TEXAS INSTRUMENTS DDC112 Technical data

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SBAS085B – JANUARY 2000 – REVISED OCTOBER 2004

Dual Current Input 20-Bit

ANALOG-TO-DIGITAL CONVERTER

DDC112

FEATURES

● MONOLITHIC CHARGE MEASUREMENT A/D

CONVERTER

● DIGITAL FILTER NOISE REDUCTION:

3.2ppm, rms

● INTEGRAL LINEARITY:

±0.005% Reading ±0.5ppm FSR

● HIGH PRECISION, TRUE INTEGRATING FUNC-

TION

● PROGRAMMABLE FULL-SCALE

● SINGLE SUPPLY

● CASCADABLE OUTPUT

APPLICATIONS

● DIRECT PHOTOSENSOR DIGITIZATION

● CT SCANNER DAS

● INFRARED PYROMETER

● PRECISION PROCESS CONTROL

● LIQUID/GAS CHROMATOGRAPHY

● BLOOD ANALYSIS

Protected by US Patent #5841310

DESCRIPTION

The DDC112 is a dual input, wide dynamic range, chargedigitizing analog-to-digital (A/D) converter with 20-bit resolution. Low-level current output devices, such as photosensors, can be directly connected to its inputs. Charge integration is continuous as each input uses two integrators; while one is being digitized, the other is integrating.

For each of its two inputs, the DDC112 combines current-tovoltage conversion, continuous integration, programmable full-scale range, A/D conversion, and digital filtering to achieve a precision, wide dynamic range digital result. In addition to the internal programmable full-scale ranges, external integrating capacitors allow an additional user-settable full-scale range of up to 1000pC.

To provide single-supply operation, the internal A/D converter utilizes a differential input, with the positive input tied to V When the integration capacitor is reset at the beginning of each integration cycle, the capacitor charges to V charge is removed in proportion to the input current. At the end of the integration cycle, the remaining voltage is compared to V

REF

The high-speed serial shift register which holds the result of the last conversion can be configured to allow multiple DDC112 units to be cascaded, minimizing interconnections. The DDC112 is available in an SO-28 or TQFP-32 package and is offered in two performance grades.

REF

. This

AGNDAV

CAP1A CAP1A

IN1

CAP1B CAP1B

CAP2A CAP2A

IN2

CAP2B CAP2B

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.

PRODUCTION DATA information is current as of publication date. Products conform to specifications per the terms of Texas Instruments standard warranty. Production processing does not necessarily include testing of all parameters.

CHANNEL 1

Dual

Switched

Integrator

CHANNEL 2

Dual

Switched

Integrator

REF

∆Σ

Modulator

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Digital

Filter

TEST

DGNDDV

DCLK

DVALID

Digital

Input/Output

Control

CLK

CONV

DXMIT DOUT DIN

RANGE2 RANGE1 RANGE0

ABSOLUTE MAXIMUM RATINGS

AVDD to DVDD.......................................................................–0.3V to +6V

to AGND ..................................................................... –0.3V to +6V

to DGND ..................................................................... –0.3V to +6V

AGND to DGND ............................................................................... ±0.3V

Voltage to AGND ........................................... –0.3V to AVDD + 0.3V

REF

Digital Input Voltage to DGND .............................. –0.3V to DV

Digital Output Voltage to DGND ........................... –0.3V to DV

Package Power Dissipation ............................................. (T

Maximum Junction Temperature (T Thermal Resistance, SO, Thermal Resistance, TQFP,

Lead Temperature (soldering, 10s)............................................... +300°C

NOTE: (1) Stresses above those listed under cause permanent damage to the device. Exposure to absolute maximum conditions for extended periods may affect device reliability.

JMAX

....................................................+150°C/W

................................................+100°C/W

(1)

+ 0.3V

– TA)/

) ...................................... +150°C

Absolute Maximum Ratings

JMAX

may

ELECTROSTATIC DISCHARGE SENSITIVITY

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.

PACKAGE/ORDERING INFORMATION

MAXIMUM SPECIFICATION

PRODUCT LINEARITY ERROR RANGE PACKAGE-LEAD DESIGNATOR NUMBER

DDC112U

INTEGRAL TEMPERATURE PACKAGE ORDERING TRANSPORT

±0.025% Reading ±1.0ppm FSR

(1)

(2)

–40°C to +85°C SO-28 DW DDC112U Rails

MEDIA

"""""DDC112U/1K Tape and Reel

DDC112UK

±0.025% Reading ±1.0ppm FSR

0°C to +70°C SO-28 DW DDC112UK Rails

"""""DDC112UK/1K Tape and Reel

DDC112Y ±0.025% Reading ±1.0ppm FSR –40°C to +85°C TQFP-32 PJT DDC112Y/250 Tape and Reel

"""""DDC112Y/2K Tape and Reel

DDC112YK ±0.025% Reading ±1.0ppm FSR 0°C to +70°C TQFP-32 PJT DDC112YK/250 Tape and Reel

"""""DDC112YK/2K Tape and Reel

NOTES: (1) For the most current package and ordering information, see the Package Option Addendum located at the end of this data shee t. (2) Models with a slash (/) are available only in Tape and Reel in the quantities indicated (/1K indicates 1000 devices per reel). Ordering 1000 pieces of piece Tape and Reel.

DDC112U/1K

will get a single 1000-

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DDC112

SBAS085B

ELECTRICAL CHARACTERISTICS

At TA = +25°C, AVDD = DVDD = +5V, DDC112U, Y: T operation, and internal integration capacitors, unless otherwise noted.

PARAMETER CONDITIONS MIN TYP MAX MIN TYP MAX UNITS ANALOG INPUTS

External, Positive Full-Scale

Range 0 C

Internal, Positive Full-Scale

Range 1 47.5 50 52.5 ✻✻✻ pC Range 2 95 100 105 ✻✻✻ pC Range 3 142.5 150 157.5 ✻✻✻ pC Range 4 190 200 210 ✻✻✻ pC Range 5 237.5 250 262.5 ✻✻✻ pC Range 6 285 300 315 ✻✻✻ pC Range 7 332.5 350 367.5 ✻✻✻ pC

Negative Full-Scale Input –0.4% of Positive FS ✻ pC

DYNAMIC CHARACTERISTICS

Conversion Rate 2 3 kHz Integration Time, T Integration Time, T System Clock Input (CLK) 1 10 12 ✻✻15 MHz

INT INT

Non-Continuous Mode 50 ✻ µs

Data Clock (DCLK) 12 15 MHz

ACCURACY

Noise, Low-Level Current Input

Differential Linearity Error ±0.005% Reading ±0.5ppm Integral Linearity Error

(1)

SENSOR

(4)

No Missing Codes 20 ✻ Bits Input Bias Current T Range Error Range 5 (250pC) 5 ✻ % of FSR Range Error Match Range Sensitivity to V Offset Error Range 5, (250pC) ±200 ✻ ±600 ppm of FSR Offset Error Match DC Bias Voltage

(5)

REF

(5)

(6)

(Input VOS) ±0.05 ±2 ✻✻ mV

Power-Supply Rejection Ratio ±25 ±200 ✻✻ppm of FSR/V Internal Test Signal 13 ✻ pC Internal Test Accuracy ±10 ✻ %

PERFORMANCE OVER TEMPERATURE

Offset Drift ±0.5 ±3 Offset Drift Stability ±0.2 ✻ ±0.7 DC Bias Voltage Drift Applied to Sensor Input 3 ±1 µV/°C Input Bias Current Drift +25°C to +45°C 0.01 1 Input Bias Current T Range Drift Range Drift Match

(7)

(5)

REFERENCE

Voltage 4.000 4.096 4.200 ✻✻✻ V Input Current

(8)

DIGITAL INPUT/OUTPUT

Logic Levels

Input Current, I Data Format

(9)

POWER-SUPPLY REQUIREMENTS

Power-Supply Voltage AV Supply Current

Analog Current AV Digital Current DV

Total Power Dissipation 80 100 85 130 mW

TEMPERATURE RANGE

Specified Performance –40 +85 0 +70 °C Storage –60 +100 ✻✻°C

✻ Specifications same as DDC112U, Y. NOTES: (1) Input is less than 1% of full scale. (2) C (4) A best-fit line is used in measuring linearity. (5) Matching between side A and side B, not input 1 to input 2. (6) Voltage produced by the DDC112 at its input which is applied to the sensor. (7) Range drift does not include external reference drift. (8) Input reference current decreases with increasing T section). (9) Data format is Straight Binary with a small offset (see the

= 500µs, CLK = 10MHz, DDC112UK, YK: T

INT

= 333.3µs, CLK = 15MHz, V

INT

= +4.096V, continuous mode

REF

DDC112U, Y DDC112UK, YK

= 250pF 1000 ✻ pC

EXT

Continuous Mode 500 1,000,000 333.3 ✻ µs

(2)

= 0pF, Range 5 (250pC) 3.2 ✻

ppm of FSR

(3)

, rms = 25pF, Range 5 (250pC) 3.8 ✻ ppm of FSR, rms = 50pF, Range 5 (250pC) 4.2 6.0 ✻ 7 ppm of FSR, rms

FSR (max) ✻

±0.005% Reading ±0.5ppm

FSR (typ) ✻

±0.025% Reading ±1.0ppm

FSR (max) ✻

= +25°C 0.1 10 ✻✻ pA

All Ranges 0.1 0.5 ✻✻% of FSR

= 4.096 ±0.1V 1:1 ✻

REF

±100 ✻ ppm of FSR

(10)

ppm of FSR/°C

(10)

ppm of FSR/minute

(10)

= +75°C250

Range 5 (250pC) 25 0 25 50

(10)

✻✻ pA/°C ✻✻ pA

(10)

ppm/°C

Range 5 (250pC) ±0.05 ✻ ppm/°C

= 500µs 150 225 275 µA

INT

4.0

–0.3 +0.8 ✻✻V

+ 0.3

✻✻V

IOH = –500µA 4.5 ✻ V

IOL = 500µA 0.4 ✻ V

–10 +10 ✻✻µA

Straight Binary ✻

and DV

= +5V 14.8 15.2 mA

= +5V 1.2 1.8 mA

is the capacitance seen at the DDC112 inputs from wiring, photodiode, etc. (3) FSR is Full-Scale Range.

SENSOR

4.75 5.25 ✻✻V

Data Retrieval

section). (10) Ensured by design but not production tested.

INT

(see the

Voltage Reference

DDC112

SBAS085B

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PIN CONFIGURATION

Top View SO

IN1

AGND CAP1B CAP1B CAP1A CAP1A

TEST

CONV

CLK

DCLK

DXMIT

DIN

1 2 3 4 5 6 7

DDC112U

9 10 11 12 13 14

IN2

AGND

CAP2B

CAP2A

REF

AGND

RANGE2 (MSB)

RANGE1

RANGE0 (LSB)

DVALID

DOUT

DGND

PIN DESCRIPTIONS

PIN LABEL DESCRIPTION

1 IN1 Input 1: analog input for Integrators 1A and 1B. The

2 AGND Analog Ground 3 CAP1B External Capacitor for Integrator 1B 4 CAP1B External Capacitor for Integrator 1B 5 CAP1A External Capacitor for Integrator 1A 6 CAP1A External Capacitor for Integrator 1A 7AV 8 TEST Test Control Input. When HIGH, a test charge is applied

9 CONV Controls which side of the integrator is connected to

10 CLK System Clock Input, 10MHz Nominal 11 DCLK Serial Data Clock Input. This input operates the serial I/

12 DXMIT Serial Data Transmit Enable Input. When LOW, this

13 DIN Serial Digital Input. Used to cascade multiple DDC112s. 14 DV 15 DGND Digital Ground 16 DOUT Serial Data Output, Hi-Z when DXMIT is HIGH 17 DVALID Data Valid Output. A LOW value indicates valid data is

18 RANGE0 Range Control Input 0 (least significant bit) 19 RANGE1 Range Control Input 1 20 RANGE2 Range Control Input 2 (most significant bit) 21 AGND Analog Ground 22 V 23 CAP2A External Capacitor for Integrator 2A 24 CAP2A External Capacitor for Integrator 2A 25 CAP2B External Capacitor for Integrator 2B 26 CAP2B External Capacitor for Integrator 2B 27 AGND Analog Ground 28 IN2 Input 2: analog input for Integrators 2A and 2B. The

integrator that is active is set by the CONV input.

Analog Supply, +5V Nominal

to the A or B integrators on the next CONV transition.

input. In continuous mode; CONV HIGH → side A is integrating, CONV LOW → side B is integrating. CONV must be synchronized with CLK (see Figure 2).

O shift register.

input enables the internal serial shift register.

Digital Supply, +5V Nominal

available in the serial I/O register.

External Reference Input, +4.096V Nominal

REF

integrator that is active is set by the CONV input.

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DDC112

SBAS085B

DDC112

SBAS085B

TYPICAL CHARACTERISTICS

At TA = +25°C, characterization done with Range 5 (250pC), T

= 500µs, V

INT

= +4.096, AVDD = DVDD = +5V, and CLK = 10MHz, unless otherwise noted.

REF

Range 0

EXT

Noise (ppm of FSR, rms)

200 8000 1000600400

4.5 C

SENSOR

= 50pF

3.5

= 0pF

SENSOR

2.5

1.5

Noise (ppm of FSR, rms)

0.5

Range 5

30 4020 9010 10070 80 1050 60

NOISE vs C

SENSOR

Range 1

= 250pF)

Range 7

(pF)

SENSOR

NOISE vs INPUT LEVEL

Input Level (% of Full-Scale)

Range 2

= 50pF

SENSOR

= 0pF

SENSOR

NOISE vs T

INT

Noise (ppm of FSR, rms)

Range 5

1 10000.1 10010

(ms)

INT

NOISE vs TEMPERATURE

9 8

Range 1

7 6 5 4 3 2

Noise (ppm of FSR, rms)

= 0pF

SENSOR

Range 2

Range 3

Range 7

–40 –15 10 35 60 85

Temperature (°C)

2000

1500

1000

500

Range Drift (ppm)

–500

–1000

–1500

–40 –15 10 35 60 85

RANGE DRIFT vs TEMPERATURE

Ranges 1 - 7

(Internal Integration Capacitor)

Temperature (°C)

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IB vs TEMPERATURE

All Ranges

(pA)

0.1

0.01 25 35 45 55 65 75 85

Temperature (°C)

DDC112

SBAS085B

DDC112

SBAS085B

THEORY OF OPERATION

The basic operation of the DDC112 is illustrated in The device contains two identical input channels where each performs the function of current-to-voltage integration followed by a multiplexed analog-to-digital (A/D) conversion. Each input has two integrators so that the current-to-voltage integration can be continuous in time. The output of the four integrators are switched to one delta-sigma (∆Σ) converter via a four input multiplexer. With the DDC112 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. With a 10MHz system clock, the integrator combined with the deltasigma converter accomplishes a single 20-bit conversion in approximately 220µs. The results from side A and side B of each signal input are stored in a serial output shift register.

Figure 1.

The DVALID

output goes LOW when the shift register

contains valid data. The digital interface of the DDC112 provides the digital

results via a synchronous serial interface consisting of a data clock (DCLK), a transmit enable pin ( (DVALID

), a serial data output pin (DOUT), and a serial data

DXMIT

), a valid data pin

input pin (DIN). The DDC112 contains only one A/D converter, so the conversion process is interleaved between the two inputs, as shown in 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 is only used when multiple converters are cascaded and should be tied to DGND otherwise. Depending on T

, CLK, and DCLK, it is

INT

possible to daisy-chain over 100 converters. This greatly simplifies the interconnection and routing of the digital outputs in cases where a large number of converters are needed.

CAP1A CAP1A

IN1

CAP1B CAP1B

CAP2A CAP2A

IN2

CAP2B CAP2B

FIGURE 1. Block Diagram.

IN1, Integrator A

Input 1

Dual

Switched

Integrator

Input 2

Dual

Switched

Integrator

Integrate

AGNDAV

REF

∆Σ

Modulator

Digital

Filter

TEST

Control

CONV

Integrate

Digital

Input/Output

CLK

DGNDDV

DCLK

DVALID DXMIT DOUT DIN

RANGE2 RANGE1 RANGE0

IN1, Integrator B

IN2, Integrator A

IN2, Integrator B

Conversion in Progress

DVALID

Integrate

IN1B IN2B IN1A

Integrate

IN2A IN1B IN2B IN1A

FIGURE 2. Basic Integration and Conversion Timing for the DDC112 (continuous mode).

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Integrate

IN2A

DDC112

SBAS085B

DDC112

SBAS085B

CONV

CLK

INTA

INTB

REF1

REF2

RESET

A/D1A

Configuration of

Integrator A

REF

WaitConvert WaitConvertIntegrate

Reset

Wait

Integrator A

Voltage Output

FIGURE 4. Basic Integrator Timing Diagram as Illustrated in Figure 3.

REF2

REF1

A/D

REF1

A/D

REF

To Converter

REF

To Converter

INT

RESET

a) Reset Configuration

INT

RESET

c) Integrate Configuration

INT

RESET

b) Wait Configuration

INT

RESET

Wait

Reset

REF1

REF2

REF

To Converter

A/D

REF2

REF1

REF

To Converter

A/D

d) Convert Configuration

FIGURE 5. Diagrams for the Four Configurations of the Front End Integrators of the DDC112.

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DDC112

SBAS085B

DDC112

SBAS085B

A low-pass filter to reduce noise connects it to an operational amplifier configured as a buffer. This amplifier should have a unity-gain bandwidth greater than 4MHz, low noise, and input/output common-mode ranges that support V

REF

Following the buffer are capacitors placed close to the DDC112 V

pin. Even though the circuit in Figure 6 might

REF

appear to be unstable due to 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 droop in V

REF

which

produces large offsets.

DDC112 Frequency Response

The frequency response of the DDC112 is set by the front end integrators and is that of a traditional continuous time integrator, as shown in Figure 7. By adjusting T

, the user can

INT

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.

Test Mode

When TEST is used, pins IN1 and IN2 are grounded and

packets

of approximately 13pC charge are transferred to the

–10

–20

–30

Gain (dB)

–40

–50

0.1

INT

Frequency

INT

FIGURE 7. Frequency Response of the DDC112.

integration capacitors of both Input 1 and Input 2. This fixed charge can be transferred to the integration capacitors either once during an integration cycle or multiple times. In the case where multiple packets are transferred during one integration period, the 13pC charge is additive. This mode can be used in both the continuous and noncontinuous mode timing. The timing diagrams for test mode are shown in Figure 8. The top three lines in Figure 8 define the timing when one packet of 13pC is sent to the integration capacitors. The bottom three lines define the timing when multiple packets are sent to the integration capacitors.

100 T

INT

Action

CONV

TEST

Action

CONV

TEST

Test Mode Disabled

Integrate B

Test Mode Disabled

Integrate B Integrate A

Integrate A

Test Mode Enabled

13pC into B 13pC into A 13pC into B 13pC into A

Test Mode Enabled

13pC into B 26pC into A 39pC into B 52pC into A

Test Mode Disabled

Integrate B Integrate A

Test Mode Disabled

Integrate B Integrate A

FIGURE 8. Timing Diagram of the Test Mode of the DDC112.

CLK = 10MHz CLK = 15MHz

SYMBOL DESCRIPTION MIN TYP MAX MIN TYP MAX UNITS

Setup Time for Test Mode Enable 100 100 ns

Setup Time for Test Mode Disable 100 100 ns

Hold Time for Test Mode Enable 100 100 ns

From Rising Edge of TEST to the Edge of CONV 5.4 3.6 µs

while Test Mode Enabled

Rising Edge to Rising Edge of TEST 5.4 3.6 µs

TABLE III. Timing for the DDC112 in the Test Mode.

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DDC112

SBAS085B

DDC112

SBAS085B

During the 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, keeping track of 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 DDC112 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. As mentioned above, in the ncont states, the inputs to the DDC112 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 the ncont mode.

When power is first applied to the DDC112, 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.

TIMING EXAMPLES Cont Mode

A few timing diagrams will now be discussed to help illustrate the operation of the state machine. These are shown in Figures 10 through 19. Table V gives generalized timing specifications in units of CLK periods. Values in µs for

Table V can be easily found for a given CLK. For example, if CLK = 10MHz, then a CLK period = 0.1µs. t

in Table V

would then be 479.4µs.

SYMBOL DESCRIPTION VALUE (CLK periods)

Cont mode m/r/az cycle. 4794

Cont mode data ready. 4212 (t

1st ncont mode data ready. 4212 ±3

2nd ncont mode data ready. 4548

Ncont mode m/r/az cycle. 9108

4212 ±3(t

> 4794)

INT

= 4794)

INT

T ABLE V . Timing Specifications Generalized in CLK Periods.

Figure 10 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 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 DDC112. It stays LOW until

DXMIT

is taken LOW by the user. In Figure 10 and the following timing diagrams, it is assumed that

DXMIT

it taken LOW soon after DVALID goes LOW. The text

below the DVALID

pulse indicates the side of the data and arrows help match the data to the corresponding integration. The signals shown in Figures 10 through 19 are drawn at approximately the same scale.

In Figure 10, the first state is ncont state 1. The DDC112 always powers up in the ncont mode. In this case, the first state is 1 because CONV is initially HIGH. 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 by side A or side B. The time needed for the m/r/az cycle, t

, is the same time that

CONV

State

Integration

Status

m/r/az Status

mbsy

DVALID

SYMBOL

t = 0

Power-Up

DESCRIPTION VALUE (CLK = 10MHz) VALUE (CLK = 15MHz)

Cont mode m/r/az cycle. 479.4µs 319.6µs Cont mode data ready. 421.2µs(T

421.2 ±0.3µs(T

432154

Integrate BIntegrate A Integrate A Integrate B

m/r/az A m/r/az B m/r/az A

Side A

FIGURE 10. Continuous Mode Timing (CONV HIGH at power-up).

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Data

> 479.4µs) 280.8µs(T

INT

= 479.4µs) 280.8 ±0.2µs(T

INT

Side B

Data

Side A

Data

> 319.6µs)

INT

= 319.6µs)

INT

DDC112

SBAS085B

DDC112

SBAS085B

Ncont Mode

Figure 13 illustrates operation in the 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 DDC112 can advance to states 3 or 6, both sides A and B must be finished with the m/r/az cycle which takes time t m/r/az cycles are completed, time t

is needed to prepare

the next side for integration. This time is required for the ncont mode because the m/r/az cycle of the ncont mode is slightly different from that of the cont mode. After the first integration ends, DVALID

CONV

goes LOW in time t8. This is the

. When the

same time as in the cont mode. The second data will be ready in time t

after the first data is ready. One result of the

naming convention used in this application bulletin is that when the DDC112 is operating in the through both

ncont mode states

ncont mode

and

cont mode states

, it passes

. 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 called

cont mode states

ncont mode states

while those that do not are

. Since integrations are performed in the ncont mode, just not continuously, some cont mode states must be used in an ncont mode state pattern.

State

Integration

Status

m/r/az

Status

mbsy

DVALID

SYMBOL

23134 4 1 2

Int BInt AInt BInt A

m/r/az Bm/r/az A

Side A

Data

DESCRIPTION VALUE (CLK = 10MHz) VALUE (CLK = 15MHz)

1st ncont mode data ready. 421.2 ±0.3µs 280.8 ±0.2µs 2nd ncont mode data ready. 454.8µs 303.2µs Ncont mode m/r/az cycle. 910.8µs 607.2µs Prepare side for integration. ≥ 24.0µs ≥ 24.0µs

Side B

Data

m/r/az A m/r/az B

Side A

Data

Side B

Data

FIGURE 13. Non-Continuous Mode Timing.

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DDC112

SBAS085B

DDC112

SBAS085B

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 DDC112 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 9). The top two signals are different CONV patterns that produce the same state. This feature can be a little confusing at first, but it does allow flexibility in generating ncont mode CONV patterns. For example, the DDC112 Evaluation Fixture operates in the ncont mode by generating a square wave with pulse width < t

. Figure 17 illustrates operation in the ncont mode using

CONV1

CONV2

mbsy

a 50% duty cycle CONV signal with T

= 1620 CLK

INT

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 (t

). This must be done by the user with

proper timing of CONV. For example, if CONV is a square wave with T CLK periods long, therefore, t

= 3042 CLK periods, state 2 will only be 18

INT

will not be met.

State

FIGURE 16. Equivalent CONV Signals in Non-Continuous Mode.

CONV

State

Integration

Status

mbsy

DVALID

Int A

Side A

Data

23134 4 1 2

23134 41

Int BInt AInt B

Side B

Data

Side A

Data

FIGURE 17. Non-Continuous Mode Timing with a 50% Duty Cycle CONV Signal.

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DDC112

SBAS085B

DDC112

SBAS085B

SPECIAL CONSIDERATIONS

NCONT MODE INTEGRATION TIME

The DDC112 uses a relatively fast clock. For CLK = 10MHz, this allows T should be synchronized to CLK. However, for the internal measurement, reset and auto-zero operations, a slower clock is more efficient. The DDC112 divides CLK by six and uses this slower clock with a period of 600ns to run the m/r/ az cycle and data ready logic.

Because of the divider, it is possible for the integration time to be a non-integer number of slow clock periods. example, if T there will be 833 1/3 slow clocks in an integration period. This non-integer relationship between T period causes the number of rising and falling slow clock edges within an integration period to change from integration to integration. The digital coupling of these edges to the integrators will in turn change from integration to integration which produces noise. The change in the clock edges is not random, but will repeat every 3 integrations. The coupling noise on the integrators appears as a tone with a frequency equal to the rate at which the coupling repeats.

To avoid this problem in cont mode, the internal slow clock is shut down after the m/r/az cycle is complete when it is no longer needed. It starts up again just after the next integration begins. Since the slow clock is always off when CONV toggles, the same number of slow clock edges fall within an integration period regardless of its length. Therefore, T

≥ 4794 CLK periods will not produce the coupling

INT

problem described above. For the ncont mode however, the slow clock must always be

left running. The m/r/az cycle is not completed before an integration ends. It is then possible to have digital coupling to the integrators. The digital coupling noise depends heavily on the layout of the printed circuit board used for the DDC112. For solid grounds and power supplies with good bypassing, it is possible to greatly reduce the coupling. However, for ensuring the best performance in the ncont mode, the integration time should be chosen to be an integer multiple of 1/(2f

SLOWCLOCK

should be an integer multiple of 300ns—T A better choice would be T

DATA READY

The DVALID signal which indicates that data is ready is generated using the internal slow clock. The phase relationship between this clock and CLK is set when power is first applied and is random. Since CONV is synchronized with CLK, it will have a random phase relationship with respect to the slow clock. When T shut down as described above. This shutdown process synchronizes the internal clock with CONV so that the time between when CONV toggles to when (t

and t8) is fixed.

to be adjusted in steps of 100ns since CONV

INT

= 5000 CLK periods (500µs for CLK = 10MHz),

INT

and the slow clock

INT

). For CLK = 10MHz, the integration time

= 100µs is not.

= 99µs.

INT

> t6, the slow clock will temporarily

INT

DVALID

goes LOW

For

For T

≤ t6, the internal slow clock, is not allowed to shut

INT

down and the synchronization never occurs. Therefore, the time between CONV toggling and DVALID

indicating data is ready has uncertainty due to the random phase relationship between CONV and the slow clock. This variation is ±1/(2f

SLOWCLOCK

) or ±3/f

. The timing to the second DVALID

CLK

in the ncont mode will not have a variation since it is triggered off the first data ready (t

) and both are derived

from the slow clock. Polling DVALID

to determine when data is ready eliminates any concern about the variation in timing since the readback is automatically adjusted as needed. If the data readback is triggered off the toggling of CONV directly (instead of polling), then waiting the maximum value of t

or t8 insures that

data will always be ready before readback occurs.

Data Retrieval

In the continuous and noncontinuous modes of operation, the data from the last conversion is available for retrieval with the falling edge of DVALID of

DXMIT

in combination with the data clock (DCLK) will

(see Figure 22). The falling edge

initiate the serial transmission of the data from the DDC112. Typically, data is retrieved from the DDC112 as soon as

DVALID

falls and completed before the next CONV transition from HIGH to LOW or LOW to HIGH occurs. If this is not the case, care should be taken to stop activity on DCLK and consequently DOUT by at least 10µs around a CONV transition. If this caution is ignored it is possible that the integration that is being initiated by CONV will have additional noise introduced.

The serial output data at DOUT is transmitted in Straight Binary Code per Table VIII. An output offset has been built into the DDC112 to allow for the measurement of input signals near and below zero. Board leakage up to

≈ –0.4%

of the positive full-scale can be tolerated before the digital output clips to all zeroes.

CODE INPUT SIGNAL

1111 1111 1111 1111 1111 FS 1111 1111 1111 1111 1110 FS – 1LSB 0000 0001 0000 0000 0001 +1LSB 0000 0001 0000 0000 0000 Zero 0000 0000 0000 0000 0000 –0.4% FS

TABLE VIII. Straight Binary Code Table.

Cascading Multiple Converters

Multiple DDC112 units can be connected in serial or parallel configurations, as illustrated in Figures 20 and 21.

DOUT can be used with DIN to devices together to minimize wiring. In this mode of operation, the serial data output is shifted through multiple DDC112s, as illustrated in Figure 20.

prevents DIN from floating when

PULLUP

Care should be taken to keep the capacitive load on DOUT as low as possible when running CLK=15MHz.

daisy-chain

several DDC112

DXMIT

is HIGH.

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DDC112

SBAS085B

DDC112

SBAS085B

CLK

DVALID

DXMIT

DCLK

(1)

DIN

DOUT

NOTE: (1) Disable DCLK (preferably LOW) when DXMIT is HIGH.

Output Disabled

Input A

Bit 1

MSB

Output Enabled

22A, t22B

Input E

Bit 20

Input F

LSB LSB Output DisabledMSB

Bit 1

Input F

Bit 20

Output Disabled

FIGURE 23. Timing Diagram When Using the DIN Function of the DDC112.

CLK = 10MHz CLK = 15MHz

SYMBOL DESCRIPTION MIN TYP MAX MIN TYP MAX UNITS

Set-Up Time From DIN to Rising Edge of DCLK 10 5 ns

Hold Time For DIN After Rising Edge of DCLK 10 10 ns

Hold Time for DXMIT HIGH Before Falling 2 1.33 µs

Edge of DVALID

TABLE X. Timing for the DDC112 Data Retrieval Using DIN.

RETRIEVAL (CONTINUOUS MODE)

This is the most straightforward method. Data retrieval begins soon after DVALID CONV toggles, see Figure 24. For best performance, data retrieval must stop t the most appropriate for longer integration times. The maximum time available for readback is T For DCLK and CLK = 10MHz, the maximum number of DDC112s that can be daisy-chained together is:

Where τ T

= 1000µs and DCLK = 10MHz, the maximum number of

INT

BEFORE

CONV TOGGLES

goes LOW and finishes before

before CONV toggles. This method is

– t27 – t28.

INT

– .431 240µ

INT

DCLK

is the period of the data clock. For example, if

DCLK

RETRIEVAL

AFTER

CONV TOGGLES

(CONTINUOUS MODE)

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 t before beginning. Figure 25 shows an example of this. The maximum time available for retrieval is t (421.2µs – 10µs – 2µs for CLK = 10MHz), regardless of T The maximum number of DDC112s that can be daisychained together is:

409 240. µs

DCLK

For DCLK = 10MHz, the maximum number of DDC112s is

102.

after CONV toggles

– t29 – t

DDC112s is:

INT

1000 431 2

µµ

– .

40 100

()( )

142 2 142 112

=→

DDC s

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DDC112

SBAS085B

DDC112

SBAS085B

RETRIEVAL

BEFORE

AND

AFTER

CONV

TOGGLES (CONTINUOUS MODE)

For the absolute maximum time for data retrieval, data can be retrieved

before and after

CONV toggles. Nearly all of T

INT

is available for data retrieval. Figure 26 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 DDC112s that can be daisy-chained together is:

Tss

––20 2

µµ

INT

DCLK

For T

= 500µs and DCLK = 10MHz, the maximum number

INT

of DDC112s is 119.

RETRIEVAL: NONCONTINUOUS MODE

Retrieving in noncontinuous mode is slightly different as compared with the continuous mode. As shown in Figure 27 and described in detail in Application Bulletin SBAA024

(available for download at www.ti.com), DVALID in time t shorter than this time, all of t

after the first integration completes. If T

is available to retrieve data

before the other side’s data is ready. For T

goes LOW

> t30, the first

INT

integration’s 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 t

– (T

– t30). The second integration’s

INT

data must be retrieved before the next round of integrations begin. 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 (t completed before new data is ready (t

and t29) and be

POWER-UP SEQUENCING

Prior to power-up, all digital and analog input pins must be LOW. At the time of power-up, these signal inputs can be biased to a voltage other than 0V, however, they should never exceed AV up is used to determine which side (A or B) will be integrated first. Before integrations can begin though, CONV must toggle; see Figure 28.

or DVDD. The level of CONV at power-

CONV

DVALID

DXMIT

DCLK

DOUT

SYMBOL DESCRIPTION MIN TYP MAX MIN TYP MAX UNITS

••• ••• ••• ••• ••• •••

••• ••• •••

Hold Time for DXMIT HIGH Before Falling 2 1.33 µs

Data Retrieval Shutdown Before Edge of CONV 10 10 µs

Data Retrieval Start-Up After dge of CONV 10 10 µs

INT

Edge of DVALID

INT

Side B

Data

••• ••• •••

Side A

Data

CLK = 10MHz CLK = 15MHz

INT

FIGURE 26. Readback

Before and After

CONV Toggles.

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DDC112

SBAS085B

DDC112

SBAS085B

Input shielding practices should be taken into consideration when designing the circuit layout for the DDC112. The inputs to the DDC112 are high impedance and extremely sensitive to extraneous noise. Leakage currents between the PCB traces can exceed the input bias current of the DDC112 if shielding is not implemented. Figure 30 illustrates an acceptable approach to this problem. A PC ground plane is placed around the inputs of the DDC112. This shield helps minimize coupled noise into the input pins. Additionally, the pins that

DDC112

10µF

< 10Ω

0.1µF

Separate +5V Supplies

0.1µF

are used for the external integration capacitors should be guarded by a ground plane when the external capacitors are used.

The approach above reduces leakage affects 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 DDC112.

IN1 IN2

Analog

Ground

Analog

Ground

Shield

external

caps when

used

Analog

Power

1 2 3 4 5 6 7 8

9 10 11 12 13 14

DDC112U

28 27 26 25 24 23 22 21 20 19 18 17 16 15

Analog

Ground

Shield

external

caps when

used

Analog Ground

One +5V Supply

FIGURE 29. Power Supply Connection Options.

Digital I/O

and

Digital Power

Digital I/O

and

Digital Power

FIGURE 30. Recommended Shield for DDC112U Layout

Design.

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DDC112

SBAS085B

PACKAGE OPTION ADDENDUM

www.ti.com

5-Oct-2007

PACKAGING INFORMATION

Orderable Device Status

(1)

Package

Type

Package Drawing

Pins Package

Qty

Eco Plan

DDC112U ACTIVE SOIC DW 28 20 Green (RoHS &

no Sb/Br)

DDC112U/1K ACTIVE SOIC DW 28 1000 Green (RoHS &

no Sb/Br)

DDC112U/1KG4 ACTIVE SOIC DW 28 1000 Green (RoHS &

no Sb/Br)

DDC112UG4 ACTIVE SOIC DW 28 20 Green (RoHS &

no Sb/Br)

DDC112UK ACTIVE SOIC DW 28 20 Green (RoHS &

no Sb/Br)

DDC112UK/1K ACTIVE SOIC DW 28 1000 Green (RoHS &

no Sb/Br)

DDC112UK/1KG4 ACTIVE SOIC DW 28 1000 Green (RoHS &

no Sb/Br)

DDC112UKG4 ACTIVE SOIC DW 28 20 Green (RoHS &

no Sb/Br)

DDC112Y/250 ACTIVE TQFP PJT 32 250 Green (RoHS &

no Sb/Br)

DDC112Y/250G4 ACTIVE TQFP PJT 32 250 Green (RoHS &

no Sb/Br)

DDC112Y/2K ACTIVE TQFP PJT 32 2000 Green (RoHS &

no Sb/Br)

DDC112Y/2KG4 ACTIVE TQFP PJT 32 2000 Green (RoHS &

no Sb/Br)

DDC112YK/250 ACTIVE TQFP PJT 32 250 Green (RoHS &

no Sb/Br)

DDC112YK/250G4 ACTIVE TQFP PJT 32 250 Green (RoHS&

no Sb/Br)

DDC112YK/2K ACTIVE TQFP PJT 32 2000 Green (RoHS &

no Sb/Br)

DDC112YK/2KG4 ACTIVE TQFP PJT 32 2000 Green (RoHS &

no Sb/Br)

(1)

The marketing status values are defined asfollows:

ACTIVE: Product device recommended for new designs. LIFEBUY: TI has announced that the devicewill be discontinued, and alifetime-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 isnot in production. Samples mayor may not be available. OBSOLETE: TI has discontinued the production ofthe device.

(2)

Lead/Ball Finish MSL Peak Temp

CU NIPDAU Level-1-260C-UNLIM

CU NIPDAU Level-2-260C-1 YEAR

(3)

(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 andadditional product content details.

TBD: The Pb-Free/Green conversion plan has notbeen 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 aresuitable for use in specifiedlead-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 exceed0.1% by weight in homogeneousmaterial)

Addendum-Page 1

PACKAGE OPTION ADDENDUM

www.ti.com

(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.

5-Oct-2007

Addendum-Page 2

PACKAGE MATERIALS INFORMATION

www.ti.com

TAPE AND REEL INFORMATION

11-Mar-2008

*All dimensions are nominal

Device Package

Type

DDC112U/1K SOIC DW 28 1000 330.0 32.4 11.35 18.67 3.1 16.0 32.0 Q1

DDC112UK/1K SOIC DW 28 1000 330.0 32.4 11.35 18.67 3.1 16.0 32.0 Q1

DDC112Y/250 TQFP PJT 32 250 330.0 16.4 9.6 9.6 1.5 12.0 16.0 Q2

DDC112Y/2K TQFP PJT 32 2000 330.0 16.4 9.6 9.6 1.5 12.0 16.0 Q2

DDC112YK/250 TQFP PJT 32 250 330.0 16.4 9.6 9.6 1.5 12.0 16.0 Q2

DDC112YK/2K TQFP PJT 32 2000 330.0 16.4 9.6 9.6 1.5 12.0 16.0 Q2

Package Drawing

Pins SPQ Reel

Diameter

(mm)

Reel

Width

W1 (mm)

A0 (mm) B0 (mm) K0 (mm) P1

(mm)W(mm)

Pin1

Quadrant

Pack Materials-Page 1

PACKAGE MATERIALS INFORMATION

www.ti.com

11-Mar-2008

*All dimensions are nominal

Device Package Type Package Drawing Pins SPQ Length (mm) Width (mm) Height (mm)

DDC112U/1K SOIC DW 28 1000 346.0 346.0 49.0

DDC112UK/1K SOIC DW 28 1000 346.0 346.0 49.0

DDC112Y/250 TQFP PJT 32 250 346.0 346.0 33.0

DDC112Y/2K TQFP PJT 32 2000 346.0 346.0 33.0

DDC112YK/250 TQFP PJT 32 250 346.0 346.0 33.0

DDC112YK/2K TQFP PJT 32 2000 346.0 346.0 33.0

Pack Materials-Page 2

MECHANICAL DATA

MPQF112 – NOVEMBER 2001

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TEXAS INSTRUMENTS DDC112 Technical data

Specifications and Main Features

Frequently Asked Questions

User Manual