Datasheet

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ADS7844

12-Bit, 8-Channel Serial Output Sampling

ANALOG-TO-DIGITAL CONVERTER

FEATURES

● SINGLE SUPPLY: 2.7V to 5V

● 8-CHANNEL SINGLE-ENDED OR

4-CHANNEL DIFFERENTIAL INPUT

● UP TO 200kHz CONVERSION RATE

● ±1 LSB MAX INL AND DNL

● NO MISSING CODES

● 72dB SINAD

● SERIAL INTERFACE

● 20-LEAD QSOP AND

20-LEAD SSOP PACKAGES

● ALTERNATE SOURCE FOR MAX147

DESCRIPTION

The ADS7844 is an 8-channel, 12-bit sampling analog-to-

digital converter (ADC) with a synchronous serial interface.

Typical power dissipation is 3mW at a 200kHz throughput

rate and a +5V supply. The reference voltage (V

REF

) can be

varied between 100mV and V

, providing a corresponding

input voltage range of 0V to V

REF

. The device includes a

shutdown mode that reduces power dissipation to under

1µW. The ADS7844 is ensured down to 2.7V operation.

Low power, high speed, and onboard multiplexer make the

ADS7844 ideal for battery-operated systems such as personal

digital assistants, portable multichannel data loggers, and

measurement equipment. The serial interface also provides

low-cost isolation for remote data acquisition. The ADS7844

is available in a 20-lead QSOP package and the MAX147

equivalent 20-lead SSOP package and is ensured over the

–40°C to +85°C temperature range.

APPLICATIONS

● DATA ACQUISITION

● TEST AND MEASUREMENT

● INDUSTRIAL PROCESS CONTROL

● PERSONAL DIGITAL ASSISTANTS

● BATTERY-POWERED SYSTEMS

CDAC

SAR

Comparator

Eight

Channel

Multiplexer

Serial

Interface

and

Control

CH4

CH5

CH6

CH7

COM

REF

CH0

CH1

CH2

CH3

SHDN

DIN

DOUT

BUSY

DCLK

ADS7844

SBAS100A – JANUARY 1998 – REVISED OCTOBER 2003

www.ti.com

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.

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.

Summary of content (22 pages)

PAGE 1
ADS 784 4 ADS7844 ADS 784 4 SBAS100A – JANUARY 1998 – REVISED OCTOBER 2003 12-Bit, 8-Channel Serial Output Sampling ANALOG-TO-DIGITAL CONVERTER FEATURES DESCRIPTION ● SINGLE SUPPLY: 2.7V to 5V The ADS7844 is an 8-channel, 12-bit sampling analog-todigital converter (ADC) with a synchronous serial interface. Typical power dissipation is 3mW at a 200kHz throughput rate and a +5V supply.
PAGE 2
SPECIFICATION: +5V At TA = –40°C to +85°C, +VCC = +5V, VREF = +5V, fSAMPLE = 200kHz, and fCLK = 16 • fSAMPLE = 3.2MHz, unless otherwise noted. ADS7844E, N PARAMETER ANALOG INPUT Full-Scale Input Span Absolute Input Range CONDITIONS MIN Positive Input - Negative Input Positive Input Negative Input 0 –0.2 –0.2 TYP Capacitance Leakage Current VREF +VCC +0.2 +1.25 ✻ ✻ ✻ TYP 0.15 0.1 30 70 ±2 ±0.5 ±3 1.0 ±4 1.
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SPECIFICATION: +2.7V At TA = –40°C to +85°C, +VCC = +2.7V, VREF = +2.5V, fSAMPLE = 125kHz, and fCLK = 16 • fSAMPLE = 2MHz, unless otherwise noted. ADS7844E, N PARAMETER ANALOG INPUT Full-Scale Input Span Absolute Input Range CONDITIONS MIN Positive Input - Negative Input Positive Input Negative Input 0 –0.2 –0.2 TYP Capacitance Leakage Current VREF +VCC +0.2 +0.2 ✻ ✻ ✻ TYP 0.15 0.1 30 70 ±2 ±0.5 ±3 1.0 ±4 1.
PAGE 4
PACKAGE/ORDERING INFORMATION(1) PRODUCT MINIMUM RELATIVE ACCURACY (LSB) MAXIMUM GAIN ERROR (LSB) SPECIFIED TEMPERATURE RANGE PACKAGE-LEAD PACKAGE DESIGNATOR ORDERING NUMBER TRANSPORT MEDIA, QUANTITY ±2 " " " ±1 " " " ±4 " " " ±3 " " " –40°C to +85°C " " " –40°C to +85°C " " " QSOP-20 " SSOP-20 " QSOP-20 " SSOP-20 " DBQ " DB " DBQ " DB " ADS7844E ADS7844E/2K5 ADS7844N ADS7844N/1K ADS7844EB ADS7844EB/2K5 ADS7844NB ADS7844NB/1K Rails, 56 Tape and Reel, 2500 Rails, 68 Tape and Reel,1000 Rails, 56
PAGE 5
TYPICAL PERFORMANCE CURVES:+5V At TA = +25°C, +VCC = +5V, VREF = +5V, fSAMPLE = 200kHz, and fCLK = 16 • fSAMPLE = 3.2MHz, unless otherwise noted. FREQUENCY SPECTRUM (4096 Point FFT; fIN = 10.3kHz, –0.2dB) 0 0 –20 –20 –40 –40 Amplitude (dB) Amplitude (dB) FREQUENCY SPECTRUM (4096 Point FFT; fIN = 1,123Hz, –0.
PAGE 6
TYPICAL PERFORMANCE CURVES:+2.7V At TA = +25°C, +VCC = +2.7V, VREF = +2.5V, fSAMPLE = 125kHz, and fCLK = 16 • fSAMPLE = 2MHz, unless otherwise noted. FREQUENCY SPECTRUM (4096 Point FFT; fIN = 10.6kHz, –0.2dB) 0 0 –20 –20 –40 –40 Amplitude (dB) –60 –80 –100 –80 –100 –120 –120 0 15.6 31.3 46.9 62.5 0 15.6 31.3 46.9 62.
PAGE 7
TYPICAL PERFORMANCE CURVES:+2.7V (CONT) At TA = +25°C, +VCC = +2.7V, VREF = +2.5V, fSAMPLE = 125kHz, and fCLK = 16 • fSAMPLE = 2MHz, unless otherwise noted. POWER DOWN SUPPLY CURRENT vs TEMPERATURE 400 140 350 120 Supply Current (nA) Supply Current (µA) SUPPLY CURRENT vs TEMPERATURE 300 250 200 100 80 60 40 150 20 100 –40 –20 0 20 40 60 80 –40 100 –20 0 40 60 80 100 DIFFERENTIAL LINEARITY ERROR vs CODE 1.00 1.00 0.75 0.75 0.50 0.
PAGE 8
TYPICAL PERFORMANCE CURVES (CONT) At TA = +25°C, +VCC = +2.7V, VREF = +2.5V, fSAMPLE = 125kHz, and fCLK = 16 • fSAMPLE = 2MHz, unless otherwise noted.
PAGE 9
THEORY OF OPERATION ANALOG INPUT Figure 2 shows a block diagram of the input multiplexer on the ADS7844. The differential input of the converter is derived from one of the eight inputs in reference to the COM pin or four of the eight inputs. Table I and Table II show the relationship between the A2, A1, A0, and SGL/DIF control bits and the configuration of the analog multiplexer. The control bits are provided serially via the DIN pin, see the Digital Interface section of this data sheet for more details.
PAGE 10
Likewise, the noise or uncertainty of the digitized output will increase with lower LSB size. With a reference voltage of 100mV, the LSB size is 24µV. This level is below the internal noise of the device. As a result, the digital output code will not be stable and vary around a mean value by a number of LSBs. The distribution of output codes will be gaussian and the noise can be reduced by simply averaging consecutive conversion results or applying a digital filter.
PAGE 11
Bit 7 (MSB) Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 (LSB) S A2 A1 A0 — SGL/DIF PD1 PD0 The SGL/DIF bit controls the multiplexer input mode: either single-ended (HIGH) or differential (LOW). In single-ended mode, the selected input channel is referenced to the COM pin. In differential mode, the two selected inputs provide a differential input. See Tables I and II and Figure 2 for more information. The last two bits (PD1 - PD0) select the powerdown mode as shown in Table V.
PAGE 12
PD1 PD0 0 0 Description SYMBOL DESCRIPTION MIN Power-down between conversions. When each conversion is finished, the converter enters a low power mode. At the start of the next conversion, the device instantly powers up to full power. There is no need for additional delays to assure full operation and the very first conversion is valid. tACQ Acquisition Time 1.
PAGE 13
Data Format FS = Full-Scale Voltage = VREF 1 LSB = VREF/4096 1 LSB 1000 fCLK = 16 • fSAMPLE Supply Current (µA) The ADS7844 output data is in straight binary format as shown in Figure 7. This figure shows the ideal output code for the given input voltage and does not include the effects of offset, gain, or noise. 100 fCLK = 2MHz 10 TA = 25°C +VCC = +2.7V VREF = +2.5V PD1 = PD0 = 0 11...111 Output Code 11...110 1 11...101 1k 10k 100k 1M fSAMPLE (Hz) 00...010 FIGURE 8.
PAGE 14
high power devices. The degree of error in the digital output depends on the reference voltage, layout, and the exact timing of the external event. The error can change if the external event changes in time with respect to the DCLK input. With this in mind, power to the ADS7844 should be clean and well bypassed. A 0.1µF ceramic bypass capacitor should be placed as close to the device as possible.
PAGE 15
PACKAGE OPTION ADDENDUM www.ti.
PAGE 16
PACKAGE OPTION ADDENDUM www.ti.com 16-Aug-2012 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.
PAGE 17
PACKAGE MATERIALS INFORMATION www.ti.com 16-Aug-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 8.0 16.0 Q1 ADS7844E/2K5 SSOP DBQ 20 2500 330.0 16.4 6.5 9.0 2.1 ADS7844EB/2K5 SSOP DBQ 20 2500 330.0 16.4 6.5 9.0 2.1 8.0 16.0 Q1 ADS7844N/1K SSOP DB 20 1000 330.0 16.4 8.2 7.5 2.5 12.0 16.
PAGE 18
PACKAGE MATERIALS INFORMATION www.ti.com 16-Aug-2012 *All dimensions are nominal Device Package Type Package Drawing Pins SPQ Length (mm) Width (mm) Height (mm) ADS7844E/2K5 SSOP DBQ 20 2500 367.0 367.0 38.0 ADS7844EB/2K5 SSOP DBQ 20 2500 367.0 367.0 38.0 ADS7844N/1K SSOP DB 20 1000 367.0 367.0 38.0 ADS7844NB/1K SSOP DB 20 1000 367.0 367.0 38.
PAGE 19
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PAGE 21
MECHANICAL DATA MSSO002E – JANUARY 1995 – REVISED DECEMBER 2001 DB (R-PDSO-G**) PLASTIC SMALL-OUTLINE 28 PINS SHOWN 0,38 0,22 0,65 28 0,15 M 15 0,25 0,09 8,20 7,40 5,60 5,00 Gage Plane 1 14 0,25 A 0°–ā8° 0,95 0,55 Seating Plane 2,00 MAX 0,10 0,05 MIN PINS ** 14 16 20 24 28 30 38 A MAX 6,50 6,50 7,50 8,50 10,50 10,50 12,90 A MIN 5,90 5,90 6,90 7,90 9,90 9,90 12,30 DIM 4040065 /E 12/01 NOTES: A. B. C. D. All linear dimensions are in millimeters.
PAGE 22
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