LTC2400 Linear Technology, LTC2400 Datasheet

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LTC2400

Manufacturer Part Number
LTC2400
Description
24-Bit uPower No Latency ADC in SO-8
Manufacturer
Linear Technology
Datasheet

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FEATURES
TYPICAL APPLICATIO
APPLICATIO S
–0.12V
24-Bit ADC in SO-8 Package
4ppm INL, No Missing Codes
4ppm Full-Scale Error
Single Conversion Settling Time
for Multiplexed Applications
0.5ppm Offset
0.3ppm Noise
Internal Oscillator—No External Components
Required
110dB Min, 50Hz/60Hz Notch Filter
Reference Input Voltage: 0.1V to V
Live Zero—Extended Input Range Accommodates
12.5% Overrange and Underrange
Single Supply 2.7V to 5.5V Operation
Low Supply Current (200 A) and Auto Shutdown
Weight Scales
Direct Temperature Measurement
Gas Analyzers
Strain-Gage Transducers
Instrumentation
Data Acquisition
Industrial Process Control
6-Digit DVMs
REF
INPUT RANGE
TO 1.12V
0.1V TO V
REFERENCE
VOLTAGE
ANALOG
1 F
2.7V TO 5.5V
REF
CC
U
V
V
V
GND
CC
REF
IN
LTC2400
SDO
SCK
CS
F
O
U
CC
3-WIRE
SPI INTERFACE
V
CC
= INTERNAL OSC/50Hz REJECTION
= EXTERNAL CLOCK SOURCE
= INTERNAL OSC/60Hz REJECTION
No Latency
2400 TA01
DESCRIPTIO
No Latency
MICROWIRE is a trademark of National Semiconductor Corporation.
The LTC
converter with an integrated oscillator, 4ppm INL and
0.3ppm RMS noise. It uses delta-sigma technology and
provides single cycle settling time for multiplexed appli-
cations. Through a single pin the LTC2400 can be config-
ured for better than 110dB rejection at 50Hz or 60Hz 2%,
or it can be driven by an external oscillator for a user
defined rejection frequency in the range 1Hz to 120Hz.
The internal oscillator requires no external frequency
setting components.
The converter accepts any external reference voltage from
0.1V to V
–12.5% V
resolves the offset and overrange problems of preceding
sensors or signal conditioning circuits.
The LTC2400 communicates through a flexible 3-wire
digital interface which is compatible with SPI and
MICROWIRE
, LTC and LT are registered trademarks of Linear Technology Corporation.
®
CC
is a trademark of Linear Technology Corporation.
2400 is a 2.7V to 5.5V micropower 24-bit
REF
. With its extended input conversion range of
TM
to 112.5% V
protocols.
–10
10
–2
–4
–6
–8
8
6
4
2
0
Total Unadjusted Error vs Output Code
0
U
V
V
T
F
O
A
CC
REF
= 25 C
= LOW
= 5V
= 5V
TM
OUTPUT CODE (DECIMAL)
24-Bit Power
REF
ADC in SO-8
, the LTC2400 smoothly
8,338,608
LTC2400
2400 TA02
16,777,215
1

Related parts for LTC2400

LTC2400 Summary of contents

Page 1

... INL and 0.3ppm RMS noise. It uses delta-sigma technology and provides single cycle settling time for multiplexed appli- cations. Through a single pin the LTC2400 can be config- ured for better than 110dB rejection at 50Hz or 60Hz 2 can be driven by an external oscillator for a user defined rejection frequency in the range 1Hz to 120Hz ...

Page 2

... Reference Input Voltage to GND .. – 0. Digital Input Voltage to GND ........ – 0. Digital Output Voltage to GND ..... – 0. Operating Temperature Range LTC2400C ............................................... LTC2400I ............................................ – Storage Temperature Range ................. – 150 C Lead Temperature (Soldering, 10 sec).................. 300 C U CONVERTER CHARACTERISTICS ...

Page 3

... CC (Note – 800 1.6mA – 800 A (Note 10 1.6mA (Note 10) O The denotes specifications which apply over the full operating temperature range, CONDITIONS (Note 12 (Note 12) CC LTC2400 MIN TYP MAX UNITS 2.5 V 2.0 V 0.8 V 0.6 V 2.5 V 2.0 V 0.8 V 0.6 V –10 ...

Page 4

... LTC2400 CHARACTERISTICS range, otherwise specifications are SYMBOL PARAMETER f External Oscillator Frequency Range EOSC t External Oscillator High Period HEO t External Oscillator Low Period LEO t Conversion Time CONV f Internal SCK Frequency ISCK D Internal SCK Duty Cycle ISCK f External SCK Frequency Range ...

Page 5

... REF – – – 5 –10 5.0 5.1 5.2 5.3 INPUT VOLTAGE (V) 2400 G08 LTC2400 Negative Input Extended Total Unadjusted Error (3V Supply REF – – – – ...

Page 6

... LTC2400 W U TYPICAL PERFOR A CE CHARACTERISTICS RMS Noise vs Reference Voltage REFERENCE VOLTAGE (V) 2400 G10 Noise Histogram 1500 REF 1000 500 0 –1.0 – 0.5 0 0.5 1.0 1.5 OUTPUT CODE (ppm) 2400 G14 Full-Scale Error vs Temperature 5 ...

Page 7

... REF – 2. –40 –60 –80 –100 SAMPLE RATE = 15.36kHz 2% –120 15100 15200 15300 15400 12 FREQUENCY AT V (Hz) IN LTC2400 PSRR vs Frequency 4. – –40 –60 –80 15,360Hz –100 –120 1 100 10k 95 120 ...

Page 8

... LTC2400 W U TYPICAL PERFOR A CE CHARACTERISTICS INL vs Output Rate OUTPUT RATE (Hz PIN FUNCTIONS V (Pin 1): Positive Supply Voltage. Bypass to GND CC (Pin 4) with tantalum capacitor in parallel with 0.1 F ceramic capacitor as close to the part as possible. ...

Page 9

... U APPLICATIONS INFORMATION Converter Operation Cycle The LTC2400 is a low power, delta-sigma analog-to- digital converter with an easy to use 3-wire serial interface. Its operation is simple and made up of three states. The converter operating cycle begins with the conversion, followed by a low power sleep state and concluded with the data output (see Figure 1) ...

Page 10

... Clocked by the on-chip oscillator, the LTC2400 rejects line frequencies (50 or 60Hz 2%) a minimum of 110dB. Ease of Use The LTC2400 data output has no latency, filter settling or redundant data associated with the conversion cycle. There is a one-to-one correspondence between the conversion and the output data ...

Page 11

... V has a very strong temperature dependency. Output Data Format The LTC2400 serial output data stream is 32 bits long. The first 4 bits represent status information indicating the sign, input range and conversion state. The next 24 bits are the conversion result, MSB first ...

Page 12

... V clamped to the value corresponding to – 0.125 • V Frequency Rejection Selection (F The LTC2400 internal oscillator provides better than 110dB normal mode rejection at the line frequency and all its harmonics for 50Hz 2% or 60Hz 2%. For 60Hz rejec- tion, F ...

Page 13

... When a fundamental rejection frequency different from 50Hz or 60Hz is required or when the converter must be synchronized with an outside source, the LTC2400 can operate with an external conversion clock. The converter automatically detects the presence of an external clock signal at the F pin and turns off the internal oscillator ...

Page 14

... SDO pin on the falling edge of the serial clock. In the Internal SCK mode of operation, the SCK pin is an output and the LTC2400 creates its own serial clock by dividing the internal conversion clock the External SCK mode of operation, the SCK pin is used as input. The ...

Page 15

... TO 1.12V REF REF GND CS BIT 31 BIT 30 BIT 29 BIT 28 BIT 27 EOC SIG EXR MSB DATA OUTPUT Figure 5. External Serial Clock, Single Cycle Operation LTC2400 50Hz REJECTION = EXTERNAL OSCILLATOR = 60Hz REJECTION BIT 26 BIT 4 BIT 0 LSB SUB LSB TEST EOC Hi-Z CONVERSION 2400 F05 15 ...

Page 16

... On the falling edge of EOC, the conversion result is loaded into an internal static shift register. The device remains in the sleep state until the first rising edge of SCK. Data 2. LTC2400 V REF V SCK REF 0. SDO IN – ...

Page 17

... TO 1.12V REF REF GND CS BIT 30 BIT 29 BIT 28 BIT 27 BIT 26 SIG EXR MSB DATA OUTPUT Figure 8. Internal Serial Clock, Single Cycle Operation LTC2400 50Hz REJECTION = EXTERNAL OSCILLATOR = 60Hz REJECTION BIT 4 BIT 0 LSB 24 CONVERSION 50Hz REJECTION = EXTERNAL OSCILLATOR ...

Page 18

... pulled HIGH while the converter is driving SCK LOW, the , the first rising internal pull-up is not available to restore SCK to a logic 2. LTC2400 V REF V SCK REF 0. ...

Page 19

... SCK pin or by never pulling CS HIGH when SCK is LOW. Whenever SCK is LOW, the LTC2400’s internal pull-up at pin SCK is disabled. Normally, SCK is not externally driven if the device is in the internal SCK timing mode. However, certain applications may require an external driver on SCK ...

Page 20

... CS falls below an internal threshold ( 1.4V), the device automatically begins outputting data. The data output cycle begins on the first rising edge of SCK and ends on the 32nd rising edge. Data is shifted out the SDO 2. LTC2400 V REF V SCK REF 0. ...

Page 21

... SCK LOW while CS is discharging. 10000 100000 DIGITAL SIGNAL LEVELS 2400 F13 The LTC2400’s digital interface is easy to use. Its digital inputs (F O accept standard TTL/CMOS logic levels and the internal hysteresis receivers can tolerate edge rates as slow as 100 s. However, some considerations are required to take advantage of exceptional accuracy and low supply current ...

Page 22

... Parallel termination near the LTC2400 pin will eliminate this problem but will increase the driver power dissipation. A series resistor between 27 and 56 placed near the driver or near the LTC2400 pin will also eliminate this problem without additional power dissipation. The actual resistor value depends upon the trace impedance and connection topology ...

Page 23

... This results in 1 input dynamic current at the extreme values REF 2400 F16 V IN PAR LTC2400 20pF 2400 F17 Figure 19. Full-Scale Error 10k 100k 2400 F18 (Small C) LTC2400 (see Figure 17) is small IN < 0. function IN > 0.01 F), the input and ...

Page 24

... LTC2400 U U APPLICATIONS INFORMATION 0. –50 –100 –150 –200 –250 –300 0 200 400 600 SOURCE Figure 21. Full-Scale Error 5V). This corresponds to a 0.3ppm shift in offset REF and full-scale readings for every 1 resistance. In addition to the input current spikes, the input ESD protection diodes have a temperature dependent leakage current ...

Page 25

... As a result of the oversampling ratio (256) and the digital filter, minimal (if any) antialias filtering is required in front of the LTC2400. If passive RC components are placed in front of the LTC2400 the input dynamic current should be considered (see Input Current section). In cases where large effective RC time constants are used, an external buffer amplifier may be required to minimize the effects of input dynamic current ...

Page 26

... To prevent the converters from autostarting a new con- version at the end of data output read fewer SCK clock signals are applied to the LTC2400 instead of 32 (the 32nd falling edge would start a conversion). The exact timing and frequency for the SCK signal is not critical since it is only shifting out the data. In this case, two LTC2400’ ...

Page 27

... IN CS GND CS GND CS Figure 28. 4 Output Rate LTC2400 System Simple Differential Front-End for the LTC2400 The circuit in Figure 29 is ideal for wide dynamic range differential signals in applications where absolute accu- racy is secondary to high resolution, have large signal swings, source impedances under 500 and use supply ...

Page 28

... Resistors R1 and R2 set the LTC1050’s gain at 101. The circuit schematic shows an optional resistor R resistor can be placed in series with the LTC2400’s input to limit current if the input goes below – 300mV. The resistor does not degrade the converter’s performance as long as any capacitance, stray or otherwise, connected between the LTC2400’ ...

Page 29

... DIFFERENTIAL INPUT 350 350 13 16 AGND OR C1 – V 0.01 F EXT 17 0.1 F – 5V Figure 30. Differential to Single-Ended Converter for Low Level Inputs, Such as Bridges, Maintains the LTC2400’s High Accuracy 1 CH0 2 CH1 3 CH2 4 CH3 5 CH4 6 CH5 7 CH6 8 CH7 Figure 31. Multiplex 8-Signal Sources with the LTC1391 and Maintain the LTC2400’s Conversion Accuracy 5V 0 ...

Page 30

... LTC2400 U TYPICAL APPLICATIONS Sample Driver for LTC2400 SPI Interface The LTC2400 has a very simple serial interface that makes interfacing to microprocessors and microcontrollers very easy. Shown in Figures 32 and 34 are listings of sample source codes that can be used to initiate conversions and retrieve data from the LTC2400. ...

Page 31

... ADhi.bit0 = Temp '16 bit variables return Figure 32. This BASIC Stamp Code is an Example of How Easy Retrieve Data from the LTC2400 The listing in Figure simple assembler routine for the 68HC11 microcontroller. It uses PORT D, configuring it for SPI data transfer between the controller and the LTC2400 ...

Page 32

... PULY Restore the Y register PULX Restore the X register RTS Figure 34. This is an Example of 68HC11 Code That Captures the LTC2400’s Conversion Results Over the SPI Serial Interface Shown in Figure 33 32 This sets the SS* output bit to a logic low, selecting the LTC2400 ...

Page 33

... TC, as should the resistors R2 and R3. Since R1 provides forward bias for the diode, its tempera- ture coefficient is not as critical. The circuit in Figure 35 uses only 12% of the LTC2400’s input range and is able to accommodate the full-scale output of all thermocouple types. The commonly used ...

Page 34

... Chopper amplifiers such as the LTC1050 can extend the noise floor of the LTC2400 by as much as a factor 20. The use of a gain front of the LTC2400 can extend the resolution of a thermocouple application to 0. better. If absolute accuracy is not important, the use of a low noise bipolar amplifier, such as the LT1028, can extend the resolution an additional order of magnitude ...

Page 35

... If high temperature resolution is required over a more limited range, Figure 38 can resolve approximately 0.01 C without additional amplification. The resistance of a platinum RTD changes by approximately 0. The 100 to 300 source impedance of this A circuit does not compromise the stability, accuracy or noise level of the LTC2400 ...

Page 36

... The 12.1k resistor should be a precision resistor such as a Vishay S102 series, or must be temperature stabilized. The excitation current is low enough for most sensors that the self-heating effect is near the noise floor of the LTC2400. The use of a bipolar amplifier configuration shown in Figure 39 offers a potential resolution of 0.001 C In order to achieve these results, the following effects must be considered ...

Page 37

... U TYPICAL APPLICATIONS pick-up from the strain bearing member is largely 60Hz, the LTC2400 will reject it. If serious high frequency noise is present on the strain bearing member, it may be necessary to add buffering in order to allow the use of noise suppression. Stable Relaxation Oscillator for External Clock Applications that require that the notch produced by the 4 LTC2400’ ...

Page 38

... LTC2400 U TYPICAL APPLICATIONS The performance of the LTC2400 can be verified using the demonstration board DC228, see Figure 42 for the sche- matic. This circuit uses the computer’s serial port to generate power and the SPI digital signals necessary for starting a conversion and reading the result. It includes a ...

Page 39

... DWG # 05-08-1610) 8 0.228 – 0.244 (5.791 – 6.197 0.053 – 0.069 (1.346 – 1.752) 0 – 8 TYP 0.014 – 0.019 (0.355 – 0.483) W LTC2400 0.189 – 0.197* (4.801 – 5.004 0.150 – 0.157** (3.810 – 3.988 0.004 – 0.010 (0.101 – ...

Page 40

... No External Components 5 V Offset, 1.6 V 0.05% Max, 5ppm/ C Drift 0.075% Max, 10ppm/ C Max Drift, 2.5V, 5V and 10V Versions 3 V Noise, 10-Pin MSOP Package, Ground Sensing Same Performance as LTC2400 6 V Noise, Pin-Compatible with LTC2400 Component Side Paste Mask Solder Side Paste Mask Noise P-P 2400fa LT/TP 0300 2K REV A • PRINTED IN USA ...

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