Datasheet

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

LTC2499

2499fd

Features

applications

Description

24-Bit 8-/16-Channel

ADC with Easy Drive Input Current

Cancellation and I

C Interface

The LTC

2499 is a 16-channel (eight differential), 24-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 LTC2499 includes a high accuracy, temperature

sensor and an integrated oscillator. This device can be

conﬁgured to measure an external signal (from combi-

nations of 16 analog input channels operating in single-

ended or differential modes) or its internal temperature

sensor. The integrated temperature sensor offers 1/30th°C

resolution and 2°C absolute accuracy.

The LTC2499 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 en-

ables optional external ampliﬁers to be shared between all

analog inputs and auto calibration continuously removes

their associated offset and drift.

Data Acquisition System with Temperature Compensation

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

Integrated High Accuracy Temperature Sensor

GND to V

Input/Reference Common Mode Range

Programmable 50Hz, 60Hz or Simultaneous 50Hz/

60Hz Rejection Mode

2ppm INL, No Missing Codes

1ppm Offset and 15ppm Full-Scale Error

2x Speed/Reduced Power Mode (15Hz Using Internal

Oscillator and 80µA at 7.5Hz Output)

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

Integrated High Performance Temperature Sensor

typical application

SCL

SDA

REF

MUXOUT/

ADCIN

MUXOUT/

ADCIN

2.7V TO 5.5V

0.1µF

1.7k

COM

REF

–

24-BIT $3 ADC

WITH EASY DRIVE

16-CHANNEL

MUX

TEMPERATURE

SENSOR

–

2499 TA01

2-WIRE

C INTERFACE

CH0

CH1

•

CH7

CH8

CH15

10µF

OSC

TEMPERATURE (°C)

–55 –30 –5

ABSOLUTE ERROR (°C)

–4

–3

–2

–1

12095704520

2499 TA02

–5

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.

Summary of content (34 pages)

PAGE 1
LTC2499 24-Bit 8-/16-Channel DS ADC with Easy Drive Input Current Cancellation and I2C Interface Description Features n n n n n n n n n n n n n n 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 I2C Interface with 27 Addresses Plus One Global Address for Synchronization 600nV RMS Noise Integrated High Accuracy Temperature Sensor GND to VCC Inpu
PAGE 2
LTC2499 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.............
PAGE 3
LTC2499 Electrical Characteristics (Normal Speed) 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 MIN TYP Total Unadjusted Error 5V ≤ VCC ≤ 5.5V, VREF = 2.5V, VIN(CM) = 1.25V 5V ≤ VCC ≤ 5.5V, VREF = 5V, VIN(CM) = 2.5V 2.7V ≤ VCC ≤ 5.5V, VREF = 2.5V, VIN(CM) = 1.25V 15 15 15 ppm of VREF ppm of VREF ppm of VREF Output Noise 2.7V < VCC < 5.5V, 2.
PAGE 4
LTC2499 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) FS Full Scale of the Differential Input (IN+ – IN–) l 0.5VREF V LSB Least Significant Bit of the Output Code l FS/224 REF+ Absolute/Common Mode REF+ Voltage l 0.
PAGE 5
LTC2499 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.
PAGE 6
LTC2499 Typical Performance Characteristics –45°C 25°C 0 85°C –1 3 VCC = 5V VREF = 2.5V VIN(CM) = 1.25V fO = GND 1 2 –45°C, 25°C, 85°C 0 –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 –0.25 0.25 0.75 INPUT VOLTAGE (V) Total Unadjusted Error (VCC = 5V, VREF = 5V) 25°C 4 0 12 –45°C –4 VCC = 5V VREF = 2.5V VIN(CM) = 1.25V fO = GND 85°C 8 –45°C 0 –4 2.5 –12 –1.25 –0.75 –0.25 0.25 0.75 INPUT VOLTAGE (V) –0.25 0.25 0.75 INPUT VOLTAGE (V) 1.
PAGE 7
LTC2499 Typical Performance Characteristics RMS Noise vs Input Differential Voltage 5 VCC = 5V TA = 25°C VREF = 5V RMS NOISE = 0.60µV VIN = 0V VIN(CM) = 2.5V 4 3 2 1 0 –1 –2 –3 0 10 30 40 20 TIME (HOURS) 50 0.7 0.6 2499 G09 0.5 0.8 0.7 0.6 75 0.4 2.7 90 3.1 3.5 3.9 4.3 VCC (V) 4.7 5.1 2499 G12 0.2 0.1 5 4 6 VCC = 5V VIN = 0V VIN(CM) = GND TA = 25°C fO = GND 0.8 0.7 0.6 0.4 5.5 0 1 2 3 VREF (V) 4 5 2499 G14 Offset Error vs Temperature 0.
PAGE 8
LTC2499 Typical Performance Characteristics 0.2 0.1 0.3 REF+ = 2.5V REF– = GND VIN = 0V VIN(CM) = GND TA = 25°C fO = GND OFFSET ERROR (ppm of VREF) OFFSET ERROR (ppm of VREF) 0.3 0 On-Chip Oscillator Frequency vs Temperature Offset Error vs VREF 0.2 0.1 –0.2 0 3.1 3.9 4.3 VCC (V) 3.5 4.7 5.1 –0.3 5.5 0 1 2 3 VREF (V) 4 304 302 2.5 3.0 3.5 4.0 VCC (V) 4.5 5.0 5.5 0 VCC = 4.1V DC VREF = 2.
PAGE 9
LTC2499 Typical Performance Characteristics Sleep Mode Current vs Temperature 500 fO = GND VREF = VCC IN+ = GND IN– = GND fO = EXT OSC TA = 25°C 450 1.6 SUPPLY CURRENT (µA) SLEEP MODE CURRENT (µA) 1.8 1.4 1.2 VCC = 5V 1.0 0.8 0.6 VCC = 2.7V 0.4 400 350 3 VCC = 5V VCC = 3V 0 –45 –30 –15 0 15 30 45 60 TEMPERATURE (°C) 75 100 90 –1 0 INL (ppm OF VREF) 2 85°C 0 –1 –45°C, 25°C –2 16 85°C 0 –45°C, 25°C –1 –2 –0.75 –0.25 0.25 0.75 INPUT VOLTAGE (V) 1.25 –3 –1.25 –0.75 –0.25 0.
PAGE 10
LTC2499 Typical Performance Characteristics 240 220 210 200 190 180 240 VREF = 2.5V VIN = 0V VIN(CM) = GND fO = GND TA = 25°C 200 OFFSET ERROR (µV) 230 OFFSET ERROR (µV) 250 VCC = 5V VREF = 5V VIN = 0V VIN(CM) = GND fO = GND Offset Error vs VCC (2x Speed Mode) 150 100 75 0 90 2 2.5 3 4 3.5 VCC (V) 4.5 210 200 190 0 –20 RREJECTION (dB) –60 –80 –100 –120 1 10 10k 100k 1k 100 FREQUENCY AT VCC (Hz) 1M 2499 G36 0 1 2 3 VREF (V) 4 –40 –60 0 VCC = 4.1V DC ±1.4V REF+ = 2.
PAGE 11
LTC2499 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 LTC2499 can only act as a slave and the SCL pin only accepts an external serial clock.
PAGE 12
LTC2499 functional block diagram TEMP SENSOR VCC GND INTERNAL OSCILLATOR CH0 CH1 CH15 COM – • • • MUX fO (INT/EXT) AUTOCALIBRATION AND CONTROL MUXOUTP ADCINP REF+ REF– + DIFFERENTIAL 3RD ORDER $3 MODULATOR I2C 2-WIRE INTERFACE SDA SCL DECIMATING FIR ADDRESS 2499 BD MUXOUTN ADCINN 2499fd 12
PAGE 13
LTC2499 Applications Information CONVERTER OPERATION Converter Operation Cycle The LTC2499 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 . Initially, at power-up, the LTC2499 performs a conversion. Once the conversion is complete, the device enters the sleep state.
PAGE 14
LTC2499 Applications Information 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. Power-Up Sequence The LTC2499 automatically enters an internal reset state when the power supply voltage VCC drops below approximately 2.0V. This feature guarantees the integrity of the conversion result and input channel selection.
PAGE 15
LTC2499 Applications Information I2C INTERFACE The START and STOP Conditions The LTC2499 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 16
LTC2499 Applications Information matches the hard wired LTC2499’s address (one of 27 pin-selectable addresses) the device is selected. When the device is addressed during the conversion state, it will not acknowledge R/W requests and will issue a NACK by leaving the SDA line HIGH. If the conversion is complete, the LTC2499 issues an ACK by pulling the SDA line LOW. The data output stream is 32 bits long and is shifted out on the falling edges of SCL (see Figure 3a).
PAGE 17
LTC2499 Applications Information and 1x output rate (auto-calibration enabled). The first conversion automatically begins at power-up using this default configuration. Once the conversion is complete, up to two words may be written into the device. Table 2. LTC2499 Status Bits BIT 31 SIG BIT 30 MSB 1 1 0V ≤ VIN < FS 1/ 0 0 –FS ≤ VIN < 0V 0 1 VIN < –FS 0 0 INPUT RANGE VIN ≥ FS The first three bits of the first input word consist of two preamble bits and one enable bit.
PAGE 18
LTC2499 Applications Information Table 3.
PAGE 19
LTC2499 Applications Information nels can be selected to form a differential input. For SGL = 1, one of 16 channels is selected as the positive input. The negative input is COM for all single-ended operations. The remaining four bits (ODD, A2, A1, A0) determine which channel(s) is/are selected and the polarity (for a differential input). following conversion will be performed on the internal temperature sensor rather than the selected input channel.
PAGE 20
LTC2499 Applications Information Rejection Mode (FA, FB) The LTC2499 includes a high accuracy on-chip oscillator with no required external components. Coupled with an integrated fourth order digital lowpass filter, the LTC2499 rejects line frequency noise. In the default mode, the LTC2499 simultaneously rejects 50Hz and 60Hz by at least 87dB. If more rejection is required, the LTC2499 can be configured to reject 50Hz or 60Hz to better than 110dB.
PAGE 21
LTC2499 Applications Information This value of slope can be used to calculate further temperature readings using: Table 5.
PAGE 22
LTC2499 Applications Information S R/W 7-BIT ADDRESS CONVERSION ACK DATA SLEEP Sr DATA TRANSFERRING P DATA INPUT/OUTPUT CONVERSION 2499 F05 Figure 6. 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 2499 F07 Figure 7.
PAGE 23
LTC2499 Applications Information selects the device, the LTC2499 generates a NACK signal indicating the conversion cycle is in progress. Continuous Read/Write Once the conversion cycle is concluded, the LTC2499 can be written to and then read from using the repeated START (Sr) command. Figure 8 shows a cycle which begins with a data write, a repeated START, followed by a read and concluded with a STOP command.
PAGE 24
LTC2499 Applications Information Driving the Input and Reference The input and reference pins of the LTC2499 are connected directly to a switched capacitor network. Depending on the relationship between the differential input voltage and the differential reference voltage, these capacitors are switched between these four pins. Each time a capacitor is switched between two of these pins, a small amount of charge is transferred. A simplified equivalent circuit is shown in Figure 11.
PAGE 25
LTC2499 Applications Information (IIN+ – IIN–) is zero. While the differential input current is 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)). In applications where the input common mode voltage is equal to the reference common mode voltage, as in the case of a balanced bridge, both the differential and common mode input current are zero.
PAGE 26
LTC2499 Applications Information op amp output enabling stable operation. The LTC6078 can also be biased at supply rails beyond those used by the LTC2499. This allows the external sensor to swing railto-rail (–0.3V to VCC + 0.3V) without the need of external level-shift circuitry. Reference Current Similar to the analog inputs, the LTC2499 samples the differential reference pins (REF+ and REF–) transferring small amounts of charge to and from these pins, thus producing a dynamic reference current.
PAGE 27
LTC2499 Applications Information approximately 0.67ppm per 100Ω of reference resistance results (see Figure 17). In applications where the input and reference common mode voltages are different, the errors increase. A 1V difference in between common mode input and common mode reference results in a 6.7ppm INL error for every 100Ω of reference resistance. INL (ppm OF VREF) R = 1k 2 R = 500Ω 0 R = 100Ω –2 –4 –6 –8 –10 –0.5 –0.3 0.1 –0.1 VIN/VREF 0.3 0.5 2499 F17 Figure 17.
PAGE 28
LTC2499 Applications Information When using the internal oscillator, the LTC2499 is designed to reject line frequencies. As shown in Figure 20, rejection nulls occur at multiples of frequency fN, where fN is determined by the input control bits FA and FB (fN = 50Hz or 60Hz or 55Hz for simultaneous rejection). Multiples of the modulator sampling rate (fS = fN • 256) only reject noise to 15dB (see Figure 21); if noise sources are present at these frequencies anti-aliasing will reduce their effects.
PAGE 29
LTC2499 Applications Information VCC = 5V VREF = 5V VIN(CM) = 2.5V VIN(P-P) = 5V TA = 25°C MEASURED DATA CALCULATED DATA –20 –40 –60 –80 –100 –120 0 15 30 45 60 75 0 NORMAL MODE REJECTION (dB) NORMAL MODE REJECTION (dB) 0 –20 –40 –80 –100 0 12.5 25 37.5 50 62.5 75 87.5 100 112.5 125 137.5 150 162.5 175 187.5 200 INPUT FREQUENCY (Hz) 2498 F22 NORMAL MODE REJECTION (dB) 0 MEASURED DATA CALCULATED DATA –20 –40 VCC = 5V VREF = 5V VIN(CM) = 2.
PAGE 30
LTC2499 Applications Information Using the 2X speed mode of the LTC2499 alters the rejection characteristics around DC and multiples of fS. The device bypasses the offset calibration in order to increase the output rate. The resulting rejection plots are shown in Figures 27 and 28. 1x type frequency rejection can be achieved using the 2x mode by performing a running average of the previous two conversion results (see Figure 29).
PAGE 31
LTC2499 Applications Information 50 OFFSET ERROR (ppm OF VREF) NO AVERAGE –90 WITH RUNNING AVERAGE –100 –110 –120 –130 30 TA = 85°C 20 10 20 RESOLUTION (BITS) –1000 –FS ERROR (ppm OF VREF) 22 TA = 25°C –2000 TA = 85°C –2500 –3000 –3500 VIN(CM) = VREF(CM) VCC = VREF = 5V fO = EXT CLOCK 12 10 0 10 20 30 40 50 60 70 80 90 100 OUTPUT DATA RATE (READINGS/SEC) 20 TA = 85°C VIN(CM) = VREF(CM) VCC = VREF = 5V VIN = 0V fO = EXT CLOCK RES = LOG 2 (VREF/NOISERMS) RESOLUTION (BITS) 20 Figure 34.
PAGE 32
LTC2499 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 33
LTC2499 Revision History (Revision history begins at Rev C) REV DATE DESCRIPTION PAGE NUMBER C 11/09 Update Tables 1 and 2 D 07/10 Revised Typical Application drawing. Added fO pin to parameters of VIHA 16 in I2C Inputs and Digital Outputs section Added text to first paragraph of I2C Interface section 1 4 15 2499fd Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use.
PAGE 34
LTC2499 Typical Application External Buffers Provide High Impedance Inputs and Amplifier Offsets are Automatically Cancelled ΔΣ ADC WITH EASY DRIVE INPUTS MUXOUTN 2 – 1/2 LTC6078 3 + 6 – 5 1/2 LTC6078 + 1 SDA SCL 1k 0.1µF 7 1k 2499 TA03 INPUT MUX MUXOUTP LTC2499 ANALOG 17 INPUTS 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.