Datasheet

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LTC1864L/LTC1865L

sn18645L 18645Lfs

APPLICATIO S

FEATURES

DESCRIPTIO

TYPICAL APPLICATIO

µPower, 3V, 16-Bit, 150ksps

1- and 2-Channel ADCs in MSOP

Single 3V Supply, 150ksps, 16-Bit Sampling ADC

Supply Current vs Sampling Frequency

The LTC

1864L/LTC1865L are 16-bit A/D converters that

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

single 3V supply. At 150ksps, the supply current is only

450µA. The supply current drops at lower speeds because

the LTC1864L/LTC1865L automatically power down

between conversions. These 16-bit switched capacitor

successive approximation ADCs include sample-and-holds.

The LTC1864L has a differential analog input with an

external reference pin. The LTC1865L offers a software-

selectable 2-channel MUX and an external 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 150ksps ADCs in MSOP Package

■

Single 3V Supply

■

Low Supply Current: 450µA (Typ)

■

Auto Shutdown Reduces Supply Current

to 10µA at 1ksps

■

True Differential Inputs

■

1-Channel (LTC1864L) or 2-Channel (LTC1865L)

Versions

■

SPI/MICROWIRE

Compatible Serial I/O

■

16-Bit Upgrade to 12-Bit LTC1285/LTC1288

■

Pin Compatible with 12-Bit LTC1860L/LTC1861L

■

No Minimum Data Transfer Rate

, 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

LTC1864L

1864 TA01

ANALOG INPUT

0V TO 3V

1µF

SERIAL DATA LINK TO

ASIC, PLD, MPU, DSP

OR SHIFT REGISTERS

MICROWIRE is a trademark of National Semiconductor Corporation.

SAMPLING FREQUENCY (kHz)

0.1

SUPPLY CURRENT (µA)

100

1000

0.01 1 10 1000

1864L/65L TA02

0.1 100

CONV LOW = 2µs

= 25°C

= 2.7V

Summary of content (16 pages)

PAGE 1
LTC1864L/LTC1865L µPower, 3V, 16-Bit, 150ksps 1- and 2-Channel ADCs in MSOP U FEATURES DESCRIPTIO ■ The LTC®1864L/LTC1865L are 16-bit A/D converters that are offered in MSOP and SO-8 packages and operate on a single 3V supply. At 150ksps, the supply current is only 450µA. The supply current drops at lower speeds because the LTC1864L/LTC1865L automatically power down between conversions. These 16-bit switched capacitor successive approximation ADCs include sample-and-holds.
PAGE 2
LTC1864L/LTC1865L W W W AXI U U ABSOLUTE RATI GS (Notes 1, 2) Supply Voltage (VCC) ................................................. 7V Ground Voltage Difference AGND, DGND LTC1865L 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
LTC1864L/LTC1865L 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 = 2.7V, VREF = 2.5V, fSCK = fSCK(MAX) as defined in Recommended Operating Conditions, unless otherwise noted.
PAGE 4
LTC1864L/LTC1865L 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.
PAGE 5
LTC1864L/LTC1865L U W TYPICAL PERFOR A CE CHARACTERISTICS Supply Current vs Sampling Frequency Sleep Current vs Temperature Supply Current vs Temperature 600 20 fS = 150kHz VCC = 2.7V VREF = 2.5V 500 100 10 1 SHUTDOWN CURRENT (µA) CONV LOW = 2µs TA = 25°C VCC = 2.7V SUPPLY CURRENT (µA) SUPPLY CURRENT (µA) 1000 400 300 200 fS = 150kHz VCC = 2.7V VREF = 2.5V 15 10 5 100 0.1 0.01 0.
PAGE 6
LTC1864L/LTC1865L U W TYPICAL PERFOR A CE CHARACTERISTICS Change in Offset vs Reference Voltage fS = 150kHz TA = 25°C VCC = 3.6V VCC = 2.7V VREF = 2.5V 10 5 0 –5 –10 3 2 1 0 –1 –2 –3 –15 –4 –20 –5 2 3 1 REFERENCE VOLTAGE (V) 0 4 50 25 75 0 TEMPERATURE (°C) –50 –25 VCC = 2.7V VREF = 2.
PAGE 7
LTC1864L/LTC1865L U U U PI FU CTIO S LTC1864L 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.
PAGE 8
LTC1864L/LTC1865L W FUNCTIONAL BLOCK DIAGRA U CONV (SDI) SCK U VCC PIN NAMES IN PARENTHESES REFER TO LTC1865L 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 Wav
PAGE 9
LTC1864L/LTC1865L U W U U APPLICATIO S I FOR ATIO LTC1864L OPERATION Analog Inputs Operating Sequence The LTC1864L 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
LTC1864L/LTC1865L U W U U APPLICATIO S I FOR ATIO LTC1865L OPERATION Operating Sequence The LTC1865L 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 LTC1865L goes into sleep mode drawing only leakage current. The LTC1865L’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.
PAGE 11
LTC1864L/LTC1865L U W U U APPLICATIO S I FOR ATIO GENERAL ANALOG CONSIDERATIONS Grounding The LTC1864L/LTC1865L 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.
PAGE 12
J1 J2 E9 E8 P3 P2 P1 P0 3.3VDIG 1 4 2 3 JP9 3 JP8 4 IN – IN + 1 2 5 6 3 2 IN – AGND 5 6 3 2 IN + 15V 15V 5 6 5 6 2 3 P3 P2 P1 P0 – + VIN U9A 74AC00 1 2 3 4 5 6 7 8 ON 1 1 6 RESET CLK P0 P1 P2 P3 ENP GND VCC RCO Q0 Q1 Q2 Q3 ENT LO U6 74HC163AD 2 JP1 +IN 3 R1 100Ω 1206 BUF 3 R3 2Ω 16 15 14 13 12 11 10 9 BUF OFF JP2 R2 100Ω –IN GND JP3 2 6 U9B 74AC00 IN– 3.3VDIG 3 C6 –15V 0.1µF 4 U2 OPT 7 IN+ 1 VOUT GND 4 C5 15V 0.1µF C20 0.
PAGE 13
LTC1864L/LTC1865L U W U U APPLICATIO S I FOR ATIO Component Side Silk Screen for LTC1864L 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 sn18645L 18645Lfs 13
PAGE 14
LTC1864L/LTC1865L U PACKAGE DESCRIPTIO MS8 Package 8-Lead Plastic MSOP (Reference LTC DWG # 05-08-1660) 0.889 ± 0.127 (.035 ± .005) 5.23 (.206) MIN 3.2 – 3.45 (.126 – .136) 3.00 ± 0.102 (.118 ± .004) (NOTE 3) 0.65 (.0256) BSC 0.42 ± 0.04 (.0165 ± .0015) TYP 8 7 6 5 0.52 (.206) REF RECOMMENDED SOLDER PAD LAYOUT 0.254 (.010) 3.00 ± 0.102 (.118 ± .004) NOTE 4 4.90 ± 0.15 (1.93 ± .006) DETAIL “A” 0° – 6° TYP GAUGE PLANE 1 0.53 ± 0.015 (.021 ± .006) DETAIL “A” 2 3 4 1.10 (.043) MAX 0.86 (.
PAGE 15
LTC1864L/LTC1865L U PACKAGE DESCRIPTIO S8 Package 8-Lead Plastic Small Outline (Narrow .150 Inch) (Reference LTC DWG # 05-08-1610) .189 – .197 (4.801 – 5.004) NOTE 3 .045 ±.005 .050 BSC 8 .245 MIN 7 6 5 .160 ±.005 .150 – .157 (3.810 – 3.988) NOTE 3 .228 – .244 (5.791 – 6.197) .030 ±.005 TYP 1 RECOMMENDED SOLDER PAD LAYOUT .010 – .020 × 45° (0.254 – 0.508) 3 2 4 .053 – .069 (1.346 – 1.752) .008 – .010 (0.203 – 0.254) .004 – .010 (0.101 – 0.254) 0°– 8° TYP .016 – .050 (0.406 – 1.270) .
PAGE 16
LTC1864L/LTC1865L U TYPICAL APPLICATIO Tiny 2-Chip Data Acquisition System 1µF 3V 3V 0.1µF 8 + 3 VIN 4 LTC6910-1 – 2 7 6 VREF 1 499Ω 5 270pF IN+ SCK LTC1864L SDO IN – GND AGND 1µF VCC CONV ADC GAIN CONTROL CONTROL LTC6910-1 (IN TSOT-23 PACKAGE) COMPACTLY ADDS 40dB OF INPUT GAIN RANGE TO THE LTC1864L (IN MSOP 8-PIN PACKAGE). SINGLE 3V SUPPLY 1864L/65L TA03 RELATED PARTS PART NUMBER SAMPLE RATE POWER DISSIPATION DESCRIPTION 12-Bit Serial I/O ADCs LTC1860L/LTC1861L 150ksps 1.