Datasheet

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LTC1864/LTC1865

18645f

APPLICATIO S

FEATURES

DESCRIPTIO

TYPICAL APPLICATIO

µPower, 16-Bit, 250ksps

1- and 2-Channel ADCs in MSOP

Single 5V Supply, 250ksps, 16-Bit Sampling ADC

Supply Current vs Sampling Frequency

The LTC

1864/LTC1865 are 16-bit A/D converters that are

offered in MSOP and SO-8 packages and operate on a

single 5V supply. At 250ksps, the supply current is only

850µA. The supply current drops at lower speeds because

the LTC1864/LTC1865 automatically power down

between conversions. These 16-bit switched capacitor

successive approximation ADCs include sample-and-holds.

The LTC1864 has a differential analog input with an

adjustable reference pin. The LTC1865 offers a software-

selectable 2-channel MUX and an adjustable reference pin

on the MSOP version.

The 3-wire, serial I/O, small MSOP or SO-8 package and

extremely high sample rate-to-power ratio make these

ADCs ideal choices for compact, low power, high speed

systems.

These ADCs can be used in ratiometric applications or

with external references. The high impedance analog

inputs and the ability to operate with reduced spans down

to 1V full scale, allow direct connection to signal sources

in many applications, eliminating the need for external

gain stages.

■

16-Bit 250ksps ADCs in MSOP Package

■

Single 5V Supply

■

Low Supply Current: 850µA (Typ)

■

Auto Shutdown Reduces Supply Current

to 2µA at 1ksps

■

True Differential Inputs

■

1-Channel (LTC1864) or 2-Channel (LTC1865)

Versions

■

SPI/MICROWIRE

Compatible Serial I/O

■

16-Bit Upgrade to 12-Bit LTC1286/LTC1298

■

Pin Compatible with 12-Bit LTC1860/LTC1861

, LTC and LT are registered trademarks of Linear Technology Corporation.

■

High Speed Data Acquisition

■

Portable or Compact Instrumentation

■

Low Power Battery-Operated Instrumentation

■

Isolated and/or Remote Data Acquisition

REF

–

GND

SCK

SDO

CONV

LTC1864

1864 TA01

ANALOG INPUT

0V TO 5V

1µF

SERIAL DATA LINK TO

ASIC, PLD, MPU, DSP

OR SHIFT REGISTERS

SAMPLING FREQUENCY (kHz)

0.01

SUPPLY CURRENT (µA)

1000

100

0.1

0.01

100

1864 TA02

0.1

1000

MICROWIRE is a trademark of National Semiconductor Corporation.

Summary of content (21 pages)

PAGE 1
LTC1864/LTC1865 µPower, 16-Bit, 250ksps 1- and 2-Channel ADCs in MSOP U FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ DESCRIPTIO 16-Bit 250ksps ADCs in MSOP Package Single 5V Supply Low Supply Current: 850µA (Typ) Auto Shutdown Reduces Supply Current to 2µA at 1ksps True Differential Inputs 1-Channel (LTC1864) or 2-Channel (LTC1865) Versions SPI/MICROWIRETM Compatible Serial I/O 16-Bit Upgrade to 12-Bit LTC1286/LTC1298 Pin Compatible with 12-Bit LTC1860/LTC1861 U APPLICATIO S ■ ■ ■ ■ High Speed Data Acquisition Portab
PAGE 2
LTC1864/LTC1865 W W W AXI U U ABSOLUTE RATI GS (Notes 1, 2) Supply Voltage (VCC) ................................................. 7V Ground Voltage Difference AGND, DGND LTC1865 MSOP Package ........... ±0.3V Analog Input ............... (GND – 0.3V) to (VCC + 0.3V) Digital Input ................................ (GND – 0.3V) to 7V Digital Output .............. (GND – 0.3V) to (VCC + 0.3V) Power Dissipation ..............................................
PAGE 3
LTC1864/LTC1865 W U U CO VERTER A D ULTIPLEXER CHARACTERISTICS The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are TA = 25°C. VCC = 5V, VREF = 5V, fSCK = fSCK(MAX) as defined in Recommended Operating Conditions, unless otherwise noted.
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LTC1864/LTC1865 U U U U WW RECO E DED OPERATI G CO DITIO S The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are TA = 25°C.
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LTC1864/LTC1865 U W TYPICAL PERFOR A CE CHARACTERISTICS Supply Current vs Sampling Frequency VCC = 5V TA = 25°C CONV LOW = 800ns 1000 900 10 1 600 400 VCC = 5V VREF = 5V fSAMPLE = 250kHz CONV HIGH = 3.2µS 200 0.1 0.01 0.01 0.1 10 100 1.
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LTC1864/LTC1865 U W TYPICAL PERFOR A CE CHARACTERISTICS Change in Offset Error vs Reference Voltage 5 20 VCC = 5V 4 VREF = 5V CHANGE IN OFFSET (LSB) VCC = 5V TA = 25°C 50 25 0 VCC = 5V 15 TA = 25°C CHANGE IN GAIN ERROR (LSB) 75 CHANGE IN OFFSET ERROR (LSB) Change in Gain Error vs Reference Voltage Change in Offset vs Temperature 3 2 1 0 –1 –2 –3 1 0 3 4 2 REFERENCE VOLTAGE (V) –5 –50 5 –25 50 0 75 25 TEMPERATURE (°C) 100 5 3 1400 0 –1 800 –2 –3 400 –4 200 729 516 125 0 1 C
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LTC1864/LTC1865 U U U PI FU CTIO S LTC1864 VREF (Pin 1): Reference Input. The reference input defines the span of the A/D converter and must be kept free of noise with respect to GND. IN +, IN– (Pins 2, 3): Analog Inputs. These inputs must be free of noise with respect to GND. GND (Pin 4): Analog Ground. GND should be tied directly to an analog ground plane. CONV (Pin 5): Convert Input. A logic high on this input starts the A/D conversion process.
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LTC1864/LTC1865 W FUNCTIONAL BLOCK DIAGRA U CONV (SDI) SCK U VCC PIN NAMES IN PARENTHESES REFER TO LTC1865 CONVERT CLK SDO SERIAL PORT BIAS AND SHUTDOWN DATA IN 16 BITS IN + (CH0) + IN – (CH1) – 16-BIT SAMPLING ADC DATA OUT 1864/65 BD GND VREF TEST CIRCUITS Load Circuit for t dDO, t r, t f, t dis and t en Voltage Waveforms for SDO Rise and Fall Times, t r, t f TEST POINT VOH SDO VOL VCC tdis WAVEFORM 2, ten 3k SDO tdis WAVEFORM 1 20pF tr tf 1864 TC04 1864 TC01 Voltage Wavefor
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LTC1864/LTC1865 U W U U APPLICATIO S I FOR ATIO LTC1864 OPERATION Analog Inputs Operating Sequence The LTC1864 has a unipolar differential analog input. The converter will measure the voltage between the “IN + ” and “IN – ” inputs. A zero code will occur when IN+ minus IN – equals zero. Full scale occurs when IN+ minus IN – equals VREF minus 1LSB. See Figure 2. Both the “IN+ ” and “IN – ” inputs are sampled at the same time, so common mode noise on the inputs is rejected by the ADC.
PAGE 10
LTC1864/LTC1865 U W U U APPLICATIO S I FOR ATIO LTC1865 OPERATION Operating Sequence The LTC1865 conversion cycle begins with the rising edge of CONV. After a period equal to t CONV, the conversion is finished. If CONV is left high after this time, the LTC1865 goes into sleep mode drawing only leakage current. The LTC1865’s 2-bit data word is clocked into the SDI input on the rising edge of SCK after CONV goes low. Additional inputs on the SDI pin are then ignored until the next CONV cycle.
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LTC1864/LTC1865 U W U U APPLICATIO S I FOR ATIO GENERAL ANALOG CONSIDERATIONS Grounding The LTC1864/LTC1865 should be used with an analog ground plane and single point grounding techniques. Do not use wire wrapping techniques to breadboard and evaluate the device. To achieve the optimum performance, use a printed circuit board.
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5VDIG IN – E9 E8 J1 4 1 4 2 3 JP9 3 1 JP8 J2 2 AGND IN + 15V 15V 5 6 5 6 R8 51Ω 0PT IN – R7 51Ω 0PT IN + – + VIN 2 JP3 1 1 1 2 3 4 5 6 7 8 JP2 JP1 RESET CLK P0 P1 P2 P3 ENP GND 2 2 VCC RCO Q0 Q1 Q2 Q3 ENT LO U6 74HC163AD 5VDIG U9A 74AC00 U9B 74AC00 C6 –15V 0.1µF U2 OPT 1 16 15 14 13 12 11 10 9 R2 510Ω R1 510Ω 6 VOUT U1 GND LT1021-5 4 C5 15V 0.1µF C27 0.1µF 2 R3 2Ω 5VDIG 5VDIG C11 390pF C10 680pF OPT C23 0.1µF 1 2 3 4 5 6 7 8 C16 0.
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LTC1864/LTC1865 U W U U APPLICATIO S I FOR ATIO Component Side Silk Screen for LTC1864 Evaluation Circuit Component Side Showing Traces (Note Wider Traces on Analog Side) Bottom Side Showing Traces (Note Almost No Analog Traces on Board Bottom) Ground Layer with Separate Analog and Digital Grounds Supply Layer with 5V Digital Supply and Analog Ground Repeated 18645f 13
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LTC1864/LTC1865 U W U U APPLICATIO S I FOR ATIO U11 15V LT1121CST-5 1 VIN 5VAN C3 10µF 6.3V 1206 VOUT GND 2 R4 2Ω 5VDIG C26 10µF 6.3V 1206 C4 0.1µF 5VDIG 1 V 2 REF IN+ 3 IN– 4 GND 1V to 5V REFERENCE 0V to VREF INPUT 5VAN 3 RN1 330 8 VCC 7 SCK 6 SDO 5 CONV 1 2 3 4 1 RO 2 RE 3 DE 4 DI 8 7 6 5 5VDIG LTC1485 8 VCC 7 B 6 A 5 GND 15V 120Ω U3 LTC1864CMS8 ANALOG GROUND PLANE C23 0.
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LTC1864/LTC1865 U W U U APPLICATIO S I FOR ATIO Q Q 6 10 12 CLK 11 13 PRE D CLK CLR Q Q 9 8 IC4A 74AC08 4 2 CLK 3 1 PRE D CLK CLR Q Q 5 10 12 CLK 11 13 VCC IC2B 74AC74 PRE D CLK CLR Q 6 Q 9 IC4B 74AC08 8 4 2 CLK 3 1 IC3A 74AC74 PRE D CLK CLR Q v 5 IC6D 74AC32 v PRE D CLK CLR v 4 DATA IN 2 CLK 3 1 IC5C 74AC86 VCC IC1A 74AC74 v VCC VCC IC2A 74AC74 v VCC Q 5 6 IC6C 74LS32D DATA DATA IC1B 74AC74 IC4C 74AC08 VCC IC3B 74AC74 10 12 CLK 11 13 PRE D CLK CLR S
PAGE 16
LTC1864/LTC1865 U W U U APPLICATIO S I FOR ATIO Transmit LTC1864 Data Over Modular Telephone Wire Using Simple Transmitter/Receiver Figure 6 shows a simple Manchester encoder and differential transmitter suitable for use with the LTC1864. This circuit allows transmission of data over inexpensive telephone wire. This is useful for measuring a remote sensor, particularly when the cost of preserving the analog signal over a long distance is high.
PAGE 17
LTC1864/LTC1865 U PACKAGE DESCRIPTIO MS8 Package 8-Lead Plastic MSOP (Reference LTC DWG # 05-08-1660) 3.00 ± 0.102 (.118 ± .004) (NOTE 3) 0.889 ± 0.127 (.035 ± .005) 5.23 (.206) MIN 0.42 ± 0.04 (.0165 ± .0015) TYP 3.2 – 3.45 (.126 – .136) 0.65 (.0256) BSC 0.254 (.010) 8 7 6 5 3.00 ± 0.102 (.118 ± .004) NOTE 4 4.88 ± 0.1 (.192 ± .004) DETAIL “A” 0.52 (.206) REF 0° – 6° TYP GAUGE PLANE 0.53 ± 0.015 (.021 ± .006) RECOMMENDED SOLDER PAD LAYOUT DETAIL “A” 1 1.10 (.043) MAX 2 3 4 0.86 (.
PAGE 18
LTC1864/LTC1865 U PACKAGE DESCRIPTIO MS Package 10-Lead Plastic MSOP (Reference LTC DWG # 05-08-1661) 3.00 ± 0.102 (.118 ± .004) (NOTE 3) 0.889 ± 0.127 (.035 ± .005) 5.23 (.206) MIN 10 9 8 7 6 3.2 – 3.45 (.126 – .136) 0.50 0.305 ± 0.038 (.0197) (.0120 ± .0015) BSC TYP RECOMMENDED SOLDER PAD LAYOUT 0.254 (.010) 3.00 ± 0.102 (.118 ± .004) NOTE 4 4.88 ± 0.10 (.192 ± .004) DETAIL “A” 0.497 ± 0.076 (.0196 ± .003) REF 0° – 6° TYP GAUGE PLANE 1 2 3 4 5 0.53 ± 0.01 (.021 ± .006) DETAIL “A” 0.86 (.
PAGE 19
LTC1864/LTC1865 U PACKAGE DESCRIPTIO S8 Package 8-Lead Plastic Small Outline (Narrow .150 Inch) (Reference LTC DWG # 05-08-1610) 0.189 – 0.197* (4.801 – 5.004) 8 7 6 5 0.150 – 0.157** (3.810 – 3.988) 0.228 – 0.244 (5.791 – 6.197) SO8 1298 1 0.010 – 0.020 × 45° (0.254 – 0.508) 0.008 – 0.010 (0.203 – 0.254) 0.053 – 0.069 (1.346 – 1.752) 0°– 8° TYP 0.016 – 0.050 (0.406 – 1.270) 0.014 – 0.019 (0.355 – 0.483) TYP *DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.006" (0.
PAGE 20
LTC1864/LTC1865 U TYPICAL APPLICATIO Sample Two Channels Simultaneously with a Single Input ADC 4096 Point FFT of Output 5V 0.1µF f1 (0V TO 0.66V) + 4.096V REF 5k 4.096V REF 100Ω 1/2 LT1492 – 100pF 0.1µF 1µF 0.1µF 1µF 8 VCC 28.7k 5pF 10k 10k 2 1µF 3 0.1µF f2 (0V TO 2V) IN+ IN– 5V 5k + 8 0.1µF 4 1 REF 7 SCK 6 LTC1864 SDO 5 CONV GND 4 100Ω 1/2 LT1492 – AMPLITUDE (dB) 20k 0 10 20 30 40 50 60 70 80 90 100 110 120 130 f1 = 7.507324kHz AT 530mVP-P f2 = 45.007324kHz AT 1.
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