LTC1857/LTC1858/LTC1859
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For more information www.linear.com/LTC1857
100kHz, 12-Bit/14-Bit/16-Bit Sampling ADC
TYPICAL APPLICATION
FEATURES
APPLICATIONS
DESCRIPTION
8-Channel, 12-/14-/16-Bit,
100ksps SoftSpan A/D
Converters with Shutdown
The LT C
®
1857/LTC1858/LTC1859 are 8-channel, low
power, 12-/14-/16-bit, 100ksps, analog-to-digital convert-
ers (ADCs). These SoftSpan™ ADCs can be software-
programmed for 0V to 5V, 0V to 10V, ±5V or ±10V input
spans and operate from a single 5V supply. The 8-channel
multiplexer can be programmed for single-ended inputs
or pairs of differential inputs or combinations of both. In
addition, all channels are fault protected to ±25V. A fault
condition on any channel will not affect the conversion
result of the selected channel.
An onboard high performance sample-and-hold and pre-
cision reference minimize external components. The low
40mW power dissipation is made even more attractive with
two user selectable power shutdown modes. DC specifica-
tions include ±3LSB INL for the LTC1859, ±1.5LSB INL
for the LTC1858 and ±1LSB for the LTC1857.
The internal clock is trimmed for 5µs maximum conversion
time and the sampling rate is guaranteed at 100ksps. A
separate convert start input and data ready signal (BUSY)
ease connections to FIFOs, DSPs and microprocessors.
n Sample Rate: 100ksps
n 8-Channel Multiplexer with ±25V Protection
n Single 5V Supply
n Software-Programmable Input Ranges:
n 0V to 5V, 0V to 10V, ±5V or ±10V
n Single-Ended or Differential
n ±3LSB INL for the LTC1859, ±1.5LSB INL for the
LTC1858, ±1LSB INL for the LTC1857
n Power Dissipation: 40mW (Typ)
n SPI/MICROWIRE™ Compatible Serial I/O
n Power Shutdown: Nap and Sleep
n Signal-to-Noise Ratio: 87dB (Typ) for the LTC1859
n Operates with Internal or External Reference
n Internal Synchronized Clock
n 28-Pin SSOP Package
n Industrial Process Control
n Multiplexed Data Acquisition Systems
n High Speed Data Acquisition for PCs
n Digital Signal Processing L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. SoftSpan is
a trademark of Linear Technology Corporation. All other trademarks are the property of their
respective owners.
LTC1859 Typical INL Curve
COM
CH0
CH1
CH2
CH3
CH4
CH5
CH6
CH7
MUXOUT+
MUXOUT–
ADC+
ADC–
AGND1
CONVST
RD
SCK
SDI
DGND
SDO
BUSY
OVDD
DVDD
AVDD
AGND3
AGND2
REFCOMP
VREF
LTC1857/
LTC1858/
LTC1859
SOFTWARE-PROGRAMMABLE
SINGLE-ENDED OR
DIFFERENTIAL INPUTS
(0V TO 5V, 0V TO 10V,
±5V OR ±10V)
10µF
10µF1µF
10µF
3V TO 5V
5V
5V
2.5V
10µF
µP
CONTROL
LINES
CODE
–32768
INL (LSB)
0
0.5
1.0
0
1859 TA02
–0.5
–1.0
–2.0 –16384 16384 32767
–1.5
2.0
1.5
LTC1857/LTC1858/LTC1859
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For more information www.linear.com/LTC1857
PIN CONFIGURATIONABSOLUTE MAXIMUM RATINGS
Supply Voltage (OVDD = DVDD = AVDD = VDD) ............. 6V
Ground Voltage Difference
DGND, AGND1, AGND2, AGND3 ........................±0.3V
Analog Input Voltage
ADC+, ADC–
(Note 3) ................. (AGND1 – 0.3V) to (AVDD + 0.3V)
CH0-CH7, COM ..................................................±25V
Digital Input Voltage (Note 4) .......(DGND – 0.3V) to 10V
Digital Output Voltage ..(DGND – 0.3V) to (DVDD + 0.3V)
Power Dissipation ...............................................500mW
Operating Temperature Range
LTC1857C/LTC1858C/LTC1859C .............. 0°C to 70°C
LTC1857I/LTC1858I/LTC1859I .............. –40°C to 85°C
Storage Temperature Range ................... –65°C to 150°C
Lead Temperature (Soldering, 10 sec) .................. 300°C
(Note 1)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
TOP VIEW
G PACKAGE
28-LEAD PLASTIC SSOP
28
27
26
25
24
23
22
21
20
19
18
17
16
15
COM
CH0
CH1
CH2
CH3
CH4
CH5
CH6
CH7
MUXOUT+
MUXOUT–
ADC+
ADC–
AGND1
CONVST
RD
SCK
SDI
DGND
SDO
BUSY
OVDD
DVDD
AVDD
AGND3
AGND2
REFCOMP
VREF
TJMAX = 110°C, θJA = 95°C/W
ORDER INFORMATION
LEAD FREE FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION TEMPERATURE RANGE
LTC1857CG#PBF LTC1857CG#TRPBF LTC1857CG 28-Lead Plastic SSOP 0°C to 70°C
LTC1857IG#PBF LTC1857IG#TRPBF LTC1857IG 28-Lead Plastic SSOP –40°C to 85°C
LTC1858CG#PBF LTC1858CG#TRPBF LTC1858CG 28-Lead Plastic SSOP 0°C to 70°C
LTC1858IG#PBF LTC1858IG#TRPBF LTC1858IG 28-Lead Plastic SSOP –40°C to 85°C
LTC1859CG#PBF LTC1859CG#TRPBF LTC1859CG 28-Lead Plastic SSOP 0°C to 70°C
LTC1859IG#PBF LTC1859IG#TRPBF LTC1859IG 28-Lead Plastic SSOP –40°C to 85°C
Consult LTC Marketing for parts specified with wider operating temperature ranges.
For more information on lead free part marking, go to: http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/
LTC1857/LTC1858/LTC1859
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For more information www.linear.com/LTC1857
The l denotes the specifications which
apply over the full operating temperature range, otherwise specifications are at TA = 25°C. MUXOUT connected to ADC inputs. (Notes 5, 6)
CONVERTER AND MULTPLEXER CHARACTERISTICS
PARAMETER CONDITIONS
LTC1857 LTC1858 LTC1859
UNITSMIN TYP MAX MIN TYP MAX MIN TYP MAX
Resolution l12 14 16 Bits
No Missing Codes l12 14 15 Bits
Transition Noise 0.06 0.26 1 LSBRMS
Integral Linearity Error (Notes 7, 15) l±1 ±1.5 ±3 LSB
Differential Linearity Error (Note 15) l–1 1 –1 1.5 –2 4 LSB
Bipolar Zero Error (Note 8) l±9 ±17 ±28 LSB
Bipolar Zero Error Drift ±0.1 ±0.1 ±0.1 ppm/°C
Bipolar Zero Error Match ±4 ±6 ±10 LSB
Unipolar Zero Error (Note 8) l±6 ±15 ±25 LSB
Unipolar Zero Error Drift ±1 ±1 ±1 ppm/°C
Unipolar Zero Error Match ±1.2 ±2 ±8 LSB
Bipolar Full-Scale Error External Reference (Note 11)
Internal Reference (Note 11)
l±0.35
±0.45
±0.15
±0.4
±0.1
±0.4
%
%
Bipolar Full-Scale Error Drift External Reference
Internal Reference
±2.5
±7
±2.5
±7
±2.5
±7
ppm/°C
ppm/°C
Bipolar Full-Scale Error Match ±5 ±10 ±15 LSB
Unipolar Full-Scale Error External Reference (Note 11)
Internal Reference (Note 11)
l±0.45
±0.75
±0.25
±0.85
±0.2
±0.75
%
%
Unipolar Full-Scale Error Drift External Reference
Internal Reference
±2.5
±7
±2.5
±7
±2.5
±7
ppm/°C
ppm/°C
Unipolar Full-Scale Error Match ±5 ±12 ±15 LSB
Input Common Mode Range Unipolar Mode
Bipolar Mode
l
l
0 to 10
±10
0 to 10
±10
0 to 10
±10
V
V
Input Common Mode Rejection Ratio 96 96 96 dB
The l denotes the specifications which apply over the full operating temperature range, otherwise
specifications are at TA = 25°C. (Note 5)
ANALOG INPUT
PARAMETER CONDITIONS MIN TYP MAX UNITS
Analog Input Range CH0 to CH7, COM 0 to 5, 0 to 10
±5, ±10
V
V
ADC+, ADC– (Note 3) 0 to 2.048
0 to 4.096
ADC– ±1.024
ADC– ±2.048
V
V
V
V
Impedance CH0 to CH7, COM
Unipolar
Bipolar
42
31
kΩ
kΩ
MUXOUT+, MUXOUT–
Unipolar
Bipolar
10
5
kΩ
kΩ
ADC+, ADC–Hi-Z kΩ
Capacitance CH0 to CH7, COM 5 pF
Sample Mode ADC+, ADC–
0V to 2.048V, ±1.024V
0V to 4.096V, ±2.048V
24
12
pF
pF
Hold Mode ADC+, ADC–4 pF
Input Leakage Current ADC+, ADC–, CONVST = Low l±1 µA
LTC1857/LTC1858/LTC1859
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For more information www.linear.com/LTC1857
DYNAMIC ACCURACY
SYMBOL PARAMETER CONDITIONS
LTC1857 LTC1858 LTC1859
UNITSMIN TYP MAX MIN TYP MAX MIN TYP MAX
S/(N + D) Signal-to-(Noise + Distortion) Ratio 1kHz Input Signal 74 83 87 dB
THD Total Harmonic Distortion 1kHz Input Signal,
First Five Harmonics
–101 –101 –101 dB
Peak Harmonic or Spurious Noise 1kHz Input Signal –103 –103 –103 dB
Channel-to-Channel Isolation 1kHz Input Signal –120 –120 –120 dB
–3dB Input Bandwidth 1 1 1 MHz
Aperture Delay –70 –70 –70 ns
Aperture Jitter 60 60 60 ps
Transient Response Full-Scale Step
(Note 9)
4 4 4 µs
Overvoltage Recovery (Note 13) 150 150 150 ns
The l denotes the specifications which apply over the full operating temperature range,
otherwise specifications are at TA = 25°C. MUXOUT connected to ADC inputs. (Notes 5, 12)
PARAMETER CONDITIONS MIN TYP MAX UNITS
VREF Output Voltage IOUT = 0 l2.475 2.5 2.525 V
VREF Output Temperature Coefficient IOUT = 0 ±10 ppm/°C
VREF Output Impedance –0.1mA ≤ IOUT ≤ 0.1mA 8 kΩ
VREFCOMP Output Voltage IOUT = 0 4.096 V
INTERNAL REFERENCE CHARACTERISTICS
The l denotes the specifications which apply over the
full operating temperature range, otherwise specifications are at TA = 25°C. (Note 5)
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 5)
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
VIH High Level Input Voltage VDD = 5.25V l2.4 V
VIL Low Level Input Voltage VDD = 4.75V l0.8 V
IIN Digital Input Current VIN = 0V to VDD l±10 µA
CIN Digital Input Capacitance 5 pF
VOH High Level Output Voltage VDD = 4.75V, IO = –10µA, OVDD = VDD
VDD = 4.75V, IO = –200µA, OVDD = VDD
l
4
4.74 V
V
VOL Low Level Output Voltage VDD = 4.75V, IO = 160µA, OVDD = VDD
VDD = 4.75V, IO = 1.6mA, OVDD = VDD
l
0.05
0.10
0.4
V
V
IOZ Hi-Z Output Leakage VOUT = 0V to VDD, RD = High l±10 µA
COZ Hi-Z Output Capacitance RD = High 15 pF
ISOURCE Output Source Current VOUT = 0V –10 mA
ISINK Output Sink Current VOUT = VDD 10 mA
POWER REQUIREMENTS
The l denotes the specifications which apply over the full operating temperature
range, otherwise specifications are at TA = 25°C. (Note 5)
PARAMETER CONDITIONS MIN TYP MAX UNITS
Positive Supply Voltage (Notes 9 and 10) 4.75 5 5.25 V
Positive Supply Current
Nap Mode
Sleep Mode
CONVST = 0V or 5V
l8
5.5
8
13
8
15
mA
mA
µA
Power Dissipation
Nap Mode
Sleep Mode
CONVST = 0V or 5V
40
27.5
40
mW
mW
µW
LTC1857/LTC1858/LTC1859
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For more information www.linear.com/LTC1857
TIMING CHARACTERISTICS
The l denotes the specifications which apply over the full operating temperature
range, otherwise specifications are at TA = 25°C. (Note 5)
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
fSAMPLE(MAX) Maximum Sampling Frequency Through CH0 to CH7 Inputs
Through ADC+, ADC– Only
l100
166
kHz
kHz
tCONV Conversion Time l4 5 µs
tACQ Acquisition Time Through CH0 to CH7 Inputs
Through ADC+, ADC– Only
l
1
4 µs
µs
fSCK SCK Frequency (Note 14) l0 20 MHz
trSDO Rise Time See Test Circuits 6 ns
tfSDO Fall Time See Test Circuits 6 ns
t1CONVST High Time l40 ns
t2CONVST to BUSY Delay CL = 25pF, See Test Circuits l15 30 ns
t3SCK Period l50 ns
t4SCK High l10 ns
t5SCK Low l10 ns
t6Delay Time, SCK↓ to SDO Valid CL = 25pF, See Test Circuits l25 45 ns
t7Time from Previous SDO Data Remains
Valid After SCK↓CL = 25pF, See Test Circuits l5 20 ns
t8SDO Valid After RD↓CL = 25pF, See Test Circuits l11 30 ns
t9RD↓ to SCK Setup Time l20 ns
t10 SDI Setup Time Before SCK↑l0 ns
t11 SDI Hold Time After SCK↑l7 ns
t12 SDO Valid Before BUSY↑RD = Low, CL = 25pF, See Test Circuits l5 20 ns
t13 Bus Relinquish Time See Test Circuits l10 30 ns
Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2: All voltage values are with respect to ground with DGND, AGND1,
AGND2 and AGND3 wired together unless otherwise noted.
Note 3: When these pin voltages are taken below ground or above AVDD =
DVDD = OVDD = VDD, they will be clamped by internal diodes. This product
can handle currents of greater than 100mA below ground or above VDD
without latchup.
Note 4: When these pin voltages are taken below ground they will be
clamped by internal diodes. This product can handle currents of greater
than 100mA below ground without latchup. These pins are not clamped
to VDD.
Note 5: VDD = 5V, fSAMPLE = 100kHz, tr = tf = 5ns unless otherwise
specified.
Note 6: Linearity, offset and full-scale specifications apply for a single-
ended analog MUX input with respect to ground or ADC+ with respect to
ADC– tied to ground.
Note 7: Integral nonlinearity is defined as the deviation of a code from a
straight line passing through the actual end points of the transfer curve.
The deviation is measured from the center of the quantization band.
Note 8: Bipolar zero error is the offset voltage measured from –0.5LSB
when the output code flickers between 0000 0000 0000 0000 and 1111
1111 1111 1111 for the LTC1859, between 00 0000 0000 0000 and 11
1111 1111 1111 for the LTC1858 and between 0000 0000 0000 and
1111 1111 1111 for the LTC1857. Unipolar zero error is the offset voltage
measured from 0.5LSB when the output codes flicker between 0000 0000
0000 0000 and 0000 0000 0000 0001 for the LTC1859, between 00 0000
0000 0000 and 00 0000 0000 0001 for the LTC1858 and between 0000
0000 0000 and 0000 0000 0001 for the LTC1857.
Note 9: Guaranteed by design, not subject to test.
Note 10: Recommended operating conditions.
Note 11: Full-scale bipolar error is the worst case of –FS or +FS
untrimmed deviation from ideal first and last code transitions, divided by
the full-scale range, and includes the effect of offset error. For unipolar
full-scale error, the deviation of the last code transition from ideal, divided
by the full-scale range, and includes the effect of offset error.
Note 12: All Specifications in dB are referred to a full-scale ±10V input.
Note 13: Recovers to specified performance after (2 • FS) input
overvoltage.
Note 14: t6 of 45ns maximum allows fSCK up to 10MHz for rising capture
with 50% duty cycle and fSCK up to 20MHz for falling capture (with 5ns
setup time for the receiving logic).
Note 15: The specification is referred to the ±10V input range.
LTC1857/LTC1858/LTC1859
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For more information www.linear.com/LTC1857
CODE
–32768
INL (LSB)
0
0.5
1.0
0
1859 G01
–0.5
–1.0
–2.0 –16384 16384 32767
–1.5
2.0
1.5
CODE
–32768
DNL (LSB)
0
0.5
1.0
0
1859 G02
–0.5
–1.0
–2.0 –16384 16384 32767
–1.5
2.0
1.5
FREQUENCY (kHz)
0 15 25 50
1869 G03
5 10 20 30 40 45
35
MAGNITUDE (dB)
–60
–40
–20
0
–80
–100
–70
–50
–30
–10
–90
–110
–130
–120
fSAMPLE = 100kHz
fIN = 1kHz
SINAD = 86.95dB
THD = –101.42dB
TYPICAL PERFORMANCE CHARACTERISTICS
LTC1859 Typical INL Curve
LTC1859 Typical DNL Curve
LTC1859 Nonaveraged
4096-Point FFT Plot
LTC1859 SINAD
vs Input Frequency
LTC1859 Total Harmonic
Distortion vs Input Frequency
LTC1859 Channel-to-Channel
Offset Error Matching vs
Temperature
LTC1859 Channel-to-Channel Gain
Error Matching vs Temperature
Internal Reference Voltage
vs Temperature
Change in REFCOMP Voltage
vs Load Current
INPUT FREQUENCY (kHz)
1
74
SINAD (dB)
78
82
90
10 100
1859 G04
86
76
80
88
84
INPUT FREQUENCY (kHz)
1
–110
TOTAL HARMONIC DISTORTION (dB)
–100
–90
–70
10 100
1859 G05
–80
TEMPERATURE (°C)
–50
–1.0
CHANNEL-TO-CHANNEL
OFFSET ERROR MATCHING (LSBs)
–0.5
0
0.5
1.0
–25 0 25 50
1959 G06
75 100
BIPOLAR MODE
UNIPOLAR MODE
TEMPERATURE (°C)
–50
–1.0
CHANNEL-TO-CHANNEL
GAIN ERROR MATCHING (LSBs)
–0.5
0
0.5
1.0
–25 0 25 50
1959 G07
75 100
BIPOLAR MODE
UNIPOLAR MODE
TEMPERATURE (°C)
–50
INTERNAL REFERENCE VOLTAGE (V)
25 75
1859 G08
–25 0 50
2.520
2.515
2.510
2.505
2.500
2.495
2.490
2.485
2.480 100
LOAD CURRENT (mA)
–50
–0.04
CHANGE IN REFCOMP VOLTAGE (V)
–0.02
0
0.02
0.04
–40 –30 –20 –10
1859 G09
0 10
LTC1857/LTC1858/LTC1859
7
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For more information www.linear.com/LTC1857
TYPICAL PERFORMANCE CHARACTERISTICS
LTC1859 Power Supply
Feedthrough vs Ripple Frequency
Supply Current vs Supply Voltage
Supply Current vs Temperature
COM (Pin 1): Common Input. This is the reference point
for all single-ended inputs. It must be free of noise and is
usually connected to the analog ground plane.
CH0 (Pin 2): Analog MUX Input.
CH1 (Pin 3): Analog MUX Input.
CH2 (Pin 4): Analog MUX Input.
CH3 (Pin 5): Analog MUX Input.
CH4 (Pin 6): Analog MUX Input.
CH5 (Pin 7): Analog MUX Input.
CH6 (Pin 8): Analog MUX Input.
CH7 (Pin 9): Analog MUX Input.
MUXOUT+ (Pin 10): Positive MUX Output. Output of the ana-
log multiplexer. Connect to ADC+ for normal operation.
MUXOUT– (Pin 11): Negative MUX Output. Output of the ana-
log multiplexer. Connect to ADC– for normal operation.
ADC+ (Pin 12): Positive Analog Input to the Analog-to-
Digital Converter.
ADC– (Pin 13): Negative Analog Input to the Analog-to-
Digital Converter.
AGND1 (Pin 14): Analog Ground.
VREF (Pin 15): 2.5V Reference Output. Bypass to analog
ground with a 1µF tantalum capacitor.
REFCOMP (Pin 16): Reference Buffer Output. Bypass to
analog ground with a 10µF tantalum and a 0.1µF ceramic
capacitor. Nominal output voltage is 4.096V.
AGND2 (Pin 17): Analog Ground.
AGND3 (Pin 18): Analog Ground. This is the substrate
connection.
AVDD (Pin 19): 5V Analog Supply. Bypass to analog ground
with a 0.1µF ceramic and a 10µF tantalum capacitor.
DVDD (Pin 20): 5V Digital Supply. Bypass to digital ground
with a 0.1µF ceramic and a 10µF tantalum capacitor.
OVDD (Pin 21): Positive Supply for the Digital Output
Buffers (3V to 5V). Bypass to digital ground with a 0.1µF
ceramic and a 10µF tantalum capacitor.
BUSY (Pin 22): Output shows converter status. It is low
when a conversion is in progress.
SDO (Pin 23): Serial Data Output.
PIN FUNCTIONS
RIPPLE FREQUENCY (Hz)
–60
POWER SUPPLY FEEDTHROUGH (dB)
–40
–20
–10
100 10k 100k 1M
1859 G10
–80
1k
–30
–50
–70
fSAMPLE = 100kHz
VRIPPLE = 60mV
SUPPLY VOLTAGE (V)
4.5
SUPPLY CURRENT (mA)
8.0
8.5
5.5
1859 G11
7.5
7.0 4.75 55.25
9.0
fSAMPLE = 100kHz
TEMPERATURE (°C)
–50
7.0
POSITIVE SUPPLY CURRENT (mA)
7.5
8.0
8.5
9.0
–25 0 25 50
1859 G12
75 100
fSAMPLE = 100kHz
LTC1857/LTC1858/LTC1859
8
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For more information www.linear.com/LTC1857
FUNCTIONAL BLOCK DIAGRAM
PIN FUNCTIONS
DGND (Pin 24): Digital Ground.
SDI (Pin 25): Serial Data Input. SDI will ignore clocked
data while RD is high.
SCK (Pin 26): Serial Data Clock.
RD (Pin 27): Read Input. This active low signal enables
the digital output pin SDO.
CONVST (Pin 28): Conversion Start. This active high signal
starts a conversion on its rising edge.
TEST CIRCUITS
2.5V
REFERENCE
INTERNAL
CLOCK
1.6384X
4.096V
8k
AGND1
CONTROL
LOGIC
SERIAL I/O
INPUT MUX
AND
RANGE
SELECT
AGND3
AGND2REFCOMPVREF
ADC–
MUXOUT+
MUXOUT–ADC+
DGND
AVDD DVDD
MUX ADDRESS AND RANGE
DATA OUT
CONVST
SDI
BUSY
SCK
RD
OVDD
SDO
1859 BD
12-/14-/16-BIT
SAMPLING ADC
+
–
COM
CH7
CH1
•
•
•
CH0
1k
(A) Hi-Z TO VOH AND VOL TO VOH
25pF
1k
DNDN
(B) Hi-Z TO VOL AND VOH TO VOL
25pF
1859 TC01
1k
(A) VOH TO Hi-Z
25pF
1k
5V
DNDN
(B) VOL TO Hi-Z
25pF
1859 TC02
Load Circuits for Access Timing Load Circuits for Output Float Delay
LTC1857/LTC1858/LTC1859
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TIMING DIAGRAMS
t1 (For Short Pulse Mode)
t1
CONVST 50%
1859 TD01
50%
t
2
(CONVST to BUSY Delay)
t2
CONVST
BUSY
2.4V
0.4V
1859 TD02
t3, t4, t5 (SCK Timing)
SCK
1859 TD03
t4t5
t3
t6 (Delay Time, SCK
↓
to SDO Valid)
t7 (Time from Previous Data Remains Valid After SCK↓)
t6
t7
SCK
SDO 2.4V
0.4V
0.4V
1859 TD04
t8 (SDO Valid After RD
↓
)
t8
RD
SDO 2.4V
0.4V
0.4V
1859 TD05
Hi-Z
t
9
(RD↓ to SCK Setup Time)
t9
0.4V
2.4V
1959 TD06
RD
SCK
t10 (SDI Setup Time Before SCK↑)
t10
SCK
SDI 2.4V
2.4V
0.4V
1859 TD07
t
11
(SDI Hold Time After SCK↑)
t11
SCK
SDI 2.4V
2.4V
0.4V
1859 TD08
t
12
(SDO Valid Before BUSY↑, RD = 0)
t12
BUSY
SDO 2.4V B15
2.4V
1859 TD09
t
13
(BUS Relinquish Time)
t13
RD
SDO
2.4V
1859 TD10
10%
90% Hi-Z
LTC1857/LTC1858/LTC1859
10
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For more information www.linear.com/LTC1857
OPERATION
OVERVIEW
The LTC1857/LTC1858/LTC1859 are innovative, multichan-
nel ADCs that provide software-selectable input ranges for
each of their eight input channels. Using on-chip resistors
and switches, it provides an attenuation and offset that can
be programmed for each channel on the fly. The precisely
trimmed attenuators ensure accurate input ranges. Because
they precede the multiplexer, errors due to multiplexer
on-resistance are eliminated.
The input word that selects the input channel also selects the
desired input range for that channel. The available ranges
are 0V to 5V, 0V to 10V (unipolar), ±5V and ±10V (bipolar).
They are achieved with the ADC running on a single 5V
supply. In addition to the range selection, single-ended
or differential inputs may be selected for each channel or
pair of channels. Finally, overrange protection is provided
for unselected channels. An overrange condition on an
unused channel will not affect the conversion result on
the selected channel.
CONVERSION DETAILS
The LTC1857/LTC1858/LTC1859 use a successive ap-
proximation algorithm and an internal sample-and-hold
circuit to convert an analog signal to a 12-/14-/16-bit serial
output respectively. The ADCs are complete with a precision
reference and an internal clock. The control logic provides
easy interface to microprocessors and DSPs. (Please refer
to the Digital Interface section for the data format.)
The analog signals applied at the MUX input channels are
rescaled by the resistor divider network formed by R1, R2
and R3 as shown below. The rescaled signals appear on
the MUXOUT (Pins 10, 11) which are also connected to
the ADC inputs (Pins 12, 13) under normal operation.
Before starting a conversion, an 8-bit data word is clocked
into the SDI input on the first eight rising SCK edges to
select the MUX address, input range and power down
mode. The ADC enters acquisition mode on the falling
edge of the sixth clock in the 8-bit data word and ends
on the rising edge of the CONVST signal which also starts
a conversion (see Figure 7). A minimum time of 4µs will
provide enough time for the sample-and-hold capacitors
to acquire the analog signal. Once a conversion cycle has
begun, it cannot be restarted.
During the conversion, the internal differential 12-/14-
/16-bit capacitive DAC output is sequenced by the SAR from
the most significant bit (MSB) to the least significant bit
(LSB). The input is successively compared with the binary
weighted charges supplied by the differential capacitive
DAC. Bit decisions are made by a high speed comparator.
At the end of a conversion, the DAC output balances the
analog input (ADC+ – ADC–). The SAR contents (a 16-bit
data word) which represents the difference of ADC+ and
ADC– are loaded into the 12-/14-/16-bit shift register.
DRIVING THE ANALOG INPUTS
The nominal input ranges for the LTC1857/LTC1858/
LTC1859 are 0V to 5V, 0V to 10V, ±5V and ±10V and the
MUX inputs are overvoltage protected to ± 25V. The input
impedance is typically 42kΩ in unipolar mode and 31kΩ
in bipolar mode, therefore, it should be driven with a low
impedance source. Wideband noise coupling into the input
can be minimized by placing a 3000pF capacitor at the input
as shown in Figure 2. An NPO-type capacitor gives the
lowest distortion. Place the capacitor as close to the device
input pin as possible. If an amplifier is to be used to drive
the input, care should be taken to select an amplifier with
adequate accuracy, linearity and noise for the application.
The following list is a summary of the op amps that are
suitable for driving the LTC1857/LTC1858/LTC1859. More
detailed information is available in the Linear Technology
data books and online at www.linear.com.
LT
®
1007: Low noise precision amplifier. 2.7mA supply
current ±5V to ±15V supplies. Gain bandwidth product
8MHz. DC applications.
MUX
INPUT
R1
25k
REFCOMP
CH SEL
R3
10k
1859 AI03
R2
17k
MUXOUT
BIPOLAR
LTC1857/LTC1858/LTC1859
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APPLICATIONS INFORMATION
LT1227: 140MHz video current feedback amplifier. 10mA
supply current. ±5V to ±15V supplies. Low noise and low
distortion.
LT1468/LT1469: Single and dual 90MHz, 16-bit accurate
op amp. Good AC/DC specs.
LT1677: Single, low noise op amp. Rail-to-rail input and
output. Up to ±15V supplies.
3000pF
1859 F02
AIN+
AIN–
CH0
CH1
MUXOUT+
MUXOUT–
ADC+
ADC–
•
•
•
•
Figure 2. Analog Input Filtering
Figure 1. LTC1857/LTC1858/LTC1859 Simplified Equivalent Circuit
LT1792: Single, low noise JFET input op amp, ±5V sup-
plies.
LT1793: Single, low noise JFET input op amp, 10pA bias
current, ±5V supplies.
LT1881/LT1882: Dual and quad, 200pA bias current, rail-
to-rail output op amps. Up to ±15V supplies.
LT1844/LT1885: Dual and quad, 400pA bias current,
rail-to-rail output op amps. Up to ±15V supplies. Faster
response and settling time.
INTERNAL VOLTAGE REFERENCE
The LTC1857/LTC1858/LTC1859 have an on-chip, tem-
perature compensated, curvature corrected, bandgap
reference, which is factory trimmed to 2.50V. The full-scale
range of the LTC1857/LTC1858/LTC1859 is equal to ±5V,
0V to 5V, ±10V or 0V to 10V. The output of the reference is
connected to the input of a gain of 1.6384x buffer through
an 8k resistor (see Figure 3). The input to the buffer or
2.5V
REFERENCE
INTERNAL
CLOCK
1.6384X
4.096V
8k
AGND1
CONTROL
LOGIC
SERIAL I/O
INPUT MUX
AND
RANGE
SELECT
AGND3
AGND2REFCOMPVREF
ADC–
MUXOUT+
MUXOUT–ADC+
DGND
AV
DD
DV
DD
MUX ADDRESS AND RANGE
DATA OUT
CONVST
SDI
SCK
OVDD
SDO
1859 BD
12-/14-/16-BIT
SAMPLING ADC
+
–
COM
CH7
CH1
•
•
•
CH0
BUSY
RD
LTC1857/LTC1858/LTC1859
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the output of the reference is available at VREF (Pin 15).
The internal reference can be overdriven with an external
reference if more accuracy is needed. The buffer output
drives the internal DAC and is available at REFCOMP (Pin
16). The REFCOMP pin can be used to drive a steady DC
load of less than 2mA. Driving an AC load is not recom-
mended because it can cause the performance of the
converter to degrade.
between successive integer LSB values (i.e., 0.5LSB,
1.5LSB, 2.5LSB, … FS – 1.5LSB). The output code is
natural binary with 1LSB = FS/65536. Figure 4b shows
the input/output transfer characteristics for the bipolar
mode in two’s complement format.
FULL SCALE AND OFFSET
In applications where absolute accuracy is important,
offset and full-scale errors can be adjusted to zero during a
calibration sequence. Offset error must be adjusted before
full-scale error. Zero offset is achieved by adjusting the
offset applied to the “–” input. For single-ended inputs, this
offset should be applied to the COM pin. For differential
inputs, the “–” input is dictated by the MUX address. For
unipolar zero offset error, apply 0.5LSB (actual voltage will
vary with input span selected) to the “+” input and adjust
the offset at the “–” input until the output code flickers
between 0000 0000 0000 0000 and 0000 0000 0000 0001
for the LTC1859, between 00 0000 0000 0000 and 00 0000
0000 0001 for the LTC1858 and between 0000 0000 0000
and 0000 0000 0001 for the LTC1857.
For bipolar zero error, apply – 0.5LSB (actual voltage will
vary with input span selected) to the “+” input and adjust
the offset at the “–” input until the output code flickers
between 0000 0000 0000 0000 and 1111 1111 1111
1111 for the LTC1859, between 00 0000 0000 0000 and
Figure 3. Internal or External Reference Source
2.5V
REFERENCE
1859 F03
12-/14-/16-BIT
CAPACITIVE DAC
1.6384X BUFFER
8k
VREF
1µF
15
2.5V
16 REFCOMP
0.1µF
4.096V
10µF
INPUT VOLTAGE (V)
0V
OUTPUT CODE
FS – 1LSB
1859 F4a
111...111
111...110
111...101
111...100
000...000
000...001
000...010
000...011
1
LSB
UNIPOLAR
ZERO
1LSB = FS
65536
INPUT VOLTAGE (V)
0V
OUTPUT CODE
–1
LSB
1859 F4b
011...111
011...110
000...001
000...000
100...000
100...001
111...110
1
LSB
BIPOLAR
ZERO
111...111
FS/2 – 1LSB–FS/2
1LSB = FS
65536
Figure 4a. Unipolar Transfer Characteristics (UNI = 1) Figure 4b. Bipolar Transfer Characteristics (UNI = 0)
For minimum code transition noise the VREF pin and the
REFCOMP pin should each be decoupled with a capacitor to
filter wideband noise from the reference and the buffer.
UNIPOLAR / BIPOLAR OPERATION
Figure 4a shows the ideal input/output characteristics
for the LTC1859. The code transitions occur midway
APPLICATIONS INFORMATION
LTC1857/LTC1858/LTC1859
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APPLICATIONS INFORMATION
Figure 5. LTC1859 Histogram for 4096 Conversions
11 1111 1111 1111 for the LTC1858 and between 0000
0000 0000 and 1111 1111 1111 for the LTC1857.
As mentioned earlier, the internal reference is factory
trimmed to 2.50V. To make sure that the reference buffer
gain is not compensating for trim errors in the reference,
REFCOMP is trimmed with an accurate external 2.5V refer-
ence applied to VREF. For unipolar inputs, an input voltage
of FS – 1.5LSBs should be applied to the “+” input and the
appropriate reference adjusted until the output code flick-
ers between 1111 1111 1111 1110 and 1111 1111 1111
1111 for the LTC1859, between 11 1111 1111 1110 and
11 1111 1111 1111 for the LTC1858 and between 1111
1111 1110 and 1111 1111 1111 for the LTC1857.
For bipolar inputs, an input voltage of FS – 1.5LSBs should
be applied to the “+” input and the appropriate reference
adjusted until the output code flickers between 0111 1111
1111 1110 and 0111 1111 1111 1111 for the LTC1859,
between 01 1111 1111 1110 and 01 1111 1111 1111 for
the LTC1858 and between 0111 1111 1110 and 0111 1111
1111 for the LTC1857.
These adjustments as well as the factory trims affect all
channels. The channel-to-channel offset and gain error
matching are guaranteed by design to meet the specifica-
tions in the Converter Characteristics table.
DC PERFORMANCE
One way of measuring the transition noise associated
with a high resolution ADC is to use a technique where
a DC signal is applied to the input of the MUX and the
resulting output codes are collected over a large number
of conversions. For example in Figure 5 the distribution
of output code is shown for a DC input that has been
digitized 4096 times. The distribution is Gaussian and the
RMS code transition is about 1LSB for the LTC1859.
DIGITAL INTERFACE
Internal Clock
The ADC has an internal clock that is trimmed to achieve
a typical conversion time of 4µs. No external adjustments
are required and, with the maximum acquisition time of
4µs, throughput performance of 100ksps is assured.
3V Input/Output Compatible
The LTC1857/LTC1858/LTC1859 operate on a 5V supply,
which makes the devices easy to interface to 5V digital
systems. These devices can also interface to 3V digital
systems: the digital input pins (SCK, SDI, CONVST and
RD) of the LTC1857/LTC1858/LTC1859 recognize 3V or 5V
inputs. The LTC1857/LTC1858/LTC1859 have a dedicated
output supply pin (OVP) that controls the output swings
of the digital output pins (SDO, BUSY) and allows the part
to interface to either 3V or 5V digital systems. The output
is two’s complement binary for bipolar mode and offset
binary for unipolar mode.
Timing and Control
Conversion start and data read are controlled by two digital
inputs: CONVST and RD. To start a conversion and put
the sample-and-hold into the hold mode bring CONVST
high for no less than 40ns. Once initiated it cannot be re-
started until the conversion is complete. Converter status
is indicated by the BUSY output and this is low while the
conversion is in progress.
Figures 6a and 6b show two different modes of opera-
tion for the LTC1859. For the 12-bit LTC1857 and 14-bit
LTC1858, the last four and two bits of the SDO will output
zeros respectively. In mode 1 (Figure 6a), RD is tied low.
The rising edge of CONVST starts the conversion. The data
outputs are always enabled. The MSB of the data output
is available after the conversion. In mode 2 (Figure 6b),
CONVST and RD are tied together. The rising edge of the
CONVST signal starts the conversion. Data outputs are in
CODE
–4 –3
0
COUNT
200
600
800
1000
2 3
1800
1859 F05
400
–2 –1 0 1 4
1200
1400
1600
LTC1857/LTC1858/LTC1859
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Figure 6a. Mode 1 for the LTC1859*. CONVST Starts a Conversion, Data Output is Always Enabled (RD = 0)
Figure 6b. Mode 2 for the LTC1859*. CONVST and RD Tied Together. CONVST Starts a Conversion, Data is Read by RD
SGL/
DIFF
1
t
4
RD = 0
SCK
SDI
SDO
CONVST
BUSY
2 3 4 5 6 7 8 15 16
ODD/
SIGN
SELECT
1
SELECT
0UNI GAIN NAP SLEEP DON’T CARE
DON’T
CARE
B14 B13 B12B15 (MSB) B11 B10 B9 B8 B1 B0 (LSB)
t
ACQ
t
7
t
6
t
2
t
CONV
t
1
t
10
t
11
SHIFT CONFIGURATION WORD IN
SGL/
DIFF
1 2 3 4 5 6 7 8 15 16
ODD/
SIGN
SELECT
1
SELECT
0UNI GAIN NAP SLEEP DON’T CARE
B14 B13 B12B15 (MSB) B11 B10 B9 B8 B1
1859 F06a
B0 (LSB)
SHIFT A/D RESULT OUT AND NEW CONFIGURATION WORD IN
t
5
t
3
t
12
t
12
SGL/
DIFF
1
t
4
CONVST = RD
SCK
SDI
Hi-Z
SDO
BUSY
2 3 4 5 6 7 8 15 16
ODD/
SIGN
SELECT
1
SELECT
0UNI GAIN NAP SLEEP DON’T CARE
DON’T
CARE
B14 B13 B12B15 (MSB) B11 B10 B9 B8 B1 B0 (LSB)
t
ACQ
t
13
t
2
t
CONV
Hi-Z
t
10
t
11
SHIFT CONFIGURATION WORD IN
SGL/
DIFF
1 2 3 4 5 6 7 8 15 16
ODD/
SIGN
SELECT
1
SELECT
0UNI GAIN NAP SLEEP DON’T CARE
B14 B13 B12B15 (MSB) B11 B10 B9 B8 B1
1859 F06b
B0 (LSB) Hi-Z
SHIFT A/D RESULT OUT AND NEW CONFIGURATION WORD IN
t
5
t
3
t
9
t
8
t
7
t
6
Figure 7. Operating Sequence for the LTC1859*
SGL/
DIFF
1
t4
RD
SCK
SDI
Hi-Z
SDO
BUSY
CONVST
2 3 4 5 6 7 8 15 16
ODD/
SIGN
SELECT
1
SELECT
0UNI GAIN NAP SLEEP DON’T CARE
DON’T
CARE
B14 B13 B12B15 (MSB) B11 B10 B9 B8 B1 B0 (LSB)
tACQ
t13
t2
t1
tCONV
Hi-Z
t10 t11
SHIFT CONFIGURATION WORD IN
SGL/
DIFF
1 2 3 4 5 6 7 8 15 16
ODD/
SIGN
SELECT
1
SELECT
0UNI GAIN NAP SLEEP DON’T CARE
B14 B13 B12B15 (MSB) B11 B10 B9 B8 B1
1859 F07
B0 (LSB) Hi-Z
SHIFT A/D RESULT OUT AND NEW CONFIGURATION WORD IN
t5
t3
t9
t8
t7
t6
*For the 12-bit LTC1857 and 14-bit LTC1858, the last four and two bits of the SDO will output zeros respectively.
APPLICATIONS INFORMATION
LTC1857/LTC1858/LTC1859
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For more information www.linear.com/LTC1857
0
1
2
3
4
5
6
7
CHANNEL
COM (–)
8 Single-Ended
+
+
+
+
+
+
+
0,1
CHANNEL
4 Differential
2,3
4,5
6,7
+ (–)+
+ (–)
+ (–)
+ (–)
– (+)
– (+)
– (+)
– (+)
4
5
6
7
CHANNEL
COM (–)
Combinations of
Differential and Single-Ended
+
+
+
+
+
+
0,1
2,3
–
–
COM (UNUSED)
Changing the
MUX Assignment “On the Fly”
COM (–)
4,5
6,7
4,5
1ST CONVERSION 2ND CONVERSION
+
–
+
–
+
–
+
+
7
6
{
{
{
{
{{
{
{
{
1859 F08
APPLICATIONS INFORMATION
three-state at this time. When the conversion is complete
(BUSY goes high), CONVST and RD go low to enable the
data output for the previous conversion.
SERIAL DATA INPUT (SDI) INTERFACE
The
LTC1857/LTC1858/LTC1859
communicate with micro-
processors and other external circuitry via a synchronous,
full duplex, 3-wire serial interface (see Figure 7). The shift
clock (SCK) synchronizes the data transfer with each bit
being transmitted on the falling SCK edge and captured
on the rising SCK edge in both transmitting and receiving
systems. The data is transmitted and received simultane-
ously (full duplex).
An 8-bit input word is shifted into the SDI input which
configures the LTC1857/LTC1858/LTC1859 for the next
conversion. Simultaneously, the result of the previous
conversion is output on the SDO line. At the end of the
data exchange the requested conversion begins by ap-
plying a rising edge on CONVST. After tCONV, the conver-
sion is complete and the results will be available on the
next data transfer cycle. As shown below, the result of a
conversion is delayed by one conversion from the input
word requesting it.
SGL/
DIFF
SELECT
1
SELECT
0UNI GAIN NAP
MUX ADDRESS
INPUT RANGE
POWER DOWN
SELECTION
1859 AI02
ODD
SIGN SLEEP
SDI
SDO SDO WORD 0
SDI WORD 1
DATA
TRANSFER
SDO WORD 2
SDI WORD 3
SDO WORD 1
SDI WORD 2
DATA
TRANSFER
tCONV
A/D
CONVERSION
tCONV
A/D
CONVERSION
1859 • AI01
Figure 8. Examples of Multiplexer Options on the LTC1857/LTC1858/LTC1859
INPUT DATA WORD
The LTC1857/LTC1858/LTC1859 8-bit data word is clocked
into the SDI input on the first eight rising SCK edges. Fur-
ther inputs on the SDI pin are then ignored until the next
conversion. The eight bits of the input word are defined
as follows:
Table 1. Multiplexer Channel Selection
MUX ADDRESS DIFFERENTIAL CHANNEL SELECTION MUX ADDRESS SINGLE-ENDED CHANNEL SELECTION
SGL/
DIFF
ODD
SIGN
SELECT
1 0 01234567SGL/
DIFF
ODD
SIGN
SELECT
1 0 01234567COM
0 0 0 0 + – 1 0 0 0 + –
0 0 0 1 + – 1 0 0 1 + –
0 0 1 0 + – 1 0 1 0 + –
0 0 1 1 + – 1 0 1 1 + –
0 1 0 0 – + 1 1 0 0 + –
0 1 0 1 – + 1 1 0 1 + –
0 1 1 0 – + 1 1 1 0 + –
0 1 1 1 – + 1 1 1 1 + –
LTC1857/LTC1858/LTC1859
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MUX ADDRESS
The first four bits of the input word assign the MUX
configuration for the requested conversion. For a given
channel selection, the converter will measure the voltage
between the two channels indicated by the + and – signs in
the selected row of Table 1. Note that in differential mode
(SGL/DIFF = 0) measurements are limited to four adjacent
input pairs with either polarity. In single-ended mode, all
input channels are measured with respect to COM. Both
the “+” and “–” inputs are sampled simultaneously so
common mode noise is rejected.
INPUT RANGE (UNI, GAIN)
The fifth and sixth input bits (UNI, GAIN) determine the
input range for the conversion. When UNI is a logical one,
a unipolar conversion will be performed. When UNI is a
logical zero, a bipolar conversion will result. The GAIN
input bit determines the input span for the conversion.
When GAIN is a logical one, either 0V to 10V or ±10V input
spans will be selected depending on UNI. When GAIN is
a logical zero, either 0V to 5V or ±5V input spans will be
chosen. The input ranges for different UNI and GAIN inputs
are shown in Table 2.
Table 2. Input Range Selection
UNI GAIN INPUT RANGE
0 0 ±5V
1 0 0V to 5V
0 1 ±10V
1 1 0V to 10V
P
OWER DOWN SELECTION (NAP, SLEEP)
The last two bits of the input word (Nap and Sleep) deter-
mine the power shutdown mode of the LTC1857/LTC1858/
LTC1859. See Table 3. Nap mode is selected when Nap =
1 and Sleep = 0. The previous conversion result will be
clocked out and a conversion will occur before entering
the Nap mode. The Nap mode starts at the end of the
conversion which is indicated by the rising edge of the
BUSY signal. Nap mode lasts until the falling edge of the
2nd SCK (see Figure 9). Automatic nap will be achieved
if Nap = 1 is selected each time an input word is written
to the ADC.
Table 3. Power Down Selection
NAP SLEEP POWER DOWN MODE
0 0 Power On
1 0 Nap
X 1 Sleep
Sleep mode will occur when Sleep = 1 is selected,
regardless of the selection of the Nap input. The previ-
ous conversion result can be clocked out and the Sleep
mode will start on the falling edge of the last (16th) SCK.
Notice that the CONVST should stay either high or low in
sleep mode (see Figure 10). To wake up from the sleep
mode, apply a rising edge on the CONVST signal and
then apply Sleep = 0 on the next SDI word and the part
will wake up on the falling edge of the last (16th) SCK
(see Figure 11).
In Sleep mode, all bias currents are shut down and only the
power on reset circuit and leakage currents (about 10µA)
remain. Sleep mode wake-up time is dependent on the value
of the capacitor connected to the REFCOMP (Pin 16). The
wake-up time is typically 40ms with the recommended
10µF capacitor connected on the REFCOMP pin.
DYNAMIC PERFORMANCE
FFT (Fast Fourier Transform) test techniques are used to
test the ADC’s frequency response, distortion and noise
at the rated throughput. By applying a low distortion
sine wave and analyzing the digital output using an FFT
algorithm, the ADC’s spectral content can be examined
for frequencies outside the fundamental. Figure 12 shows
a typical LTC1859 FFT plot which yields a SINAD of 87dB
and THD of –101dB.
APPLICATIONS INFORMATION
LTC1857/LTC1858/LTC1859
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APPLICATIONS INFORMATION
Figure 9. Nap Mode Operation for the LTC1859*
SGL/
DIFF
1
RD
SCK
SDI
Hi-Z
SDO
BUSY
CONVST
2 3 4 5 6 7 8 15 16
ODD/
SIGN
SELECT
1
SELECT
0UNI GAIN NAP = 1 SLEEP = 0 DON’T CARE
DON’T
CARE
B14 B13 B12B15 (MSB) B11 B10 B9 B8 B1 B0 (LSB)
t
CONV
Hi-Z
NAPt
ACQ
t
ACQ
SHIFT CONFIGURATION WORD IN
SGL/
DIFF
1 2 3 4 5 6 7 8 15 16
ODD/
SIGN
SELECT
1
SELECT
0UNI GAIN NAP SLEEP DON’T CARE
B14 B13 B12B15 MSB B11 B10 B9 B8 B1
1859 F09
B0 (LSB) Hi-Z
SHIFT A/D RESULT OUT FROM PREVIOUS CONVERSION AND NEW CONFIGURATION WORD IN
Figure 11. Wake Up from Sleep Mode for the LTC1859*
Figure 10. Sleep Mode Operation for the LTC1859*
SGL/
DIFF
1
RD
SCK
SDI
SDO
BUSY
CONVST
2 3 4 5 6 7 8 15 16
ODD/
SIGN
SELECT
1
SELECT
0UNI GAIN NAP SLEEP = 0 DON’T CARE
DON’T
CARE
B14 B13 B12B15 (MSB) B11 B10 B9 B8 B1 B0 (LSB)
WAKE-UP
TIME
READY
tCONV
SLEEP
SHIFT WAKE-UP CONFIGURATION WORD IN
SGL/
DIFF
1 2 3 4 5 6 7 8 15 16
ODD/
SIGN
SELECT
1
SELECT
0UNI GAIN NAP SLEEP DON’T CARE
B14 B13 B12B15 (MSB) B11 B10 B9 B8 B1
1859 F11
B0 (LSB)
A/D RESULT NOT VALID
SHIFT A/D RESULT OUT AND NEW CONFIGURATION WORD IN
tCONV
*For the 12-bit LTC1857 and 14-bit LTC1858, the last four and two bits of the SDO will output zeros respectively.
SGL/
DIFF
1
RD
SCK
SDI
SDO
BUSY
CONVST
2 3 4 5 6 7 8 15 16
ODD/
SIGN
SELECT
1
SELECT
0UNI GAIN NAP SLEEP = 1 DON’T CARE
DON’T
CARE
B14 B13 B12B15 (MSB) B11 B10 B9 B8 B1 B0 (LSB)
SHIFT WAKE-UP CONFIGURATION WORD IN
1859 F10
A/D RESULT NOT VALID
CONVST SHOULD STAY EITHER HIGH OR LOW IN SLEEP MODE
t
CONV
SLEEP
LTC1857/LTC1858/LTC1859
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FREQUENCY (kHz)
0
MAGNITUDE (dB)
–60
–40
–20
0
40
1859 F12
–80
–100
–70
–50
–30
–10
–90
–110
–130
–120
10 20 30
5 45
15 25 35 50
fSAMPLE = 100kHz
fIN = 1kHz
SINAD = 86.95dB
THD = –101.42dB
APPLICATIONS INFORMATION
SIGNAL-TO-NOISE RATIO
The Signal-to-Noise and Distortion Ratio (SINAD) is the
ratio between the RMS amplitude of the fundamental input
frequency to the RMS amplitude of all other frequency
components at the A/D output. The output is band limited
to frequencies from above DC and below half the sampling
frequency. Figure 12 shows a typical SINAD of 87dB with
a 100kHz sampling rate and a 1kHz input.
TOTAL HARMONIC DISTORTION
Total Harmonic Distortion (THD) is the ratio of the RMS
sum of all harmonics of the input signal to the fundamental
itself. The out-of-band harmonics alias into the frequency
band between DC and half the sampling frequency. THD
is expressed as:
THD = 20log V22324
22
1
++ +VV V
V
N
...
where V1 is the RMS amplitude of the fundamental fre-
quency and V2 through VN are the amplitudes of the second
through Nth harmonics.
BOARD LAYOUT, POWER SUPPLIES
AND DECOUPLING
Wire wrap boards are not recommended for high reso-
lution or high speed A/D converters. To obtain the best
performance from the LTC1857/LTC1858/LTC1859, a
printed circuit board is required. Layout for the printed
circuit board should ensure the digital and analog signal
lines are separated as much as possible. In particular, care
should be taken not to run any digital track alongside an
analog signal track or underneath the ADC. The analog
input should be screened by AGND.
In applications where the MUX is connected to the ADC, it is
possible to get noise coupling into the ADC from the trace
connecting the MUXOUT to the ADC. Therefore, reducing
the length of the traces connecting the MUXOUT pins (Pins
10, 11) to the ADC pins (Pins 12, 13) can minimize the
problem. The unused MUX inputs should be grounded to
prevent noise coupling into the inputs.
Figure 13 shows the power supply grounding that will help
obtain the best performance from the 12-bit/14-bit/16-bit
ADCs. Pay particular attention to the design of the analog
and digital ground planes. The DGND pin of the LTC1857/
Figure 12. LTC1859 Nonaveraged 4096 Point FFT Plot
LTC1857/LTC1858/LTC1859
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APPLICATIONS INFORMATION
1859 F13
ADC+
LTC1857/LTC1858/LTC1859 DIGITAL
SYSTEM
OVDD
DGND
24 21
ADC–
10µF
DVDD
20
10µF
AVDD
19
AGND
14, 17, 18
10µF
REFCOMP
16
10µF
VREF
15
12
MUXOUT+
LTC1857/
LTC1858/
LTC1859
MUXOUT–
10
CH0
CH1
CH2
CH3
CH4
CH5
CH6
CH7
COM
11 13
1µF
ANALOG GROUND PLANE
+
–
Figure 13. Power Supply Grounding Practice
LTC1858/LTC1859
can be tied to the analog ground plane.
Placing the bypass capacitor as close as possible to the
power supply pins, the reference and reference buffer out-
put is very important. Low impedance common returns for
these bypass capacitors are essential to low noise operation
of the ADC, and the foil width for these tracks should be
as wide as possible. Also, since any potential difference in
grounds between the signal source and ADC appears as
an error voltage in series with the input signal, attention
should be paid to reducing the ground circuit impedance
as much as possible. The digital output latches and the
onboard sampling clock have been placed on the digital
ground plane. The two ground planes are tied together at
the power supply ground connection.
LTC1857/LTC1858/LTC1859
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For more information www.linear.com/LTC1857
PACKAGE DESCRIPTION
G28 SSOP 0204
0.09 – 0.25
(.0035 – .010)
0° – 8°
0.55 – 0.95
(.022 – .037)
5.00 – 5.60**
(.197 – .221)
7.40 – 8.20
(.291 – .323)
1 2 3 4 5678 9 10 11 12 1413
9.90 – 10.50*
(.390 – .413)
2526 22 21 20 19 18 17 16 1523242728
2.0
(.079)
MAX
0.05
(.002)
MIN
0.65
(.0256)
BSC 0.22 – 0.38
(.009 – .015)
TYP
MILLIMETERS
(INCHES)
DIMENSIONS DO NOT INCLUDE MOLD FLASH. MOLD FLASH
SHALL NOT EXCEED .152mm (.006") PER SIDE
DIMENSIONS DO NOT INCLUDE INTERLEAD FLASH. INTERLEAD
FLASH SHALL NOT EXCEED .254mm (.010") PER SIDE
*
**
NOTE:
1. CONTROLLING DIMENSION: MILLIMETERS
2. DIMENSIONS ARE IN
3. DRAWING NOT TO SCALE
0.42 ±0.03 0.65 BSC
5.3 – 5.7
7.8 – 8.2
RECOMMENDED SOLDER PAD LAYOUT
1.25 ±0.12
G Package
28-Lead Plastic SSOP (5.3mm)
(Reference LTC DWG # 05-08-1640)
Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings.
LTC1857/LTC1858/LTC1859
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For more information www.linear.com/LTC1857
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 representa-
tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.
REVISION HISTORY
REV DATE DESCRIPTION PAGE NUMBER
B 06/15 Added part marking.
Updated SDI pin functionality description.
2
8
(Revision history begins at Rev B)
LTC1857/LTC1858/LTC1859
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For more information www.linear.com/LTC1857
© LINEAR TECHNOLOGY CORPORATION 2004
LT 0615 REV B • PRINTED IN USA
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com/LTC1857
RELATED PARTS
TYPICAL APPLICATION
2.5V
REFERENCE
INTERNAL
CLOCK
1.6384X
4.096V
8k
AGND1
CONTROL
LOGIC
SERIAL I/O
INPUT MUX
AND
RANGE
SELECT
AGND3
AGND2
REFCOMP
VREF
ADC–
MUXOUT+
MUXOUT–ADC+DGND
AVDD DVDD
MUX ADDRESS AND RANGE
DATA OUT
CONVST 28
25
22
26
27
21
23
3V TO 5V
SDI
BUSY
SCK
RD
OVDD
SDO
1859 TA03
12-/14-/16-BIT
SAMPLING ADC
+
–
COM
19 20
5V
5V
1
2
3
9CH7
14 11 10 12 13 15 16 17 18 24
1µF 0.1µF
CH1
SINGLE-ENDED
OR DIFFERENTIAL
CHANNEL
SELECTION
(SEE TABLE 1)
INPUT RANGES:
0V TO 5V
0V TO 10V
±5V AND ±10V
•
•
•
CH0
10µF
0.1µF10µF
8-BIT SERIAL
DATA INPUT
16 SHIFT CLOCK CYCLES
16-BIT SERIAL DATA OUT
10µF 0.1µF10µF 0.1µF
PART NUMBER DESCRIPTION COMMENTS
Sampling ADCs
LTC1417 14-Bit, 400ksps Serial ADC 5V or ±5V, 20mW, 81dB SINAD and –95dB THD
LTC1418 14-Bit, 200ksps, Single 5V or ±5V ADC 15mW, Serial/Parallel I/O
LTC1604 16-Bit, 333ksps, ±5V ADC 90dB SINAD, 220mW Power Dissipation, Pin Compatible with LTC1608
LTC1605 16-Bit, 100ksps, Single 5V ADC ±10V Inputs, 55mW, Byte or Parallel I/O, Pin Compatible with LTC1606
LTC1606 16-Bit, 250ksps, Single 5V ADC ±10V Inputs, 75mW, Byte or Parallel I/O, Pin Compatible with LTC1605
LTC1608 16-Bit, 500ksps, ±5V ADC 90dB SINAD, 270mW Power Dissipation, Pin Compatible with LTC1604
LTC1609 16-Bit, 200ksps Serial ADC Configurable Unipolar/Bipolar Input, Single 5V Supply
LTC1850/LTC1851 10-Bit/12-Bit, 8-Channel, 1.25Msps ADC Programmable MUX and Sequencer, Parallel I/O
LTC1852/LTC1853 10-Bit/12-Bit, 8-Channel, 400ksps ADC Single 3V-5V, Programmable MUX and Sequencer, Parallel I/O
LTC1864/LTC1865 16-Bit, 1-/2-Channel, 250ksps ADC in MSOP Single 5V Supply, 850µA with Autoshutdown
LTC1864L/LTC1865L 3V, 16-Bit, 1-/2-Channel, 150ksps ADC in MSOP Single 3V Supply, 450µA with Autoshutdown
DACs
LTC1588/LTC1589/
LTC1592
12-/14-/16-Bit, Serial, SoftSpan IOUT DACs Software-Selectable Spans, ±1LSB INL/DNL
LTC1595 16-Bit Serial Multiplying IOUT DAC in SO-8 ±1LSB Max INL/DNL, Low Glitch, DAC8043 16-Bit Upgrade
LTC1596 16-Bit Serial Multiplying IOUT DAC ±1LSB Max INL/DNL, Low Glitch, AD7543/DAC8143 16-Bit Upgrade
LTC1597 16-Bit Parallel, Multiplying DAC ±1LSB Max INL/DNL, Low Glitch, 4 Quadrant Resistors
LTC1650 16-Bit Serial VOUT DAC Low Power, Low Gritch, 4-Quadrant Multiplication
Op Amps
LT1468/LT1469 Single/Dual 90MHz, 22V/µs, 16-Bit Accurate Op Amp Low Input Offset : 75µV/125µV