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CS5581
±2.5 V / 5 V, 200 kSps, 16-bit, High-throughput ∆Σ ADC
Features & Description
General Description
Single-ended Analog Input
The CS5581 is a single-channel, 16-bit analog-to-digital
converter capable of 200 kSps conversion rate. The input
accepts a single-ended analog input signal. On-chip buffers provide high input impedance for both the AIN input
and the VREF+ input. This significantly reduces the drive
requirements of signal sources and reduces errors due to
source impedances. The CS5581 is a delta-sigma converter capable of switching multiple input channels at a high
rate with no loss in throughput. The ADC uses a low-latency digital filter architecture. The filter is designed for fast
settling and settles to full accuracy in one conversion. The
converter's 16-bit data output is in serial format, with the
serial port acting as either a master or a slave. The converter is designed to support bipolar, ground-referenced
signals when operated from ±2.5V analog supplies.
On-chip Buffers for High Input Impedance
Conversion Time = 5 µS
Settles in One Conversion
Linearity Error = 0.0008%
Signal-to-Noise = 80 dB
S/(N + D) = 80 dB
DNL = ±0.1 LSB Max.
Simple three/four-wire serial interface
Power Supply Configurations:
- Analog: +5V/GND; IO: +1.8V to +3.3V
- Analog: ±2.5V; IO: +1.8V to +3.3V
Power Consumption:
The converter can operate from an analog supply of 0-5V
or from ±2.5V. The digital interface supports standard logic
operating from 1.8, 2.5, or 3.3 V.
- ADC Input Buffers On: 85 mW
- ADC Input Buffers Off: 60 mW
V1+
ORDERING INFORMATION:
See Ordering Information on page 32.
VL
V2+
CS5581
VREF+
SMODE
VREF-
CS
SERIAL
INTERFACE
DIGITAL
FILTER
LOGIC
ADC
AIN
SCLK
SDO
ACOM
RDY
BUFEN
RST
CONV
DIGITAL CONTROL
OSC/CLOCK
GENERATOR
BP/UP
MCLK
V1-
V2-
TST
Preliminary Product Information
http://www.cirrus.com
DCR
VLR
VLR2
VLR3
This document contains information for a new product.
Cirrus Logic reserves the right to modify this product without notice.
Copyright © Cirrus Logic, Inc. 2008
(All Rights Reserved)
MAR ‘08
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CS5581
TABLE OF CONTENTS
1. CHARACTERISTICS AND SPECIFICATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
ANALOG CHARACTERISTICS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
SWITCHING CHARACTERISTICS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
DIGITAL CHARACTERISTICS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
GUARANTEED LOGIC LEVELS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
RECOMMENDED OPERATING CONDITIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
ABSOLUTE MAXIMUM RATINGS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
2. OVERVIEW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
3. THEORY OF OPERATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
3.1 Converter Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
3.2 Clock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
3.3 Voltage Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
3.4 Analog Input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
3.5 Output Coding Format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
3.6 Typical Connection Diagrams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
3.7 AIN & VREF Sampling Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
3.8 Converter Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
3.9 Digital Filter Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
3.10 Serial Port . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
3.10.1 SSC Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
3.10.2 SEC Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
3.11 Power Supplies & Grounding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
3.12 Using the CS5581 in Multiplexing Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
3.13 Synchronizing Multiple Converters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
4. PIN DESCRIPTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
5. PACKAGE DIMENSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
6. ORDERING INFORMATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
7. ENVIRONMENTAL, MANUFACTURING, & HANDLING INFORMATION . . . . . . . . . . . . . . 32
8. REVISION HISTORY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
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CS5581
LIST OF FIGURES
Figure 1. SSC Mode - Read Timing, CS remaining low . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Figure 2. SSC Mode - Read Timing, CS falling after RDY falls . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Figure 3. SEC Mode - Continuous SCLK Read Timing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Figure 4. SEC Mode - Discontinuous SCLK Read Timing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Figure 5. Voltage Reference Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Figure 6. CS5581 Configured Using ±2.5V Analog Supplies . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Figure 7. CS5581 Configured for Unipolar Measurement Using a Single 5V Analog Supply . . . . 18
Figure 8. CS5581 Configured for Bipolar Measurement Using a Single 5V Analog Supply . . . . . 19
Figure 9. CS5581 DNL Plot. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Figure 10. CS5581 DNL Error Plot with DNL Histogram. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Figure 11. Spectral Performance, 0 dB. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Figure 12. Spectral Performance, -6 dB . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Figure 13. Spectral Performance, -12 dB . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Figure 14. Spectral Performance, -80 dB . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Figure 15. Spectral Performance, -100 dB . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Figure 16. Spectral Plot of Noise with Shorted Input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Figure 17. Noise Histogram (4096 Conversions) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Figure 18. CS5581 Spectral Response (DC to fs/2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Figure 19. CS5581 Spectral Response (DC to 20 kHz) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Figure 20. CS5581 Spectral Response (DC to 8fs) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Figure 21. Simple Multiplexing Scheme . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Figure 22. More Complex Multiplexing Scheme . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
LIST OF TABLES
Table 1. Output Coding, Two’s Complement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Table 2. Output Coding, Offset Binary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
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CS5581
1. CHARACTERISTICS AND SPECIFICATIONS
•
Min / Max characteristics and specifications are guaranteed over the specified operating conditions.
•
Typical characteristics and specifications are measured at nominal supply voltages and TA = 25°C.
•
VLR = 0 V. All voltages measured with respect to 0 V.
ANALOG CHARACTERISTICS
TA = -40 to +85 °C; V1+ = V2+ = +2.5 V, ±5%; V1- = V2- = -2.5 V,
±5%; VL -VLR = 3.3 V, ±5%; VREF = (VREF+) - (VREF-) = 4.096V; MCLK = 16 MHz; SMODE = VL, unless otherwise stated; BUFEN = V1+ unless otherwise stated. Connected per Figure 6. Bipolar mode unless otherwise
stated.
Parameter
Min
Typ
Max
Unit
-
0.0008
-
±%FS
-
-
±0.1
LSB16
Positive Full-scale Error
-
1.0
-
%FS
Negative Full-scale Error
-
1.0
-
%FS
(Note 2, 3)
-
±1
-
LSB16
(Note 3)
-
±15
-
LSB16
(Note 2, 3)
-
±1
-
LSB16
-
140
-
µVrms
1 kHz, -0.5 dB Input
12 kHz, -0.5 dB Input
-
-96
-96
-
dB
dB
1 kHz, -0.5 dB Input
-
-95
-82
dB
77
80
-
dB
-0.5 dB Input, 1 kHz
-60 dB Input, 1 kHz
-
80
21
-
dB
dB
(Note 4)
-
168
-
kHz
Accuracy
Linearity Error
Differential Linearity Error
Full-scale Drift
Bipolar Offset
Bipolar Offset Drift
(Note 1)
Noise
Dynamic Performance
Peak Harmonic or Spurious Noise
Total Harmonic Distortion
Signal-to-Noise
S/(N + D) Ratio
-3 dB Input Bandwidth
1.
2.
3.
4.
4
No missing codes is guaranteed at 16 bits resolution over the specified temperature range.
Total drift over specified temperature range after reset at power-up, at 25º C.
One LSB is equivalent to VREF ÷ 216 or 4.096 ÷ 65536 = 62.5 µV.
Scales with MCLK.
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CS5581
ANALOG CHARACTERISTICS (CONTINUED)
TA = -40 to +85 °C; V1+ = V2+ = +2.5 V, ±5%; V1- =
V2- = -2.5 V, ±5%; VL -VLR = 3.3 V, ±5%; VREF = (VREF+) - (VREF-) = 4.096V; MCLK = 16 MHz; SMODE = VL,
unless otherwise stated; BUFEN = V1+ unless otherwise stated. Connected per Figure 6.
Parameter
Min
Typ
Max
Unit
Analog Input
Analog Input Range
Unipolar
Bipolar
Input Capacitance
CVF Current
(Note 5)
AIN Buffer On (BUFEN = V+)
AIN Buffer Off (BUFEN = V-)
ACOM
0 to +VREF / 2
±VREF / 2
V
V
-
10
-
pF
-
600
130
130
-
nA
µA
µA
2.4
4.096
4.2
V
-
10
-
pF
-
3
1
1
-
µA
mA
mA
-
-
18
1.8
0.6
mA
mA
mA
Voltage Reference Input
Voltage Reference Input Range
(VREF+) – (VREF-)
(Note 6)
Input Capacitance
CVF Current
VREF+ Buffer On (BUFEN = V+)
VREF+ Buffer Off (BUFEN = V-)
VREF-
Power Supplies
DC Power Supply Currents
IV1
IV2
IVL
Power Consumption
Normal Operation Buffers On
Buffers Off
-
85
60
101
80
mW
mW
Power Supply Rejection
(Note 7)
-
80
80
-
dB
dB
5.
6.
7.
DS796PP1
V1+ , V2+ Supplies
V1-, V2- Supplies
Measured using an input signal of 1 V DC.
For optimum performance, VREF+ should always be less than (V+) - 0.2 volts to prevent saturation of the VREF+ input buffer.
Tested with 100 mVP-P on any supply up to 1 kHz. V1+ and V2+ supplies at the same voltage potential, V1- and V2- supplies at
the same voltage potential.
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CS5581
SWITCHING CHARACTERISTICS
TA = -40 to +85 °C; V1+ = V2+ = +2.5 V, ±5%; V1- = V2- = -2.5 V, ±5%;
VL - VLR = 3.3 V, ±5%, 2.5 V, ±5%, or 1.8 V, ±5%
Input levels: Logic 0 = 0V = Low; Logic 1 = VD+ = High; CL = 15 pF.
Parameter
Master Clock Frequency
Internal Oscillator
External Clock
Symbol
Min
Typ
Max
Unit
XIN
fclk
12
0.5
14
16
16
16.2
MHz
MHz
40
-
60
%
Master Clock Duty Cycle
Reset
RST Low Time
(Note 8)
tres
1
-
-
µs
Internal Oscillator
External Clock
twup
-
120
1536
-
µs
MCLKs
tcpw
4
-
-
MCLKs
tscn
0
-
-
ns
CONV low to start of conversion
tscn
-
-
2
MCLKs
Perform Single Conversion (CONV high before RDY falling)
tbus
20
-
-
MCLKs
tbuh
-
-
84
MCLKs
RST rising to RDY falling
Conversion
CONV Pulse Width
BP/UP setup to CONV falling
Conversion Time
8.
9.
10.
6
(Note 9)
(Note 10)
Start of Conversion to RDY falling
Reset must not be released until the power supplies and the voltage reference are within specification.
BP/UP can be changed coincident CONV falling. BP/UP must remain stable until RDY falls.
If CONV is held low continuously, conversions occur every 80 MCLK cycles.
If RDY is tied to CONV, conversions will occur every 82 MCLKs.
If CONV is operated asynchronously to MCLK, a conversion may take up to 84 MCLKs.
RDY falls at the end of conversion.
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CS5581
SWITCHING CHARACTERISTICS (CONTINUED)
TA = -40 to +85 °C; V1+ = V2+ = +2.5 V, ±5%; V1- = V2- = -2.5 V, ±5%;
VL - VLR = 3.3 V, ±5%, 2.5 V, ±5%, or 1.8 V, ±5%
Input levels: Logic 0 = 0V = Low; Logic 1 = VD+ = High; CL = 15 pF.
Parameter
Symbol
Min
Typ
Max
Unit
RDY falling to MSB stable
t1
-
-2
-
MCLKs
Data hold time after SCLK rising
t2
-
10
-
ns
t3
t4
50
50
-
-
ns
ns
t5
-
8
-
MCLKs
Serial Port Timing in SSC Mode (SMODE = VL)
Serial Clock (Out)
(Note 11, 12)
Pulse Width (low)
Pulse Width (high)
RDY rising after last SCLK rising
11.
SDO and SCLK will be high impedance when CS is high. In some systems SCLK and SDO may require pull-down
resistors.
12. SCLK = MCLK/2.
MCLK
RDY
t5
t1
CS
t2
t3
t4
SCLK(o)
SDO
MSB
MSB–1
LSB+1
LSB
Figure 1. SSC Mode - Read Timing, CS remaining low (Not to Scale)
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CS5581
SWITCHING CHARACTERISTICS (CONTINUED)
TA = -40 to +85 °C; V1+ = V2+ = +2.5 V, ±5%; V1- = V2- = -2.5 V, ±5%;
VL - VLR = 3.3 V, ±5%, 2.5 V, ±5%, or 1.8 V, ±5%
Input levels: Logic 0 = 0V = Low; Logic 1 = VD+ = High; CL = 15 pF.
Parameter
Symbol
Min
Typ
Max
Unit
t7
-
10
-
ns
t8
t9
50
50
-
-
ns
ns
RDY rising after last SCLK rising
t10
-
8
-
MCLKs
CS falling to MSB stable
t11
-
10
-
ns
First SCLK rising after CS falling
t12
-
8
-
MCLKs
CS hold time (low) after SCLK rising
t13
10
-
-
ns
SCLK, SDO tristate after CS rising
t14
-
5
-
ns
Serial Port Timing in SSC Mode (SMODE = VL)
Data hold time after SCLK rising
Serial Clock (Out)
(Note 13, 14)
Pulse Width (low)
Pulse Width (high)
13.
SDO and SCLK will be high impedance when CS is high. In some systems SCLK and SDO may require pull-down
resistors.
14. SCLK = MCLK/2.
MCLK
t10
RDY
t13
CS
t12
t7
t8
t9
t14
SCLK(o)
t11
SDO
MSB
MSB–1
LSB+1
LSB
Figure 2. SSC Mode - Read Timing, CS falling after RDY falls (Not to Scale)
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CS5581
SWITCHING CHARACTERISTICS (CONTINUED)
TA = -40 to +85 °C; V1+ = V2+ = +2.5 V, ±5%; V1- = V2- = -2.5 V, ±5%;
VL - VLR = 3.3 V, ±5%, 2.5 V, ±5%, or 1.8 V, ±5%
Input levels: Logic 0 = 0V = Low; Logic 1 = VD+ = High; CL = 15 pF.
Parameter
Symbol
Min
Typ
Max
Unit
SCLK(in) Pulse Width (High)
-
30
-
-
ns
SCLK(in) Pulse Width (Low)
-
30
-
-
ns
CS hold time (high) after RDY falling
t15
10
-
-
ns
CS hold time (high) after SCLK rising
t16
10
-
-
ns
t17
-
10
-
ns
Data hold time after SCLK rising
t18
-
10
-
ns
Data setup time before SCLK rising
t19
10
-
-
ns
CS hold time (low) after SCLK rising
t20
10
-
1
10
SCLK
ns
RDY rising after SCLK falling
t21
-
10
-
ns
Serial Port Timing in SEC Mode (SMODE = VLR)
CS low to SDO out of Hi-Z
15.
(Note 15)
SDO will be high impedance when CS is high. In some systems SDO may require a pull-down resistor.
MCLK
t21
RDY
t15
t20
CS
t16
SCLK(i)
t17
SDO
t18 t19
MSB
LSB
Figure 3. SEC Mode - Continuous SCLK Read Timing (Not to Scale)
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CS5581
MCLK
t21
RDY
t15
t20
CS
SCLK(i)
t17
SDO
t18 t19
MSB
LSB
Figure 4. SEC Mode - Discontinuous SCLK Read Timing (Not to Scale)
DIGITAL CHARACTERISTICS
TA = TMIN to TMAX; VL = 3.3V, ±5% or VL = 2.5V, ±5% or 1.8V, ±5%; VLR = 0V
Parameter
Symbol
Min
Typ
Max
Unit
Input Leakage Current
Iin
-
-
2
µA
Digital Input Pin Capacitance
Cin
-
3
-
pF
Digital Output Pin Capacitance
Cout
-
3
-
pF
10
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CS5581
GUARANTEED LOGIC LEVELS
TA = -40 to +85 °C; V1+ = V2+ = +2.5 V, ±5%; V1- = V2- = -2.5 V, ±5%;
VL - VLR = 3.3 V, ±5%, 2.5 V, ±5%, or 1.8 V, ±5%
Input levels: Logic 0 = 0V = Low; Logic 1 = VD+ = High; CL = 15 pF.
Guaranteed Limits
Parameter
Sym
VL
Min
3.3
1.9
2.5
1.6
1.8
1.2
Typ
Max
Unit
Conditions
Logic Inputs
Minimum High-level Input Voltage:
Maximum Low-level Input Voltage:
VIH
VIL
V
3.3
1.1
2.5
0.95
1.8
0.6
V
Logic Outputs
Minimum High-level Output Voltage:
Maximum Low-level Output Voltage:
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VOH
VOL
3.3
2.9
2.5
2.1
1.8
1.65
3.3
0.36
2.5
0.36
1.8
0.44
V
IOH = -2 mA
V
IOH = -2 mA
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CS5581
RECOMMENDED OPERATING CONDITIONS
(VLR = 0V, see Note 16)
Parameter
Symbol
Min
Typ
Max
Unit
(Note 16)
V1+
V2+
V1V2-
V1+
V2V1+
V2-
4.75
4.75
-
5.0
5.0
0
0
5.25
5.25
-
V
V
V
V
(Note 16)
V1+
V2+
V1V2-
V1+
V2V1+
V2-
+2.375
+2.375
-2.375
-2.375
+2.5
+2.5
-2.5
-2.5
+2.625
+2.625
-2.625
-2.625
V
V
V
V
VREF
2.4
4.096
4.2
V
Single Analog Supply
DC Power Supplies:
Dual Analog Supplies
DC Power Supplies:
Analog Reference Voltage
16.
17.
(Note 17)
[VREF+] – [VREF-]
The logic supply can be any value VL – VLR = +1.71 to +3.465 volts as long as VLR ≥ V2- and VL ≤ 3.465 V.
The differential voltage reference magnitude is constrained by the V1+ or V1- supply magnitude.
ABSOLUTE MAXIMUM RATINGS
(VLR = 0V)
Parameter
Symbol
Min
Typ
Max
Unit
-
0
0
-
5.5
6.1
V
V
IIN
-
-
±10
mA
VINA
(V1-) – 0.3
-
(V1+) + 0.3
V
Digital Input Voltage
VIND
VLR – 0.3
-
VL + 0.3
V
Storage Temperature
Tstg
-65
-
150
°C
DC Power Supplies:
[V1+] – [V1-] (Note 18)
VL + [ |V1-| ] (Note 19)
Input Current, Any Pin Except Supplies
Analog Input Voltage
(Note 20)
(AIN and VREF pins)
Notes: 18. V1+ = V2+; V1- = V219.
20.
V1- = V2Transient currents of up to 100 mA will not cause SCR latch-up.
WARNING:
Recommended Operating Conditions indicate limits to which the device is functionally operational. Absolute Maximum Ratings indicate limits beyond which permanent damage to the device may occur. The
Absolute Maximum Ratings are stress ratings only and the device should not be operated at these limits.
Operation at conditions beyond the Recommended Operating Conditions may affect device reliability, and
functional operation beyond Recommended Operating Conditions is not implied. Performance specifications are intended for the conditions specified for each table in the Characteristics and Specifications section.
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CS5581
2. OVERVIEW
The CS5581 is a 16-bit analog-to-digital converter capable of 200 kSps conversion rate. The analog input
accepts a single-ended input with a magnitude of ±VREF / 2 volts. The ADC uses a low-latency digital filter
architecture. The filter is designed for fast settling and settles to full accuracy in one conversion.
The converter is a serial output device. The serial port can be configured to function as either a master or
a slave.
The converter can operate from an analog supply of 5V or from ±2.5V. The digital interface supports standard logic operating from 1.8, 2.5, or 3.3 V.
The CS5581 may convert at rates up to 200 kSps when operating from a 16 MHz input clock.
3. THEORY OF OPERATION
The CS5581 converter provides high-performance measurement of DC or AC signals. The converter can
be used to perform single conversions or continuous conversions upon command. Each conversion is independent of previous conversions and settles to full specified accuracy, even with a full-scale input voltage step. This is due to the converter architecture which uses a combination of a high-speed delta-sigma
modulator and a low-latency filter architecture.
Once power is established to the converter, a reset must be performed. A reset initializes the internal converter logic.
If CONV is held low, the converter will convert continuously with RDY falling every 80 MCLKs. This is
equivalent to 200 kSps if MCLK = 16.0 MHz. If CONV is tied to RDY, a conversion will occur every 82
MCLKs. If CONV is operated asynchronously to MCLK, it may take up to 84 MCLKs from CONV falling to
RDY falling.
Multiple converters can operate synchronously if they are driven by the same MCLK source and CONV
to each converter falls on the same MCLK falling edge. Alternately, CONV can be held low and all devices
can be synchronized if they are reset with RST rising on the same falling edge of MCLK.
The output coding of the conversion word is a function of the BP/UP pin.
3.1 Converter Operation
The converter should be reset after the power supplies and voltage reference are stable.
The CS5581 converts at 200 kSps when synchronously operated (CONV = VLR) from a 16.0 MHz master
clock. Conversion is initiated by taking CONV low. A conversion lasts 80 master clock cycles, but if CONV
is asynchronous to MCLK there may be an uncertainty of 0-4 MCLK cycles after CONV falls to when a
conversion actually begins. This may extend the throughput to 84 MCLKs per conversion.
When the conversion is completed, the output word is placed into the serial port and RDY goes low. To
convert continuously, CONV should be held low. In continuous conversion mode with CONV held low, a
conversion is performed in 80 MCLK cycles. Alternately RDY can be tied to CONV and a conversion will
occur every 82 MCLK cycles.
To perform only one conversion, CONV should return high at least 20 master clock cycles before RDY
falls.
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CS5581
Once a conversion is completed and RDY falls, RDY will return high when all the bits of the data word are
emptied from the serial port or if the conversion data is not read and CS is held low, RDY will go high two
MCLK cycles before the end of conversion. RDY will fall at the end of the next conversion when new data
is put into the port register.
See Serial Port on page 24 for information about reading conversion data.
Conversion performance can be affected by several factors. These include the choice of clock source for
the chip, the timing of CONV, and the choice of the serial port mode.
The converter can be operated from an internal oscillator. This clock source has greater jitter than an
external crystal-based clock. Jitter may not be an issue when measuring DC signals, or very-low-frequency AC signals, but can become an issue for higher frequency AC signals. For maximum performance
when digitizing AC signals, a low-jitter MCLK should be used.
To maximize performance, the CONV pin should be held low in the continuous conversion state to perform multiple conversions, or CONV should occur synchronous to MCLK, falling when MCLK falls.
If the converter is operated at maximum throughput, the SSC serial port mode is less likely to cause interference to measurements as the SCLK output is synchronized to the MCLK. Alternately, any interference due to serial port clocking can also be minimized if data is read in the SEC serial port mode when a
conversion is not in progress.
3.2 Clock
The CS5581 can be operated from its internal oscillator or from an external master clock. The state of
MCLK determines which clock source will be used. If MCLK is tied low, the internal oscillator will start and
be used as the clock source for the converter. If an external CMOS-compatible clock is input into MCLK,
the converter will power down the internal oscillator and use the external clock. If the MCLK pin is held
high, the internal oscillator will be held in the stopped state. The MCLK input can be held high to delete
clock cycles to aid in synchronizing multiple converters in different phase relationships.
The internal oscillator can be used if the signals to be measured are essentially DC. The internal oscillator
exhibits jitter at about 500 picoseconds rms. If the CS5581 is used to digitize AC signals, an external
low-jitter clock source should be used.
If the internal oscillator is used as the clock for the CS5581, the maximum conversion rate will be dictated
by the oscillator frequency.
If driven from an external MCLK source, the fast rise and fall times of the MCLK signal can result in clock
coupling from the internal bond wire of the IC to the analog input. Adding a 50 ohm resistor on the external
MCLK source significantly reduces this effect.
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CS5581
3.3 Voltage Reference
The voltage reference for the CS5581 can range from 2.4 volt to 4.2 volts. A 4.096 volt reference is required to achieve the specified signal-to-noise performance. Figure 6 and Figure 7 illustrate the connection of the voltage reference with either a single +5 V analog supply or with ±2.5 V.
For optimum performance, the voltage reference device should be one that provides a capacitor connection to provide a means of noise filtering, or the output should include some type of bandwidth-limiting filter.
Some 4.096 volt reference devices need only 5 volts total supply for operation and can be connected as
shown in Figure 6 or Figure 7. The reference should have a local bypass capacitor and an appropriate
output capacitor.
Some older 4.096 voltage reference designs require more headroom and must operate from an input voltage of 5.5 to 6.5 volts. If this type of voltage reference is used ensure that when power is applied to the
system, the voltage reference rise time is slower than the rise time of the V1+ and V1- power supply voltage to the converter. An example circuit to slow the output startup time of the reference is illustrated in
Figure 5.
5.5 to 15 V
2k
10µF
VIN
VOUT
4.096 V
GND
Refer to V1- and VREF1 pins.
Figure 5. Voltage Reference Circuit
3.4 Analog Input
The analog input of the converter is single-ended with a full-scale input of ±2.048 volts, relative to the
ACOM pin. This is illustrated in Figure 6 and Figure 7. These diagrams also illustrate a differential buffer
amplifier configuration for driving the CS5581.
The capacitors at the outputs of the amplifiers provide a charge reservoir for the dynamic current from the
A/D inputs while the resistors isolate the dynamic current from the amplifier. The amplifiers can be powered from higher supplies than those used by the A/D but precautions should be taken to ensure that the
op amp output voltage remains within the power supply limits of the A/D, especially under start-up conditions.
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CS5581
3.5 Output Coding Format
The reference voltage directly defines the input voltage range in both the unipolar and bipolar configurations. In the unipolar configuration (BP/UP low), the first code transition occurs 0.5 LSB above zero, and
the final code transition occurs 1.5 LSBs below VREF. In the bipolar configuration (BP/UP high), the first
code transition occurs 0.5 LSB above -VREF and the last transition occurs 1.5 LSBs below +VREF. See
Table 1 for the output coding of the converter.
Table 1. Output Coding, Two’s Complement
Bipolar Input Voltage
Two’s
Complement
>(VREF-1.5 LSB)
7F FF
7F FF
VREF-1.5 LSB
7F FE
00 00
-0.5 LSB
FF FF
80 01
-VREF+0.5 LSB
80 00
<(-VREF+0.5 LSB)
80 00
NOTE: VREF = [(VREF+) - (VREF-)] / 2
Table 2. Output Coding, Offset Binary
Unipolar Input Voltage
Offset
Binary
>(VREF-1.5 LSB)
FF FF
FF FF
VREF-1.5 LSB
FF FE
80 00
(VREF/2)-0.5 LSB
7F FF
00 01
+0.5 LSB
00 00
<(+0.5 LSB)
00 00
NOTE: VREF = [(VREF+) - (VREF-)] / 2
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CS5581
3.6 Typical Connection Diagrams
The following figure depicts the CS5581 powered from bipolar analog supplies, +2.5 V and - 2.5 V.
+2.048 V
0V
CS5571
CS5581
-2.048 V
49.9
AIN
150pF
4700pF
C0G
SMODE
2k
CS
5
CS3003
SCLK
5
ACOM
SDO
RDY
(V+) Buffers On
BUFEN
+2.5 V
CONV
(V-) Buffers Off
BP/UP
+4.096
Voltage
Reference
(NOTE 1)
VREF+
10 µF
RST
0.1 µF
50
MCLK
VREFTST
-2.5 V
+3.3 V to +1.8 V
+2.5 V
V1+
VL
10
0.1 µF
V2+
0.1 µF
0.1 µF
10
V20.1 µF
X7R
VLR3
DCR
VLR2
V1-
VLR
-2.5 V
NOTES
1. See Section 3.3 Voltage Reference for information on required
voltage reference performance criteria.
2.Locate capacitors so as to minimize loop length.
3. The ±2.5 V supplies should also be bypassed to ground at the converter.
4. VLR and the power supply ground for the ±2.5 V should be
connected to the same ground plane under the chip.
5. SCLK and SDO may require pull-down resistors in some applications.
Figure 6. CS5581 Configured Using ±2.5V Analog Supplies
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CS5581
The following figure depicts the CS5581 part powered from a single 5V analog supply and configured for
unipolar measurement.
0 V to +2.048 V
CS5581
CS5571
49.9
AIN
150pF
SMODE
4700pF
C0G
CS
2k
4
SCLK
CS3003 / CS3004
4
ACOM
SDO
RDY
(V+) Buffers On
BUFEN
+5 V
CONV
(V-) Buffers Off
BP/UP
+4.096
Voltage
Reference
(NOTE 1)
VREF+
10 µF
RST
0.1 µF
50
MCLK
VREFTST
+3.3 V to 1.8 V
+5 V
V1+
0.1 µF
VL
10
V2+
0.1 µF
0.1 µF
V20.1 µF
X7R
VLR3
DCR
VLR2
V1-
VLR
NOTES
1. See Section 3.3 Voltage Reference for information on
required voltage reference performance criteria.
2. Locate capacitors so as to minimize loop length.
3. V1-, V2-, and VLR should be connected to the same
ground plane under the chip.
4. SCLK and SDO may require pull-down resistors in
some applications.
Figure 7. CS5581 Configured for Unipolar Measurement Using a Single 5V Analog Supply
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CS5581
The following figure depicts the CS5581 part powered from a single 5V analog supply and configured for
bipolar measurement, referenced to a common mode voltage of 2.5 V.
0.458 to 4.548 V
49.9
AIN
150pF
CS5581
CS5571
CS5581
4700pF
C0G
2k
SMODE
CS3003 / CS3004
Common Mode Voltage
(2.5 V Typ.)
CS
4
SCLK
49.9
ACOM
150pF
4700pF
C0G
4
SDO
2k
RDY
CS3003 / CS3004
(V+) Buffers On
CONV
BUFEN
+5 V
BP/UP
(V-) Buffers Off
+4.096
Voltage
Reference
(NOTE 1)
VREF+
10 µF
RST
0.1 µF
50
MCLK
VREFTST
+3.3 V to 1.8 V
+5 V
V1+
0.1 µF
VL
10
V2+
0.1 µF
0.1 µF
V20.1 µF
X7R
VLR3
DCR
VLR2
V1-
VLR
NOTES
1. See Section 3.3 Voltage Reference for information on
required voltage reference performance criteria.
2. Locate capacitors so as to minimize loop length.
3. V1-, V2-, and VLR should be connected to the same
ground plane under the chip.
4. SCLK and SDO may require pull-down resistors in
some applications.
Figure 8. CS5581 Configured for Bipolar Measurement Using a Single 5V Analog Supply
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CS5581
3.7 AIN & VREF Sampling Structures
The CS5581 uses on-chip buffers on the AIN and the VREF+ inputs. Buffers provide much higher input
impedance and therefore reduce the amount of drive current required from an external source. This helps
minimize errors.
The Buffer Enable (BUFEN) pin determines if the on-chip buffers are used or not. If the BUFEN pin is
connected to the V1+ supply, the buffers will be enabled. If the BUFEN pin is connected to the V1- pin,
the buffers are off. The converter will consume about 30 mW less power when the buffers are off, but the
input impedances of AIN, ACOM and VREF+ will be significantly less than with the buffers enabled.
3.8 Converter Performance
The CS5581 achieves excellent differential nonlinearity (DNL) as shown in Figures 9 and 10. Figure 9
illustrates the code widths on the typical scale of ±1 LSB. Figure 10 illustrates a zoomed scale of ±0.1
LSB. The DNL error histogram in Figure 10 indicates that more than half the codes are accurate to better
than ±0.01 LSB.
DNL Error in LSBs
1.00
0.75
0.50
0.25
0.00
-0.25
-0.50
-0.75
-1.00
1
65535
Codes
Figure 9. CS5581 DNL Plot
+0.1
+0.10
+0.09
+0.08
+0.08
+0.07
+0.06
+0.06
+0.04
+0.03
+0.02
+0.02
+0.01
0
0
-0.01
-0.02
-0.02
-0.03
-0.04
DNL Error in LSBs
DNL Error in LSBs
+0.05
+0.04
-0.04
-0.05
-0.06
-0.06
-0.07
-0.08
-0.08
-0.09
-0.10
1
65535
Codes
18k
16k
14k
12k
10k
8k
6k
4k
2k
0
-0.1
Counts per 0.01 LSB Error
Figure 10. CS5581 DNL Error Plot with DNL Histogram
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CS5581
Figures 11 through 16 illustrate the performance of the CS5581 when driven by a 5.55 kHz sine wave at
various amplitudes. In each case, the captured data was windowed with a seven-term window function
that exhibits 4.3 dB of attenuation before being processed by the FFT.
Figure 14 illustrates the converter performance with an input that is 1/10,000 of full scale. This is a signal
magnitude of about 6.5 codes, peak to peak.
Figure 15 illustrates the converter performance with an input that is 1/100,000 of full scale, or about 0.65
of a code, peak to peak. These plots illustrate that this converter has excellent small-signal performance
due to the near-perfect DNL of the converter.
0
0
5.55 kHz, 0 dB
32k Samples @ 200 kSps
-20
-40
-40
-60
-60
-80
-80
-100
-100
-120
-120
-140
-140
-160
-160
0
20k
40k
60k
Frequency (Hz)
80k
5.55 kHz, -6 dB
32k Samples @ 200 kSps
-20
100k
0
Figure 11. Spectral Performance, 0 dB
20k
40k
60k
Frequency (Hz)
80k
100k
Figure 12. Spectral Performance, -6 dB
0
0
5.55 kHz, -12 dB
32k Samples @ 200 kSps
-20
5.55 kHz, -80 dB
32k Samples @ 200 kSps
-20
-40
-40
-60
-60
-80
-80
-100
-100
-120
-120
-140
-140
-160
-160
0
20k
40k
60k
Frequency (Hz)
80k
Figure 13. Spectral Performance, -12 dB
100k
0
20k
40k
60k
Frequency (Hz)
80k
100k
Figure 14. Spectral Performance, -80 dB
0
5.55 kHz, -100 dB
32k Samples @ 200 kSps
-20
-40
-60
-80
-100
-120
-140
-160
0
20k
40k
60k
Frequency (Hz)
80k
100k
Figure 15. Spectral Performance, -100 dB
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CS5581
Figure 16 illustrates the noise floor of the converter from 0.1 Hz to 100 kHz. While the plot does exhibit
some 1/f noise at lower frequencies, the noise floor is entirely free of spurious frequency content due to
digital activity inside the chip.
Figure 17 illustrates a noise histogram of 4096 samples.
0
Shorted Input
2M Samples @ 200 kSps
16 Averages
-20
-40
-60
-80
-100
-120
-140
-160
0.1
1
10
100
Frequency (Hz)
1k
10k
100k
Figure 16. Spectral Plot of Noise with Shorted Input
900
Mean = -0.61
Std. Dev = 2.33
800
700
600
500
400
300
200
100
0
-8
-7
-6
-5
-4
-3
-2
-1
0
1
2
3
4
5
6
7
8
Output (Codes)
Figure 17. Noise Histogram (4096 Conversions)
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CS5581
3.9 Digital Filter Characteristics
The digital filter is designed for fast settling, therefore it exhibits very little in-band attenuation. The filter
attenuation is 0.26347 dB at 100 kHz when sampling at 200 kSps.
0.00
-0.01049 dB
-0.05
fs = 200 kSps
-0.04206 dB
-0.10
-0.09443 dB
-0.15
-0.16813 dB
-0.20
-0.25
-0.26347 dB
-0.30
0
20k
40k
60k
80k
100k
Frequency (Hz)
Figure 18. CS5581 Spectral Response (DC to fs/2)
0.00
fs = 200 kSps
-0.006283 dB
-0.002622 dB
-0.005
-0.005901 dB
-0.01
-0.01049 dB
-0.015
0
5k
10k
15k
20k
Frequency (Hz)
Figure 19. CS5581 Spectral Response (DC to 20 kHz)
0
fs = 200 kSps
-20
-40
-60
-80
-100
-120
0
400k
800k
1.2M
1.6M
Frequency (Hz)
Figure 20. CS5581 Spectral Response (DC to 8fs)
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CS5581
3.10 Serial Port
The serial port on the CS5581 can operate in two different modes: synchronous self clock (SSC) mode &
synchronous external clock (SEC) mode.
3.10.1 SSC Mode
If the SMODE pin is high (SMODE = VL), the serial port operates in the SSC (Synchronous Self Clock)
mode. In the SSC mode the port shifts out conversion data words with SCLK as an output. SCLK is generated inside the converter from MCLK. Data is output from the SDO (Serial Data Output) pin. If CS is
high, the SDO and SCLK pins will stay in a high-impedance state. If CS is low when RDY falls, the conversion data word will be output from SDO MSB first. Data is output on the rising edge of SCLK and should
be latched into the external logic on the subsequent rising edge of SCLK. When all bits of the conversion
word are output from the port the RDY signal will return to high.
3.10.2 SEC Mode
If the SMODE pin is low (SMODE = VLR), the serial port operates in the SEC (Synchronous External
Clock mode). In this mode, the user usually monitors RDY. When RDY falls at the end of a conversion,
the conversion data word is placed into the output data register in the serial port. CS is then activated low
to enable data output. Note that CS can be held low continuously if it is not necessary to have the SDO
output operate in the high impedance state. When CS is taken low (after RDY falls) the conversion data
word is then shifted out of the SDO pin by driving the SCLK pin from system logic external to the converter.
Data bits are advanced on rising edges of SCLK and latched by the subsequent rising edge of SCLK.
If CS is held low continuously, the RDY signal will fall at the end of a conversion and the conversion data
will be placed into the serial port. If the user starts a read, the user will maintain control over the serial port
until the port is empty. However, if SCLK is not toggled, the converter will overwrite the conversion data
at the completion of the next conversion. If CS is held low and no read is performed, RDY will rise just
prior to the end of the next conversion and then fall to signal that new data has been written into the serial
port.
3.11 Power Supplies & Grounding
The CS5581 can be configured to operate with its analog supply operating from 5V, or with its analog supplies operating from ±2.5V. The digital interface supports digital logic operating from either 1.8V, 2.5V, or
3.3V.
Figure 6 on page 17 illustrates the device configured to operate from ±2.5V analog. Figure 7 on page 18
illustrates the device configured to operate from 5V analog.
To maximize converter performance, the analog ground and the logic ground for the converter should be
connected at the converter. In the dual analog supply configuration, the analog ground for the ±2.5V supplies should be connected to the VLR pin at the converter with the converter placed entirely over the analog ground plane.
In the single analog supply configuration (+5V), the ground for the +5V supply should be directly tied to
the VLR pin of the converter with the converter placed entirely over the analog ground plane. Refer to
Figure 7 on page 18.
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CS5581
3.12 Using the CS5581 in Multiplexing Applications
The CS5581 is a delta-sigma A/D converter. Delta-sigma converters use oversampling as means to
achieve high signal to noise. This means that once a conversion is started, the converter takes many samples to compute the resulting output word. The analog input for the signal to be converted must remain
active during the entire conversion until RDY falls.
The CS5581 can be used in multiplexing applications, but the system timing for changing the multiplexer
channel and for starting a new conversion will depend upon the multiplexer system architecture.
The simplest system is illustrated in Figure 21. Any time the multiplexer is changed, the analog signal
presented to the converter must fully settle. After the signal has settled, the CONV signal is issued to the
converter to start a conversion. Being a delta-sigma converter, the signal must remain present at the input
of the converter until the conversion is completed. Once the conversion is completed, RDY falls. At this
time the multiplexer can be changed to the next channel and the data can be read from the serial port.
The CONV signal should be delayed until after the data is read and until the new analog signal has settled.
In this configuration, the throughput of the converter will be dictated by the settling time of the analog input
circuit and the conversion time of the converter. The conversion data can be read from the serial port after
the multiplexer is changed to the new channel while the analog input signal is settling.
CS5581
CH1
CH2
CH3
CH4
90
AIN
150pF
2k
4700pF
C0G
ACOM
Amplifier
Settling Time
Conversion Time
Amplifier
Settling Time
CONV
RDY
Advance
Mux
CH1
CH2
Throughput
Figure 21. Simple Multiplexing Scheme
A more complex multiplexing scheme can be used to increase the throughput of the converter is illustrated
in Figure 22. In this circuit, two banks of multiplexers are used.
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CS5581
At the same time the converter is performing a conversion on a channel from one bank of multiplexers,
the second multiplexer bank is used to select the channel for the next conversion. This configuration allows the buffer amplifier for the second multiplexer bank to fully settle while a conversion is being performed on the channel from the first multiplexer bank. The multiplexer on the output of the buffer amplifier
and the CONV signal can be changed at the same time in this configuration. This multiplexing architecture allows for maximum multiplexing throughput from the A/D converter. The following figure depicts the
recommended analog input amplifier circuit.
CH1
CH3
SW2
CS5581
150pF
2k
CH2
CH4
A1
90
SW1
4700pF
C0G
AIN
A2
SW3
90
150pF
2k
4700pF
C0G
ACOM
CONV
SW1
Select A1
Select A2
SW2
Select CH1
Select CH3
SW3
Select CH2
Convert on CH1
Select A1
Select A2
Select CH1
Select CH4
Convert on CH2
Select A1
Convert on CH3
Select CH2
Convert on CH4
Convert on CH1
Figure 22. More Complex Multiplexing Scheme
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CS5581
3.13 Synchronizing Multiple Converters
Many measurement systems have multiple converters that need to operate synchronously. The converters should all be driven from the same master clock. In this configuration, the converters will convert synchronously if the same CONV signal is used to drive all the converters, and CONV falls on a falling edge
of MCLK. If CONV is held low continuously, reset (RST) can be used to synchronize multiple converters
if RST is released on a falling edge of MCLK.
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4. PIN DESCRIPTIONS
Chip Select
Factory Test
Serial Mode Select
Analog Input
Analog Return
Negative Power 1
Positive Power 1
Buffer Enable
Voltage Reference Input
Voltage Reference Input
Bipolar/Unipolar Select
Logic Interface Return 2
CS
TST
SMODE
AIN
ACOM
V1V1+
BUFEN
VREF+
VREFBP/UP
VLR2
1
2
3
4
5
6
7
8
9
10
11
12
24
23
22
21
20
19
18
17
16
15
14
13
RDY
SCLK
SDO
VL
VLR
MCLK
V2V2+
DCR
CONV
VLR3
RST
Ready
Serial Clock Input/Output
Serial Data Output
Logic Interface Power
Logic Interface Return
Master Clock
Negative Voltage 2
Positive Voltage 2
Digital Core Regulator
Convert
Logic Interface Return 3
Reset
CS – Chip Select, Pin 1
The Chip Select pin allows an external device to access the serial port. When held high, the
SDO output will be held in a high-impedance output state.
TST – Factory Test, Pin 2
For factory use only. Connect to VLR.
SMODE – Serial Mode Select, Pin 3
The serial interface mode pin (SMODE) dictates whether the serial port behaves as a master or
slave interface. If SMODE is tied high (to VL), the port will operate in the Synchronous
Self-Clocking (SSC) mode. In SSC mode, the port acts as a master in which the converter outputs both the SDO and SCLK signals. If SMODE is tied low (to VLR), the port will operate in the
Synchronous External Clocking (SEC) mode. In SEC mode, the port acts as a slave in which
the external logic or microcontroller generates the SCLK used to output the conversion data
word from the SDO pin.
AIN – Analog Input, Pin 4
AIN is the single-ended input.
ACOM – Analog Return, Pin 5
ACOM is the analog return for the input signal.
V1- – Negative Power 1, Pin 6
The V1- and V2- pins provide a negative supply voltage to the core circuitry of the chip. These
two pins should be decoupled as shown in the application block diagrams. V1- and V2- should
be supplied from the same source voltage. For single-supply operation, these two voltages are
nominally 0 V (Ground). For dual-supply, operation they are nominally -2.5 V.
V1+ – Positive Power 1, Pin 7
The V1+ and V2+ pins provide a positive supply voltage to the core circuitry of the chip. These
two pins should be decoupled as shown in the application block diagrams. V1+ and V2+ should
be supplied from the same source voltage. For single-supply operation, these two voltages are
nominally +5 V. For dual-supply operation, they are nominally +2.5 V.
BUFEN – Buffer Enable, Pin 8
Buffers on input pins AIN and ACOM are enabled if BUFEN is connected to V1+ and disabled if
connected to V1-.
VREF+, VREF- – Voltage Reference Input, Pins 9, 10
A differential voltage reference input on these pins functions as the voltage reference for the
converter. The voltage between these pins can range between 2.4 volts and 4.2 volts, with
4.096 volts being the nominal reference voltage value.
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BP/UP – Bipolar/Unipolar Select, Pin 11
The BP/UP pin determines the span and the output coding of the converter. When set high to
select BP (bipolar), the input span of the converter is -2.048 volts to +2.048 volts (assuming the
voltage reference is 4.096 volts) and output data is coded in two's complement format. When
set low to select UP (unipolar), the input span is 0 to +2.048 and the output data is coded in
binary format.
RST – Reset, Pin 13
Reset is necessary after power is initially applied to the converter. When the RST input is taken
low, the logic in the converter will be reset. When RST is released to go high, certain portions of
the analog circuitry are started. RDY falls when reset is complete.
CONV – Convert, Pin 15
The CONV pin initiates a conversion cycle if taken low, unless a previous conversion is in
progress. When the conversion cycle is completed, the conversion word is output to the serial
port register and the RDY signal goes low. If CONV is held low and remains low when RDY
falls, another conversion cycle will be started.
DCR – Digital Core Regulator, Pin 16
DCR is the output of the on-chip regulator for the digital logic core. DCR should be bypassed
with a capacitor to V2- as shown in Typical Connection Diagrams on page 17. The DCR pin is
not designed to power any external load.
V2+ – Positive Power 2, Pin 17
The V1+ and V2+ pins provide a positive supply voltage to the circuitry of the chip. These two
pins should be decoupled as shown in the application block diagrams. V1+ and V2+ should be
supplied from the same source voltage. For single-supply operation, these two voltages are
nominally +5 V. For dual-supply operation, they are nominally +2.5 V.
V2- – Negative Power 2, Pin 18
The V1- and V2- pins provide a negative supply voltage to the circuitry of the chip. These two
pins should be decoupled as shown in the application block diagrams. V1- and V2- should be
supplied from the same source voltage. For single-supply operation, these two voltages are
nominally 0 V (Ground). For dual-supply operation, they are nominally -2.5 V.
MCLK – Master Clock, Pin 19
The master clock pin (MCLK) is a multi-function pin. If tied low (MCLK = VLR), the on-chip oscillator will be enabled. If tied high (MCLK = VL), all clocks to the internal circuitry of the converter
will stop. When MCLK is held high the internal oscillator will also be stopped. MCLK can also
function as the input for an external CMOS-compatible clock that conforms to supply voltages
on the VL and VLR pins.
VLR2, VLR3, – Logic Interface Power/Return, Pins 12, 14, 20, 21
VLR, VL VL and VLR are the supply voltages for the digital logic interface. VL and VLR can be configured with a wide range of common mode voltage. The following interface pins function from the
VL/VLR supply: SMODE, CS, SCLK, TST, SDO, RDY, CONV, RST, BP/UP, and MCLK.
SDO – Serial Data Output, Pin 22
SDO is the output pin for the serial output port. Data from this pin will be output at a rate determined by SCLK and in a format determined by the BP/UP pin. Data is output MSB first and
advances to the next data bit on the rising edges of SCLK. SDO will be in a high impedance
state when CS is high.
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SCLK – Serial Clock Input/Output, Pin 23
The SMODE pin determines whether the SCLK signal is an input or an output signal. SCLK
determines the rate at which data is clocked out of the SDO pin. If the converter is in SSC
mode, the SCLK frequency will be determined by the master clock frequency of the converter
(either MCLK or the internal oscillator). In SEC mode, the user determines the SCLK frequency.
If SCLK is an output (SMODE = VL), it will be in a high-impedance state when CS is high.
RDY – Ready, Pin 24
At the end of any conversion RDY falls to indicate that a conversion word has been placed into
the serial port. RDY will return high after all data bits are shifted out of the serial port or two master clock cycles before new data becomes available if the CS pin is inactive (high); or two master clock cycles before new data becomes available if the user holds CS low but has not started
reading the data from the converter when in SEC mode.
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5. PACKAGE DIMENSIONS
24L SSOP PACKAGE DRAWING
N
D
E11
A2
E
e
b2
SIDE VIEW
A
∝
A1
L
END VIEW
SEATING
PLANE
1 2 3
TOP VIEW
DIM
A
A1
A2
b
D
E
E1
e
L
MIN
-0.002
0.064
0.009
0.311
0.291
0.197
0.022
0.025
0°
∝
INCHES
NOM
-0.006
0.068
-0.323
0.307
0.209
0.026
0.03
4°
MAX
0.084
0.010
0.074
0.015
0.335
0.323
0.220
0.030
0.041
8°
MIN
-0.05
1.62
0.22
7.90
7.40
5.00
0.55
0.63
0°
MILLIMETERS
NOM
-0.13
1.73
-8.20
7.80
5.30
0.65
0.75
4°
NOTE
MAX
2.13
0.25
1.88
0.38
8.50
8.20
5.60
0.75
1.03
8°
2,3
1
1
JEDEC #: MO-150
Controlling Dimension is Millimeters.
Notes:
1.“D” and “E1” are reference datums and do not included mold flash or protrusions, but do include mold mismatch and are measured
at the parting line, mold flash or protrusions shall not exceed 0.20 mm per side.
2.Dimension “b” does not include dambar protrusion/intrusion. Allowable dambar protrusion shall be 0.13 mm total in excess of “b”
dimension at maximum material condition. Dambar intrusion shall not reduce dimension “b” by more than 0.07 mm at least
material condition.
3.These dimensions apply to the flat section of the lead between 0.10 and 0.25 mm from lead tips.
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6. ORDERING INFORMATION
Model
CS5581-ISZ
Linearity
Temperature
Conversion Time
Throughput
Package
.0008%
-40 to +85 °C
5 µs
200 kSps
24-pin SSOP
7. ENVIRONMENTAL, MANUFACTURING, & HANDLING INFORMATION
Model Number
Peak Reflow Temp
MSL Rating*
Max Floor Life
260 °C
3
7 Days
CS5581-ISZ
* MSL (Moisture Sensitivity Level) as specified by IPC/JEDEC J-STD-020.
8. REVISION HISTORY
Revision
PP1
Date
MAR 2008
Changes
Preliminary release.
Contacting Cirrus Logic Support
For all product questions and inquiries contact a Cirrus Logic Sales Representative.
To find the one nearest to you go to www.cirrus.com
IMPORTANT NOTICE
"Preliminary" product information describes products that are in production, but for which full characterization data is not yet available.
Cirrus Logic, Inc. and its subsidiaries ("Cirrus") believe that the information contained in this document is accurate and reliable. However, the information is subject
to change without notice and is provided "AS IS" without warranty of any kind (express or implied). Customers are advised to obtain the latest version of relevant
information to verify, before placing orders, that information being relied on is current and complete. All products are sold subject to the terms and conditions of sale
supplied at the time of order acknowledgment, including those pertaining to warranty, indemnification, and limitation of liability. No responsibility is assumed by Cirrus
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