this eliminates the need for external input protection circuitry.
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LAYOUT (continued)
INTERMEDIATE LATCHES
The ADS8504 does have 3-state outputs for the parallel port, but intermediate latches should be used if the bus
is to be active during conversions. If the bus is not active during conversion, the 3-state outputs can be used to
isolate the A/D from other peripherals on the same bus. The 3-state outputs can also be used when the A/D is
the only peripheral on the data bus.
Intermediate latches are beneficial on any monolithic A/D converter. The ADS8504 has an internal LSB size of
610 µV. Transients from fast switching signals on the parallel port, even when the A/D is 3-stated, can be
coupled through the substrate to the analog circuitry causing degradation of converter performance.
16
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Revision History
NOTE: Page numbers for previous revisions may differ from page numbers in the current version.
Changes from Original (June, 2005) to A Revision ....................................................................................................... Page
•
•
•
•
•
Deleted text from basic operation description ...................................................................................................................... 8
Changed text in starting a conversion description................................................................................................................ 8
Changed operation descriptions and R/C in table ................................................................................................................ 9
Added SAR Reset Timing................................................................................................................................................... 12
Added ADC RESET section ............................................................................................................................................... 12
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PACKAGE OPTION ADDENDUM
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10-Dec-2020
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
(2)
Lead finish/
Ball material
MSL Peak Temp
Op Temp (°C)
Device Marking
(3)
(4/5)
(6)
ADS8504IBDW
ACTIVE
SOIC
DW
28
20
RoHS & Green
NIPDAU
Level-2-260C-1 YEAR
-40 to 85
ADS8504IB
ADS8504IBDWR
ACTIVE
SOIC
DW
28
1000
RoHS & Green
NIPDAU
Level-2-260C-1 YEAR
-40 to 85
ADS8504IB
(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)
RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance
do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may
reference these types of products as "Pb-Free".
RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption.
Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of
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