Datasheet

ManualsBrandsLINEAR TECHNOLOGY ManualsData collecting ICsData acquisition IC - AD converter (ADC) Internal QFN 38

LTC2497

2497fa

SOURCE

(Ω)

+FS ERROR (ppm)

–20

1k 100k

2497 TA01b

–40

–60

–80

10 100 10k

= 5V

REF

= 5V

= 3.75V

–

= 1.25V

= GND

= 25°C

= 1mF

16-Bit 8-/16-Channel

ADC with Easy Drive Input Current

Cancellation and I

C Interface

Typical applicaTion

FeaTures

applicaTions

DescripTion

The LTC

2497 is a 16-channel (eight differential), 16-bit,

No Latency DS

ADC with Easy Drive technology and a

2-wire, I

C interface. The patented sampling scheme elimi-

nates dynamic input current errors and the shortcomings

of on-chip buffering through automatic cancellation of

differential input current. This allows large external source

impedances and rail-to-rail input signals to be directly

digitized while maintaining exceptional DC accuracy.

The LTC2497 includes an integrated oscillator. This device

can be configured to measure an external signal from com-

binations of 16 analog input channels operating in single-

ended or differential modes. It automatically rejects line

frequencies of 50Hz and 60Hz simultaneously.

The LTC2497 allows a wide, common mode input range

(0V to V

), independent of the reference voltage. Any

combination of single-ended or differential inputs can be

selected and the first conversion, after a new channel is

selected, is valid. Access to the multiplexer output enables

optional external amplifiers to be shared between all

analog inputs and auto calibration continuously removes

their associated offset and drift.

L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and

No Latency ∆∑ and Easy Drive are trademarks of Linear Technology Corporation. All other

trademarks are the property of their respective owners.

Easy Drive

Data Acquisition System

Up to Eight Differential or 16 Single-Ended Inputs

Easy Drive

Technology Enables Rail-to-Rail

Inputs with Zero Differential Input Current

Directly Digitizes High Impedance Sensors with

Full Accuracy

2-Wire I

C Interface with 27 Addresses Plus One

Global Address for Synchronization

600nV RMS Noise (0.02LSB Transition Noise)

GND to V

Input/Reference Common Mode Range

Simultaneous 50Hz/60Hz Rejection

2ppm INL, No Missing Codes

1ppm Offset and 15ppm Full-Scale Error

No Latency: Digital Filter Settles in a Single Cycle,

Even After a New Channel Is Selected

Single Supply, 2.7V to 5.5V Operation (0.8mW)

Internal Oscillator

Tiny 5mm × 7mm QFN Package

Direct Sensor Digitizer

Direct Temperature Measurement

Instrumentation

Industrial Process Control

+FS Error vs R

SOURCE

at IN

and IN

–

SCL

SDA

REF

MUXOUT/

ADCIN

MUXOUT/

ADCIN

2.7V TO 5.5V

10µF

1.7k

COM

REF

–

16-BIT ∆∑ ADC

WITH EASY DRIVE

16-CHANNEL

MUX

–

2497 TA01

2-WIRE

C INTERFACE

CH0

CH1

•

CH7

CH8

CH15

0.1µF

OSC

Summary of content (28 pages)

PAGE 1
LTC2497 16-Bit 8-/16-Channel DS ADC with Easy Drive Input Current Cancellation and I2C Interface Features n n n n n n n n n n n n n Description Up to Eight Differential or 16 Single-Ended Inputs Easy DriveTM Technology Enables Rail-to-Rail Inputs with Zero Differential Input Current Directly Digitizes High Impedance Sensors with Full Accuracy 2-Wire I2C Interface with 27 Addresses Plus One Global Address for Synchronization 600nV RMS Noise (0.
PAGE 2
LTC2497 Absolute Maximum Ratings Pin Configuration (Notes 1, 2) GND GND GND fO CA0 CA2 CA1 TOP VIEW Supply Voltage (VCC).................................... –0.3V to 6V Analog Input Voltage (CH0-CH15, COM).....................–0.3V to (VCC + 0.3V) REF+, REF –. ...............................–0.3V to (VCC + 0.3V) ADCINN, ADCINP, MUXOUTP MUXOUTN...............–0.3V to (VCC + 0.3V) Digital Input Voltage......................–0.3V to (VCC + 0.3V) Digital Output Voltage....................–0.
PAGE 3
LTC2497 Electrical Characteristics The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. (Notes 3, 4) PARAMETER CONDITIONS Resolution (No Missing Codes) 0.1V ≤ VREF ≤ VCC, –FS ≤ VIN ≤ +FS (Note 5) MIN TYP MAX UNITS Integral Nonlinearity 5V ≤ VCC ≤ 5.5V, VREF = 5V, VIN(CM) = 2.5V (Note 6) 2.7V ≤ VCC ≤ 5.5V, VREF = 2.5V, VIN(CM) = 1.25V (Note 6) Offset Error 2.
PAGE 4
LTC2497 Analog Input and Reference The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. (Note 3) IDC_LEAK(IN–) IN– DC Leakage Current IDC_LEAK(REF+) REF+ DC Leakage Current IDC_LEAK(REF–) REF– DC Leakage Current tOPEN MUX Break-Before-Make QIRR MUX Off Isolation Sleep Mode, IN– = GND l –10 1 10 nA Sleep Mode, REF+ = VCC l –100 1 100 nA Sleep Mode, REF– = GND l –100 1 100 nA VIN = 2VP-P DC to 1.
PAGE 5
LTC2497 Digital Inputs And Digital Outputs The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. (Note 3) SYMBOL PARAMETER CONDITIONS fEOSC External Oscillator Frequency Range (Note 16) MAX UNITS l tHEO tLEO tCONV Conversion Time MIN 10 4000 kHz External Oscillator High Period l 0.125 100 µs External Oscillator Low Period l 0.125 100 µs l 144.1 149.
PAGE 6
LTC2497 Typical Performance Characteristics –45°C 1 2 25°C 0 85°C –1 Integral Nonlinearity (VCC = 5V, VREF = 2.5V) 3 VCC = 5V VREF = 2.5V VIN(CM) = 1.25V fO = GND 1 2 INL (ppm OF VREF) 2 –45°C, 25°C, 85°C 0 –2 –1 –3 –2.5 –2 –1.5 –1 –0.5 0 0.5 1 1.5 INPUT VOLTAGE (V) 2 –3 –1.25 2.5 –0.75 4 12 8 85°C 25°C 0 TUE (ppm OF VREF) TUE (ppm OF VREF) 8 –45°C –4 VCC = 5V VREF = 2.5V VIN(CM) = 1.25V fO = GND 85°C –45°C 0 –4 –0.75 0 –0.2 VCC = 5V VREF = 5V VIN = 0V fO = GND 0.
PAGE 7
LTC2497 Typical Performance Characteristics 0.1 0 –0.1 308 308 306 304 302 –0.2 –0.3 310 0 1 2 3 VREF (V) 300 –45 –30 –15 5 4 2497 G10 –20 –40 REJECTION (dB) REJECTION (dB) –40 –60 –80 304 302 0 15 30 45 60 TEMPERATURE (°C) 75 300 90 VCC = 4.1V DC ±1.4V VREF = 2.5V IN+ = GND IN– = GND fO = GND TA = 25°C –60 –80 2497 G14 Conversion Current vs Temperature 2.0 fO = GND SCL = 0 SDA = 1 VCC = 5V 160 140 VCC = 2.7V 120 VCC = 5V 1.0 0.8 VCC = 2.7V 0.
PAGE 8
LTC2497 Pin Functions GND (Pins 1, 4, 6, 31, 32, 33, 34): Ground. Multiple ground pins internally connected for optimum ground current flow and VCC decoupling. Connect each one of these pins to a common ground plane through a low impedance connection. All seven pins must be connected to ground for proper operation. SCL (Pin 2): Serial Clock Pin of the I2C Interface. The LTC2497 can only act as a slave and the SCL pin only accepts an external serial clock.
PAGE 9
LTC2497 Functional Block Diagram INTERNAL OSCILLATOR VCC MUXOUTP ADCINP GND CH0 CH1 CH15 COM – • • • MUX fO (INT/EXT) AUTOCALIBRATION AND CONTROL REF+ REF– + DIFFERENTIAL 3RD ORDER ∆∑ MODULATOR I2C 2-WIRE INTERFACE SDA SCL DECIMATING FIR ADDRESS 2497 BD MUXOUTN ADCINN 2497fa
PAGE 10
LTC2497 Applications Information CONVERTER OPERATION Converter Operation Cycle The LTC2497 is a multichannel, low power, delta-sigma analog-to-digital converter with a 2-wire, I2C interface. Its operation is made up of four states (see Figure 1). The converter operating cycle begins with the conversion, followed by the sleep state and ends with the data input/output cycle.
PAGE 11
LTC2497 Applications Information common mode reference (see the Automatic Differential Input Current Cancellation section). This unique architecture does not require on-chip buffers, thereby enabling signals to swing beyond ground and VCC. Moreover, the cancellation does not interfere with the transparent offset and full-scale auto-calibration and the absolute accuracy (full scale + offset + linearity + drift) is maintained even with external RC networks.
PAGE 12
LTC2497 Applications Information I2C INTERFACE The LTC2497 communicates through an I2C interface. The I2C interface is a 2-wire open-drain interface supporting multiple devices and multiple masters on a single bus. The connected devices can only pull the data line (SDA) low and can never drive it high. SDA is required to be externally connected to the supply through a pull-up resistor. When the data line is not being driven, it is high.
PAGE 13
LTC2497 Applications Information The LTC2497 has two registers. The output register (24 bits long) contains the last conversion result. The input register (8 bits long) sets the input channel. are HIGH, the differential input voltage is equal to or above +FS. If both bits are set low, the input voltage is below –FS. The function of these bits is summarized in Table 2. The 16 bits following the MSB bit are the conversion result in binary two’s complement format. The remaining six bits are always 0.
PAGE 14
LTC2497 Applications Information INPUT DATA FORMAT If the first three bits are 000 or 100, the following data is ignored (don’t care) and the previously selected input channel remains valid for the next conversion. The LTC2497 serial input is 8 bits long and is written into the device in one 8-bit word. SGL, ODD, A2, A1, A0 are used to select the input channel.
PAGE 15
LTC2497 Applications Information Table 3.
PAGE 16
LTC2497 Applications Information Initiating a New Conversion When the LTC2497 finishes a conversion, it automatically enters the sleep state. Once in the sleep state, the device is ready for a read operation. After the device acknowledges a read request, the device exits the sleep state and enters the data output state. The data output state concludes and the LTC2497 starts a new conversion once a Stop condition is issued by the master or all 24 bits of data are read out of the device.
PAGE 17
LTC2497 Applications Information S R/W 7-BIT ADDRESS CONVERSION ACK DATA SLEEP Sr DATA TRANSFERRING P DATA INPUT/OUTPUT CONVERSION 2497 F04 Figure 4. Conversion Sequence S 7-BIT ADDRESS CONVERSION R ACK SLEEP READ P S 7-BIT ADDRESS CONVERSION DATA OUTPUT R ACK SLEEP READ P DATA OUTPUT CONVERSION 2497 F05 Figure 5.
PAGE 18
LTC2497 Applications Information all 24 bits are read out of the device or after a Stop command. The following conversion will be performed using the newly programmed data. Discarding a Conversion Result and Initiating a New Conversion with Optional Write At the conclusion of a conversion cycle, a write cycle can be initiated. Once the write cycle is acknowledged, a Stop command will start a new conversion.
PAGE 19
LTC2497 Applications Information Automatic Differential Input Current Cancellation of charge is transferred. A simplified equivalent circuit is shown in Figure 9. In applications where the sensor output impedance is low (up to 10kW with no external bypass capacitor or up to 500W with 0.001µF bypass), complete settling of the input occurs. In this case, no errors are introduced and direct digitization is possible.
PAGE 20
LTC2497 Applications Information zero, the common mode input current (IIN+ + IIN–)/2 is proportional to the difference between the common mode input voltage (VIN(CM)) and the common mode reference voltage (VREF(CM)). type sensors), the common mode input current varies proportionally with input voltage. For the case of balanced input impedances, the common mode input current effects are rejected by the large CMRR of the LTC2497, leading to little degradation in accuracy.
PAGE 21
LTC2497 Applications Information source impedances are not possible. One pair of external buffers/amplifiers can be shared between all 17 analog inputs. The LTC2497 performs an internal offset calibration every conversion cycle in order to remove the offset and drift of the ADC. This calibration is performed through a combination of front end switching and digital processing. Since the external amplifier is placed between the multiplexer and the ADC, it is inside this correction loop.
PAGE 22
LTC2497 Applications Information In cases where large bypass capacitors are required on the reference inputs (CREF > 0.01µF), full-scale and linearity errors are proportional to the value of the reference resistance. Every ohm of reference resistance produces a full-scale error of approximately 0.5ppm (while operating with the internal oscillator) (see Figures 13 and 14). If the input common mode voltage is equal to the reference common mode voltage, a linearity error of approximately 0.
PAGE 23
LTC2497 Applications Information When using the internal oscillator, the LTC2497 is designed to reject line frequencies. As shown in Figure 16, rejection nulls occur at multiples of frequency fN, where fN = 55Hz for simultaneous 50Hz/60Hz rejection. Multiples of the modulator sampling rate (fS = fN • 256) only reject noise to 15dB (see Figure 17); if noise sources are present at these frequencies antialiasing will reduce their effects.
PAGE 24
LTC2497 Applications Information MEASURED DATA CALCULATED DATA –20 –40 VCC = 5V VREF = 5V VIN(CM) = 2.5V VIN(P-P) = 5V TA = 25°C –60 –80 –100 –120 0 20 40 60 80 100 120 140 INPUT FREQUENCY (Hz) 160 180 200 220 0 NORMAL MODE REJECTION (dB) NORMAL MODE REJECTION (dB) 0 VIN(P-P) = 5V VIN(P-P) = 7.5V (150% OF FULL SCALE) –20 VCC = 5V VREF = 5V VIN(CM) = 2.
PAGE 25
LTC2497 Applications Information 40 30 3000 TA = 85°C 20 10 –1000 TA = 85°C 2000 –2000 TA = 25°C 1000 0 –3000 VIN(CM) = VREF(CM) VCC = VREF = 5V VIN = 0V fO = EXT CLOCK RES = LOG 2 (VREF/NOISERMS) 0 10 20 30 40 50 60 70 80 90 100 OUTPUT DATA RATE (READINGS/SEC) 16 TA = 25°C TA = 85°C 14 12 VIN(CM) = VREF(CM) VCC = VREF = 5V fO = EXT CLOCK RES = LOG 2 (VREF/INLMAX) 10 0 10 20 30 40 50 60 70 80 90 100 OUTPUT DATA RATE (READINGS/SEC) 2497 F23 Figure 23.
PAGE 26
LTC2497 Package Description UHF Package 38-Lead Plastic QFN (5mm × 7mm) (Reference LTC DWG # 05-08-1701 Rev C) 0.70 p 0.05 5.50 p 0.05 5.15 ± 0.05 4.10 p 0.05 3.00 REF 3.15 ± 0.05 PACKAGE OUTLINE 0.25 p 0.05 0.50 BSC 5.5 REF 6.10 p 0.05 7.50 p 0.05 RECOMMENDED SOLDER PAD LAYOUT APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED 5.00 p 0.10 0.75 p 0.05 PIN 1 NOTCH R = 0.30 TYP OR 0.35 s 45o CHAMFER 3.00 REF 37 0.00 – 0.05 38 0.40 p0.10 PIN 1 TOP MARK (SEE NOTE 6) 1 2 5.15 ± 0.10 5.50 REF 7.
PAGE 27
LTC2497 Revision History REV DATE DESCRIPTION PAGE NUMBER A 7/10 Revised Typical Application drawing Revised Parameter for VIHA in I2C Inputs and Digital Outputs section 1 4 2497fa Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
PAGE 28
LTC2497 Typical Application External Buffers Provide High Impedance Inputs and Amplifier Offsets are Automatically Cancelled ∆∑ ADC WITH EASY DRIVE INPUTS MUXOUTN INPUT MUX MUXOUTP LTC2497 ANALOG 17 INPUTS 2 – 1/2 LTC6078 3 + 6 – 5 1/2 LTC6078 1 SDA SCL 1k 0.1µF 7 + 1k 2497 TA02 0.1µF Related Parts PART NUMBER DESCRIPTION COMMENTS LT1236A-5 Precision Bandgap Reference, 5V 0.05% Max Initial Accuracy, 5ppm/°C Drift LT1460 Micropower Series Reference 0.