TI1 DDC114IRTCT Quad current input, 20-bit analog-to-digital converter Datasheet

DDC114
SBAS255C − JUNE 2004 − REVISED APRIL 2009
Quad Current Input, 20-Bit
Analog-To-Digital Converter
FEATURES
D
D
D
D
D
D
D
D
DESCRIPTION
SINGLE-CHIP SOLUTION TO DIRECTLY
MEASURE FOUR LOW-LEVEL CURRENTS
HIGH PRECISION, TRUE INTEGRATING
FUNCTION
INTEGRAL LINEARITY:
±0.01% of Reading ±0.5ppm of FSR
VERY LOW NOISE: 5.2ppm of FSR
LOW POWER: 13.5mW/channel
ADJUSTABLE DATA RATE: Up to 3.125kSPS
PROGRAMMABLE FULL SCALE
DAISY-CHAINABLE SERIAL INTERFACE
The DDC114 is a 20-bit, quad channel, current-input
analog-to-digital (A/D) converter. It combines both
current-to-voltage and A/D conversion so that four
low-level current output devices, such as photodiodes, can
be directly connected to its inputs and digitized.
For each of the four inputs, the DDC114 provides a
dual-switched integrator front-end. This design allows for
continuous current integration: while one integrator is
being digitized by the onboard A/D converter, the other is
integrating the input current. Adjustable full-scale ranges
from 12pC to 350pC and adjustable integration times from
50µs to 1s allow currents from fAs to µAs to be measured
with outstanding precision. Low-level linearity is ±0.5ppm
of the full-scale range and noise is 5.2ppm of the full-scale
range.
APPLICATIONS
D
D
D
D
CT SCANNER DAS
PHOTODIODE SENSORS
INFRARED PYROMETERS
LIQUID/GAS CHROMATOGRAPHY
Two modes of operation are provided. In Low-Power
mode, total power dissipation is only 13.5mW per channel
with a maximum data rate of 2.5kSPS. High-Speed mode
supports data rates up to 3.125kSPS with a corresponding
dissipation of 18mW per channel.
Protected by US Patent #5841310
AVDD
VREF
DVDD
The DDC114 has a serial interface designed for
daisy-chaining in multi-device systems. Simply connect
the output of one device to the input of the next to create
the chain. Common clocking feeds all the devices in the
chain so that the digital overhead in a multi-DDC114
system is minimal.
CLK
CONV
IN1
RANGE0
Dual
Switched
Integrator
∆Σ
Modulator
Digital
Filter
RANGE1
Control
RANGE2
TEST
CLK_4X
IN3
HISPD/LOPWR
Dual
Switched
Integrator
RESET
FORMAT
DCLK
The DDC114 is a single-supply device using a +5V analog
supply and supporting a +2.7V to +5.25V digital supply.
Operating over the industrial temperature range of −40°C
to +85°C, the DDC114 is offered in a QFN-48 package.
IN2
DCLK
Dual
Switched
Integrator
∆Σ
Modulator
Digital
Filter
Digital
Input/Output
DVALID
DOUT
DOUT
IN4
DIN
Dual
Switched
Integrator
AGND
DIN
DGND
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.
All trademarks are the property of their respective owners.
Copyright  2004−2009, Texas Instruments Incorporated
! ! www.ti.com
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SBAS255C − JUNE 2004 − REVISED APRIL 2009
PACKAGE/ORDERING INFORMATION
For the most current package and ordering information,
see the Package Option Addendum at the end of this
document, or see the TI website at www.ti.com.
ABSOLUTE MAXIMUM RATINGS(1)
Analog Input Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 750µA
AVDD to DVDD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . −0.3V to +6V
AVDD to AGND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . −0.3V to +6V
DVDD to DGND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . −0.3V to +6V
AGND to DGND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ±0.2V
VREF Input to AGND . . . . . . . . . . . . . . . . . . 2.0V to AVDD + 0.3V
Analog Input to AGND . . . . . . . . . . . . . . . . . . . . . . . −0.3V to +0.7V
Digital Input Voltage to DGND . . . . . . . . . . . −0.3V to DVDD + 0.3V
Digital Output Voltage to DGND . . . . . . . . . −0.3V to AVDD + 0.3V
Operating Temperature . . . . . . . . . . . . . . . . . . . . . . . −40°C to +85°C
Storage Temperature . . . . . . . . . . . . . . . . . . . . . . . . −60°C to +150°C
Junction Temperature (TJ) . . . . . . . . . . . . . . . . . . . . . . . . . . . +150°C
(1) Stresses above these ratings may cause permanent damage.
Exposure to absolute maximum conditions for extended periods
may degrade device reliability. These are stress ratings only, and
functional operation of the device at these or any other conditions
beyond those specified is not implied.
2
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.
""#
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SBAS255C − JUNE 2004 − REVISED APRIL 2009
ELECTRICAL CHARACTERISTICS
At TA = +25°C, AVDD = +5V, DVDD = 3V, VREF = +4.096V, Range 5 (250pC), and continuous mode operation, unless otherwise noted.
Low-Power Mode: TINT = 400µs and CLK = 4MHz; High-Speed Mode: TINT = 320µs and CLK = 4.8MHz.
Low-Power Mode
PARAMETER
TEST CONDITIONS
ANALOG INPUT RANGE
Range 0
Range 1
Range 2
Range 3
Range 4
Range 5
Range 6
Range 7
Negative Full-Scale Range
Input Current(2)
MIN
TYP
10.2
12
13.8
47.5
50
52.5
95
100
105
142.5
150
157.5
190
200
210
237.5
250
262.5
285
300
315
332.5
350
367.5
−0.4% of Positive Full-Scale Range
750
DYNAMIC CHARACTERISTICS
Data Rate
Integration Time, TINT
High-Speed Mode
MAX
Continuous Mode
Non-continuous Mode, Range 1 to 7
2.5
1,000,000
400
50
System Clock Input (CLK)
CLK_4X = 0
CLK_4X = 1
Data Clock (DCLK)
MIN
TYP
MAX
∗(1)
∗
∗
∗
∗
∗
∗
∗
∗
∗
∗
∗
∗
∗
∗
∗
∗
∗
∗
∗
∗
∗
∗
∗
∗
∗
∗
4
16
16
pC
pC
pC
pC
pC
pC
pC
pC
pC
µA
3.125
kSPS
µS
µS
4.8
19.2
MHz
MHz
MHz
∗
320
UNITS
∗
ACCURACY
Noise, Low-Level Input(3)
CSENSOR(4) = 50pF, Range 5 (250pC)
Integral Linearity Error(6)
Resolution
Input Bias Current
Range Error Match(7)
Range Sensitivity to VREF
Offset Error
Offset Error Match(7)
DC Bias Voltage(9)
Power-Supply Rejection Ratio
Internal Test Signal
Internal Test Accuracy
FORMAT = 1
FORMAT = 0
All Ranges
VREF = 4.096 ± 0.1V
Low-Level Input (< 1% FSR)
at dc
5.2
6.5
±0.01% Reading ± 0.5ppm FSR, typ
±0.025% Reading ± 1.0ppm FSR, max
20
16
0.1
10
0.1
0.5
1:1
±400
±1000
±100
±0.05
±2
±25
±200
11
±10
5.5
∗
∗
7
∗
∗
∗
∗
∗
∗
∗
∗
∗
∗
∗
∗
∗
∗
∗
∗
∗
∗
∗
∗
∗
∗
∗
∗
∗
ppm of
FSR(5), rms
Bits
Bits
pA
% of FSR
ppm of FSR
ppm of FSR
mV
ppm of FSR/V
pC
%
PERFORMANCE OVER TEMPERATURE
Offset Drift
±0.5
±3(8)
Offset Drift Stability
±0.2
±1(8)
DC Bias Voltage Drift(9)
Input Bias Current Drift
Range Drift(10)
3
0.01
25
1(8)
REFERENCE
Voltage
Input Current(11)
TA = +25°C to +45°C
4.000
Average Value
4.096
75
4.200
∗
95
∗
ppm of
FSR/°C
ppm of FSR/
minute
µV/°C
pA/°C
ppm/°C
V
µA
(1) ∗ indicates that specification is the same as Low-Power Mode.
(2) Exceeding maximum input current specification may damage device.
(3) Input is less than 1% of full scale.
(4) C
SENSOR is the capacitance seen at the DDC114 inputs from wiring, photodiode, etc.
(5) FSR is Full-Scale Range.
(6) A best-fit line is used in measuring nonlinearity.
(7) Matching between side A and side B of the same input.
(8) Ensured by design, not production tested.
(9) Voltage produced by the DDC114 at its input which is applied to the sensor.
(10)Range drift does not include external reference drift.
(11)Input reference current decreases with increasing TINT (see the Voltage Reference section, page 11).
3
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SBAS255C − JUNE 2004 − REVISED APRIL 2009
ELECTRICAL CHARACTERISTICS (continued)
At TA = +25°C, AVDD = +5V, DVDD = 3V, VREF = +4.096V, Range 5 (250pC), and continuous mode operation, unless otherwise noted.
Low-Power Mode: TINT = 400µs and CLK = 4MHz; High-Speed Mode: TINT = 320µs and CLK = 4.8MHz.
Low-Power Mode
PARAMETER
DIGITAL INPUT/OUTPUT
Logic Levels
VIH
VIL
VOH
VOL
Input Current (IIN)
Data Format(12)
POWER-SUPPLY REQUIREMENTS
Analog Power-Supply Voltage (AVDD)
Digital Power-Supply Voltage (DVDD)
Supply Current
Total Analog Current
Total Digital Current
Total Power Dissipation
Total Power Dissipation per Channel
TEST CONDITIONS
IOH = −500µA
IOL = 500µA
0 < VIN < DVDD
MIN
TYP
0.8DVDD
− 0.1
DVDD − 0.4
High-Speed Mode
MAX
MIN
DVDD + 0.1
0.2DVDD
∗
∗
0.4
±10
DVDD = +3V
DVDD = +3V
DVDD = +3V
5.25
5.25
10.5
0.5
54
13.5
75
18.75
∗
∗
14.0
0.67
72
18
(12)Data format is Straight Binary with a small offset. The number of bits in the output word is controlled by the FORMAT pin (see text).
4
MAX
∗
∗
∗
Straight Binary
4.75
2.7
TYP
UNITS
∗
∗
V
V
V
V
µA
∗
∗
V
V
100
25
mA
mA
mW
mW
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SBAS255C − JUNE 2004 − REVISED APRIL 2009
DGND
CONV
DGND
DVALID
DGND
CLK
DGND
DCLK
DCLK
DGND
DVDD
Top View
DGND
PIN CONFIGURATIONS
48
47
46
45
44
43
42
41
40
39
38
37
QFN
DOUT
1
36 DIN
DOUT
2
35 DIN
CLK_4X
3
34 NC
FORMAT
4
33 NC
HISPD/LOPWR
5
32 RESET
RANGE0
6
RANGE1
7
30 DGND
RANGE2
8
29 DGND
AGND
31 TEST
DDC114
16
17
18
19
20
21
22
23
24
AIN2
AIN1
AGND
15
AGND
14
AGND
13
AGND
25 AGND
AIN3
AGND 12
AGND
26 AGND
AGND
AGND 11
AIN4
27 AVDD
AGND
28 AGND
AGND
9
VREF 10
PIN DESCRIPTIONS
PIN
NUMBER
FUNCTION
DOUT
1
Digital Output
DESCRIPTION
Serial Data Output
DOUT
2
Digital Output
Serial Data Output: Complementary Signal
CLK_4X
3
Digital Input
Master Clock Divider Control: 0 = divide by 1, 1 = divide by 4
FORMAT
4
Digital Input
Digital Output Word Format: 0 = 16 Bits, 1 = 20 Bits
HISPD/LOPWR
5
Digital Input
Mode Control: 0 = Low-Power, 1 = High-Speed
RANGE0
6
Digital Input
Range Control 0 (least significant bit)
RANGE1
7
Digital Input
Range Control 1
RANGE2
8
Digital Input
Range Control 2 (most significant bit)
AGND
9, 11-14, 16, 18-20,
22, 24-26, 28
Analog
VREF
10
Analog Input
External Voltage Reference Input, 4.096V Nominal
AIN4
15
Analog Input
Analog Input 4
AIN3
17
Analog Input
Analog Input 3
AIN2
21
Analog Input
Analog Input 2
AIN1
23
Analog Input
Analog Input 1
AVDD
27
Analog
Analog Power Supply, 5V Nominal
DGND
29, 30, 38, 41, 43, 45,
47, 48
Digital
Digital Ground
TEST
31
Digital Input
Test Mode Control
RESET
32
Digital Input
Resets the Digital Circuitry, Active Low
NC
33, 34
—
DIN
35
Digital Input
Serial Data Input: Complementary Signal (optional, see text on page 13)
DIN
36
Digital Input
Serial Data Input
DVDD
37
Digital
DCLK
39
Digital Input
Serial Data Clock Input: Complementary Signal (optional, see text on page 13)
DCLK
40
Digital Input
Serial Data Clock Input
CLK
42
Digital Input
Master Clock Input
DVALID
44
Digital Output
CONV
46
Digital Input
Analog Ground
No Connection
Digital Power Supply, 3V Nominal
Data Valid Output, Active Low
Conversion Control Input: 0 = Integrate on Side B, 1 = Integrate on Side A
5
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SBAS255C − JUNE 2004 − REVISED APRIL 2009
TYPICAL CHARACTERISTICS
At TA = +25°C, characterization done with Range 5 (250pC), AVDD = +5V, DVDD = 3V, VREF = +4.096V, Low Power Mode: TINT = 400µs and CLK = 4MHz, unless
otherwise noted.
NOISE vs CSENSOR
Noise (ppm of FSR, rms)
NOISE vs CSENSOR
45
Noise (ppm of FSR, rms)
40
CSENSOR Range Range Range Range Range Range Range Range
5
7
(pF)
0
1
2
3
4
6
Range 1
35
0
23.6
7.3
5.2
4.4
4.2
4.0
3.8
3.7
24
30.8
10.4
6.7
5.5
4.9
4.5
4.3
4.1
50
36.3
12.3
8.2
6.5
5.6
5.1
4.8
4.4
20
75
41.3
14.4
8.9
7.2
6.0
5.4
5.1
4.7
15
100
46.1
16.0
10.0
8.0
6.7
5.9
5.4
5.0
150
57.0
18.8
11.9
9.2
7.8
6.8
6.1
5.7
200
68.1
21.7
13.5
10.2
8.6
7.6
6.8
6.4
300
89.3
27.7
16.3
12.5
10.6
9.0
8.1
7.4
500
134.0
38.9
22.4
16.6
13.5
11.7
10.4
9.5
30
25
Range 2
10
5
Range 7
0
0
100
200
300
400
500
CSENSOR (pF)
NOISE vs TINT
6
NOISE vs INPUT LEVEL
8
7
Noise (ppm of FSR, rms)
Noise (ppm of FSR, rms)
CSENSOR = 50pF
5
4
CSENSOR = 0pF
3
2
1
6
CSENSOR = 50pF
5
CSENSOR = 0pF
4
3
2
1
Range 5
Range 5
0
0
0.1
1
10
100
1000
0
10
20
TINT (µs)
50
60
70
80
90
100
2000
CSENSOR = 50pF
All Ranges
1500
12
Range 1
10
Range Drift (ppm)
Noise (ppm of FSR, rms)
40
RANGE DRIFT vs TEMPERATURE
NOISE vs TEMPERATURE
14
Range 3
Range 2
8
6
4
1000
500
0
−500
−1000
Range 7
2
−1500
−2000
0
−40
−15
10
35
Temperature (_C)
6
30
Input Level (% of Full−Scale)
60
85
−40
−15
10
35
Temperature (_ C)
60
85
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SBAS255C − JUNE 2004 − REVISED APRIL 2009
TYPICAL CHARACTERISTICS (continued)
At TA = +25°C, characterization done with Range 5 (250pC), AVDD = +5V, DVDD = 3V, VREF = +4.096V, Low Power Mode: TINT = 400µs and CLK = 4MHz, unless
otherwise noted.
IB vs TEMPERATURE
OFFSET DRIFT vs TEMPERATURE
10
100
Offset Drift (ppm of FSR)
All Ranges
IB (pA)
1
0.1
50
0
−50
−100
0.01
25
35
45
55
65
75
25
85
35
45
Temperature (_ C)
55
65
75
85
Temperature (_ C)
DIGITAL SUPPLY CURRENT vs TEMPERATURE
ANALOG SUPPLY CURRENT vs TEMPERATURE
14
1.2
Low Power−Mode
Low−Power Mode
DVDD = 5V
12
1.0
Current (mA)
Current (mA)
10
8
6
4
0.8
0.6
DVDD = 3V
0.4
0.2
2
0
−40
0
−15
10
35
60
−40
85
Temperature (_C)
35
500
30
Occurences
25
20
15
60
85
Repeated measurement
of offset drift over a
one minute interval.
Range 5
400
300
200
10
100
5
Power per Channel (mW)
16.00
15.75
15.50
15.25
15.00
14.75
14.50
14.25
14.00
13.75
13.50
13.25
13.00
12.75
12.50
12.25
0
12.00
Occurences (%)
35
OFFSET DRIFT OVER TIME HISTOGRAM
600
Low−Power Mode
Data collected
from multiple lots.
10
Temperature (_C)
POWER CONSUMPTION HISTOGRAM
40
−15
0
−1.0 −0.8 −0.6 −0.4 −0.2
0
0.2
0.4
0.6
0.8
1.0
Offset Drift (ppm of FSR/minute)
7
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THEORY OF OPERATION
The block diagram of the DDC114 is shown in Figure 1.
The device contains four identical input channels that
perform the function of current-to-voltage integration
followed by a multiplexed A/D conversion. Each input has
two integrators so that the current-to-voltage integration
can be continuous in time. The output of the eight
integrators are switched to two delta-sigma (∆Σ)
converters via two four-input multiplexers. With the
AVDD
VREF
DDC114 in the continuous integration mode, the output of
the integrators from one side of both of the inputs will be
digitized while the other two integrators are in the
integration mode, as illustrated in the timing diagram in
Figure 2. This integration and A/D conversion process is
controlled by the system clock, CLK. The results from side
A and side B of each signal input are stored in a serial
output shift register. The DVALID output goes low when
the shift register contains valid data.
DVDD
CLK
CONV
IN1
RANGE0
Dual
Switched
Integrator
∆Σ
RANGE1
Digital
Filter
Modulator
RANGE2
Control
TEST
CLK_4X
IN3
HISPD/LOPWR
Dual
Switched
Integrator
RESET
FORMAT
DCLK
IN2
DCLK
Dual
Switched
Integrator
∆Σ
Digital
Filter
Modulator
DVALID
Digital
Input/Output
DOUT
DOUT
IN4
DIN
Dual
Switched
Integrator
DIN
AGND
DGND
Figure 1. DDC114 Block Diagram
IN1 and IN2, Integrator A
Integrate
Integrate
IN1 and IN2, Integrator B
Integrate
IN3 and IN4, Integrator A
Integrate
Integrate
Integrate
IN3 and IN4, Integrator B
Conversion in Progress
Integrate
IN1B
IN2B
IN3B
IN4B
IN1A
IN2A
IN3A
IN4A
Integrate
IN1B
IN2B
IN3B
IN4B
IN1A
IN2A
IN3A
IN4A
DVALID
Figure 2. Basic Integration and Conversion Timing for the DDC114 (continuous mode)
8
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SBAS255C − JUNE 2004 − REVISED APRIL 2009
The digital interface of the DDC114 provides the digital
results via a synchronous serial interface consisting of
differential data clocks (DCLK and DCLK), a valid data pin
(DVALID), differential serial data output pins (DOUT and
DOUT), and differential serial data input pins (DIN and
DIN). The DDC114 contains only two A/D converters, so
the conversion process is interleaved (see Figure 2). The
integration and conversion process is fundamentally
independent of the data retrieval process. Consequently,
the CLK frequency and DCLK frequencies need not be the
same. DIN and DIN are only used when multiple
converters are cascaded, and otherwise should both be
tied to DGND.
implement the integration cycle. The timing relationships
of all of the switches shown in Figure 3 are illustrated in
Figure 4. Figure 4 is used to conceptualize the operation
of the integrator input stage of the DDC114 and should not
be used as an exact timing tool for design. See Figure 5 for
the block diagrams of the reset, integrate, wait and convert
states of the integrator section of the DDC114. This
internal switching network is controlled externally with the
convert
pin
(CONV),
range
selection
pins
(RANGE0−RANGE2), and the system clock (CLK). For
the best noise performance, CONV must be synchronized
with the rising edge of CLK. It is recommended that CONV
toggle within ±10ns of the rising edge of CLK.
DEVICE OPERATION
The noninverting inputs of the integrators are connected to
ground. Consequently, the DDC114 analog ground should
be as clean as possible. The range switches, along with
the internal and external capacitors (CF), are shown in
parallel between the inverting input and output of the
operational amplifier. At the beginning of a conversion, the
switches SA/D, SINTA, SINTB, SREF1, SREF2, and SRESET are
set (see Figure 4).
Basic Integration Cycle
The topology of the front end of the DDC114 is an analog
integrator, as shown in Figure 3. In this diagram, only Input
IN1 is shown. This representation of the input stage
consists of an operational amplifier, a selectable feedback
capacitor network (CF), and several switches that
SREF1
VREF
3pF
50pF
RANGE2
25pF
RANGE1
12.5pF
RANGE0
Input
Current
SINTA
SREF2
IN1
SA/D1A
SRESET
Photodiode
ESD
Protection
Diodes
SINTB
To Converter
Integrator A
Integrator B (same as A)
Figure 3. Basic Integration Configuration for Input 1, Shown with a 250pC (CF = 62.5pF) Input Range
9
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SBAS255C − JUNE 2004 − REVISED APRIL 2009
CONV
CLK
SINTA
SINTB
SREF1
SREF2
SRESET
Integrate
Convert
Wait
W a it
Wait
R e se t
Convert
W a it
Configuration of
Integrator A
R e se t
SA/D1A
VREF
Integrator A
Voltage Output
Figure 4. Basic Integration Timing Diagram (as shown in Figure 3)
SREF1
CF
VREF
SINT
SREF2
CF
IN
SREF1
VREF
To Converter
SRESET
SA/D
SINT
SREF2
IN
To Converter
SRESET
SA/D
a) Reset Configuration
CF
SREF1
b) Wait Configuration
VREF
SINT
SREF2
CF
IN
SRESET
SREF1
VREF
To Converter
SA/D
SINT
SREF2
IN
SRESET
c) Integrate Configuration
To Converter
SA/D
d) Convert Configuration
Figure 5. Diagrams for the Four Configurations of the Front End Integrators of the DDC114
10
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Voltage Reference
At the completion of an A/D conversion, the charge on the
integration capacitor (CF) is reset with SREF1 and SRESET
(see Figure 4 and Figure 5a). In this manner, the selected
capacitor is charged to the reference voltage, VREF. Once
the integration capacitor is charged, SREF1 and SRESET are
switched so that VREF is no longer connected to the
amplifier circuit while it waits to begin integrating (see
Figure 5b). With the rising edge of CONV, SINTA closes,
which begins the integration of side A. This process puts
the integrator stage into its integrate mode (see Figure 5c).
The external voltage reference is used to reset the
integration capacitors before an integration cycle begins.
It is also used by the ∆Σ converter while the converter is
measuring the voltage stored on the integrators after an
integration cycle ends. During this sampling, the external
reference must supply the charge needed by the ∆Σ
converter. For an integration time of 400µs, this charge
translates to an average VREF current of approximately
75µA. The amount of charge needed by the ∆Σ converter
is independent of the integration time; therefore,
increasing the integration time lowers the average current.
For example, an integration time of 800µs lowers the
average VREF current to 37.5µA.
Charge from the input signal is collected on the integration
capacitor, causing the voltage output of the amplifier to
decrease. The falling edge of CONV stops the integration
by switching the input signal from side A to side B (SINTA
and SINTB). Prior to the falling edge of CONV, the signal on
side B was converted by the A/D converter and reset
during the time that side A was integrating. With the falling
edge of CONV, side B starts integrating the input signal.
Now the output voltage of the side A operational amplifier
is presented to the input of the ∆Σ A/D converter (see
Figure 5d).
It is critical that VREF be stable during the different modes
of operation (see Figure 5). The ∆Σ converter measures
the voltage on the integrator with respect to VREF. Since
the integrator capacitors are initially reset to VREF, any
drop in VREF from the time the capacitors are reset to the
time when the converter measures the integrator output
will introduce an offset. It is also important that VREF be
stable over longer periods of time because changes in
VREF correspond directly to changes in the full-scale
range. Finally, VREF should introduce as little additional
noise as possible.
Integration Capacitors
There are eight different capacitors available on-chip for
both sides of every channel in the DDC114. These internal
capacitors are trimmed in production to achieve the
specified performance for range error of the DDC114. The
range control pins (RANGE0−RANGE2) change the
capacitor value for all four integrators. Consequently, all
inputs and both sides of each input will always have the
same full-scale range. Table 1 shows the capacitor value
selected for each range selection.
For these reasons, it is strongly recommended that the
external reference source be buffered with an operational
amplifier, as shown in Figure 6. In this circuit, the voltage
reference is generated by a 4.096V reference. A low-pass
filter to reduce noise connects the reference to an
operational amplifier configured as a buffer. This amplifier
should have low noise and input/output common-mode
ranges that support VREF. Following the buffer are
capacitors placed close to the DDC114 VREF pin. Even
though the circuit in Figure 6 might appear to be unstable
because of the large output capacitors, it works well for
most operational amplifiers. It is NOT recommended that
series resistance be placed in the output lead to improve
stability since this can cause a drop in VREF, producing
large offsets.
Table 1. Range Selection of the DDC114
RANGE2
RANGE1
RANGE0
CF
(pF, typ)
INPUT RANGE
(pC, typ)
0
0
0
0
1
1
1
1
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
3
12.5
25
37.5
50
62.5
75
87.5
−0.048 to 12
–0.2 to 50
–0.4 to 100
–0.6 to 150
–0.8 to 200
–0.1 to 250
–1.2 to 300
–1.4 to 350
+5V
+5V
0.10µF
0.47µF
7
2
1
REF3140
10kΩ
3
OPA350
+
+
10µF
3
To VREF
Pin 10 of
the DDC114
6
2
0.10µF
10µF
0.1µF
4
Figure 6. Recommended External Voltage Reference Circuit for Best Low-Noise Operation with the DDC114
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DDC114 Frequency Response
Test Mode
The frequency response of the DDC114 is set by the front
end integrators and is that of a traditional continuous time
integrator, as shown in Figure 7. By adjusting TINT, the user
can change the 3dB bandwidth and the location of the
notches in the response. The frequency response of the
∆Σ converter that follows the front end integrator is of no
consequence because the converter samples a held
signal from the integrators. That is, the input to the ∆Σ
converter is always a DC signal. Since the output of the
front end integrators are sampled, aliasing can occur.
Whenever the frequency of the input signal exceeds
one-half of the sampling rate, the signal will fold back down
to lower frequencies.
When Test Mode is used, the inputs (IN1, IN2, IN3, and
IN4) are disconnected from the DDC114 integrators to
enable the user to measure a zero input signal regardless
of the current supplied to the inputs. In addition, packets of
charge can be transferred to the integrators in 11pC
intervals to measure non-zero values. The test mode
works with both the continuous and non-continuous
modes. The timing diagram for the test mode is shown in
Figure 8 with the timing specifications given in Table 2.
To enter Test Mode, hold TEST high while CONV
transitions. If TEST is held high during the entire
integration period, the integrators measure a zero value.
This mode can be used to help debug a design or perform
diagnostic tests. To apply packets of charge during Test
Mode, simply strobe TEST low then high before the next
CONV transition. Each rising edge of TEST causes
approximately 11pC of charge to be transferred to the
integrators. This charge transfer is independent of the
integration time. Data retrieval during Test Mode is
identical to normal operation. To exit Test Mode, take
TEST low and allow several cycles after exiting before
using the data.
0
G ain (dB)
−10
−20
−30
−40
−50
1
TINT
0.1
TINT
10
TINT
100
TINT
Frequency
Figure 7. Frequency Response of the DDC114
Test Mode Enabled: Inputs Disconnected
Test Mode Disabled
Test Mode Disabled
Action
Integrate B
Integrate A
0pC into B
11pC into A
22pC into B
33pC into A
Integrate B
Integrate A
CONV
t4
t6
t2
TEST
t1
t3
t5
t4
Figure 8. Timing Diagram of the Test Mode of the DDC114
Table 2. Timing for the DDC114 in the Test Mode
12
SYMBOL
DESCRIPTION
MIN
t1
Setup Time for Test Mode Enable
100
TYP
MAX
UNITS
ns
t2
Setup Time for Test Mode Disable
100
ns
t3
Hold Time for Test Mode Enable
100
ns
t4
From Rising Edge of TEST to the Edge of CONV while Test Mode
Enabled
1
µs
t5
Falling Edge to Rising Edge of TEST
1
µs
t6
Rising Edge to Falling Edge of TEST
1
µs
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DIGITAL INTERFACE
The digital interface of the DDC114 provides the digital
results via a synchronous serial interface consisting of
differential data clocks (DCLK and DCLK), a valid data pin
(DVALID), differential serial data output pins (DOUT and
DOUT), and differential serial data input pins (DIN and
DIN). The DDC114 contains only two A/D converters, so
the conversion process is interleaved (see Figure 2,
page 8). The integration and conversion processes are
independent of the data retrieval process. Consequently,
the CLK frequency and DCLK frequencies need not be the
same. DIN and DIN are used when multiple converters are
cascaded. Cascading or daisy-chaining greatly simplifies
the interconnection and routing of the digital outputs in
cases where a large number of converters are needed.
Refer to the Cascading Multiple Converters section of this
data sheet for more detail.
High-Speed and Low-Power Modes
(HISPD/LOPWR)
The HISPD/LOPWR input controls the power dissipation
and in turn the maximum allowable CLK frequency and
data rate, as shown in Table 4. With HISPD/LOPWR = 0,
the Low-Power Mode is selected with a typical 13.5mW/
channel and a maximum data rate of 2.5kSPS. Setting
HISPD/LOPWR = 1 selects the High-Speed Mode, which
supports a maximum data rate of 3.125kSPS with a corresponding typical power of 18.0mW/channel.
Table 4. HISPD/LOPWR Pin Operation
HISPD/
LOPWR
MODE
TYPICAL
POWER/
CHANNEL
MAXIMUM
CLK FREQUENCY
(CLK_4X = 0)
MAXIMUM
DATA
RATE
0
Low Power
13.5mW/ch
4.0MHz
2.5kSPS
1
High Speed
18.0mW/ch
4.8MHz
3.125kSPS
Data Valid (DVALID)
Complementary Signals (DCLK, DIN, and DOUT)
The DDC114 provides optional complementary inputs
(DCLK, DIN) to help reduce digital coupling to the analog
inputs. If using these inputs, connect a complementary
signal to each. If these inputs are not connected on the
DDC114, they should be tied to DGND. DOUT is a
complementary output designed to drive DIN. If not using
DOUT, leave it floating.
System and Data Clocks (CLK and CONV)
The system clock is supplied to CLK and the data clock is
supplied to DCLK. Make sure the clock signals are
clean—avoid overshoot or ringing. For best performance,
generate both clocks from the same clock source. DCLK
should be disabled by taking it low after the data has been
shifted out or while CONV is transitioning.
When using multiple DDC114s, pay close attention to the
DCLK distribution on the printed circuit board (PCB). In
particular, make sure to minimize skew in the DCLK signal
as this can lead to timing violations in the serial interface
specifications. See the Cascading Multiple Converters
section for more details.
System Clock Divider (CLK_4X)
The DVALID signal indicates that data is ready. Data
retrieval may begin after DVALID goes low. This signal is
generated using an internal clock divided down from the
system clock CLK. The phase relationship between this
internal clock and CLK is set when power is first applied,
and is random. Since the user must synchronize CONV
with CLK, the DVALID signal will have a random phase
relationship with CONV. This uncertainty is ±1/fCLK. Polling
DVALID eliminates any concern about this relationship. If
data read back is timed from CONV, wait the maximum
value of t7 or t8 to insure data is valid.
Reset (RESET)
The DDC114 is reset asynchronously by taking the
RESET input low, as shown in Figure 9. Make sure the
reset pulse is at least 50µs wide. After resetting the
DDC114, wait at least four conversions before using the
data. It is very important to make sure the RESET is glitch
free to avoid unintended resets. The RESET pin is used
during power-up; see the Power-Up Sequence section for
more details.
> 50µs
RESET
The CLK_4X input enables an internal divider on the
system clock as shown in Table 3. When CLK_4X = 1, the
system clock is divided by four. This allows a 4X faster
system clock, which in turn provides a finer quantization of
the integration time as the CONV signal needs to be
synchronized with the system clock for the best
performance.
Table 3. CLK_4X Pin Operation
CLK_4X
PIN
CLK DIVIDER
VALUE
CLK FREQUENCY
INTERNAL CLOCK
FREQUENCY
0
1
4MHz
4MHz
1
4
16MHz
4MHz
Figure 9. Reset Timing
Convert (CONV)
CONV controls the integration time (TINT). For optimum
analog performance, make sure CONV is synchronized to
CLK.
This recommendation implies that while SPEED is low,
TINT needs to be adjusted in steps of 250ns if CLK_4X is
low and CLK = 4MHz. If CLK_4X is high and CLK =
16MHz, this allows TINT to be adjusted in steps of 62.5ns.
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Conversion Rate
The conversion rate of the DDC114 is set by a combination
of the integration time (determined by the user) and the
speed of the A/D conversion process. The A/D conversion
time is primarily a function of the system clock (CLK)
speed. One A/D conversion cycle encompasses the
conversion of two signals (one side of each dual integrator
feeding the modulator) and the reset time for each of the
integrators involved in the two conversions. In most
situations, the A/D conversion time is shorter than the
integration time. If this condition exists, the DDC114 will
operate in continuous mode. When the DDC114 is in
continuous mode, the sensor output is continuously
integrated by one of the two sides of each input.
In the event that the A/D conversion takes longer than the
integration time, the DDC114 will switch into a
non-continuous mode. In non-continuous mode, the A/D
converter is not able to keep pace with the speed of the
integration process. Consequently, the integration
process is periodically halted until the digitizing process
catches up. These two basic modes of operation for the
DDC114—continuous and non-continuous modes—are
described below.
Continuous and Non-Continuous Operational
Modes
Figure 10 shows the state diagram of the DDC114. In all,
there are eight states. Table 5 provides a brief explanation
of each state.
Table 5. State Descriptions
STATE
MODE
DESCRIPTION
1
Ncont
Complete m/r/az of side A, then side B (if previous
state is state 4). Initial power-up state when CONV
is initially held HIGH.
2
Ncont
Prepare side A for integration.
3
Cont
Integrate on side A.
4
Cont
Integrate on side B; m/r/az on side A.
5
Cont
Integrate on side A; m/r/az on side B.
6
Cont
Integrate on side B.
7
Ncont
Prepare side B for integration.
8
Ncont
Complete m/r/az of side B, then side A (if previous
state is state 5). Initial power-up state when CONV
is initially held LOW.
Four signals are used to control progression around the
state diagram: CONV, mbsy, and their complements. The
state machine uses the level as opposed to the edges of
CONV to control the progression. mbsy is an internallygenerated signal not available to the user. It is active
whenever a measurement/reset/auto-zero (m/r/az) cycle
is in progress.
14
CONV|mbsy
1
2
CONV × mbsy
Ncont
Ncont
CONV
3
Int A
Cont
CONV × mbsy
CONV
4
5
CONV × mbsy
Int B/Meas A
Cont
CONV × mbsy
Int A/Meas B
Cont
CONV
6
CONV × mbsy
Int B
Cont
CONV
7
Ncont
8
CONV × mbsy
Ncont
CONV|mbsy
Figure 10. Integrate/Measure State Diagram
During cont mode, mbsy is not active when CONV toggles.
The non-integrating side is always ready to begin
integrating when the other side finishes its integration.
Consequently, monitoring the current status of CONV is all
that is needed to know the current state. Cont mode
operation corresponds to states 3-6. Two of the states, 3
and 6, only perform an integration (no m/r/az cycle).
mbsy becomes important when operating in the ncont
mode, states 1, 2, 7, and 8. Whenever CONV is toggled
while mbsy is active, the DDC114 will enter or remain in
either ncont state 1 (or 8). After mbsy goes inactive, state
2 (or 7) is entered. This state prepares the appropriate side
for integration. In ncont states, the inputs to the DDC114
are grounded.
One interesting observation from the state diagram is that
the integrations always alternate between sides A and B.
This relationship holds for any CONV pattern and is
independent of the mode. States 2 and 7 insure this
relationship during ncont mode.
When power is first applied to the DDC114, the beginning
state is either 1 or 8, depending on the initial level of CONV.
For CONV held high at power-up, the beginning state is 1.
Conversely, for CONV held low at power-up, the beginning
state is 8. In general, there is a symmetry in the state
diagram between states 1-8, 2-7, 3-6, and 4-5. Inverting
CONV results in the states progressing through their
symmetrical match.
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TIMING EXAMPLES
mbsy is shown next. Finally, DVALID is given. As
described in the data sheet, DVALID goes active low when
data is ready to be retrieved from the DDC114. It stays low
until DCLK is taken high and then back low by the user. The
text below the DVALID pulse indicates the side of the data
available to be read, and arrows help match the data to the
corresponding integration. The signals illustrated in
Figure 11 through Figure 19 are drawn at approximately
the same scale.
Cont Mode
A few timing diagrams help illustrate the operation of the
state machine. These diagrams are shown in Figure 11
through Figure 19. Table 6 gives generalized timing
specifications in units of CLK periods for CLK_4X = 0. If
CLK_4X = 1, these values increase by a factor of four
because of the internal clock divider. Values (in µs) for
Table 6 can be easily found for a given CLK. For example,
if CLK = 4MHz, then a CLK period = 0.25µs. t6 in Table 6
would then be 367.50 ± 0.125µs.
In Figure 11, the first state is ncont state 8. The DDC114
always powers up in the ncont mode. In this case, the first
state is 8 because CONV is initially low. After the first two
states, cont mode operation is reached and the states
begin toggling between 4 and 5. From now on, the input is
being continuously integrated, either on side A or side B.
The time needed for the m/r/az cycle, or t6, is the same time
that determines the boundary between the cont and ncont
modes described earlier in the Overview section. DVALID
goes low after CONV toggles in time t7, indicating that data
is ready to be retrieved. As shown in Figure 11, there are
two values for t6 and t7. The reason for this is discussed in
the Special Considerations section.
Table 6. Timing Specifications Generalized in
CLK Periods
DESCRIPTION
VALUE
(CLK periods with CLK_4X = 0)
t6
Cont mode m/r/az cycle
1470 ± 0.5
t7
Cont mode data ready
1380 ± 0.5
t8
1st ncont mode data ready
1379 ± 1
t9
2nd ncont mode data ready
1450
t10
Ncont mode m/r/az cycle
2901 ± 1
SYMBOL
Figure 11 shows a few integration cycles beginning with
initial power-up for a cont mode example. The top signal
is CONV and is supplied by the user. The next line
indicates the current state in the state diagram. The
following two traces show when integrations and
measurement cycles are underway. The internal signal
See Figure 12 for the timing diagram of the internal
operations occurring during continuous mode operation.
Table 7 gives the timing specifications in the continuous
mode.
CONV
State
8
Integration
Status
7
6
5
4
5
Integrate B
Integrate A
Integrate B
Integrate A
m/r/az
Status
m/r/az B
m/r/az A
m/r/az B
t6
mbsy
DVALID
t7
t=0
Power−Up
Side B
Data
Side A
Data
Side B
Data
SYMBOL
DESCRIPTION
VALUE (CLK = 4MHz, CLK_4X = 0)
VALUE (CLK = 4.8MHz, CLK_4X = 0)
t6
Cont Mode m/r/az Cycle
367.50 ± 0.125µs
306.25 ± 0.104µs
t7
Cont Mode Data Ready
345.00 ± 0.125µs
287.5 ± 0.104µs
Figure 11. Continuous Mode Timing
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End Integration Side A
Start Integration Side B
End Integration Side B
Start Integration Side A
TINT
CONV
TINT
Side A
A/D Conversion
Input 1 and 2 (Internal)
End Integration Side A
Start Integration Side B
t14
Side B
Side A
t 12
Side A
A/D Conversion
Input 3 and 4 (Internal)
t 13
Side B
t12
t13
t 14
DVALID
Side A
Data Ready
Side B
Data Ready
Figure 12. Timing Diagram of the Internal Operation in Continuous Mode of the DDC114
Table 7. Timing for the Internal Operation in Continuous Mode
CLK = 4MHz, CLK_4X = 0
SYMBOL
TINT
16
DESCRIPTION
MIN
Integration Period (continuous mode)
400
TYP
CLK = 4.8MHz, CLK_4X = 0
MAX
MIN
1,000,000
320
TYP
MAX
UNITS
1,000,000
µs
169.5
141.25
µs
A/D Conversion Reset Time (internally controlled)
4
3.333
µs
Integrator and A/D Conversion Reset Time
(internally controlled)
23
19.167
µs
t12
A/D Conversion Time (internally controlled)
t13
t14
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Ncont Mode
Non-continuous (ncont) mode of operation is intended for
ranges 1 to 7. It is not recommended to use Range 0 when
operating in non-continuous mode. Figure 13 illustrates
operation in ncont mode. The integrations come in pairs
(that is, sides A/B or sides B/A) followed by a time during
which no integrations occur. During that time, the previous
integrations are being measured, reset and auto-zeroed.
Before the DDC114 can advance to states 3 or 6, both
sides A and B must be finished with the m/r/az cycle, which
takes time t10. When the m/r/az cycles are completed, time
t11 is needed to prepare the next side for integration. This
time is required for ncont mode because the m/r/az cycle
of ncont mode is slightly different from that of cont mode.
After the first integration ends, DVALID goes low in time t8.
This time is the same as in cont mode. The second data will
be ready in time t9 after the first data is ready. One result
of the naming convention used in this data sheet is that
when the DDC114 is operating in ncont mode, it passes
through both ncont mode states and cont mode states. For
example, in Figure 13, the state pattern is 3, 4, 1, 2, 3, 4,
1, 2, 3, 4 ... where 3 and 4 are cont mode states. Ncont
mode, by definition, means that for some portion of the
time, neither side A nor B is integrating. States that perform
an integration are labeled cont mode states, while those
that do not are called ncont mode states. Since
integrations are performed in ncont mode, just not
continuously, some cont mode states must be used in an
ncont mode state pattern.
CONV
State
3
4
1
2
3
4
1
2
t 11
Integration
Status
m/r/az
Status
Int A
Int B
Int A
m/r/az A
Int B
m/r/az A
m/r/az B
m/r/az B
t 10
mbsy
t9
DVALID
t8
Side A
Data
Side B
Data
Side A
Data
Side B
Data
SYMBOL
DESCRIPTION
VALUE (CLK = 4MHz, CLK_4X = 0)
VALUE (CLK = 4.8MHz, CLK_4X = 0)
t8
t9
t10
t11
1st ncont Mode Data Ready
2nd ncont Mode Data Ready
ncont Mode m/r/az Cycle
Prepare Side for Integration
344.75 ± 0.25µs
362.5µs
725.25 ± 0.25µs
≥ 18µs
287.292 ± 0.208µs
302.083µs
604.375 ± 0.208µs
≥ 15µs
Figure 13. Non-Continuous Mode Timing
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Start Integration Side A
Start Integration Side A
End Integration Side A
Start Integration Side B
End Integration Side B
Release
State
Wait State
TINT
t17
CONV
TINT
t16
A/D Conversion
Input 1 and 2
t12
A/D Conversion
Input 3 and 4
t12
t13
t15
DVALID
Side A
Data Ready
Side B
Data Ready
Figure 14. Conversion Detail for the Internal Operation of Non-Continuous Mode
with Side A Integrated First
Table 8. Internal Timing for the DDC114 in Non-Continuous Mode
CLK = 4MHz, CLK_4X = 0
SYMBOL
TINT
DESCRIPTION
MIN
Integration Time (non-continuous mode)
TYP
400
t12
A/D Conversion Time (internally controlled)
t13
A/D Conversion Reset Time (internally controlled)
t15
Integrator and A/D Conversion Reset Time
(internally controlled)
t16
Total A/D Conversion and Reset Time (internally controlled)
t17
Release Time
CLK = 4.8MHz, CLK_4X = 0
MAX
MIN
1,000,000
320
TYP
MAX
1,000,000
UNITS
µs
169.5
141.25
µs
4
3.333
µs
19.5
16.25
µs
604.375 ± 0.208
µs
725.25 ± 0.25
18
µs
15
Start Integration Side B
Start Integration Side B
End Integration Side B
Start Integration Side A
End Integration Side A
Release
State
Wait State
CONV
TINT
TINT
t 17
t16
A/D Conversion
Inputs 1 and 2
t12
A/D Conversion
Inputs 3 and 4
t 12
t13
t 15
DVALID
Side B
Data Ready
Side A
Data Ready
Figure 15. Internal Operation Timing Diagram of Non-Continuous Mode with Side B Integrated First
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CONV signal with TINT = 512 CLK periods. Care must be
exercised when using a square wave to generate CONV.
There are certain integration times that must be avoided
since they produce very short intervals for state 2 (or state
7 if CONV is inverted). As seen in the state diagram, the
state progresses from 2 to 3 as soon as CONV is high. The
state machine does not insure that the duration of state 2
is long enough to properly prepare the next side for
integration (t11). This must be done by the user with proper
timing of CONV. For example, if CONV is a square wave
with TINT = 970 CLK periods, state 2 will only be 9 CLK
periods long; therefore, t11 will not be met.
Looking at the state diagram, one can see that the CONV
pattern needed to generate a given state progression is not
unique. Upon entering states 1 or 8, the DDC114 remains
in those states until mbsy goes low, independent of CONV.
As long as the m/r/az cycle is underway, the state machine
ignores CONV (see Figure 10, page 14). The top two
signals in Figure 16 are different CONV patterns that
produce the same state. This feature allows flexibility in
generating ncont mode CONV patterns. For example, the
DDC114 Evaluation Fixture operates in ncont mode by
generating a square wave with pulse width < t6. Figure 17
illustrates operation in ncont mode using a 50% duty cycle
CONV1
CONV2
mbsy
State
3
4
1
2
3
4
1
2
Figure 16. Equivalent CONV Signals in Non-Continuous Mode
CONV
State
Integration
Status
3
4
Int A
Int B
1
2
3
4
Int A
Int B
1
mbsy
DVALID
Side A
Data
Side B
Data
Side A
Data
Figure 17. Non-Continuous Mode Timing with a 50% Duty Cycle CONV Signal
19
""#
www.ti.com
SBAS255C − JUNE 2004 − REVISED APRIL 2009
Changing Between Modes
Changing from ncont to cont mode occurs when TINT is
increased so that TINT is always ≥ t6 as shown in Figure 19
(see Figure 14 and Table 8, page 18). With a longer TINT,
the m/r/az cycle has enough time to finish before the next
integration begins and continuous integration of the input
signal is possible. For the special case of the very first
integration when changing to cont mode, TINT can be < t6.
This is allowed because there is no simultaneous m/r/az
cycle on the side B during state 3—there is no need to wait
for it to finish before ending the integration on side A.
Changing from cont to ncont mode occurs whenever TINT
< t6. Figure 18 shows an example of this transition. In this
figure, cont mode is entered when the integration on side
A is completed before the m/r/az cycle on side B is
complete. The DDC114 completes the measurement on
sides B and A during states 8 and 7 with the input signal
shorted to ground. Ncont integration begins with state 6.
CONV
State
5
4
5
8
Continuous
Integration
Status
m/r/az
Status
Integrate A
Integrate B
m/r/az B
m/r/az A
7
6
5
Int B
Int A
Non−Continuous
Int A
m/r/az B
m/r/az A
m/r/az B
mbsy
Figure 18. Changing from Continuous Mode to Non-Continuous Mode
CONV
State
3
4
1
2
Non−Continuous
Integration
Status
m/r/az
Status
Int A
Int B
m/r/az A
3
Continuous
Integrate A
m/r/az B
4
Integrate B
m/r/az A
mbsy
Figure 19. Changing from Non-Continuous Mode to Continuous Mode
20
""#
www.ti.com
SBAS255C − JUNE 2004 − REVISED APRIL 2009
DATA FORMAT (FORMAT)
DATA RETRIEVAL
The serial output data is provided in an offset binary code
as shown in Table 9. The digital input pin FORMAT selects
how many bits are used in the output word. When
FORMAT is high (1), 20 bits are used. When FORMAT is
low (0), the lower 4 bits are truncated so that only 16 bits
are used. Note that the LSB size is 16 times bigger when
FORMAT = 0. An offset is included in the output to allow
slightly negative inputs, from board leakages for example,
from clipping the reading. This offset is approximately
0.4% of the positive full−scale.
Table 9. Ideal Output Code(1) vs Input Signal
INPUT
SIGNAL
IDEAL OUTPUT CODE
FORMAT = HIGH (1)
IDEAL OUTPUT CODE
FORMAT = LOW (0)
≥ 100% FS
1111 1111 1111 1111 1111
1111 1111 1111 1111
0.001531% FS
0000 0001 0000 0001 0000
0000 0001 0000 0001
0.001436% FS
0000 0001 0000 0000 1111
0000 0001 0000 0000
0.000191% FS
0000 0001 0000 0000 0010
0000 0001 0000 0000
0.000096% FS
0000 0001 0000 0000 0001
0000 0001 0000 0000
0% FS
0000 0001 0000 0000 0000
0000 0001 0000 0000
−0.3955% FS
0000 0000 0000 0000 0000
0000 0000 0000 0000
In both the continuous and non-continuous modes of
operation, the data from the last conversion is available for
retrieval on the falling edge of DVALID (see Figure 20 and
Table 10, on page 22). Data is shifted out on the falling
edge of the data clock, DCLK. Make sure not to retrieve
data while CONV changes as this can introduce noise.
Stop activity on DCLK at least 10µs before or after a CONV
transition.
Setting the FORMAT pin = 0 (16-bit output word) reduces
the time needed to retrieve data by 20%, since there are
fewer bits to shift out. This time reduction can be useful in
multichannel systems requiring only 16 bits of resolution.
(1) Excludes the effects of noise, INL, offset, and gain errors.
CLK
t18
DVALID
t20
t20
t19
DCLK
t21
DOUT
Input 4
MSB
Input 4
LSB
Input 3
MSB
Input 3
LSB
Input 2
MSB
Input 2
LSB
Input 1
MSB
Input 1
LSB
Input 4
MSB
Figure 20. Digital Interface Timing Diagram for Data Retrieval From a Single DDC114
Table 10. Timing for the DDC114 Data Retrieval
CLK = 4MHz, CLK_4X = 0
SYMBOL
DESCRIPTION
MIN
t18
Propagation Delay from Falling Edge of CLK to DVALID LOW
5
t19
Propagation Delay from Falling Edge of DCLK to DVALID HIGH
5
t20
Hold Time that DOUT is Valid Before the Falling Edge of DVALID
t21
Hold Time that DOUT is Valid After Falling Edge of DCLK
t21A(1)
Propagation Delay from Falling Edge of DCLK to Valid DOUT
TYP
MAX
CLK = 4.8MHz, CLK_4X = 0
MIN
TYP
MAX
5
ns
5
1.75
ns
µs
1.458
5
5
10
UNITS
ns
10
ns
(1) With a maximum load of one DDC114 (4pF typical) with an additional load of 5pF.
21
""#
www.ti.com
SBAS255C − JUNE 2004 − REVISED APRIL 2009
DOUT can be used with DIN to daisy-chain several
DDC114 devices together to minimize wiring. In this mode
of operation, the serial data output is shifted through
multiple DDC114s, as illustrated in Figure 21.
SPECIAL CONSIDERATIONS
Cascading Multiple Converters
Multiple DDC114 units can be connected in serial
configuration, as illustrated in Figure 21.
See Figure 22 for the timing diagram when the DIN input
is used to daisy-chain several devices. Table 11 gives the
timing specification for data retrieval using DIN.
DOUT
Data Retrievel
Outputs
DDC114
DCLK
DVALID
DCLK
DCLK
DIN
DDC114
IN4
IN3
IN2
IN1
DIN
IN1
DOUT
IN2
DOUT
DIN
IN3
DIN
IN4
DDC114
IN1
DOUT
IN2
DOUT
DIN
IN3
DIN
IN4
DOUT
DCLK
DVALID
DCLK
DCLK
DVALID
Data Clock
Sensor A
B
C
D
E
F
G
H
I
J
K
L
Figure 21. Daisy-Chained DDC114s
CLK
t18
DVALID
t20
t 20
t19
DCLK
t21
t 23
t22
DIN
Input A
MSB
DOUT
Input A
LSB
Input B
MSB
Input F
LSB
Input G
MSB
Input K
LSB
Input L
MSB
Input L
LSB
Input A
MSB
Figure 22. Timing Diagram When Using the DIN Function of the DDC114
Table 11. Timing for the DDC114 Data Retrieval Using DIN
22
SYMBOL
DESCRIPTION
MIN
TYP
MAX
UNITS
t22
Set-Up Time From DIN to Falling Edge of DCLK
5
ns
t23
Hold Time For DIN After Falling Edge of DCLK
4
ns
""#
www.ti.com
SBAS255C − JUNE 2004 − REVISED APRIL 2009
RETRIEVAL BEFORE CONV TOGGLES
(CONTINUOUS MODE)
NOTE: 64τDCLK is used for FORMAT = low.
where τDCLK is the period of the data clock. For example,
if TINT = 1000µs and DCLK = 10MHz, the maximum
number of DDC114s (FORMAT = high) is shown in
Equation 2:
Data retrieval before CONV toggles is the most
straightforward method. Data retrieval begins soon after
DVALID goes low and finishes before CONV toggles; as
shown in Figure 23. For best performance, data retrieval
must stop t28 before CONV toggles. This method is most
appropriate for longer integration times. The maximum
time available for readback is TINT – t27 – t28. For DCLK =
10MHz and CLK = 4MHz, the maximum number of
DDC114s that can be daisy-chained together (FORMAT =
high) is calculated by Equation 1:
T INT * 355.125ms
80tDCLK
CONV
DVALID
1000ms * 355.125ms
+ 80.60 ³ 80 DDC114s
(80)(100ns)
(1)
TINT
TINT
t27
t28
DCLK
…
…
DOUT
…
…
Side B
Data
Side A
Data
CLK = 4MHz, CLK_4X = 0
SYMBOL
(2)
(or 100 for FORMAT = low).
CLK = 4.8MHz, CLK_4X = 0
DESCRIPTION
UNITS
MIN
TYP
MAX
MIN
345.00 ± 0.125
t27
Cont Mode Data Ready
t28
Data Retrieval Shutdown Before Edge of CONV
10
TYP
287.5 ± 0.104
10
MAX
µs
µs
Figure 23. Readback Before CONV Toggles
23
""#
www.ti.com
SBAS255C − JUNE 2004 − REVISED APRIL 2009
RETRIEVAL AFTER CONV TOGGLES
(CONTINUOUS MODE)
of DDC114s that can be daisy-chained together (FORMAT
= high) is calculated by Equation 3:
For shorter integration times, more time is available if data
retrieval begins after CONV toggles and ends before the
new data is ready. Data retrieval must wait t29 after CONV
toggles before beginning. See Figure 24 for an example of
this. The maximum time available for retrieval is
t27 − t29 – t26 (344.875µs – 10µs – 1.75µs for
CLK = 4MHz), regardless of TINT. The maximum number
TINT
CONV
333.125ms
80tDCLK
(3)
NOTE: 64τDCLK is used for FORMAT = low.
For DCLK = 10MHz, the maximum number of DDC114s is
41 (or 52 for FORMAT = low).
TINT
TINT
DVALID
t27
t29
DCLK
…
DOUT
t26
…
…
…
…
…
Side A
Data
Side B
Data
Side A
Data
CLK = 4MHz, CLK_4X = 0
SYMBOL
DESCRIPTION
MIN
t26
Hold Time that DOUT is Valid Before Falling Edge of DVALID
t27
Cont Mode Data Ready
t29
Data Retrieval Start-Up After Edge of CONV
TYP
MAX
MIN
TYP
MAX
UNITS
1.75
1.458
µs
345.00 ± 0.125
287.5 ± 0.104
µs
10
Figure 24. Readback After CONV Toggles
24
CLK = 4.8MHz, CLK_4X = 0
10
µs
""#
www.ti.com
SBAS255C − JUNE 2004 − REVISED APRIL 2009
RETRIEVAL BEFORE AND AFTER CONV
TOGGLES (CONTINUOUS MODE)
RETRIEVAL: NONCONTINUOUS MODE
Retrieving in noncontinuous mode is slightly different than
compared with the continuous mode. As illustrated in
Figure 26, DVALID goes low in time t30 after the first
integration completes. If TINT is shorter than this time, all
of t31 is available to retrieve data before the other side data
is ready. For TINT > t30, the first integration data is ready
before the second integration completes. Data retrieval
must be delayed until the second integration completes,
leaving less time available for retrieval. The time available
is t31 – (TINT – t30). The second integration data must be
retrieved before the next round of integration begins. This
time is highly dependent on the pattern used to generate
CONV. As with the continuous mode, data retrieval must
halt before and after CONV toggles (t28, t29) and be
completed before new data is ready (t26).
For the absolute maximum time for data retrieval, data can
be retrieved before and after CONV toggles. Nearly all of
TINT is available for data retrieval. Figure 25 illustrates how
this is done by combining the two previous methods. You
must pause the retrieval during CONV toggling to prevent
digital noise, as discussed previously, and finish before the
next data is ready. The maximum number of DDC114s that
can be daisy-chained together (FORMAT = high) is:
T INT * 20ms * 1.75ms
80t DCLK
NOTE: 64τDCLK is used for FORMAT = low.
For TINT = 400µs and DCLK = 10MHz, the maximum
number of DDC114s is 47 (or 59 for FORMAT = low).
CONV
TINT
TINT
t29
DVALID
t26
t28
DCLK
DOUT
TINT
…
…
…
…
…
…
…
…
…
…
…
…
Side B
Data
SYMBOL
t26
t28
t29
Side A
Data
CLK = 4MHZ, CLK_4X = 0
DESCRIPTION
MIN
Hold Time that DOUT is Valid Before Falling Edge of DVALID
Data Retrieval Shutdown Before Edge of CONV
Data Retrieval Start-Up After Edge of CONV
TYP
CLK = 4.8MHZ, CLK_4X = 0
MAX
MIN
1.75
TYP
MAX
1.458
10
10
10
10
UNITS
µs
µs
µs
Figure 25. Readback Before and After CONV Toggles
T IN T
CONV
TIN T
T IN T
T IN T
DVALID
t3 0
SYMBOL
t30
t31
t3 1
DCLK
…
…
D OUT
…
…
Side A
Data
Side B
Data
DESCRIPTION
1st ncont Mode Data Ready
2nd ncont Mode Data Ready
CLK = 4MHz, CLK_4X = 0
MIN
TYP
MAX
CLK = 4.8MHz, CLK_4X = 0
MIN
TYP
MAX
UNITS
344.75 ± 0.25
362.500
287.292 ± 0.208
302.083
µs
µs
Figure 26. Readback in Non-Continuous Mode
25
""#
www.ti.com
SBAS255C − JUNE 2004 − REVISED APRIL 2009
POWER-UP SEQUENCING
Prior to power-up, all digital and analog inputs must be low.
After the power supplies have settled, release RESET
after time t32. (See Figure 28 and Table 12.) Wait for time
t33 to begin applying the digital signals CONV and CLK.
The first CONV pulse will complete the release state and
begin integration.
VA
AVDD
10µF
DDC114
VD
DVDD
10µF
LAYOUT
AGND
0.1µF
DGND
0.1µF
POWER SUPPLIES AND GROUNDING
Separate Supplies
Both AVDD and DVDD should be as quiet as possible. It
is particularly important to eliminate noise from AVDD that
is non-synchronous with the DDC114 operation. Figure 27
illustrates two acceptable ways to supply power to the
DDC114. The first case shows two separate +5V supplies
for AVDD and DVDD. In this case, each +5V supply of the
DDC114 should be bypassed with 10µF solid tantalum
capacitors and 0.1µF ceramic capacitors. The second
case shows the DVDD power supply derived from the
AVDD supply with a < 10Ω isolation resistor. In both cases,
the 0.1µF capacitors should be placed as close to the
DDC114 package as possible. It is recommended that
both the analog and digital grounds (AGND and DGND) be
connected to a single ground plane on the printed circuit
board (PCB).
+5V
AVDD
10µF
AGND
0.1µF
DDC114
< 10Ω
DVDD
DGND
0.1µF
Single +5V Supply
THERMAL PAD
Figure 27. Power-Supply Connection Options
It is strongly recommended that the thermal pad on the
DDC114 be connected to ground on the PCB. No PCB
traces should be routed underneath the thermal pad.
AVDD
DVDD
t32
Release State
RESET
Start Integration
t 33
CONV
t34
CLK
…
Integrate Side B
Figure 28. Timing Diagram at Power-Up of the DDC114
Table 12. Timing for the DDC114 Power-Up Sequence
26
SYMBOL
DESCRIPTION
MIN
t32
Power Supplies Settled to RESET Release
10
TYP
MAX
UNITS
ms
t33
RESET Release to CONV, CLK Begin
50
µs
t34
First CONV Pulse Width
50
µs
""#
www.ti.com
SBAS255C − JUNE 2004 − REVISED APRIL 2009
Shielding Analog Signal Paths
currents between the PCB traces can exceed the input
bias current of the DDC114 if shielding is not implemented.
Figure 29 illustrates an acceptable approach to this
problem. A PC ground plane is placed around the inputs
of the DDC114. This shield helps minimize coupled noise
into the input pins.
As with any precision circuit, careful PCB layout ensures
the best performance. It is essential to make short, direct
interconnections
and
avoid
stray
wiring
capacitance—particularly at the analog input pins. Digital
signals should be kept as far from the analog input signals
as possible on the PCB.
This approach reduces leakage effects by surrounding
these sensitive pins with a low impedance analog ground.
Leakage currents from other portions of the circuit will flow
harmlessly to the low impedance analog ground rather
than into the analog input stage of the DDC114.
Input shielding practices should be taken into
consideration when designing the circuit layout for the
DDC114. The inputs to the DDC114 are high impedance
and extremely sensitive to extraneous noise. Leakage
Digital I/O and Digital Power
48
47
46
45
44
43
42
41
40
39
38
37
1
36
2
35
3
34
4
33
5
32
6
31
DDC114
7
30
8
29
9
28
10
27
11
26
12
25
13
14
15
16
17
Analog
Ground
18
19
20
21
22
23
Analog
Ground
IN4
24
Analog
Ground
IN2
IN3
Analog Power
IN1
Analog Ground
Figure 29. Recommended Shield for DDC114 Layout Design
27
www.ti.com
SBAS255C − JUNE 2004 − REVISED APRIL 2009
Revision History
DATE
REV
4/09
C
PAGE
SECTION
1
Front Page
9
Theory of Operation
DESCRIPTION
Updated front page appearance.
Changed last sentence of first paragraph on page 9.
NOTE: Page numbers for previous revisions may differ from page numbers in the current version.
28
PACKAGE OPTION ADDENDUM
www.ti.com
21-May-2010
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package
Drawing
Pins
Package Qty
Eco Plan
(2)
Lead/
Ball Finish
MSL Peak Temp
(3)
Samples
(Requires Login)
DDC114IRTCR
ACTIVE
VQFN
RTC
48
2500
Green (RoHS
& no Sb/Br)
CU SN
Level-3-260C-168 HR
DDC114IRTCRG3
ACTIVE
VQFN
RTC
48
2500
Green (RoHS
& no Sb/Br)
CU SN
Level-3-260C-168 HR
DDC114IRTCT
ACTIVE
VQFN
RTC
48
250
Green (RoHS
& no Sb/Br)
CU SN
Level-3-260C-168 HR
DDC114IRTCTG3
ACTIVE
VQFN
RTC
48
250
Green (RoHS
& no Sb/Br)
CU SN
Level-3-260C-168 HR
(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.
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 1
PACKAGE MATERIALS INFORMATION
www.ti.com
16-Feb-2012
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
DDC114IRTCR
VQFN
RTC
48
2500
330.0
16.4
7.3
7.3
1.5
12.0
16.0
Q2
DDC114IRTCT
VQFN
RTC
48
250
330.0
16.4
7.3
7.3
1.5
12.0
16.0
Q2
Pack Materials-Page 1
PACKAGE MATERIALS INFORMATION
www.ti.com
16-Feb-2012
*All dimensions are nominal
Device
Package Type
Package Drawing
Pins
SPQ
Length (mm)
Width (mm)
Height (mm)
DDC114IRTCR
VQFN
RTC
48
2500
336.6
336.6
28.6
DDC114IRTCT
VQFN
RTC
48
250
336.6
336.6
28.6
Pack Materials-Page 2
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