NSC ADC12041CIVX 12-bit plus sign 216 khz sampling analog-to-digital converter Datasheet

ADC12041
12-Bit Plus Sign 216 kHz Sampling Analog-to-Digital
Converter
General Description
Operating from a single 5V power supply, the ADC12041 is a
12 bit + sign, parallel I/O, self-calibrating, sampling
analog-to-digital converter (ADC). The maximum sampling
rate is 216 kHz. On request, the ADC goes through a
self-calibration process that adjusts linearity, zero and
full-scale errors.
The ADC12041 can be configured to work with many popular
microprocessors/microcontrollers and DSPs including National’s HPC family, Intel386 and 8051, TMS320C25, Motorola MC68HC11/16, Hitachi 64180 and Analog Devices
ADSP21xx.
For complementary voltage references see the LM4040,
LM4041 or LM9140.
Features
n Fully differential analog input
n Programmable acquisition times and user-controllable
throughput rates
n Programmable data bus width (8/13 bits)
n Built-in Sample-and-Hold
n Programmable auto-calibration and auto-zero cycles
n Low power standby mode
n No missing codes
Key Specifications
(fCLK = 12 MHz)
n Resolution
n 13-bit conversion time
n 13-bit throughput rate
n Integral Linearity Error (ILE)
n Single supply
n VIN range
n Power consumption
— Normal operation
— Stand-by mode
12-bits + sign
3.6 µs, max
216 ksamples/s, min
± 1 LSB, max
+5V ± 10%
GND to VA+
33 mW, max
75 µw, max
Applications
n
n
n
n
n
Medical instrumentation
Process control systems
Test equipment
Data logging
Inertial guidance
Block Diagram
DS012441-1
TRI-STATE ® is a registered trademark of National Semiconductor Corporation.
© 2000 National Semiconductor Corporation
DS012441
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ADC12041 12-Bit Plus Sign 216 kHz Sampling Analog-to-Digital Converter
April 2000
ADC12041
Connection Diagrams
28-Pin SSOP
28-Pin PLCC
DS012441-3
Order Number ADC12041CIV
See NS Package Number V28A
DS012441-2
Order Number ADC12041CIMSA
See NS Package Number MSA28
Ordering Information
NS
Industrial Temperature Range
−40˚C ≤ TA ≤ +85˚C
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Package
Number
ADC12041CIV
PLCC
ADC12041CIMSA
SSOP
2
ADC12041
Pin Descriptions
PLCC and
Pin
SSOP Pkg.
Name
Description
Pin Number
5
6
VIN+
VIN−
The analog ADC inputs. VIN+ is the non-inverting (positive) input and VIN− is the inverting (negative)
input into the ADC.
10
VREF+
Positive reference input. The operating voltage range for this input is 1V ≤ VREF+ ≤ VA+ (see Figure
3 and Figure 4). This pin should be bypassed to AGND at least with a parallel combination of a 10
µF and a 0.1 µF (ceramic) capacitor. The capacitors should be placed as close to the part as
possible.
9
VREF−
Negative reference input. The operating voltage range for this input is 0V ≤ VREF− ≤ VREF+ −1 (see
Figure 3 and Figure 4). This pin should be bypassed to AGND at least with a parallel combination of
a 10 µF and a 0.1 µF (ceramic) capacitor. The capacitors should be placed as close to the part as
possible.
4
WMODE
The logic state of this pin at power-up determines which edge of the write signal (WR ) will latch in
data from the data bus. If tied low, the ADC12041 will latch in data on the rising edge of the WR
signal. If tied to a logic high, data will be latched in on the falling edge of the WR signal. The state of
this pin should not be changed after power-up.
27
SYNC
The SYNC pin can be programmed as an input or an output. The Configuration register’s bit b4
controls the function of this pin. When programmed as an input pin (b4 = 1), a rising edge on this
pin causes the ADC’s sample-and-hold to hold the analog input signal and begin conversion. When
programmed as an output pin (b4 = 0), the SYNC pin goes high when a conversion begins and
returns low when completed.
12–20
23–26
D0–D8
D9–D12
13-bit Data bus of the ADC12041. D12 is the most significant bit and D0 is the least significant. The
BW(bus width) bit of the Configuration register (b3) selects between an 8-bit or 13-bit data bus width.
When the BW bit is cleared (BW = 0), D7–D0 are active and D12–D8 are always in TRI-STATE ® .
When the BW bit is set (BW = 1), D12–D0 are active.
28
CLK
The clock input pin used to drive the ADC12041. The operating range is 0.05 MHz to 12 MHz.
1
WR
WR is the active low WRITE control input pin. A logic low on this pin and the CS will enable the
input buffers of the data pins D12–D0. The signal at this pin is used by the ADC12041 to latch in
data on D12–D0. The sense of the WMODE pin at power-up will determine which edge of the WR
signal the ADC12041 will latch in data. See WMODE pin description.
2
RD
RD is the active low read control input pin. A logic low on this pin and CS will enable the active
output buffers to drive the data bus.
3
CS
CS is the active low Chip Select input pin. Used in conjunction with the WR and RD signals to
control the active data bus input/output buffers of the data bus.
11
RDY
RDY is an active low output pin. The signal at this pin indicates when a requested function has
begun or ended. Refer to section Functional Description and the digital timing diagrams for more
detail.
7
VA+
Analog supply input pin. The device operating supply voltage range is +5V ± 10%. Accuracy is
guaranteed only if the VA+ and VD+ are connected to the same potential. This pin should be
bypassed to AGND with a parallel combination of a 10 µF and a 0.1 µF (ceramic) capacitor. The
capacitors should be placed as close to the supply pins of the part as possible.
8
AGND
Analog ground pin. This is the device’s analog supply ground connection. It should be connected
through a low resistance and low inductance ground return to the system power supply.
21
VD+
Digital supply input pins. The device operating supply voltage range is +5V ± 10%. Accuracy is
guaranteed only if the VA+ and VD+ are connected to the same potential. This pin should be
bypassed to DGND with a parallel combination of a 10 µF and a 0.1 µF (ceramic) capacitor. The
capacitors should be placed as close to the supply pins of the part as possible.
22
DGND
Digital ground pin. This is the device’s digital supply ground connection. It should be connected
through a low resistance and low inductance ground return to the system power supply.
3
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ADC12041
Absolute Maximum Ratings (Notes 1, 2)
Operating Ratings (Notes 1, 2, 6, 7, 8, 9)
Supply Voltage (VA+ and VD+)
Voltage at all Inputs
|VA + − VD+|
|AGND − DGND|
Input Current at Any Pin (Note 3)
Package Input Current (Note 3)
Power Dissipation (Note 4)
at TA = 25˚C
Storage Temperature
Lead Temperature
SSOP Package
Vapor Phase (60 sec.)
Infared (15 sec.)
V Package, Infared (15 sec.)
ESD Susceptibility (Note 5)
Temperature Range
(Tmin ≤ TA ≤ Tmax)
Supply Voltage
VA+, VD+
|VA+ − VD+|
|AGND − DGND|
VIN Voltage
Range at all Inputs
VREF+ Input Voltage
VREF− Input Voltage
VREF+ − VREF−
VREF Common Mode
(Note 16)
6.0V
−0.3V to V+ + 0.3V
300 mV
300 mV
± 30 mA
± 120 mA
500 mW
−65˚C to +150˚C
210˚C
220˚C
300˚C
3.0 kV
−40˚C ≤ TA ≤ 85˚C
4.5V to 5.5V
≤100 mV
≤100 mV
GND ≤ VIN+ ≤ VA+
1V ≤ VREF+ ≤ VA+
0 ≤ VREF− ≤ VREF+ − 1V
1V ≤ VREF ≤ VA+
0.1 VA+ ≤ VREFCM ≤ 0.6 VA+
Converter DC Characteristics
The following specifications apply to the ADC12041 for VA+ = VD+ = 5V, VREF+ = 4.096V, VREF− = 0.0V, 12-bit + sign conversion mode, fCLK = 12.0 MHz, RS = 25Ω, source impedance for VREF+ and VREF− ≤ 1Ω, fully differential input with fixed
2.048V common-mode voltage (VINCM), and minimum acquisition time, unless otherwise specified. Boldface limits apply for
TA = TJ = TMIN to TMAX; all other limits TA = TJ = 25˚C
Symbol
ILE
DNL
Parameter
Conditions
Resolution with No Missing Codes
After Auto-Cal
Positive and Negative Integral
After Auto-Cal
Linearity Error
(Notes 12, 17)
Differential Non-Linearity
After Auto-Cal
Zero Error
After Auto-Cal (Notes 13, 17)
Typical
Limits
(Note 10)
(Note 11)
(Limit)
13
Bits (max)
± 0.6
VINCM = 5.0V
VINCM = 2.048V
VINCM = 0V
TUE
Positive Full-Scale Error
After Auto-Cal (Notes 12, 17)
Negative Full-Scale Error
After Auto-Cal (Notes 12, 17)
DC Common Mode Error
After Auto-Cal (Note 14)
Total Unadjusted Error
After Auto-Cal (Note 18)
± 1.0
± 1.0
±2
±1
±1
Units
LSB (max)
±1
LSB (max)
± 5.5
± 2.0
± 5.5
± 2.5
± 2.5
± 5.5
LSB (max)
LSB (max)
LSB (max)
LSB (max)
LSB (max)
LSB (max)
LSB
Power Supply Characteristics
The following specifications apply to the ADC12041 for VA+ = VD+ = 5V, VREF+ = 4.096V, VREF− = 0.0V, 12-bit + sign conversion mode, fCLK = 12.0 MHz, RS = 25Ω, source impedance for VREF+ and VREF− 1Ω, fully differential input with fixed 2.048V
common-mode voltage, and minimum acquisition time, unless otherwise specified. Boldface limits apply for TA = TJ = TMIN
to TMAX; all other limits TA = TJ = 25˚C
Symbol
PSS
Parameter
Power Supply Sensitivity
Conditions
Zero Error
VREF+ = 4.096V
Full-Scale Error
VREF− = 0V
VD+ Digital Supply Current
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Limits
Unit
(Note 11)
(Limit)
VD+ = VA+ = 5.0V ± 10% (Note 15)
± 0.1
± 0.5
± 0.1
Linearity Error
ID+
Typical
(Note 10)
LSB
LSB
LSB
Start Command (Performing a conversion)
with SYNC configured as an input and driven
with a 214 kHz signal. Bus width set to 13.
fCLK = 12.0 MHz, Reset Mode
850
fCLK = 12.0 MHz, Conversion
2.45
4
µA
2.6
mA (max)
(Continued)
The following specifications apply to the ADC12041 for VA+ = VD+ = 5V, VREF+ = 4.096V, VREF− = 0.0V, 12-bit + sign conversion mode, fCLK = 12.0 MHz, RS = 25Ω, source impedance for VREF+ and VREF− 1Ω, fully differential input with fixed 2.048V
common-mode voltage, and minimum acquisition time, unless otherwise specified. Boldface limits apply for TA = TJ = TMIN
to TMAX; all other limits TA = TJ = 25˚C
Symbol
Parameter
IA+
VA+ Analog Supply Current
IST
Conditions
Typical
Limits
Unit
(Note 10)
(Note 11)
(Limit)
Start Command (Performing a conversion)
with SYNC configured as an input and driven
with a 214 kHz signal. Bus width set to 13.
fCLK = 12.0 MHz, Reset Mode
2.3
fCLK = 12.0 MHz, Conversion
2.3
4.0
mA (max)
5
15
µA (max)
100
120
µA (max)
Standby Supply Current
Standby Mode
(ID+ + IA+)
fCLK = Stopped
fCLK = 12.0 MHz
mA
Analog Input Characteristics
The following specifications apply to the ADC12041 for VA+ = VD+ = 5V, VREF+ = 4.096V, VREF− = 0.0V, 12-Bit + sign conversion mode, fCLK = 12.0 MHz, RS = 25Ω, source impedance for VREF+ and VREF+ ≤ 1Ω, fully differential input with fixed 2.048V
common-mode voltage, and minimum acquisition time, unless otherwise specified. Boldface limits apply for TA = TJ = TMIN
to TMAX; all other limits TA = TJ = 25˚C
Symbol
IIN
Parameter
VIN+ and VIN− Input Leakage Current
Conditions
Typical
Limits
Unit
(Note 10)
(Note 11)
(Limit)
± 0.05
2.0
µA (max)
VIN+ = 5V
VIN− = 0V
RON
ADC Input On Resistance
VIN = 2.5V
1000
Ω
10
pF
Refer to section titled INPUT CURRENT.
CVIN
ADC Input Capacitance
Reference Inputs
The following specifications apply to the ADC12041 for VA+ = VD+ = 5V, VREF+ = 4.096V, VREF− = 0.0V, 12-bit + sign conversion mode, fCLK = 12.0 MHz, RS = 25Ω, source impedance for VREF+ and VREF− ≤ 1Ω, fully differential input with fixed
2.048V common-mode voltage, and minimum acquisition time, unless otherwise specified. Boldface limits apply for TA = TJ
= TMIN to TMAX; all other limits TA = TJ = 25˚C
Symbol
IREF
CREF
Parameter
Reference Input Current
Conditions
Typical
Limits
Unit
(Note 10)
(Note 11)
(Limit)
VREF+ 4.096V, VREF− = 0V
Analog Input Signal: 1 kHz
145
µA
(Note 20) 80 kHz
136
µA
85
pF
Reference Input Capacitance
Digital Logic Input/Output Characteristics
The following specifications apply to the ADC12041 for VA+ = VD+ = 5V, VREF+ = 4.096V, VREF− = 0.0V, 12-bit + sign conversion mode, fCLK = 12.0 MHz, RS = 25Ω, source impedance for VREF+ and VREF− ≤ 1Ω, fully differential input with fixed
2.048V common-mode voltage, and minimum acquisition time, unless otherwise specified. Boldface limits apply for TA = TJ
= TMIN to TMAX; all other limits TA = TJ = 25˚C
Symbol
Parameter
Conditions
Typical
Limits
Unit
(Note 10)
(Note 11)
(Limit)
2.2
V (min)
VIH
Logic High Input Voltage
VA+ = VD+ = 5.5V
VIL
Logic Low Input Voltage
VA+ = VD+ = 4.5V
0.8
V (max)
IIH
Logic High Input Current
VIN = 5V
0.035
2.0
µA (max)
IIL
Logic Low Input Current
VIN = 0V
−0.035
−2.0
µA (max)
VOH
Logic High Output Voltage
VA+ = VD+ = 4.5V
2.4
2.4
V (min)
IOUT = −1.6 mA
5
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ADC12041
Power Supply Characteristics
ADC12041
Digital Logic Input/Output Characteristics
(Continued)
The following specifications apply to the ADC12041 for VA+ = VD+ = 5V, VREF+ = 4.096V, VREF− = 0.0V, 12-bit + sign conversion mode, fCLK = 12.0 MHz, RS = 25Ω, source impedance for VREF+ and VREF− ≤ 1Ω, fully differential input with fixed
2.048V common-mode voltage, and minimum acquisition time, unless otherwise specified. Boldface limits apply for TA = TJ
= TMIN to TMAX; all other limits TA = TJ = 25˚C
Symbol
VOL
Parameter
Conditions
Logic Low Output Voltage
Typical
Limits
Unit
(Note 10)
(Note 11)
(Limit)
0.4
0.4
V (max)
± 2.0
µA (max)
VA+ = VD+ = 4.5V
IOUT = 1.6 mA
IOFF
TRI-STATE Output Leakage Current
VOUT = 0V
VOUT =5V
CIN
D12–D0 Input Capacitance
10
pF
Converter AC Characteristics
The following specifications apply to the ADC12041 for VS+ = VD+ = 5V, VREF+ = 4.096V, VREF− = 0.0V, 12-bit + sign conversion mode, fCLK = 12.0 MHz, RS = 25Ω, source impedance for VREF+ and VREF− ≤ 1Ω, fully differential input with fixed
2.048V common-mode voltage, and minimum acquisition time, unless otherwise specified. Boldface limits apply for TA = TJ
= TMIN to TMAX; all other limits TA = TJ = 25˚C
Symbol
Parameter
tZ
Auto Zero Time
tCAL
Full Calibration Time
Conditions
Typical
Limits
Unit
(Note 10)
(Note 11)
(Limit)
78
78 clks + 120 ns
clks (max)
4946
4946 clks + 120 ns
clks (max)
40
% (min)
60
% (max)
CLK Duty Cycle
50
%
tCONV
Conversion Time
Sync-Out Mode
44
44
clks (max)
tAcqSYNCOUT
Acquisition Time
Minimum for 13 Bits
9
9 clks + 120 ns
clks (max)
(Programmable)
Maximum for 13 Bits
79
79 clks + 120 ns
clks (max)
Digital Timing Characteristics
The following specifications apply to the ADC12041, 13-bit data bus width, VA+ = VD+ = 5V, fCLK = 12 MHz, tf = 3 ns and CL
= 50 pF on data I/O lines
Symbol
Parameter
tTPR
Throughput Rate
tCSWR
Falling Edge of CS
Conditions
Sync-Out Mode (SYNC Bit = “0”)
9 Clock Cycles of Acquisition Time
Typical
Limits
Unit
(Note 10)
(Note 11)
(Limit)
222
kHz
0
ns
0
ns
to Falling Edge of WR
tWRCS
Active Edge of WR
to Rising Edge of CS
tWR
WR Pulse Width
30
ns (min)
tWRSETFalling
Write Setup Time
WMODE = “1”
20
20
ns (min)
tWRHOLDFalling
Write Hold Time
WMODE = “1”
5
ns (min)
tWRSETRising
Write Setup Time
WMODE = “0”
20
ns (min)
tWRHOLDRising
Write Hold Time
WMODE = “0”
5
ns (min)
tCSRD
Falling Edge of CS to Falling
Edge of RD
0
ns
tRDCS
Rising Edge of RD
0
ns
to Rising Edge of CS
tRDDATA
Falling Edge of RD to Valid Data
8-Bit Mode (BW Bit = “0”)
tRDDATA
Falling Edge of RD to Valid Data
13-Bit Mode (BW Bit = “1”)
tRDHOLD
Read Hold Time
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6
40
58
ns (max)
26
44
ns (max)
23
32
ns (max)
(Continued)
The following specifications apply to the ADC12041, 13-bit data bus width, VA+ = VD+ = 5V, fCLK = 12 MHz, tf = 3 ns and CL
= 50 pF on data I/O lines
Symbol
tRDRDY
Parameter
Conditions
Rising Edge of RD
to Rising Edge of RDY
tWRRDY
Active Edge of WR
to Rising Edge of RDY
WMODE = “1”
tSTDRDY
Active Edge of WR
WMODE = “0”. Writing the
to Falling Edge of RDY
RESET Command into the
Typical
Limits
Unit
(Note 10)
(Note 11)
(Limit)
24
38
ns (max)
37
60
ns (max)
1.4
2.5
ms (max)
5
10
ns (min)
Configuration Register
tSYNC
Minimum SYNC Pulse Width
Notes on Specifications
Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is
functional, but do not guarantee specific performance limits. For guaranteed specifications and test conditions, see the Electrical Characteristics. The guaranteed
specifications apply only for the test conditions listed. Some performance characteristics may degrade when the device is not operated under the listed test conditions.
Note 2: All voltages are measured with respect to GND, unless otherwise specified.
Note 3: When the input voltage (VIN) at any pin exceeds the power supply rails (VIN < GND or VIN > (VA+ or VD+)), the current at that pin should be limited to 30
mA. The 120 mA maximum package input current limits the number of pins that can safely exceed the power supplies with an input current of 30 mA to four.
Note 4: The maximum power dissipation must he derated at elevated temperatures and is dictated by TJmax, (maximum junction temperature), θJA (package junction to ambient thermal resistance), and TA (ambient temperature). The maximum allowable power dissipation at any temperature is PDmax = (TJmax − TA)/θJA or
the number given in the Absolute Maximum Ratings, whichever is lower. For this device, TJmax = 150˚C, and the typical thermal resistance (θJA) of the ADC12041
in the V package, when board mounted, is 55˚C/W, and in the SSOP package, when board mounted, is 130˚C/W.
Note 5: Human body model, 100 pF discharged through 1.5 Ωk resistor.
Note 6: Each input is protected by a nominal 6.5V breakdown voltage zener diode to GND, as shown below, input voltage magnitude up to 5V above VA+ or 5V
below GND will not damage the ADC12041. There are parasitic diodes that exist between the inputs and the power supply rails and errors in the A/D conversion
can occur if these diodes are forward biased by more than 50 mV. As an example, if VA+ is 4.50 VDC, full-scale input voltage must be 4.55 VDC to ensure accurate
conversions.
DS012441-4
Note 7: VA+ and VD+ must be connected together to the same power supply voltage and bypassed with separate capacitors at each V+ pin to assure conversion/
comparison accuracy. Refer to the Power Supply Considerations section for a detailed discussion.
Note 8: Accuracy is guaranteed when operating at fCLK = 12 MHz.
Note 9: With the test condition for VREF (VREF+ − VREF−) given as + 4.096V, the 12-bit LSB is 1.000 mV.
Note 10: Typicals are at TA = 25˚C and represent most likely parametric norm.
Note 11: Limits are guaranteed to National’s AOQL (Average Outgoing Quality Level).
Note 12: Positive integral linearity error is defined as the deviation of the analog value, expressed in LSBs, from the straight line that passes through positive
full-scale and zero. For negative integral linearity error, the straight line passes through negative full-scale and zero.
Note 13: Zero error is a measure of the deviation from the mid-scale voltage (a code of zero), expressed in LSB. It is the average value of the code transitions between −1 to 0 and 0 to + 1 (see Figure 8).
Note 14: The DC common-mode error is measured with both inputs shorted together and driven from 0V to 5V. The measured value is referred to the resulting output value when the inputs are driven with a 2.5V input.
Note 15: Power Supply Sensitivity is measured after an Auto-Zero and Auto Calibration cycle has been completed with VA+ and VD+ at the specified extremes.
Note 16: VREFCM (Reference Voltage Common Mode Range) is defined as
7
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ADC12041
Digital Timing Characteristics
ADC12041
Notes on Specifications
(Continued)
Note 17: The ADC12041’s self-calibration technique ensures linearity and offset errors as specified, but noise inherent in the self-calibration process will result in
a repeatability uncertainty of ± 0.20 LSB.
Note 18: Total Unadjusted Error (TUE) includes offset, full scale linearity and MUX errors.
Note 19: The ADC12041 parts used to gather the information for these curves were auto-calibrated prior to taking the measurements at each test condition. The
auto-calibration cycle cancels any first order drifts due to test conditions. However, each measurement has a repeatability uncertainty error of 0.2 LSB. See Note
17.
Note 20: The reference input current is a DC average current drawn by the reference input with a full-scale sinewave input. The ADC12041 is continuously converting with a throughput rate of 206 kHz.
Note 21: These typical curves were measured during continuous conversions with a positive half-scale DC input. A 240 ns RD pulse was applied 25 ns after the
RDY signal went low. The data bus lines were loaded with 2 HC family CMOS inputs (CL ∼ 20 pF).
Note 22: Any other values placed in the command field are meaningless. However, if a code of 101 or 110 is placed in the command field and the CS , RD and WR
go low at the same time, the ADC12041 will enter a test mode. These test modes are only to be used by the manufacturer of this device. A hardware power-off and
power-on reset must be done to get out of these test modes.
Electrical Characteristics
DS012441-5
FIGURE 1. Output Digital Code vs the Operating Input Voltage Range (General Case)
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8
ADC12041
Electrical Characteristics
(Continued)
DS012441-6
FIGURE 2. Output Digital Code vs the Operating Input Voltage Range for VREF = 4.096V
DS012441-7
FIGURE 3. VREF Operating Range (General Case)
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ADC12041
Electrical Characteristics
(Continued)
DS012441-8
FIGURE 4. VREF Operating Range for VA = 5V
DS012441-9
FIGURE 5. Transfer Characteristic
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ADC12041
Electrical Characteristics
(Continued)
DS012441-10
FIGURE 6. Simplified Error vs Output Code without Auto-Calibration or Auto-Zero Cycles
DS012441-11
FIGURE 7. Simplified Error vs Output Code after Auto-Calibration Cycle
DS012441-12
FIGURE 8. Offset or Zero Error Voltage (Note 13)
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ADC12041
Timing Diagrams
DS012441-13
FIGURE 9. Sync-Out Write (WMODE = 1, BW = 1), Read and Convert Cycles
DS012441-14
FIGURE 10. Sync-In Write (WMODE = 1, BW = 1), Read and Convert Cycles
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ADC12041
Timing Diagrams
(Continued)
DS012441-46
FIGURE 11. Sync-Out Write (WMODE = 0, BW = 1), Read and Convert Cycles
DS012441-47
FIGURE 12. Sync-In Write (WMODE = 0, BW = 1), Read and Convert Cycles
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ADC12041
Timing Diagrams
(Continued)
DS012441-48
FIGURE 13. Sync-Out Read and Convert Cycles
DS012441-49
FIGURE 14. Sync-In Read and Convert Cycles
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ADC12041
Timing Diagrams
(Continued)
DS012441-50
FIGURE 15. 8-bit Bus Read Cycle (Sync-Out)
DS012441-51
FIGURE 16. 8-bit Bus Read Cycle (Sync-In)
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ADC12041
Timing Diagrams
(Continued)
DS012441-15
FIGURE 17. Write Signal Negates RDY (Writing the Standby, Auto-Cal or Auto-Zero Command)
DS012441-16
FIGURE 18. Standby and Reset Timing (13-Bit Data Bus Width)
Typical Performance Characteristics
Integral Linearity Error (INL)
Change vs Clock Frequency
(See (Note 19), Electrical Characteristic Section)
Full-Scale Error Change vs Clock
Frequency
Zero Error Change vs Clock
Frequency
DS012441-18
DS012441-17
DS012441-19
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Integral Linearity Error (INL)
Change vs Temperature
(See (Note 19), Electrical Characteristic Section) (Continued)
Full-Scale Error Change vs
Temperature
DS012441-21
DS012441-20
Integral Linearity Error (INL)
Change vs Reference Voltage
Full-Scale Error Change vs
Reference Voltage
DS012441-23
Zero Error Change vs Temperature
DS012441-22
Zero Error Change vs Reference
Voltage
DS012441-24
DS012441-25
Integral Linearity Error (INL)
Change vs Supply Voltage
Full-Scale Error Change vs Supply
Voltage
Zero Error Change vs Supply
Voltage
DS012441-26
DS012441-28
DS012441-27
17
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ADC12041
Typical Performance Characteristics
ADC12041
Typical Performance Characteristics
(See (Note 21), Electrical Characteristic Section) (Continued)
Supply Current vs Clock Frequency
Reference Current vs Clock Frequency
DS012441-29
Analog Supply Current vs Temperature
DS012441-30
Digital Supply Current vs Temperature
DS012441-31
DS012441-32
Typical Performance Characteristics
(Continued) The curves were obtained under the following
conditions. RS = 50Ω, TA = 25˚C, VA+ = VD+ = 5V, VREF = 4.096V, fCLK = 12 MHz, and the sampling rate fS = 215 kHz unless otherwise stated.
Full Scale Differential 1,099 Hz Sine Wave Input
Full Scale Differential 18,677 Hz Sine Wave Input
DS012441-33
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DS012441-34
18
(Continued) The curves were obtained under the following
conditions. RS = 50Ω, TA = 25˚C, VA+ = VD+ = 5V, VREF = 4.096V, fCLK = 12 MHz, and the sampling rate fS = 215 kHz
unless otherwise stated. (Continued)
Full Scale Differential 38,452 Hz Sine Wave Input
Full Scale Differential 79,468 Hz Sine Wave Input
DS012441-35
Half Scale Differential 1 kHz Sine Wave Input, fS =
153.6 kHz
DS012441-36
Half Scale Differential 20 kHz Sine Wave Input, fS =
153.6 kHz
DS012441-37
DS012441-38
Half Scale Differential 40 kHz Sine Wave Input, fS =
153.6 kHz
Half Scale Differential 75 kHz Sine Wave Input, fS =
153.6 kHz
DS012441-39
DS012441-40
Register Bit Description
CONFIGURATION REGISTER (Write Only)
This is an 8-bit write-only register that is used to program the functionality of the ADC12041. All data written to the ADC12041 will
always go to this register only. The contents of this register cannot be read.
MSB
b7
LSB
b6
b5
COMMAND
b4
b3
b2
b1
SYNC
BW
SE
ACQ TIME
b0
FIELD
Power on State: 10 Hex
19
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ADC12041
Typical Performance Characteristics
ADC12041
Register Bit Description
(Continued)
b1–b0: The ACQ TIME bits select one of four possible acquistion times in the SYNC-OUT mode (b4 = 0). (Refer to Selectable
Acquisition Time section, page 22).
b1
b0
Clocks
0
0
9
0
1
15
1
0
47
1
1
79
b2: When the Single-Ended bit (SE bit) is a ’1’, conversion results will be limited to positive values only and any negative conversion results will appear as a code of zero in the Data register. The SE bit is cleared at power-up.
b3: This is the Bus Width (BW) bit. When this bit is a ’0’ the ADC12041 is configured to interface with an 8-bit data bus; data pins
D7–D0 are active and pins D12–D9 are in TRI-STATE. When the BW bit is a ’1’, the ADC12041 is configured to interface with a
16-bit data bus and data pins D12–D0 are all active. The BW bit is cleared at power-up.
b4: The SYNC bit. When the SYNC bit is a ’1’, the SYNC pin is programmed as an input and the converter is in synchronous
mode. In this mode a rising edge on the SYNC pin causes the ADC to hold the input signal and begin a conversion. When b8 is
a ’0’, the SYNC pin is programmed as an output and the converter is in an asynchronous mode. In this mode the signal at the
SYNC pin indicates the status of the converter. The SYNC pin is high when a conversion is taking place. The SYNC bit is set at
power-up .
b7–b5: The command field. These bits select the mode of operation of the ADC12041. Power-up value is 000. (See Note 22)
b7
b6
b5
Command
0
0
0
Standby command. This puts the ADC in a low power consumption mode.
0
0
1
Ful-Cal command. This will cause the ADC to perform a self-calibrating cycle that will correct linearity and zero
errors.
0
1
0
Auto-zero command. This will cause the ADC to perform an auto-zero cycle that corrects offset errors.
0
1
1
Reset command. This puts the ADC in an idle mode.
1
0
0
Start command. This will put the converter in a start mode, preparing it to perform a conversion. If in
asynchronous mode (b4 = “0”), conversions will immediately begin after the programmed acquisition time has
ended. In synchronous mode (b4 = “1”), conversions will begin after a rising edge appears on the SYNC pin.
DATA REGISTER (Read Only)
This is a 13-bit read only register that holds the 12-bit + sign conversion result in two’s complement form. All reads performed from
the ADC12041 will place the contents of this register on the data bus. When reading the data register in 8-bit mode, the sign bit
is extended.
MSB
b12
LSB
b11
b10
b9
b8
sign
b7
b6
b5
b4
b3
b2
b1
b0
Conversion Data
Power on State: 0000Hex
b11–b0: b11 is the most significant bit and b0 is the least significant bit of the conversion result.
b12: This bit contains the sign of the conversion result. 0 for positive results and 1 for negative.
Functional Description
Features and Operating Modes
The ADC12041 is programmed through a digital interface
that supports an 8-bit or 16-bit data bus. The digital interface
consists of a 13-bit data input/output bus (D12–D0), digital
control signals and two internal registers: a write only 8-bit
Configuration register and a read only 13-bit Data register.
The Configuration register programs the functionality of the
ADC12041. The 8 bits of the Configuration register are divided into 5 fields. Each field controls a specific function of
the ADC12041: the acquisition time, synchronous or asynchronous conversions, mode of operation and the data bus
size.
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SELECTABLE BUS WIDTH
The ADC12041 can be programmed to interface with an 8-bit
or 16-bit data bus. The BW bit (b3) in the Configuration register controls the bus size. The bus width is set to 8 bits
(D7–D0 are active and D12–D8 are in TRI-STATE) if the BW
bit is cleared or 13 bits (D12–D0 are active) if the BW bit is
set. At power-up the default bus width is 8 bits (BW = 0).
In 8-bit mode the Configuration register is accessed with a
single write. When reading the ADC in 8-bit mode, the first
read cycle places the lower byte of the Data register on the
data bus followed by the upper byte during the next read
cycle.
In 13-bit mode all bits of the Data register and Configuration
register are accessible with a single read or write cycle.
20
to 12 bits in less than 500 ns. When source resistance or
source settling time increase beyond these limits, the acquisition time must also be increased to preserve precision.
(Continued)
Since the bus width of the ADC12041 defaults to 8 bits after
power-up, the first action when 13-bit mode is desired must
be to set the bus width to 13 bits.
In asynchronous (SYNC-OUT) mode, the acquisition time is
controlled by an internal counter. The minimum acquisition
period is 9 clock cycles, which corresponds to the nominal
value of 750 ns when the clock frequency is 12 MHz. Bits b0
and b1 of the Configuration Register are used to select the
acquisition time from among four possible values (9, 15, 47,
or 79 clock cycles). Since acquisition time in the asynchronous mode is based on counting clock cycles, it is also inversely proportional to clock frequency:
WMODE
The WMODE pin is used to determine the active edge of the
write pulse. The state of this pin determines which edge of
the WR signal will cause the ADC to latch in data. This is processor dependent. If the processor has valid data on the bus
during the falling edge of the WR signal, the WMODE pin
must be tied to VD+. This will cause the ADC to latch the data
on the falling edge of the WR signal. If data is valid on the rising edge of the WR signal, the WMODE pin must be tied to
DGND causing the ADC to latch in the data on the rising
edge of the WR signal.
Note that the actual acquisition time will be longer than TACQ
because acquisition begins either when the multiplexer
channel is changed or when RDY goes low, if the multiplexer
channel is not changed. After a read is performed, RDY goes
high, which starts the TACQ counter (see Figure 9).
In synchronous (SYNC-IN) mode, bits b0 and b1 are ignored,
and the acquisition time depends on the sync signal applied
to the SYNC pin. The acquisition period begins on the falling
edge of RDY , which occurs at the end of the previous conversion (or at the end of an autozero or autocalibration procedure. The acquisition period ends when SYNC goes high.
To estimate the acquisition time necessary for accurate conversions when the source resistance is greater than 1 kΩ,
use the following expression:
ANALOG INPUTS
The ADCIN+ and ADCIN− are the fully differential noninverting (positive) and inverting (negative) inputs into the
analog-to-digital converter (ADC) of the ADC12041.
STANDBY MODE
The ADC12041 has a low power consumption mode (75 µW
@ 5V). This mode is entered when a Standby command is
written in the command field of the Configuration register.
The RDY ouput pin is high when the ADC12041 is in the
Standby mode. Any command other than the Standby command written to the Configuration register will get the
ADC12041 out of the Standby mode. The RDY pin will immediately switch to a logic “0” when the ADC12041 is out of
the standby mode. The ADC12041 defaults to the Standby
mode following a hardware power-up.
where RS is the source resistance, and RS/H is the sample/
hold “On” resistance.
If the settling time of the source is greater than 500 ns, the
acquisition time should be about 300 ns longer than the settling time for a “well-behaved”, smooth settling characteristic.
SYNC/ASYNC MODE
The ADC12041 may be programmed to operate in synchronous (SYNC-IN) or asynchronous (SYNC-OUT) mode. To
enter synchronous mode, the SYNC bit in the Configuration
register must be set. The ADC12041 is in synchronous mode
after a hardware power-up. In this mode, the SYNC pin is
programmed as an input and conversions are synchronized
to the rising edges of the signal applied at the SYNC pin. Acquisition time can also be controlled by the SYNC signal
when in synchronous mode. Refer to the sync-in timing diagrams. When the SYNC bit is cleared, the ADC is in asynchronous mode and the SYNC pin is programmed as an output. In asynchronous mode, the signal at the SYNC pin
indicates the status of the converter. This pin is high when
the converter is performing a conversion. Refer to the
sync-out timing diagrams.
FULL CALIBRATION CYCLE
A full calibration cycle compensates for the ADC’s linearity
and offset errors. The converter’s DC specifications are
guaranteed only after a full calibration has been performed.
A full calibration cycle is initated by writing a Ful-Cal command to the ADC12041. During a full calibration, the offset
error is measured eight times, averaged and a correction coefficient is created. The offset correction coefficient is stored
in an internal offset correction register.
The overall linearity correction is achieved by correcting the
internal DAC’s capacitor mismatches. Each capacitor is
compared eight times against all remaining smaller value capacitors. The errors are averaged out and correction coefficients are created.
Once the converter has been calibrated, an arithmetic logic
unit (ALU) uses the offset and linearity correction coefficients
to reduce the conversion offset and linearity errors to within
guaranteed limits.
SELECTABLE ACQUISITION TIME
The ADC12041’s internal sample/hold circuitry samples an
input voltage by connecting the input to an internal sampling
capacitor (approximately 70 pF) through an effective resistance equal to the “On” resistance of the analog switch at the
input to the sample/hold circuit (2500Ω typical) and the effective output resistance of the source. For conversion results
to be accurate, the period during which the sampling capacitor is connected to the source (the “acquisition time”) must
be long enough to charge the capacitor to within a small fraction of an LSB of the input voltage. An acquisition time of 750
ns is sufficient when the external source resistance is less
than 1 kΩ and any active or reactive source circuitry settles
AUTO-ZERO CYCLE
During an auto-zero cycle, the offset is measured only once
and a correction coefficient is created and stored in an internal offset register. An auto-zero cycle is initiated by writing an
Auto-Zero command to the ADC12041.
21
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ADC12041
Features and Operating Modes
ADC12041
Features and Operating Modes
13-bit mode: The acquisition time should be set, the BW bit
set, the SYNC bit cleared and the START command issued
with a write to the ADC12041. In order to initiate a conversion, a single read must be performed from the ADC12041.
The rising edge of the read signal will force the RDY signal
high and begin the programmed acquisition time selected by
bits b1 and b0 of the configuration register. The SYNC pin will
go high indicating that a conversion sequence has begun following the end of the acquisition period. The RDY and SYNC
signal will fall low when the conversion is done. At this time
new information, such as a new acquisition time and operational command can be written into the Configuration register or it can remain unchanged. With the START command in
the Configuration register, a read from the ADC12041 will
place the entire 13-bit conversion result stored in the data
register on the data bus. The rising edge of the read pulse
will immediately force the RDY output high and begin the
programmed acquisition time selected by bits b1 and b0 of
the configuration register. The SYNC will then go high at the
end of the programmed acquisition time.
SYNC-IN/Synchronous
For the SYNC-IN case, it is assumed that a series of SYNC
pulses at the desired sampling rate are applied at the SYNC
pin of the ADC12041.
8-bit mode: A write to the ADC12041 should set the SYNC
bit, write the START command and clear the BW bit. The
programmed acquisition time in bits b1 and b0 is a don’t care
condition in the SYNC-IN mode.
A rising edge on the SYNC pin or the second rising edge of
two consecutive reads from the ADC12041 will force the
RDY signal high. It is recommended that the action of reading from the ADC12041 (not the rising edge of the SYNC signal) be used to raise the RDY signal. This will ensure that the
conversion result is read during the acquisition period of the
next conversion cycle, eliminating a read from the
ADC12041 while it is performing a conversion. Noise generated by accessing the ADC12041 while it is converting may
degrade the conversion result. In the SYNC-IN mode, only
the rising edge of the SYNC signal will begin a conversion
cycle. The rising edge of the SYNC also ends the acquisition
period. The acquisition period begins after the falling edge of
the RDY signal. The input is sampled until the rising edge of
the SYNC pulse, at which time the signal will be held and
conversion begins. The RDY signal will go low when the conversion is done and a new operational command may be
written into the Configuration register at this time, if needed.
Two consecutive read cycles are required to retrieve the entire 13-bit conversion result from the ADC12041’s Data register. The first read will place the lower byte of the conversion
result contained in the Data register on the data bus. The
second read will place the upper byte of the conversion result stored in the Data register on the data bus. With the
START command in the configuration register, the rising
edge of the second read pulse will raise the RDY signal high
and begin a conversion cycle following a rising edge on the
SYNC pin.
13-bit mode: The SYNC bit and the BW bit should be set and
the START command issued with a write to the ADC12041.
A rising edge on the SYNC pin or on the RD pin will force the
RDY signal high. It is recommended that the action of reading from the ADC12041 (not the rising edge of the SYNC signal) be used to raise the RDY signal. This will ensure that the
conversion result is read during the acquisition period of the
next conversion cycle, eliminating a read from the
ADC12041 while it is performing a conversion. Noise generated by accessing the ADC12041 while it is converting may
(Continued)
DIGITAL INTERFACE
The digital control signals are CS, RD, WR and RDY. Specific timing relationships are associated with the interaction
of these signals. Refer to the Digital Timing Diagrams section for detailed timing specifications. The active low RDY
signal indicates when a certain event begins and ends. It is
recommended that the ADC12041 should only be accessed
when the RDY signal is low. It is in this state that the
ADC12041 is ready to accept a new command. This will
minimize the effect of noise generated by a switching data
bus on the ADC. The only exception to this is when the
ADC12041 is in the standby mode at which time the RDY is
high. The ADC12041 is in the standby mode at power up or
when a STANDBY command is issued. A Ful-Cal, Auto-Zero,
Reset or Start command will get the ADC12041 out of the
standby mode. This may be observed by monitoring the status of the RDY signal. The RDY signal will go low when the
ADC12041 leaves the standby mode.
The following describes the state of the digital control signals
for each programmed event in both 8-bit and 13-bit mode.
RDY should be low before each command is issued except
for the case when the device is in standby mode.
FUL-CAL OR AUTO-ZERO COMMAND
8-bit mode: A Ful-Cal or Auto-Zero command must be issued
and the BW bit (b3) cleared. The active edge of the write
pulse on the WR pin will force the RDY signal high. At this
time the converter begins executing a full calibration or
auto-zero cycle. The RDY signal will automatically go low
when the full calibration or auto-zero cycle is done.
13-bit mode: A Ful-Cal or Auto-Zero command must be issued and the BW bit (b3) set. The active edge of the write
pulse on the WR pin will force the RDY signal high. At this
time the converter begins executing a full calibration or
auto-zero cycle. The RDY signal will automatically go low
when the full calibration or auto-zero cycle is done.
STARTING A CONVERSION: START COMMAND
In order to completely describe the events associated with
the Start command, both the SYNC-OUT and SYNC-IN
modes must be considered.
SYNC-OUT/Asynchronous
8-bit mode: A write to the ADC12041 should set the acquisition time, clear the BW and SYNC bit and select the START
command in the Configuration register. In order to initiate a
conversion, two reads must be performed from the
ADC12041. The rising edge of the second read pulse will
force the RDY pin high and begin the programmed acquisition time selected by bits b1 and b0 of the Configuration register. The SYNC pin will go high indicating that a conversion
sequence has begun following the end of the acquisition period. The RDY and SYNC signal will fall low when the conversion is done. At this time new information, such as a new
acquisition time and operational command can be written
into the Configuration register or it can remain unchanged.
Assuming that the START command is in the Configuration
register, the previous conversion can be read. The first read
places the lower byte of the conversion result contained in
the Data register on the data bus. The second read will place
the upper byte of the conversion result stored in the Data
register on the data bus. The rising edge on the second read
pulse will begin another conversion sequence and raise the
RDY and SYNC signals appropriately.
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22
put voltage is proportional to the voltage used for the ADC’s
reference voltage. This technique relaxes the system reference requirements because the analog input voltage moves
with the ADC’s reference. The system power supply can be
used as the reference voltage by connecting the VREF+ pin
to VA+ and the VREF− pin to AGND. For absolute accuracy,
where the analog input voltage varies between very specific
voltage limits, a time and temperature stable voltage source
can be connected to the reference inputs. Typically, the reference voltage’s magnitude will require an initial adjustment
to null reference voltage induced full-scale errors.
The reference voltage inputs are not fully differential. The
ADC12041 will not generate correct conversions if
(VREF+) – (VREF−) is below 1V. Figure 19 shows the allowable relationship between VREF+ and VREF−.
(Continued)
degrade the conversion result. In the SYNC-IN mode, only
the rising edge of the SYNC signal will begin a conversion
cycle. The RDY signal will go low when the conversion cycle
is done. The acquisition time is controlled by the SYNC signal. The acquisition period begins after the falling edge of the
RDY signal. The input is sampled until the rising edge of the
SYNC pulse, at which time the signal will be held and conversion begins. The RDY signal will go low when the conversion is done and a new operational command may be written
into the Configuration register at this time, if needed. With
the START command in the Configuration register, a read
from the ADC12041 will place the entire conversion result
stored in the Data register on the data bus and the rising
edge of the read pulse will force the RDY signal high.
STANDBY COMMAND
8-bit mode: A write to the ADC12041 should clear the BW bit
and issue the Standby command.
13-bit mode: A write to the ADC12041 should set the BW bit
and issue the Standby command.
RESET
The RESET command places the ADC12041 into a ready
state and forces the RDY signal low. The RESET command
can be used to interrupt the ADC12041 while it is performing
a conversion, full-calibration or auto-zero cycle. It can also
be used to get the ADC12041 out of the standby mode.
Analog Application Information
DS012441-43
FIGURE 19. VREF Operating Range
REFERENCE VOLTAGE
The ADC12041 has two reference inputs, VREF+ and VREF−.
They define the zero to full-scale range of the analog input
signals over which 4095 positive and 4096 negative codes
exist. The reference inputs can be connected to span the entire supply voltage range (VREF− = AGND, VREF+ = VA+) or
they can be connected to different voltages when other input
spans are required. The reference inputs of the ADC12041
have transient capacitive switching currents. The voltage
sources driving VREF+ and VREF− must have very low output
impedence and noise and must be adequately bypassed.
The circuit in Figure 20 is an example of a very stable reference source.
The ADC12041 can be used in either ratiometric or absolute
reference applications. In ratiometric systems, the analog in-
OUTPUT DIGITAL CODE VERSUS ANALOG INPUT
VOLTAGE
The ADC12041’s fully differential 12-bit + sign ADC generates a two’s complement output that is found by using the
equation shown below:
Round off the result to the nearest integer value between
-4096 and 4095.
23
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ADC12041
Features and Operating Modes
ADC12041
Analog Application Information
(Continued)
DS012441-44
*Tantalum
**Ceramic
FIGURE 20. Low Drift Extremely Stable Reference Circuit
Part Number
Output Voltage
Temperature
Tolerance
Coefficient
LM4041CI-Adj
LM4040AI-4.1
LM4050
LM4120
LM9140BYZ-4.1
Circuit of Figure 20
± 0.5%
± 0.1%
± 0.2%
± 0.1%
± 0.5%
Adjustable
INPUT CURRENT
At the start of the acquisition window (tAcqSYNOUT) a charging current (due to capacitive switching) flows through the
analog input pins (ADCIN+ and ADCIN−). The peak value of
this input current will depend on the amplitude and frequency
of the input voltage applied, the source impedance and the
ADCIN+ and ADCIN− input switch ON resistance of 2500Ω.
For low impedance voltage sources ( < 1000 Ω for 12 MHz
operation), the input charging current will decay to a value
that will not introduce any conversion errors before the end
of the default sample-and-hold (S/H) acquisition time
(9 clock cycles). For higher source impedances ( > 1000 Ω
for 12 MHz operation), the S/H acquisition time should be increased to allow the charging current to settle within specified limits. In asynchronous mode, the acquisition time may
be increased to 15, 47 or 79 clock cycles. If different acquisition times are needed, the synchronous mode can be used
to fully control the acquisition time.
version decisions. The ADC is especially sensitive to power
supply spikes that occur during the auto-zero or linearity calibration cycles.
The ADC12041 is designed to operate from a single +5V
power supply. The separate supply and ground pins for the
analog and digital portions of the circuit allow separate external bypassing. To minimize power supply noise and ripple,
adequate bypass capacitors should be placed directly between power supply pins and their associated grounds. Both
supply pins should be connected to the same supply source.
In systems with separate analog and digital supplies, the
ADC should be powered from the analog supply. At least a
10 µF tantalum electrolytic capacitor in parallel with a 0.1 µF
monolithic ceramic capacitor is recommended for bypassing
each power supply. The key consideration for these capacitors is to have low series resistance and inductance. The capacitors should be placed as close as physically possible to
the supply and ground pins with the smaller capacitor closer
to the device. The capacitors also should have the shortest
possible leads in order to minimize series lead inductance.
Surface mount chip capacitors are optimal in this respect
and should be used when possible.
When the power supply regulator is not local on the board,
adequate bypassing (a high value electrolytic capacitor)
should be placed at the power entry point. The value of the
capacitor depends on the total supply current of the circuits
on the PC board. All supply currents should be supplied by
the capacitor instead of being drawn from the external supply lines, while the external supply charges the capacitor at a
steady rate.
The ADC has two VD+ and DGND pins. It is recommended to
use a 0.1 µF plus a 10 µF capacitor between pin 21(VD+)
INPUT BYPASS CAPACITANCE
External capacitors (0.01 µF–0.1 µF) can be connected between the ADCIN+ and ADCIN− analog input pins and the
analog ground to filter any noise caused by inductive pickup
associated with long leads.
POWER SUPPLY CONSIDERATIONS
Decoupling and bypassing the power supply on a high resolution ADC is an important design task. Noise spikes on the
VA+ (analog supply) or VD+ (digital supply) can cause conversion errors. The analog comparator used in the ADC will
respond to power supply noise and will make erroneous con-
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± 100ppm/˚C
± 100ppm/˚C
± 50ppm/˚C
± 50ppm/˚C
± 25ppm/˚C
± 2ppm/˚C
24
ADC12041. Having a continuous digital ground plane under
the data and clock traces is very important. This reduces the
overshoot/undershoot and high frequency ringing on these
lines that can be capacitively coupled to analog circuitry sections through stray capacitances.
(Continued)
and 22 (DGND) the SSOP and PLCC package. The layout
diagram in Figure 21 shows the recommended placement
for the supply bypass capacitors.
The AGND and DGND in the ADC12041 are not internally
connected together. They should be connected together on
the PC board right at the chip. This will provide the shortest
return path for the signals being exchanged between the internal analog and digital sections of the ADC.
It is also a good design practice to have power plane layers
in the PC board. This will improve the supply bypassing (an
effective distributed capacitance between power and ground
plane layers) and voltage drops on the supply lines. However, power planes are not as essential as ground planes are
for satisfactory performance. If power planes are used, they
should be separated into two planes and the area and connections should follow the same guidelines as mentioned for
the ground planes. Each power plane should be laid out over
its associated ground planes, avoiding any overlap between
power and ground planes of different types. When the power
planes are not used, it is recommended to use separate supply traces for the VA+ and VD+ pins from a low impedance
supply point (the regulator output or the power entry point to
the PC board). This will help ensure that the noisy digital
supply does not corrupt the analog supply.
PC BOARD LAYOUT AND GROUNDING
CONSIDERATlONS
To get the best possible performance from the ADC12041,
the printed circuit boards should have separate analog and
digital ground planes. The reason for using two ground
planes is to prevent digital and analog ground currents from
sharing the same path until they reach a very low impedance
power supply point. This will prevent noisy digital switching
currents from being injected into the analog ground.
Figure 21 illustrates a favorable layout for ground planes,
power supply and reference input bypass capacitors. It
shows a layout using a 28-pin PLCC socket and
through-hole assembly. A similar approach should be used
for the SSOP package.
The analog ground plane should encompass the area under
the analog pins and any other analog components such as
the reference circuit, input amplifiers, signal conditioning circuits, and analog signal traces.
The digital ground plane should encompass the area under
the digital circuits and the digital input/output pins of the
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ADC12041
Analog Application Information
ADC12041
Analog Application Information
(Continued)
DS012441-45
FIGURE 21. Top View of Printed Circuit Board for a 28-Pin PLCC ADC12041
When measuring AC input signals, any crosstalk between
analog input lines and the reference lines (ADCIN ± , VREF ± )
should be minimized. Crosstalk is minimized by reducing
any stray capacitance between the lines. This can be done
by increasing the clearance between traces, keeping the
traces as short as possible, shielding traces from each other
by placing them on different sides of the AGND plane, or running AGND traces between them.
tween the VREF+ and VREF−, and by bypassing in a manner
similar to that described for the supply pins. When a single
ended reference is used, VREF− is connected to AGND and
only two capacitors are used between VREF+ and VREF− (0.1
µF + 10 µF). It is recommended to directly connect the
AGND side of these capacitors to the VREF− instead of connecting VREF− and the ground sides of the capacitors separately to the ground planes. This provides a significantly
lower-impedance connection when using surface mount
technology.
Figure 21 also shows the reference input bypass capacitors.
Here the reference inputs are considered to be differential.
The performance improves by having a 0.1 µF capacitor be-
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26
ADC12041
Physical Dimensions
inches (millimeters) unless otherwise noted
28-Lead Molded Plastic Leaded Chip Carrier
Order Number ADC12041CIV
NS Package Number V28A
27
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ADC12041 12-Bit Plus Sign 216 kHz Sampling Analog-to-Digital Converter
Physical Dimensions
inches (millimeters) unless otherwise noted (Continued)
28-Lead SSOP
Order Number ADC12041CIMSA
NS Package Number MSA28
LIFE SUPPORT POLICY
NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT
DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL
COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein:
1. Life support devices or systems are devices or
systems which, (a) are intended for surgical implant
into the body, or (b) support or sustain life, and
whose failure to perform when properly used in
accordance with instructions for use provided in the
labeling, can be reasonably expected to result in a
significant injury to the user.
National Semiconductor
Corporation
Americas
Tel: 1-800-272-9959
Fax: 1-800-737-7018
Email: [email protected]
www.national.com
National Semiconductor
Europe
Fax: +49 (0) 180-530 85 86
Email: [email protected]
Deutsch Tel: +49 (0) 69 9508 6208
English Tel: +44 (0) 870 24 0 2171
Français Tel: +33 (0) 1 41 91 8790
2. A critical component is any component of a life
support device or system whose failure to perform
can be reasonably expected to cause the failure of
the life support device or system, or to affect its
safety or effectiveness.
National Semiconductor
Asia Pacific Customer
Response Group
Tel: 65-2544466
Fax: 65-2504466
Email: [email protected]
National Semiconductor
Japan Ltd.
Tel: 81-3-5639-7560
Fax: 81-3-5639-7507
National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications.