CS5531/32/33/34-AS
16-bit and 24-bit ADCs with Ultra-low-noise PGIA
Features
General Description
Chopper-stabilized
The CS5531/32/33/34 are highly integrated ∆Σ Analogto-Digital Converters (ADCs) which use charge-balance
techniques to achieve 16-bit (CS5531/33) and 24-bit
(CS5532/34) performance. The ADCs are optimized for
measuring low-level unipolar or bipolar signals in weigh
scale, process control, scientific, and medical
applications.
PGIA (Programmable
Gain Instrumentation Amplifier, 1x to 64x)
– 12 nV/√Hz @ 0.1 Hz (No 1/f noise) at 64x
– 1200 pA Input Current with Gains >1
Delta-sigma Analog-to-digital Converter
– Linearity Error: 0.0007% FS
– Noise Free Resolution: Up to 23 bits
Two-
or Four-channel Differential MUX
Scalable Input Span via Calibration
– ±5 mV to differential ±2.5V
Scalable
VREF Input: Up to Analog Supply
Simple Three-wire Serial Interface
– SPI™ and Microwire™ Compatible
– Schmitt Trigger on Serial Clock (SCLK)
R/W
Calibration Registers Per Channel
Selectable
Word Rates: 6.25 to 3,840 Sps
Selectable
50 or 60 Hz Rejection
Power Supply Configurations
– VA+ = +5 V; VA- = 0 V; VD+ = +3 V to +5 V
– VA+ = +2.5 V; VA- = -2.5 V; VD+ = +3 V to +5 V
– VA+ = +3 V; VA- = -3 V; VD+ = +3 V
VA+
C1
AIN1+
C2
VREF+
PGIA
1,2,4,8,16
32,64
AIN1-
To accommodate these applications, the ADCs come as
either two-channel (CS5531/32) or four-channel
(CS5533/34) devices and include a very low noise chopper-stabilized instrumentation amplifier (6 nV/√Hz @ 0.1
Hz) with selectable gains of 1×, 2×, 4×, 8×, 16×, 32×, and
64×. These ADCs also include a fourth order ∆Σ modulator followed by a digital filter which provides twenty
selectable output word rates of 6.25, 7.5, 12.5, 15, 25, 30,
50, 60, 100, 120, 200, 240, 400, 480, 800, 960, 1600,
1920, 3200, and 3840 Sps (MCLK = 4.9152 MHz).
To ease communication between the ADCs and a microcontroller, the converters include a simple three-wire serial interface which is SPI and Microwire compatible with
a Schmitt-trigger input on the serial clock (SCLK).
High dynamic range, programmable output rates, and
flexible power supply options makes these ADCs ideal
solutions for weigh scale and process control
applications.
ORDERING INFORMATION
See page 47
VREF-
VD+
DIFFERENTIAL
4TH ORDER ∆Σ
MODULATOR
PROGRAMMABLE
SINC FIR FILTER
CS
AIN2+
SCLK
(CS5533/34
SHOWN)
AIN3-
CLOCK
GENERATOR
LATCH
AIN4+
AIN4-
VA-
http://www.cirrus.com
SDO
MUX
AIN2AIN3+
SDI
SERIAL
INTERFACE
A0/GUARD
A1
OSC1
OSC2
Copyright © Cirrus Logic, Inc. 2008
(All Rights Reserved)
CALIBRATION
SRAM/CONTROL
LOGIC
DGND
OCT ‘08
DS289F5
CS5531/32/33/34-AS
TABLE OF CONTENTS
1. CHARACTERISTICS AND SPECIFICATIONS ..........................................................4
ANALOG CHARACTERISTICS..........................................................................4
TYPICAL RMS NOISE (NV), CS5531/32/33/34 .................................................7
TYPICAL NOISE-FREE RESOLUTION(BITS), CS5532/34 ...............................7
5 V DIGITAL CHARACTERISTICS ....................................................................8
3 V DIGITAL CHARACTERISTICS ....................................................................8
DYNAMIC CHARACTERISTICS ........................................................................9
ABSOLUTE MAXIMUM RATINGS .....................................................................9
SWITCHING CHARACTERISTICS ..................................................................10
2. GENERAL DESCRIPTION .......................................................................................12
2.1. Analog Input ....................................................................................................12
2.1.1. Analog Input Span .................................................................................... 13
2.1.2. Multiplexed Settling Limitations ............................................................13
2.1.3. Voltage Noise Density Performance .....................................................13
2.1.4. No Offset DAC ......................................................................................14
2.2. Overview of ADC Register Structure and Operating Modes ............................14
2.2.1. System Initialization ..............................................................................15
2.2.2. Serial Port Interface ..............................................................................22
2.2.3. Reading/Writing On-Chip Registers ......................................................23
2.3. Configuration Register .....................................................................................23
2.3.1. Power Consumption .............................................................................23
2.3.2. System Reset Sequence ......................................................................23
2.3.3. Input Short ............................................................................................24
2.3.4. Guard Signal .........................................................................................24
2.3.5. Voltage Reference Select .....................................................................24
2.3.6. Output Latch Pins .................................................................................24
2.3.7. Offset and Gain Select ..........................................................................25
2.3.8. Filter Rate Select ..................................................................................25
2.4. Setting up the CSRs for a Measurement .........................................................27
2.5. Calibration ........................................................................................................30
2.5.1. Calibration Registers ............................................................................30
2.5.2. Performing Calibrations ........................................................................31
2.5.3. Self-calibration ......................................................................................31
2.5.4. System Calibration ................................................................................32
2.5.5. Calibration Tips .....................................................................................32
2.5.6. Limitations in Calibration Range ...........................................................33
2.6. Performing Conversions ..................................................................................33
2.6.1. Single Conversion Mode .......................................................................33
2.6.2. Continuous Conversion Mode ..............................................................34
2.6.3. Examples of Using CSRs to Perform Conversions and Calibrations ....35
2.7. Using Multiple ADCs Synchronously ...............................................................36
2.8. Conversion Output Coding ..............................................................................36
2.9. Digital Filter ......................................................................................................38
2.10. Clock Generator ...............................................................................................39
2.11. Power Supply Arrangements ...........................................................................39
2.12. Getting Started ................................................................................................43
2.13. PCB Layout .....................................................................................................43
3. PIN DESCRIPTIONS ...............................................................................................44
4. SPECIFICATION DEFINITIONS ...............................................................................46
5. ORDERING INFORMATION .....................................................................................47
6. ENVIRONMENTAL, MANUFACTURING, & HANDLING INFORMATION ..............47
7. PACKAGE DRAWINGS ...........................................................................................48
2
DS289F5
CS5531/32/33/34-AS
LIST OF FIGURES
Figure 1. SDI Write Timing (Not to Scale)............................................................................... 11
Figure 2. SDO Read Timing (Not to Scale)............................................................................. 11
Figure 3. Multiplexer Configuration ......................................................................................... 12
Figure 4. Input models for AIN+ and AIN- pins ....................................................................... 13
Figure 5. Measured Voltage Noise Density............................................................................. 13
Figure 6. CS5531/32/33/34 Register Diagram ........................................................................ 14
Figure 7. Command and Data Word Timing ........................................................................... 22
Figure 8. Guard Signal Shielding Scheme .............................................................................. 24
Figure 9. Input Reference Model when VRS = 1 .................................................................... 25
Figure 10. Input Reference Model when VRS = 0 .................................................................. 25
Figure 11. Self-calibration of Offset......................................................................................... 32
Figure 12. Self-calibration of Gain........................................................................................... 32
Figure 13. System Calibration of Offset .................................................................................. 32
Figure 14. System Calibration of Gain .................................................................................... 32
Figure 15. Synchronizing Multiple ADCs................................................................................. 36
Figure 16. Digital Filter Response (Word Rate = 60 Sps) ....................................................... 38
Figure 17. 120 Sps Filter Magnitude Plot to 120 Hz ............................................................... 38
Figure 18. 120 Sps Filter Phase Plot to 120 Hz ...................................................................... 38
Figure 19. Z-Transforms of Digital Filters................................................................................ 38
Figure 20. On-chip Oscillator Model........................................................................................ 39
Figure 21. CS5532 Configured with a Single +5 V Supply ..................................................... 40
Figure 22. CS5532 Configured with ±2.5 V Analog Supplies.................................................. 41
Figure 23. CS5532 Configured with ±3 V Analog Supplies..................................................... 41
Figure 24. CS5532 Configured for Thermocouple Measurement ........................................... 42
Figure 25. Bridge with Series Resistors .................................................................................. 42
LIST OF TABLES
Table 1. Conversion Timing – Single Mode ............................................................................ 34
Table 2. Conversion Timing – Continuous Mode .................................................................... 34
Table 3. Command Byte Pointer ............................................................................................. 35
Table 4. Output Coding for 16-bit CS5531 and CS5533......................................................... 36
Table 5. Output Coding for 24-bit CS5532 and CS5534......................................................... 37
DS289F5
3
CS5531/32/33/34-AS
1. CHARACTERISTICS AND SPECIFICATIONS
ANALOG CHARACTERISTICS
(VA+, VD+ = 5 V ±5%; VREF+ = 5 V; VA-, VREF-, DGND = 0 V; MCLK = 4.9152 MHz;
OWR (Output Word Rate) = 60 Sps; Bipolar Mode; Gain = 32)
(See Notes 1 and 2.)
CS5531/CS5533
Parameter
Accuracy
Linearity Error
No Missing Codes
Bipolar Offset
Unipolar Offset
Offset Drift
Bipolar Full-scale Error
Unipolar Full-scale Error
Full-scale Drift
(Notes 3 and 4)
(Note 4)
Min
Typ
Max
Unit
16
-
±0.0015
±1
±0.003
±2
%FS
Bits
LSB16
-
±2
±4
LSB16
-
10
±8
±16
2
±31
±62
-
nV/°C
ppm
ppm
ppm/°C
CS5532/CS5534
Parameter
Accuracy
Linearity Error
No Missing Codes
Bipolar Offset
Unipolar Offset
Offset Drift
Bipolar Full-scale Error
Unipolar Full-scale Error
Full-scale Drift
(Notes 3 and 4)
(Note 4)
Min
Typ
Max
Unit
24
-
±0.0015
±16
±0.003
±32
%FS
Bits
LSB24
-
±32
±64
LSB24
-
10
±8
±16
2
±31
±62
-
nV/°C
ppm
ppm
ppm/°C
Notes: 1. Applies after system calibration at any temperature within -40 °C ~ +85 °C.
2. Specifications guaranteed by design, characterization, and/or test. LSB is 16 bits for the CS5531/33 and
LSB is 24 bits for the CS5532/34.
3. This specification applies to the device only and does not include any effects by external parasitic
thermocouples.
4. Drift over specified temperature range after calibration at power-up at 25 °C.
4
DS289F5
CS5531/32/33/34-AS
ANALOG CHARACTERISTICS
(Continued)
(See Notes 1 and 2.)
Parameter
Min
Typ
Analog Input
Common Mode + Signal on AIN+ or AIN-Bipolar/Unipolar Mode
Gain = 1
VAGain = 2, 4, 8, 16, 32, 64
(Note 5) VA- + 0.7
CVF Current on AIN+ or AINGain = 1
(Note 6, 7)
50
Gain = 2, 4, 8, 16, 32, 64
1200
Input Current Noise
Gain = 1
200
Gain = 2, 4, 8, 16, 32, 64
1
Input Leakage for Mux when Off (at 25 °C)
10
Off-channel Mux Isolation
120
Open Circuit Detect Current
100
300
Common Mode Rejection
dc, Gain = 1
90
dc, Gain = 64
130
50, 60 Hz
120
Input Capacitance
60
Guard Drive Output
20
Voltage Reference Input
Range
(VREF+) - (VREF-)
1
2.5
CVF Current
(Note 6, 7)
50
Common Mode Rejection
dc
120
50, 60 Hz
120
Input Capacitance
11
System Calibration Specifications
Full-scale Calibration Range
Bipolar/Unipolar Mode
3
Offset Calibration Range
Bipolar Mode
-100
Offset Calibration Range
Unipolar Mode
-90
-
Max
Unit
VA+
VA+ - 1.7
-
V
V
nA
pA
pA/√Hz
pA/√Hz
pA
dB
nA
dB
dB
dB
pF
µA
(VA+)-(VA-)
22
V
nA
dB
dB
pF
110
100
90
%FS
%FS
%FS
Notes: 5. The voltage on the analog inputs is amplified by the PGIA, and becomes VCM ± Gain*(AIN+ - AIN-)/2 at
the differential outputs of the amplifier. In addition to the input common mode + signal requirements for
the analog input pins, the differential outputs of the amplifier must remain between (VA- + 0.1 V) and
(VA+ - 0.1 V) to avoid saturation of the output stage.
6. See the section of the data sheet which discusses input models.
7. Input current on AIN+ or AIN- (with Gain = 1), or VREF+ or VREF- may increase to 250 nA if operated
within 50 mV of VA+ or VA-. This is due to the rough charge buffer being saturated under these
conditions.
DS289F5
5
CS5531/32/33/34-AS
ANALOG CHARACTERISTICS
(Continued)
(See Notes 1 and 2.)
Parameter
Min
Typ
Max
Unit
-
6
0.6
8
1
mA
mA
-
35
5
500
45
-
mW
mW
µW
-
115
115
-
dB
dB
Power Supplies
DC Power Supply Currents (Normal Mode)
Power Consumption
Normal Mode
Standby
Sleep
Power Supply Rejection
IA+, IAID+
(Notes 8 and 9)
(Note 10)
dc Positive Supplies
dc Negative Supply
8. All outputs unloaded. All input CMOS levels.
9. Power is specified when the instrumentation amplifier (Gain ≥ 2) is on. Analog supply current is reduced
by approximately 1/2 when the instrumentation amplifier is off (Gain = 1).
10. Tested with 100 mV change on VA+ or VA-.
6
DS289F5
CS5531/32/33/34-AS
TYPICAL RMS NOISE (nV), CS5531/32/33/34
(See notes 11, 12 and 13)
Output Word
-3 dB Filter
Rate (Sps)
Frequency (Hz)
7.5
1.94
15
3.88
30
7.75
60
15.5
120
31
240
62
480
122
960
230
1,920
390
3,840
780
x64
17
24
34
48
68
115
163
229
344
1390
x32
17
25
35
49
70
160
230
321
523
2710
Instrumentation Amplifier Gain
x16
x8
x4
19
26
42
27
36
59
39
51
84
54
72
118
77
102
167
276
527
1040
392
748
1480
554
1060
2090
946
1840
3650
5390
10800
21500
x2
79
111
157
222
314
2070
2950
4170
7290
43000
x1
155
218
308
436
616
4150
5890
8340
14600
86100
Notes: 11. Wideband noise aliased into the baseband. Referred to the input. Typical values shown for 25 °C.
12. For peak-to-peak noise multiply by 6.6 for all ranges and output rates.
13. Word rates and -3dB points with FRS = 0. When FRS = 1, word rates and -3dB points scale by 5/6.
TYPICAL NOISE-FREE RESOLUTION(BITS), CS5532/34 (See Notes 14 and 15)
Output Word
-3 dB Filter
Rate (Sps)
Frequency (Hz)
7.5
1.94
15
3.88
30
7.75
60
15.5
120
31
240
62
480
122
960
230
1,920
390
3,840
780
x64
19
19
18
18
17
16
16
15
15
13
x32
20
20
19
19
18
17
17
16
15
13
Instrumentation Amplifier Gain
x16
x8
x4
21
22
22
21
21
21
20
21
21
20
20
20
19
20
20
17
17
17
17
17
17
16
16
16
15
15
15
13
13
13
x2
22
22
21
21
20
17
17
16
15
13
x1
22
22
21
21
20
17
17
16
15
13
14. Noise-free resolution listed is for bipolar operation, and is calculated as LOG((Input Span)/(6.6xRMS
Noise))/LOG(2) rounded to the nearest bit. For unipolar operation, the input span is 1/2 as large, so one
bit is lost. The input span is calculated in the analog input span section of the data sheet. The noise-free
resolution table is computed with a value of 1.0 in the gain register. Values other than 1.0 will scale the
noise, and change the noise-free resolution accordingly.
15. “Noise-free resolution” is not the same as “effective resolution”. Effective resolution is based on the
RMS noise value, while noise-free resolution is based on a peak-to-peak noise value specified as 6.6
times the RMS noise value. Effective resolution is calculated as LOG((Input Span)/(RMS
Noise))/LOG(2).
Specifications are subject to change without notice.
DS289F5
7
CS5531/32/33/34-AS
5 V DIGITAL CHARACTERISTICS
(VA+, VD+ = 5 V ±5%; VA-, DGND = 0 V;
See Notes 2 and 16.)
Parameter
Symbol
Min
Typ
Max
Unit
High-level Input Voltage
All Pins Except SCLK
SCLK
VIH
0.6 VD+
(VD+) - 0.45
-
VD+
VD+
V
Low-level Input Voltage
All Pins Except SCLK
SCLK
VIL
0.0
0.0
-
0.8
0.6
V
High-level Output Voltage
A0 and A1, Iout = -1.0 mA
SDO, Iout = -5.0 mA
VOH
(VA+) - 1.0
(VD+) - 1.0
-
-
V
Low-level Output Voltage
A0 and A1, Iout = 1.0 mA
SDO, Iout = 5.0 mA
VOL
-
-
(VA-) + 0.4
0.4
V
Input Leakage Current
Iin
-
±1
±10
µA
SDO Tri-state Leakage Current
IOZ
-
-
±10
µA
Digital Output Pin Capacitance
Cout
-
9
-
pF
Symbol
Min
Typ
Max
Unit
3 V DIGITAL CHARACTERISTICS
(TA = 25 °C; VA+ = 5V ±5%; VD+ = 3.0V±10%; VA-, DGND = 0V;
See Notes 2 and 16.)
Parameter
High-level Input Voltage
All Pins Except SCLK
SCLK
VIH
0.6 VD+
(VD+) - 0.45
-
VD+
VD+
V
Low-level Input Voltage
All Pins Except SCLK
SCLK
VIL
0.0
0.0
-
0.8
0.6
V
High-level Output Voltage
A0 and A1, Iout = -1.0 mA
SDO, Iout = -5.0 mA
VOH
(VA+) - 1.0
(VD+) - 1.0
-
-
V
Low-level Output Voltage
A0 and A1, Iout = 1.0 mA
SDO, Iout = 5.0 mA
VOL
-
-
(VA-) + 0.4
0.4
V
Input Leakage Current
Iin
-
±1
±10
µA
SDO Tri-state Leakage Current
IOZ
-
-
±10
µA
Digital Output Pin Capacitance
Cout
-
9
-
pF
16. All measurements performed under static conditions.
8
DS289F5
CS5531/32/33/34-AS
DYNAMIC CHARACTERISTICS
Parameter
Symbol
Ratio
Unit
Modulator Sampling Rate
fs
MCLK/16
Sps
Filter Settling Time to 1/2 LSB (Full-scale Step Input)
Single Conversion mode (Notes 17, 18, and 19)
Continuous Conversion mode, OWR < 3200 Sps
Continuous Conversion mode, OWR ≥ 3200 Sps
ts
ts
ts
1/OWRSC
5/OWRsinc5 + 3/OWR
5/OWR
s
s
s
17. The ADCs use a Sinc5 filter for the 3200 Sps and 3840 Sps output word rate (OWR) and a Sinc5 filter
followed by a Sinc3 filter for the other OWRs. OWRsinc5 refers to the 3200 Sps (FRS = 1) or 3840 Sps
(FRS = 0) word rate associated with the Sinc5 filter.
18. The single conversion mode only outputs fully settled conversions. See Table 1 for more details about
single conversion mode timing. OWRSC is used here to designate the different conversion time
associated with single conversions.
19. The continuous conversion mode outputs every conversion. This means that the filter’s settling time
with a full-scale step input in the continuous conversion mode is dictated by the OWR.
ABSOLUTE MAXIMUM RATINGS
(DGND = 0 V; See Note 20.)
Parameter
Symbol
Min
Typ
Max
Unit
(Notes 21 and 22)
Positive Digital
Positive Analog
Negative Analog
VD+
VA+
VA-
-0.3
-0.3
+0.3
-
+6.0
+6.0
-3.75
V
V
V
(Notes 23 and 24)
IIN
-
-
±10
mA
IOUT
-
-
±25
mA
(Note 25)
PDN
-
-
500
mW
VREF pins
AIN Pins
VINR
VINA
(VA-) -0.3
(VA-) -0.3
-
(VA+) + 0.3
(VA+) + 0.3
V
V
VIND
-0.3
-
(VD+) + 0.3
V
Ambient Operating Temperature
TA
-40
-
85
°C
Storage Temperature
Tstg
-65
-
150
°C
DC Power Supplies
Input Current, Any Pin Except Supplies
Output Current
Power Dissipation
Analog Input Voltage
Digital Input Voltage
Notes: 20.
21.
22.
23.
24.
All voltages with respect to ground.
VA+ and VA- must satisfy {(VA+) - (VA-)} ≤ +6.6 V.
VD+ and VA- must satisfy {(VD+) - (VA-)} ≤ +7.5 V.
Applies to all pins including continuous overvoltage conditions at the analog input (AIN) pins.
Transient current of up to 100 mA will not cause SCR latch-up. Maximum input current for a power
supply pin is ±50 mA.
25. Total power dissipation, including all input currents and output currents.
WARNING: Operation at or beyond these limits may result in permanent damage to the device.
Normal operation is not guaranteed at these extremes.
DS289F5
9
CS5531/32/33/34-AS
SWITCHING CHARACTERISTICS
(VA+ = 2.5 V or 5 V ±5%; VA- = -2.5V±5% or 0 V; VD+ = 3.0 V ±10% or 5 V ±5%;DGND = 0 V;
Levels: Logic 0 = 0 V, Logic 1 = VD+; CL = 50 pF; See Figures 1 and 2.)
Parameter
Min
Typ
Max
Unit
1
4.9152
5
MHz
40
-
60
%
-
50
1.0
100
-
µs
µs
ns
-
50
1.0
100
-
µs
µs
ns
tost
-
20
-
ms
SCLK
0
-
2
MHz
t1
t2
250
250
-
-
ns
ns
CS Enable to Valid Latch Clock
t3
50
-
-
ns
Data Set-up Time prior to SCLK rising
t4
50
-
-
ns
Data Hold Time After SCLK Rising
t5
100
-
-
ns
SCLK Falling Prior to CS Disable
t6
100
-
-
ns
CS to Data Valid
t7
-
-
150
ns
SCLK Falling to New Data Bit
t8
-
-
150
ns
CS Rising to SDO Hi-Z
t9
-
-
150
ns
Master Clock Frequency
Symbol
(Note 26)
External Clock or Crystal Oscillator
MCLK
Master Clock Duty Cycle
Rise Times
Fall Times
(Note 27)
Any Digital Input Except SCLK
SCLK
Any Digital Output
trise
(Note 27)
Any Digital Input Except SCLK
SCLK
Any Digital Output
tfall
Start-up
Oscillator Start-up Time
XTAL = 4.9152 MHz
(Note 28)
Serial Port Timing
Serial Clock Frequency
Serial Clock
Pulse Width High
Pulse Width Low
SDI Write Timing
SDO Read Timing
Notes: 26. Device parameters are specified with a 4.9152 MHz clock.
27. Specified using 10% and 90% points on waveform of interest. Output loaded with 50 pF.
28. Oscillator start-up time varies with crystal parameters. This specification does not apply when using an
external clock source.
10
DS289F5
CS5531/32/33/34-AS
CS
t3
SDI
M SB
M S B -1
t4
LSB
t5
t1
t6
SC LK
t2
Figure 1. SDI Write Timing (Not to Scale)
CS
t7
SDO
t9
MSB
M S B -1
LS B
t2
t8
SC LK
t1
Figure 2. SDO Read Timing (Not to Scale)
DS289F5
11
CS5531/32/33/34-AS
2. GENERAL DESCRIPTION
The CS5531/32/33/34 are highly integrated ∆Σ Analog-to-Digital Converters (ADCs) which use
charge-balance techniques to achieve 16-bit
(CS5531/33) and 24-bit (CS5532/34) performance.
The ADCs are optimized for measuring low-level
unipolar or bipolar signals in weigh scale, process
control, scientific, and medical applications.
To accommodate these applications, the ADCs
come as either two-channel (CS5531/32) or fourchannel (CS5533/34) devices and include a verylow-noise, chopper-stabilized, programmable-gain
instrumentation amplifier (PGIA, 6 nV/√Hz @ 0.1
Hz) with selectable gains of 1×, 2×, 4×, 8×, 16×,
32×, and 64×. These ADCs also include a fourth order ∆Σ modulator followed by a digital filter which
provides twenty selectable output word rates of 6.25,
7.5, 12.5, 15, 25, 30, 50, 60, 100, 120, 200, 240, 400,
480, 800, 960, 1600, 1920, 3200, and 3840 Samples
per second (MCLK = 4.9152 MHz).
To ease communication between the ADCs and a
microcontroller, the converters include a simple
three-wire serial interface which is SPI and Mi-
AIN2+
AIN2AIN1+
AIN1-
CS5531/32 IN+
M
U
INX
M
U
X
XGAIN
The instrumentation amplifier is chopper stabilized
and operates with a chop clock frequency of
MCLK/128. The CVF (sampling) current into the
VREF+
VREF-
X1
X1
C1 PIN
C2 PIN
22 nF
X1
Differential
4 th Order
∆Σ
Modulator
1000 Ω
IN+
IN-
The unity gain buffer is designed to accommodate
rail to rail input signals. The common-mode plus
signal range for the unity gain buffer amplifier is
VA- to VA+. Typical CVF (sampling) current for
the unity gain buffer amplifier is about 50 nA
(MCLK = 4.9152 MHz, see Figure 4).
1000 Ω
IN-
CS5533/34
2.1. Analog Input
Figure 3 illustrates a block diagram of the
CS5531/32/33/34. The front end consists of a multiplexer, a unity gain coarse/fine charge input buffer,
and a programmable gain chopper-stabilized instrumentation amplifier. The unity gain buffer is activated any time conversions are performed with a gain
of one and the instrumentation amplifier is activated
any time conversions are performed with gain settings greater than one.
X1
X1
IN+
AIN4+
AIN4*
*
*
AIN1+
AIN1-
crowire compatible with a Schmitt-trigger input on
the serial clock (SCLK).
5
Sinc
Digital
Filter
Programmable
Sinc3
Digital Filter
Serial
Port
X1
GAIN is the gain setting of the PGIA (i.e. 2, 4, 8, 16, 32, 64)
Figure 3. Multiplexer Configuration
12
DS289F5
CS5531/32/33/34-AS
instrumentation amplifier is typically 1200 pA
over
-40°C to +85°C (MCLK=4.9152 MHz).
The common-mode plus signal range of the instrumentation amplifier is (VA-) + 0.7 V to (VA+) 1.7 V.
Figure 4 illustrates the input models for the amplifiers. The dynamic input current for each of the
pins can be determined from the models shown.
Gain = 2, 4, 8, 16, 32, 64
AIN
C = 3 .9 pF
Vos ≤ 8 mV
in = fVos C
f=
MCLK
128
Gain = 1
φ1 Fine
φ1 Coarse
AIN
C = 14 pF
Vos ≤ 12 mV
in = fVos C
f = MCLK
16
Figure 4. Input models for AIN+ and AIN- pins
Note:
The C=3.9pF and C = 14pF capacitors are
for input current modeling only. For physical
input capacitance see ‘Input Capacitance’
specification under Analog Characteristics.
2.1.1. Analog Input Span
The full-scale input signal that the converter can
digitize is a function of the gain setting and the reference voltage connected between the VREF+ and
VREF- pins. The full-scale input span of the converter is [(VREF+) - (VREF-)]/(GxA), where G is
the gain of the amplifier and A is 2 for VRS = 0, or
A is 1 for VRS = 1. VRS is the Voltage Reference
DS289F5
Select bit, and must be set according to the differential voltage applied to the VREF+ and VREF- pins
on the part. See section 2.3.5 for more details.
After reset, the unity gain buffer is engaged. With a
2.5V reference this would make the full-scale input
range default to 2.5 V. By activating the instrumentation amplifier (i.e. a gain setting other than 1) and
using a gain setting of 32, the full-scale input range
can quickly be set to 2.5/32 or about 78 mV. Note
that these input ranges assume the calibration registers are set to their default values (i.e. Gain = 1.0 and
Offset = 0.0).
2.1.2. Multiplexed Settling Limitations
The settling performance of the CS5531/32/33/34
in multiplexed applications is affected by the single-pole, low-pass filter which follows the instrumentation amplifier (see Figure 3). To achieve data
sheet settling and linearity specifications, it is recommended that a 22 nF C0G capacitor be used.
Capacitors as low as 10 nF or X7R type capacitors
can also be used with some minor increase in distortion for AC signals.
2.1.3. Voltage Noise Density Performance
Figure 5 illustrates the measured voltage noise
density versus frequency from 0.025 Hz to 10 Hz
of a CS5532-AS. The device was powered with
±2.5 V supplies, using 30 Sps OWR, the 64x gain
range, bipolar mode, and with the input short bit
enabled.
1000
100
10
1
0.025
0.10
1.00
Frequency (Hz)
10.00
Figure 5. Measured Voltage Noise Density, 64x
13
CS5531/32/33/34-AS
An offset DAC was not included in the CS553X
family because the high dynamic range of the converter eliminates the need for one. The offset register can be manipulated by the user to mimic the
function of a DAC if desired.
2.2. Overview of ADC Register Structure
and Operating Modes
The CS5531/32/33/34 ADCs have an on-chip controller, which includes a number of user-accessible
registers. The registers are used to hold offset and
gain calibration results, configure the chip's operating modes, hold conversion instructions, and to
store conversion data words. Figure 6 depicts a
block diagram of the on-chip controller’s internal
registers.
Each of the converters has 32-bit registers to function as offset and gain calibration registers for each
channel. The converters with two channels have
two offset and two gain calibration registers, the
Offset Registers (4 x 32)
Gain Registers (4 x 32)
converters with four channels have four offset and
four gain calibration registers. These registers hold
calibration results. The contents of these registers
can be read or written by the user. This allows calibration data to be off-loaded into an external EEPROM. The user can also manipulate the contents
of these registers to modify the offset or the gain
slope of the converter.
The converters include a 32-bit configuration register which is used for setting options such as the
power down modes, resetting the converter, shorting the analog inputs, and enabling diagnostic test
bits like the guard signal.
A group of registers, called Channel Setup Registers, are used to hold pre-loaded conversion instructions. Each channel setup register is 32 bits
long, and holds two 16-bit conversion instructions
referred to as Setups. Upon power up, these registers can be initialized by the system microcontroller with conversion instructions. The user can then
Channel Setup
Registers (4 x 32)
Offset 1 (1 x 32)
Gain 1 (1 x 32)
Setup 1
(1 x 16)
Setup 2
(1 x 16)
Offset 2 (1 x 32)
Gain 2 (1 x 32)
Setup 3
(1 x 16)
Setup 4
(1 x 16)
Offset 3 (1 x 32)
Gain 3 (1 x 32)
Setup 5
(1 x 16)
Setup 6
(1 x 16)
Offset 4 (1 x 32)
Gain 4 (1 x 32)
Setup 7
(1 x 16)
Setup 8
(1 x 16)
Conversion Data
Register (1 x 32)
Data (1 x 32)
Read Only
2.1.4. No Offset DAC
Configuration Register (1 x 32)
Power Save Select
Reset System
Input Short
Guard Signal
Voltage Reference Select
Output Latch
Output Latch Select
Offset/Gain Select
Filter Rate Select
CS
SDI
SDO
SCLK
W rite Only
Serial
Interface
Channel Select
Gain
W ord Rate
Unipolar/Bipolar
Output Latch
Delay Time
Open Circuit Detect
Offset/Gain Pointer
Com mand
Register (1 × 8)
Figure 6. CS5531/32/33/34 Register Diagram
14
DS289F5
CS5531/32/33/34-AS
instruct the converter to perform single or multiple
conversions or calibrations with the converter in
the mode defined by one of these Setups.
Using the single conversion mode, an 8-bit command word can be written into the serial port. The
command includes pointer bits which ‘point’ to a
16-bit command in one of the Channel Setup Registers which is to be executed. The 16-bit Setups
can be programmed to perform a conversion on any
of the input channels of the converter. More than
one of the 16-bit Setups can be used for the same
analog input channel. This allows the user to convert on the same signal with either a different conversion speed, a different gain range, or any of the
other options available in the channel setup registers. Alternately, the user can set up the registers to
perform different conversion conditions on each of
the input channels.
The ADCs also include continuous conversion capability. The ADCs can be instructed to continuously convert, referencing one 16-bit command
Setup. In the continuous conversions mode, the
conversion data words are loaded into a shift register. The converter issues a flag on the SDO pin
when a conversion cycle is completed so the user
can read the register, if need be. See the section on
Performing Conversions for more details.
The following pages document how to initialize the
converter, perform offset and gain calibrations, and
how to configure the converter for the various conversion modes. Each of the bits of the configuration
register and of the Channel Setup Registers is described. A list of examples follows the description
section. Also the Command Register Quick Reference can be used to decode all valid commands (the
first 8-bits into the serial port).
2.2.1. System Initialization
The CS5531/32/33/34 provide no power-on-reset
function. To initialize the ADCs, the user must perform a software reset by resetting the ADC’s serial
port with the Serial Port Initialization sequence.
DS289F5
This sequence resets the serial port to the command
mode and is accomplished by transmitting at least
15 SYNC1 command bytes (0xFF hexadecimal),
followed by one SYNC0 command (0xFE hexadecimal). Note that this sequence can be initiated at
anytime to reinitialize the serial port. To complete
the system initialization sequence, the user must
also perform a system reset sequence which is as
follows: Write a logic 1 into the RS bit of the configuration register. This will reset the calibration
registers and other logic (but not the serial port). A
valid reset will set the RV bit in the configuration
register to a logic 1. After writing the RS bit to a
logic 1, wait 20 microseconds, then write the RS bit
back to logic 0. While this involves writing an entire word into the configuration register, the RV bit
is a read only bit, therefore a write to the configuration register will not overwrite the RV bit. After
clearing the RS bit back to logic 0, read the configuration register to check the state of the RV bit as
this indicates that a valid reset occurred. Reading
the configuration register clears the RV bit back to
logic 0.
Completing the reset cycle initializes the on-chip
registers to the following states:
Configuration Register:
Offset Registers:
Gain Registers:
Channel Setup Registers:
Note:
00000000(H)
00000000(H)
01000000(H)
00000000(H)
Previous datasheets stated that the RS bit
would clear itself back to logic 0 and therefore
the user was not required to write the RS bit
back to logic 0. The current data sheet
instruction that requires the user to write into
the configuration register to clear the RS bit
has been added to insure that the RS bit is
cleared. Characterization across multiple lots
of silicon has indicated some chips do not
automatically reset the RS bit to logic 0 in the
configuration register, although the reset
function is completed. This occurs only on
small number of chips when the VA- supply is
negative with respect to DGND. This has not
15
CS5531/32/33/34-AS
caused an operational issue for customers
because their start-up sequence includes
writing a word (with RS=0) into the
configuration register after performing a
reset. The change in the reset sequence to
include writing the RS bit back to 0 insures
the clearing of the RS bit in the event that a
user does not write into the configuration
register after the RS bit has been set.
The RV bit in the Configuration Register is set to
indicate a valid reset has occurred. The RS bit
should be written back to logic “0” to complete the
16
reset cycle. After a system initialization or reset,
the on-chip controller is initialized into command
mode where it waits for a valid command (the first
8-bits written into the serial port are shifted into the
command register). Once a valid command is received and decoded, the byte instructs the converter
to either acquire data from or transfer data to an internal register(s), or perform a conversion or a calibration. The Command Register Descriptions
section can be used to decode all valid commands.
DS289F5
CS5531/32/33/34-AS
2.2.2. Command Register Quick Reference
D7(MSB)
D6
D5
D4
D3
D2
D1
D0
0
ARA
CS1
CS0
R/W
RSB2
RSB1
RSB0
BIT
NAME
D7
Command Bit, C
VALUE FUNCTION
0
1
Must be logic 0 for these commands.
These commands are invalid if this bit is logic 1.
D6
Access Registers as
Arrays, ARA
0
1
Ignore this function.
Access the respective registers, offset, gain, or channel-setup, as an array of registers. The particular registers accessed are determined by the RS bits. The registers
are accessed MSB first with physical channel 0 accessed first followed by physical
channel 1 next and so forth.
D5-D4
Channel Select Bits,
CS1-CS0
00
01
10
11
CS1-CS0 provide the address of one of the two (four for CS5533/34) physical input
channels. These bits are also used to access the calibration registers associated
with the respective physical input channel. Note that these bits are ignored when
reading data register.
D3
Read/Write, R/W
0
1
Write to selected register.
Read from selected register.
D2-D0
Register Select Bit,
RSB3-RSB0
000
001
010
011
101
110
111
Reserved
Offset Register
Gain Register
Configuration Register
Channel-Setup Registers
Reserved
Reserved
D7(MSB)
D6
D5
D4
D3
D2
D1
D0
1
MC
CSRP2
CSRP1
CSRP0
CC2
CC1
CC0
BIT
NAME
D7
Command Bit, C
0
1
These commands are invalid if this bit is logic 0.
Must be logic 1 for these commands.
D6
Multiple Conversions, MC
0
1
Perform fully settled single conversions.
Perform conversions continuously.
D5-D3
Channel-Setup Register Pointer Bits,
CSRP
000
...
111
These bits are used as pointers to the Channel-Setup registers. Either a single conversion or continuous conversions are performed on the channel setup register
pointed to by these bits.
D2-D0
Conversion/Calibration Bits, CC2-CC0
000
001
010
011
100
101
110
111
Normal Conversion
Self-Offset Calibration
Self-Gain Calibration
Reserved
Reserved
System-Offset Calibration
System-Gain Calibration
Reserved
DS289F5
VALUE FUNCTION
17
CS5531/32/33/34-AS
2.2.3. Command Register Descriptions
READ/WRITE ALL OFFSET CALIBRATION REGISTERS
D7(MSB)
0
Function:
D6
1
D5
0
D4
0
D3
R/W
D2
0
D1
0
D0
1
D1
1
D0
0
D1
0
D0
1
These commands are used to access the offset registers as arrays.
R/W (Read/Write)
0
Write to selected registers.
1
Read from selected registers.
READ/WRITE ALL GAIN CALIBRATION REGISTERS
D7(MSB)
0
Function:
D6
1
D5
0
D4
0
D3
R/W
D2
0
These commands are used to access the gain registers as arrays.
R/W (Read/Write)
0
Write to selected registers.
1
Read from selected registers.
READ/WRITE ALL CHANNEL-SETUP REGISTERS
D7(MSB)
0
Function:
D6
1
D5
0
D4
0
D3
R/W
D2
1
These commands are used to access the channel-setup registers as arrays.
R/W (Read/Write)
0
Write to selected registers.
1
Read from selected registers.
READ/WRITE INDIVIDUAL OFFSET REGISTER
D7(MSB)
0
Function:
D6
0
D5
CS1
D4
CS0
D3
R/W
D2
0
D1
0
D0
1
These commands are used to access each offset register separately. CS1 - CS0 decode the
registers accessed.
R/W (Read/Write)
0
Write to selected register.
1
Read from selected register.
CS[1:0] (Channel Select Bits)
00
18
Offset Register 1 (All devices)
01
Offset Register 2 (All devices)
10
Offset Register 3 (CS5533/34 only)
11
Offset Register 4 (CS5533/34 only)
DS289F5
CS5531/32/33/34-AS
READ/WRITE INDIVIDUAL GAIN REGISTER
D7(MSB)
0
Function:
D6
0
D5
CS1
D4
CS0
D3
R/W
D2
0
D1
1
D0
0
These commands are used to access each gain register separately. CS1 - CS0 decode the registers accessed.
R/W (Read/Write)
0
Write to selected register.
1
Read from selected register.
CS[1:0] (Channel Select Bits)
00
Gain Register 1 (All devices)
01
Gain Register 2 (All devices)
10
Gain Register 3 (CS5533/34 only)
11
Gain Register 4 (CS5533/34 only)
READ/WRITE INDIVIDUAL CHANNEL-SETUP REGISTER
D7(MSB)
0
Function:
D6
0
D5
CS1
D4
CS0
D3
R/W
D2
1
D1
0
D0
1
These commands are used to access each channel-setup register separately. CS1 - CS0 decode the registers accessed.
R/W (Read/Write)
0
Write to selected register.
1
Read from selected register.
CS[1:0] (Channel Select Bits)
00
Channel-Setup Register 1 (All devices)
01
Channel-Setup Register 2 (All devices)
10
Channel-Setup Register 3 (All devices)
11
Channel-Setup Register 4 (All devices)
READ/WRITE CONFIGURATION REGISTER
D7(MSB)
0
Function:
D6
0
D5
0
D4
0
D3
R/W
D2
0
D1
1
D0
1
These commands are used to read from or write to the configuration register.
R/W (Read/Write)
DS289F5
0
Write to selected register.
1
Read from selected register.
19
CS5531/32/33/34-AS
PERFORM CONVERSION
D7(MSB)
1
Function:
D6
MC
D5
CSRP2
D4
CSRP1
D3
CSRP0
D2
0
D1
0
D0
0
These commands instruct the ADC to perform either a single, fully-settled conversion or continuous conversions on the physical input channel pointed to by the pointer bits (CSRP2 CRSP0) in the channel-setup register.
MC (Multiple Conversions)
0
Perform a single conversion.
1
Perform continuous conversions.
CSRP [2:0] (Channel Setup Register Pointer Bits)
20
000
Setup 1 (All devices)
001
Setup 2 (All devices)
010
Setup 3 (All devices)
011
Setup 4 (All devices)
100
Setup 5 (All devices)
101
Setup 6 (All devices)
110
Setup 7 (All devices)
111
Setup 8 (All devices)
DS289F5
CS5531/32/33/34-AS
PERFORM CALIBRATION
D7(MSB)
1
Function:
D6
0
D5
CSRP2
D4
CSRP1
D3
CSRP0
D2
CC2
D1
CC1
D0
CC0
These commands instruct the ADC to perform a calibration on the physical input channel selected by the setup register which is chosen by the command byte pointer bits (CSRP2 CSRP0).
CSRP [2:0] (Channel Setup Register Pointer Bits)
000
Setup 1 (All devices)
001
Setup 2 (All devices)
010
Setup 3 (All devices)
011
Setup 4 (All devices)
100
Setup 5 (All devices)
101
Setup 6 (All devices)
110
Setup 7 (All devices)
111
Setup 8 (All devices)
CC [2:0] (Calibration Control Bits)
000
Reserved
001
Self-Offset Calibration
010
Self-Gain Calibration
011
Reserved
100
Reserved
101
System-Offset Calibration
110
System-Gain Calibration
111
Reserved
SYNC1
D7(MSB)
1
Function:
D6
1
D5
1
D4
1
D3
1
D2
1
D1
1
D0
1
D2
1
D1
1
D0
0
D2
0
D1
0
D0
0
Part of the serial port re-initialization sequence.
SYNC0
D7(MSB)
1
Function:
D6
1
D5
1
D4
1
D3
1
End of the serial port re-initialization sequence.
NULL
D7(MSB)
0
Function:
DS289F5
D6
0
D5
0
D4
0
D3
0
This command is used to clear a port flag and keep the converter in the continuous conversion mode.
21
CS5531/32/33/34-AS
2.2.4. Serial Port Interface
The CS5531/32/33/34’s serial interface consists of
four control lines: CS, SDI, SDO, SCLK. Figure 7
details the command and data word timing.
CS, Chip Select, is the control line which enables
access to the serial port. If the CS pin is tied low,
the port can function as a three-wire interface.
SDI, Serial Data In, is the data signal used to transfer data to the converters.
SDO, Serial Data Out, is the data signal used to
transfer output data from the converters. The SDO
output will be held at high impedance any time CS
is at logic 1.
SCLK, Serial Clock, is the serial bit-clock which
controls the shifting of data to or from the ADC’s
serial port. The CS pin must be held low (logic 0)
before SCLK transitions can be recognized by the
port logic. To accommodate optoisolators SCLK is
designed with a Schmitt-trigger input to allow an
optoisolator with slower rise and fall times to directly drive the pin. Additionally, SDO is capable
of sinking or sourcing up to 5 mA to directly drive
an optoisolator LED. SDO will have less than a 400
mV loss in the drive voltage when sinking or sourcing 5 mA.
CS
SCLK
SDI
LSB
MSB
Command Time
8 SCLKs
Data Time 32 SCLKs
Write Cycle
CS
SCLK
SDI
Command Time
8 SCLKs
SDO
LSB
MSB
Data Time 32 SCLKs
Read Cycle
CS
SCLK
SDI
Command Time
8 SCLKs
SDO
MCLK /OWR
Clock Cycles
td*
8 SCLKs Clear SDO Flag
Data Conversion Cycle
MSB
LSB
Data Time 32 SCLKs
* td is the time it takes the ADC to perform a conversion. See the Single
Conversion and Continuous Conversion sections of the data sheet for more
details about conversion timing.
Figure 7. Command and Data Word Timing
22
DS289F5
CS5531/32/33/34-AS
2.2.5. Reading/Writing On-Chip Registers
2.3.1. Power Consumption
The CS5531/32/33/34’s offset, gain, configuration,
and channel-setup registers are readable and writable while the conversion data register is read only.
The CS5531/32/33/34 accommodate three power
consumption modes: normal, standby, and sleep.
The default mode, “normal mode”, is entered after
power is applied. In this mode, the
CS5531/32/33/34 devices typically consume
35 mW. The other two modes are referred to as the
power-save modes. They power down most of the
analog portion of the chip and stop filter convolutions. The power-save modes are entered whenever
the power-down (PDW) bit of the configuration
register is set to logic 1. The particular power-save
mode entered depends on state of the PSS (Power
Save Select) bit. If PSS is logic 0, the converter enters the standby mode reducing the power consumption to 4 mW. The standby mode leaves the
oscillator and the on-chip bias generator for the analog portion of the chip active. This allows the converter to quickly return to the normal mode once
PDW is set back to a logic 1. If PSS and PDW are
both set to logic 1, the sleep mode is entered reducing the consumed power to around 500 µW. Since
this sleep mode disables the oscillator, approximately a 20 ms oscillator start-up delay period is
required before returning to the normal mode. If an
external clock is used, there will be no delay. Further note that when the chips are used in the
Gain = 1 mode, the PGIA is powered down. With
the PGIA powered down, the power consumed in
the normal power mode is reduced by approximately 1/2. Power consumption in the sleep and standby
modes is not affected by the amplifier setting.
As shown in Figure 7, to write to a particular register the user must transmit the appropriate write
command and then follow that command by 32 bits
of data. For example, to write 0x80000000 (hexadecimal) to physical channel one’s gain register,
the user would first transmit the command byte
0x02 (hexadecimal) followed by the data
0x80000000 (hexadecimal). Similarly, to read a
particular register the user must transmit the appropriate read command and then acquire the 32 bits of
data. Once a register is written to or read from, the
serial port returns to the command mode.
In addition to accessing the internal registers one at
a time, the gain and offset registers as well as the
channel setup registers can be accessed as arrays
(i.e. the entire register set can be accessed with one
command). In the CS5531/32, there are two gain
and offset registers, and in the CS5533/34, there are
four gain and offset registers. There are four channel setup registers in all parts. As an example, to
write 0x80000000 (hexadecimal) to all four gain
registers in the CS5533, the user would transmit the
command 0x42 (hexadecimal) followed by four iterations of 0x80000000 (hexadecimal), (i.e. 0x42
followed
by
0x80000000,
0x80000000,
0x80000000, 0x80000000). The registers are written to or read from in sequential order (i.e, 1, followed by 2, 3, and 4). Once the registers are written
to or read from, the serial port returns to the command mode.
2.3. Configuration Register
To ease the architectural design and simplify the
serial interface, the configuration register is 32
long, however, only eleven of the 32 bits are used.
The following sections detail the bits in the configuration register.
DS289F5
2.3.2. System Reset Sequence
The reset system (RS) bit permits the user to perform a system reset. A system reset can be initiated
at any time by writing a logic 1 to the RS bit in the
configuration register. After the RS bit has been
set, the internal logic of the chip will be initialized
to a reset state. The reset valid (RV) bit is set indicating that the internal logic was properly reset.
The RV bit is cleared after the configuration regis-
23
CS5531/32/33/34-AS
ter is read. The on-chip registers are initialized to
the following default states:
Configuration Register:
Offset Registers:
Gain Registers:
Channel Setup Registers:
00000000(H)
00000000(H)
01000000(H)
00000000(H)
After reset, the RS bit should be written back to
logic 0 to complete the reset cycle. The ADC will
return to the command mode where it waits for a
valid command. Also, the RS bit is the only bit in
the configuration register that can be set when initiating a reset (i.e. a second write command is needed to set other bits in the Configuration Register
after the RS bit has been cleared).
2.3.3. Input Short
The input short bit allows the user to internally
ground all the inputs of the multiplexer. This is a
useful function because it allows the user to easily
test the grounded input performance of the ADC
and eliminate the noise effects due to the external
system components.
2.3.4. Guard Signal
The guard signal bit is a bit that modifies the function of A0. When set, this bit outputs the common
mode voltage of the instrumentation amplifier on
A0. This feature is useful when the user wants to
connect an external shield to the common mode potential of the instrumentation amplifier to protect
against leakage. Figure 8 illustrates a typical connection diagram for the guard signal.
buffer which reduces the dynamic current demand
of the external reference.
The reference’s input buffer is designed to accommodate rail-to-rail (common-mode plus signal) input voltages. The differential voltage between the
VREF+ and VREF- can be any voltage from 1.0 V
up to the analog supply (depending on how VRS is
configured), however, the VREF+ cannot go above
VA+ and the VREF- pin can not go below VA-.
Note that the power supplies to the chip should be
established before the reference voltage.
2.3.6. Output Latch Pins
The A1-A0 pins of the ADCs mimic the D21D20/D5-D4 bits of the channel-setup registers if
the output latch select (OLS) bit is logic 0 (default).
If the OLS bit is logic 1, A1-A0 mimic the output
latch bit settings in the configuration register.
These two options give the user a choice of allowing the latch outputs to change anytime a different
CSR is selected for a conversion, or to allow the
latch bits to remain latched to a fixed state (determined by the configuration register bit) for all CSR
selections. In either case, A1-A0 can be used to
control external multiplexers and other logic functions outside the converter. The A1-A0 outputs can
sink or source at least 1 mA, but it is recommended
to limit drive currents to less than 20 µA to reduce
self-heating of the chip. These outputs are powered
C S 5 5 3 1 /3 2 /3 3 /3 4
A 0 /G U A R D
+5 V A +
A IN +
2.3.5. Voltage Reference Select
The voltage reference select (VRS) bit selects the
size of the sampling capacitor used to sample the
voltage reference. The bit should be set based upon
the magnitude of the reference voltage to achieve
optimal performance. Figures 9 and 10 model the
effects on the reference’s input impedance and input current for each VRS setting. As the models
show, the reference includes a coarse/fine charge
24
out p
V IN +
c e n te r
C o m m o n M o d e = 2 .5 V
x1
V IN -
A IN -
out m
Figure 8. Guard Signal Shielding Scheme
DS289F5
CS5531/32/33/34-AS
φ1 Fine
φ1 Fine
φ2 Coarse
VREF
C = 14pF
Vos ≤ 8 mV
in = fVos C
MCLK
16
VRS = 1; 1 V ≤ VREF ≤ 2.5 V
f=
Figure 9. Input Reference Model when VRS = 1
from VA+ and VA-. Their output voltage will be
limited to the VA+ voltage for a logic 1 and VAfor a logic 0.
2.3.7. Offset and Gain Select
The Offset and Gain Select bit (OGS) is used to select the source of the calibration registers to use
when performing conversions and calibrations.
When the OGS bit is set to ‘0’, the offset and gain
registers corresponding to the desired physical
channel (CS1-CS0 in the selected Setup) will be accessed. When the OGS bit is set to ‘1’, the offset
and gain registers pointed to by the OG1-OG0 bits
in the selected Setup will be accessed. This feature
allows multiple calibration values (e.g. for different
gain settings) to be used on a single physical channel without having to re-calibrate or manipulate the
calibration registers.
DS289F5
φ2 Coarse
VREF
C = 7 pF
Vos ≤ 16 mV
i n = fV os C
MCLK
16
VRS = 0; 2.5 V < VREF ≤ VA+
f=
Figure 10. Input Reference Model when VRS = 0
2.3.8. Filter Rate Select
The Filter Rate Select bit (FRS) modifies the output
word rates of the converter to allow either 50 Hz or
60 Hz rejection when operating from a
4.9152 MHz crystal. If FRS is cleared to logic 0,
the word rates and corresponding filter characteristics can be selected (using the Channel Setup Registers) from 7.5, 15, 30, 60, 120, 240, 480, 960,
1920, or 3840 Sps when using a 4.9152 MHz clock.
If FRS is set to logic 1, the word rates and corresponding filter characteristics scale by a factor of
5/6, making the selectable word rates 6.25, 12.5,
25, 50, 100, 200, 400, 800, 1600, and 3200 Sps
when using a 4.9152 MHz clock. When using other
clock frequencies, these selectable word rates will
scale linearly with the clock frequency that is used.
25
CS5531/32/33/34-AS
2.3.9. Configuration Register Descriptions
D31(MSB) D30
PSS
PDW
D15
D14
NU
NU
D29
RS
D13
NU
D28
RV
D12
NU
D27
IS
D11
NU
D26
GB
D10
NU
D25
VRS
D9
NU
D24
A1
D8
NU
D23
A0
D7
NU
D22
OLS
D6
NU
D21
NU
D5
NU
D20
OGS
D4
NU
D19
FRS
D3
NU
D18
NU
D2
NU
D17
NU
D1
NU
D16
NU
D0
NU
PSS (Power Save Select)[31]
0
Standby Mode (Oscillator active, allows quick power-up).
1
Sleep Mode (Oscillator inactive).
PDW (Power Down Mode)[30]
0
Normal Mode
1
Activate the power save select mode.
RS (Reset System)[29]
0
Normal Operation.
1
Activate a Reset cycle. See System Reset Sequence in the datasheet text.
RV (Reset Valid)[28]
0
Normal Operation
1
System was reset. This bit is read only. Bit is cleared to logic zero after the configuration register is read.
IS (Input Short)[27]
0
Normal Input
1
All signal input pairs for each channel are disconnected from the pins and shorted internally.
GB (Guard Signal Bit)[26]
0
Normal Operation of A0 as an output latch.
1
A0’s output is modified to output the common mode output voltage of the instrumentation amplifier (typically
2.5 V). The output latch select bit is ignored when the guard buffer is activated.
VRS (Voltage Reference Select)[25]
0
2.5 V < VREF ≤ [(VA+) - (VA-)]
1
1 V ≤ VREF ≤ 2.5V
A1-A0 (Output Latch bits)[24:23]
The latch bits (A0 and A1) will be set to the logic state of these bits upon command word execution if the output
latch select bit (OLS) is set. Note that these logic outputs are powered from VA+ and VA-.
00
A0 = 0, A1 = 0
01
A0 = 0, A1 = 1
10
A0 = 1, A1 = 0
11
A0 = 1, A1 = 1
Output Latch Select, OLS[22]
0
When low, uses the Channel-Setup Register as the source of A1 and A0.
1
When set, uses the Configuration Register as the source of A1 and A0.
NU (Not Used)[21]
0
Must always be logic 0. Reserved for future upgrades.
Offset and Gain Select OGS[20]
26
0
Calibration registers used are based on the CS1-CS0 bits of the referenced Setup.
1
Calibration registers used are based on the OG1-OG0 bits of the referenced Setup.
DS289F5
CS5531/32/33/34-AS
Filter Rate Select, FRS[19]
0
Use the default output word rates.
1
Scale all output word rates and their corresponding filter characteristics by a factor of 5/6.
NU (Not Used)[18:0]
0
Must always be logic 0. Reserved for future upgrades.
2.4. Setting up the CSRs for a Measurement
The CS5531/32/33/34 have four channel-setup registers (CSRs). Each CSR contains two 16-bit Setups
which are programmed by the user to contain data
conversion information such as: 1) which physical
channel will be converted, 2) at what gain will the
channel be converted, 3) at what word rate will the
channel be converted, 4) will the output conversion
be unipolar or bipolar, 5) what will be the state of the
output latch during the conversion, 6) will the converter delay the start of a conversion to allow time
for the output latch to settle before the conversion is
begun, and 7) will the open circuit detect current
source be activated for that Setup. In addition, when
the OGS bit in the Configuration Register is set, the
Setup selects which set of offset and gain registers to
use when performing conversions or calibrations.
Note that a particular physical input channel can be
DS289F5
represented in more than one Setup with different
output rates, gain ranges, etc. (i.e. each Setup is independently defined). Refer to section 2.4.1 for
more details about the Channel Setup Registers.
Each 32-bit CSR is individually accessible and
contains two 16-bit Setups. As an example, to configure Setup 1 in the CS5531/32/33/34 with the
write individual channel-setup register command
(0x05 hexadecimal), bits 31 to 16 of CSR 1 contains the information for Setup 1 and bits 15 to 0
contain the information for Setup 2. Note that while
reading/writing CSRs, two Setups are accessed in
pairs as a single 32-bit CSR register. Even if one of
the Setups isn’t used, it must be written to or read.
Examples detailing the power of the CSRs are provided in section 2.6.3.
27
CS5531/32/33/34-AS
2.4.1. Channel-Setup Register Descriptions
CSR
#1
Setup 1
Bits <127:112>
Setup 2
Bits <111:96>
#4
Setup 7
Bits <31:16>
Setup 8
Bits <15:0>
D31(MSB)
CS1
D15
CS1
D30
CS0
D14
CS0
D29
G2
D13
G2
D28
G1
D12
G1
D27
G0
D11
G0
D26
WR3
D10
WR3
D25
WR2
D9
WR2
D24
WR1
D8
WR1
D23
WR0
D7
WR0
D22
U/B
D6
U/B
D21
OL1
D5
OL1
D20
OL0
D4
OL0
D19
DT
D3
DT
D18
OCD
D2
OCD
D17
OG1
D1
OG1
D16
OG0
D0
OG0
CS1-CS0 (Channel Select Bits) [31:30] [15:14]
00
Select physical channel 1 (All devices)
01
Select physical channel 2 (All devices)
10
Select physical channel 3 (CS5533/34 only)
11
Select physical channel 4 (CS5533/34 only)
G2-G0 (Gain Bits) [29:27] [13:11]
For VRS = 0, A = 2; For VRS = 1, A = 1; Bipolar input span is twice the unipolar input span.
000
Gain = 1, (Input Span = [(VREF+)-(VREF-)]/1*A for unipolar).
001
Gain = 2, (Input Span = [(VREF+)-(VREF-)]/2*A for unipolar).
010
Gain = 4, (Input Span = [(VREF+)-(VREF-)]/4*A for unipolar).
011
Gain = 8, (Input Span = [(VREF+)-(VREF-)]/8*A for unipolar).
100
Gain = 16, (Input Span = [(VREF+)-(VREF-)]/16*A for unipolar).
101
Gain = 32, (Input Span = [(VREF+)-(VREF-)]/32*A for unipolar).
110
Gain = 64, (Input Span = [(VREF+)-(VREF-)]/64*A for unipolar).
WR3-WR0 (Word Rate) [26:23] [10:7]
The listed Word Rates are for continuous conversion mode using a 4.9152 MHz clock. All word rates will
scale linearly with the clock frequency used. The very first conversion using continuous conversion mode
will last longer, as will conversions done with the single conversion mode. See the section on Performing
Conversions and Tables 1 and 2 for more details.
Bit
WR (FRS = 0)
WR (FRS = 1)
0000
120 Sps
100 Sps
0001
60 Sps
50 Sps
0010
30 Sps
25 Sps
0011
15 Sps
12.5 Sps
0100
7.5 Sps
6.25 Sps
1000
3840 Sps
3200 Sps
1001
1920 Sps
1600 Sps
1010
960 Sps
800 Sps
1011
480 Sps
400 Sps
1100
240 Sps
200 Sps
All other combinations are not used.
28
DS289F5
CS5531/32/33/34-AS
U/B (Unipolar / Bipolar) [22] [6]
0
Select Bipolar mode.
1
Select Unipolar mode.
OL1-OL0 (Output Latch Bits) [21:20] [5:4]
The latch bits will be set to the logic state of these bits upon command word execution when the output
latch select bit (OLS) in the configuration register is logic 0. Note that the logic outputs on the chip are
powered from VA+ and VA-.
00
A0 = 0, A1 = 0
01
A0 = 0, A1 = 1
10
A0 = 1, A1 = 0
11
A0 = 1, A1 = 1
DT (Delay Time Bit) [19] [3]
When set, the converter will wait for a delay time before starting a conversion. This allows settling time for
A0 and A1 outputs before a conversion begins. The delay time will be 1280 MCLK cycles when FRS = 0,
and 1536 MCLK cycles when FRS = 1.
0
Begin Conversions Immediately.
1
Wait 1280 MCLK cycles (FRS = 0) or 1536 MCLK cycles (FRS = 1) before starting conversion.
OCD (Open Circuit Detect Bit) [18] [2]
When set, this bit activates a 300 nA current source on the input channel (AIN+) selected by the channel
select bits. Note that the 300nA current source is rated at 25°C. At -55°C, the current source doubles to
approximately 600 nA. This feature is particularly useful in thermocouple applications when the user wants
to drive a suspected open thermocouple lead to a supply rail.
0
Normal mode.
1
Activate current source.
OG1-OG0 (Offset / Gain Register Pointer Bits) [17:16] [1:0]
These bits are only used when OGS in the Configuration Register is set to ‘1’. They allow the user to select
the offset and gain register to use while performing a conversion or calibration. When the OGS bit in the
Configuration Register is set to ‘0’, the offset and gain register for the referenced physical channel (CS1CS0 bits of the Setup) will be used.
DS289F5
00
Use offset and gain register from physical channel 1
01
Use offset and gain register from physical channel 2
10
Use offset and gain register from physical channel 3
11
Use offset and gain register from physical channel 4
29
CS5531/32/33/34-AS
2.5. Calibration
Calibration is used to set the zero and gain slope of
the ADC’s transfer function. The CS5531/32/33/34
offer both self-calibration and system calibration.
Note:
After the ADCs are reset, they are functional
and can perform measurements without
being calibrated (remember that the VRS bit
in the configuration register must be properly
configured). In this case, the converter will
utilize the initialized values of the on-chip
registers (Gain = 1.0, Offset = 0.0) to
calculate output words. Any initial offset and
gain errors in the internal circuitry of the chip
will remain.
tion of the input span (bipolar span is 2 times the
unipolar span, gain register = 1.000...000 decimal).
The MSB in the offset register determines if the
offset to be trimmed is positive or negative (0 positive, 1 negative). Note that the magnitude of the
offset that is trimmed from the input is mapped
through the gain register. The converter can typically trim ±100% of the input span. As shown in the
Gain Register section, the gain register spans from
0 to (64 - 2-24). The decimal equivalent meaning of
the gain register is
29
D = b
2.5.1. Calibration Registers
5
D29
2 +b
4
D28
2 +b
3
D27
2 +…+b
D0
2
– 24
∑ bDi 2
) =
( – 24 + i )
i=0
The CS5531/32/33/34 converters have an individual offset and gain register for each channel input.
The gain and offset registers, which are used during
both self and system calibration, are used to set the
zero and gain slope of the converter’s transfer function. As shown in Offset Register section, one LSB
in the offset register is 1.835007966 x 2-24 propor-
where the binary numbers have a value of either
zero or one (bD29 is the binary value of bit D29).
While gain register settings of up to 64 - 2-24 are
available, the gain register should never be set to
values above 40.
2.5.2. Gain Register
MSB
NU
D30
NU
D29
D28
D27
D26
D25
D24
D23
D22
D21
D20
D19
D18
D17
D16
25
24
23
22
21
20
2-1
2-2
2-3
2-4
2-5
2-6
2-7
0
0
0
0
0
0
0
1
0
0
0
0
0
0
0
2-8
0
D15
D14
D13
D12
D11
D10
D9
D8
D7
D6
D5
D4
D3
D2
D1
LSB
2-9
0
2-10
0
2-11
0
2-12
0
2-13
0
2-14
0
2-15
0
2-16
0
2-17
0
2-18
0
2-19
0
2-20
0
2-21
0
222
0
2-23
0
2-24
0
The gain register span is from 0 to (64-2-24). After Reset D24 is 1, all other bits are ‘0’.
2.5.3. Offset Register
MSB
Sign
D30
D29
D28
D27
D26
D25
D24
D23
D22
D21
D20
D19
D18
D17
D16
2-4
2-5
2-6
2-7
2-8
2-9
2-10
2-11
2-12
2-13
2-14
2-15
0
2
0
2-3
0
0
0
0
0
0
0
0
0
0
0
0
0
2-16
0
D15
D14
D13
D12
D11
D10
D9
D8
2-17
0
2-18
0
2-19
0
2-20
0
2-21
0
2-22
0
2-23
0
2-24
0
D7
NU
D6
NU
D5
NU
D4
NU
D3
NU
D2
NU
D1
NU
LSB
NU
0
0
0
0
0
0
0
0
-2
One LSB represents 1.835007966 X 2-24 proportion of the input span (bipolar span is 2 times unipolar span).
Offset and data word bits align by MSB. After reset, all bits are ‘0’.
The offset register is stored as a 32-bit, two’s complement number, where the last 8 bits are all 0.
30
DS289F5
CS5531/32/33/34-AS
2.5.4. Performing Calibrations
To perform a calibration, the user must send a command byte with its MSB = 1, its pointer bits
(CSRP2-CSRP0) set to address the desired Setup to
calibrate, and the appropriate calibration bits (CC2CC0) set to choose the type of calibration to be performed. Note that calibration assumes that the
CSRs have been previously initialized because the
information concerning the physical channel, its
filter rate, gain range, and polarity, comes from the
channel-setup register addressed by the pointer bits
in the command byte. Once the CSRs are initialized, a calibration can be performed with one command byte.
The length of time it takes to do a calibration is
slightly less than the amount of time it takes to do
a single conversion (see Table 1 for single conversion timing). Offset calibration takes 608 clock cycles less than a single conversion when FRS = 0,
and 729 clock cycles less when FRS = 1. Gain calibration takes 128 clock cycles less than a single
conversion when FRS = 0, and 153 clock cycles
less when FRS = 1.
Once a calibration cycle is complete, SDO falls and
the results are automatically stored in either the
gain or offset register for the physical channel being calibrated when the OGS bit in the Configuration Register is set to ‘0’. If the OGS bit is set to ‘1’,
the results will be stored in the register specified by
the OG1-OG0 bits of the selected Setup. See the
OGS bit description for more details (Section
2.3.7). SDO will remain low until the next command word is begun. If additional calibrations are
performed while referencing the same calibration
registers, the last calibration results will replace the
DS289F5
effects from the previous calibration as only one
offset and gain register is available per physical
channel. Only one calibration is performed with
each command byte. To calibrate all the channels,
additional calibration commands are necessary.
2.5.5. Self-calibration
The CS5531/32/33/34 offer both self-offset and
self-gain calibrations. For the self-calibration of
offset, the converters internally tie the inputs of the
1x amplifier together and routes them to the AINpin as shown in Figure 11. For accurate self calibration of offset to occur, the AIN pins must be at the
proper common-mode voltage as specified in the
Analog Characteristics section. Self-offset calibration uses the 1x gain amplifier, and is therefore not
valid in the 2x-64x gain ranges. A self-offset calibration of these gain ranges can be performed by setting
the IS bit in the configuration register to a ‘1’, and
performing a system offset calibration. The IS bit
must be returned to ‘0’ afterwards for normal operation of the device.
For self calibration of gain, the differential inputs
of the modulator are connected to VREF+ and
VREF- as shown in Figure 12. Self calibration of
gain will not work with (VREF+ - VREF-) > 2.5V.
Self calibration of gain is performed in the
GAIN = 1x mode without regard to the setup register’s gain setting. Gain errors in the PGIA gain
steps 2x to 64x are not calibrated as this would require an accurate low-voltage source other than the
reference voltage. A system calibration of gain
should be performed if accurate gains are to be
achieved on the ranges other than 1x, or when
(VREF+ – VREF-) > 2.5V.
31
CS5531/32/33/34-AS
2.5.6. System Calibration
For the system calibration functions, the user must
supply the converter’s calibration signals which represent ground and full scale. When a system offset
calibration is performed, a ground-referenced signal
must be applied to the converters. Figure 13 illustrates system offset calibration.
As shown in Figure 14, the user must input a signal
representing the positive full-scale point to perform
a system gain calibration. In either case, the calibration signals must be within the specified calibration limits for each specific calibration step (refer
to the System Calibration Specifications).
2.5.7. Calibration Tips
Calibration steps are performed at the output word
rate selected by the WR2-WR0 bits of the channel
setup registers. Due to limited register lengths in
the faster word-rate filters (240 Sps and higher),
channels that are used at these rates should also be
calibrated in one of these word rates, and channels
used in the lower word rates (120 Sps and lower)
should be calibrated at one of these lower rates.
Since higher word rates result in conversion words
with more peak-to-peak noise, calibration should
be performed at the lowest possible output word
rate for maximum accuracy. For the 7.5 Sps to 120
Sps word rate settings, calibrations can be performed at 7.5 Sps, and for 240 Sps and higher, calibration can be performed at 240 Sps. To minimize
digital noise near the device, the user should wait
for each calibration step to be completed before
reading or writing to the serial port. Reading the
calibration registers and averaging multiple calibrations together can produce a more accurate calibration result. Note that accessing the ADC’s
serial port before a calibration has finished may result in the loss of synchronization between the mi-
OPEN
AIN+
AIN+
+
+
+
XGAIN
1X GAIN
AIN-
_
_
AIN-
+
-
-
OPEN
VREF+
Reference +
- VREF-
CLOSED
CLOSED
Figure 12. Self-calibration of Gain
Figure 11. Self-calibration of Offset
External
Connections
External
Connections
+
+
+
AIN+
0V +AIN-
Figure 13. System Calibration of Offset
32
Full Scale +-
XGAIN
-
CM +-
+
AIN+
XGAIN
-
-
CM +-
AIN-
Figure 14. System Calibration of Gain
DS289F5
CS5531/32/33/34-AS
crocontroller and the ADC, and may prematurely
halt the calibration cycle.
For maximum accuracy, calibrations should be performed for both offset and gain (selected by changing the G2-G0 bits of the channel-setup registers).
Note that only one gain range can be calibrated per
physical channel when the OGS bit in the Configuration Register is set to ‘0’. Multiple gain ranges
can be calibrated for a single channel by manipulating the OGS bit and the OG1-OG0 bits of the selected Setup (see Section 2.3.7 for more details). If
factory calibration of the user’s system is performed using the system calibration capabilities of
the CS5531/32/33/34, the offset and gain register
contents can be read by the system microcontroller
and recorded in non-volatile memory. These same
calibration words can then be uploaded into the offset and gain registers of the converter when power
is first applied to the system, or when the gain range
is changed.
When the device is used without calibration, the
uncalibrated gain accuracy is about ±1% and the
gain tracking from range to range (2x to 64x) is approximately ±0.3 percent.
Note that the gain from the offset register to the
output is 1.83007966 decimal, not 1. If a user wants
to adjust the calibration coefficients externally,
they will need to divide the information to be written to the offset register by the scale factor of
1.83007966. (This discussion assumes that the gain
register is 1.000...000 decimal. The offset register
is also multiplied by the gain register before being
applied to the output conversion words).
2.5.8. Limitations in Calibration Range
System calibration can be limited by signal headroom in the analog signal path inside the chip as
discussed under the Analog Input section of this
data sheet. For gain calibration, the full-scale input
signal can be reduced to 3% of the nominal fullscale value. At this point, the gain register is approximately equal to 33.33 (decimal). While the
DS289F5
gain register can hold numbers all the way up to
64 – 2-24, gain register settings above a decimal
value of 40 should not be used. With the converter’s intrinsic gain error, this minimum full-scale input signal may be higher or lower. In defining the
minimum Full Scale Calibration Range (FSCR)
under Analog Characteristics, margin is retained to
accommodate the intrinsic gain error. Inversely, the
input full-scale signal can be increased to a point in
which the modulator reaches its 1’s density limit of
86 percent, which under nominal conditions occurs
when the full-scale input signal is 1.1 times the
nominal full-scale value. With the chip’s intrinsic
gain error, this maximum full-scale input signal
maybe higher or lower. In defining the maximum
FSCR, margin is again incorporated to accommodate the intrinsic gain error.
2.6. Performing Conversions
The CS5531/32/33/34 offers two distinctly different conversion modes. The three sections that follow detail the differences and provide examples
illustrating how to use the conversion modes with
the channel-setup registers.
2.6.1. Single Conversion Mode
Based on the information provided in the channelsetup registers (CSRs), after the user transmits the
conversion command, a single, fully settled conversion is performed. The command byte includes
a pointer address to the Setup register to be used
during the conversion. Once transmitted, the serial
port enters data mode where it waits until the conversion is complete. When the conversion data is
available, SDO falls to logic 0. Forty SCLKs are
then needed to read the conversion data word. The
first 8 SCLKs are used to clear the SDO flag. During the first 8 SCLKs, SDI must be logic 0. The last
32 SCLKs are needed to read the conversion result.
Note that the user is forced to read the conversion
in single conversion mode as SDO will remain low
(i.e. the serial port is in data mode) until SCLK
transitions 40 times. After reading the data, the se-
33
CS5531/32/33/34-AS
rial port returns to the command mode, where it
waits for a new command to be issued. The single
conversion mode will take longer than conversions
performed in the continuous conversion mode. The
number of clock cycles a single conversion takes
for each Output Word Rate (OWR) setting is listed
in Table 1. The ± 8 (FRS = 0) or ± 10 (FRS = 1)
clock ambiguity is due to internal synchronization
between the SCLK input and the oscillator.
Note:
In the single conversion mode, more than one
conversion is actually performed, but only the
final, fully settled result is output to the
conversion data register.
Table 1. Conversion Timing – Single Mode
(WR3-WR0)
Clock Cycles
FRS = 0
FRS = 1
0000
171448 ± 8
205738 ± 10
0001
335288 ± 8
402346 ± 10
0010
662968 ± 8
795562 ± 10
0011
1318328 ± 8
1581994 ± 10
0100
2629048 ± 8
3154858 ± 10
1000
7592 ± 8
9110 ± 10
1001
17848 ± 8
21418 ± 10
1010
28088 ± 8
33706 ± 10
1011
48568 ± 8
58282 ± 10
1100
89528 ± 8
107434 ± 10
2.6.2. Continuous Conversion Mode
Based on the information provided in the channelsetup registers (CSRs), continuous conversions are
performed using the Setup register contents pointed
to by the conversion command. The command byte
includes a pointer address to the Setup register to
be used during the conversion. Once transmitted,
the serial port enters data mode where it waits until
a conversion is complete. After the conversion is
34
done, SDO falls to logic 0. Forty SCLKs are then
needed to read the conversion. The first 8 SCLKs
are used to clear the SDO flag. The last 32 SCLKs
are needed to read the conversion result. If
‘00000000’ is provided to SDI during the first 8
SCLKs when the SDO flag is cleared, the converter
remains in this conversion mode and continues to
convert the selected channel using the same CSR
Setup. In continuous conversion mode, not every
conversion word needs to be read. The user needs
only to read the conversion words required for the
application as SDO rises and falls to indicate the
availability of new conversion data. Note that if a
conversion is not read before the next conversion
data becomes available, it will be lost and replaced
by the new conversion data. To exit this conversion
mode, the user must provide ‘11111111’ to the SDI
pin during the first 8 SCLKs after SDO falls. If the
user decides to exit, 32 SCLKs are required to
clock out the last conversion before the converter
returns to command mode. The number of clock
cycles a continuous conversion takes for each Output Word Setting is listed in Table 2. The first conversion from the part in continuous conversion
mode will be longer than the following conversions
due to start-up overhead. The ± 8 (FRS = 0) or ± 10
(FRS = 1) clock ambiguity is due to internal synchronization between the SCLK input and the oscillator.
Note:
When changing channels, or after performing
calibrations and/or single conversions, the
user must ignore the first three (for OWRs
less than 3200 Sps, MCLK = 4.9152 MHz) or
first five (for OWR ≥ 3200 Sps) conversions in
continuous conversion mode, as residual
filter coefficients must be flushed from the
filter before accurate conversions are
performed.
DS289F5
CS5531/32/33/34-AS
Table 2. Conversion Timing – Continuous Mode
FRS (WR3-WR0)
0
0
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
1
1
0000
0001
0010
0011
0100
1000
1001
1010
1011
1100
0000
0001
0010
0011
0100
1000
1001
1010
1011
1100
Clock Cycles
Clock Cycles
(First Conversion) (All Other
Conversions)
89528 ± 8
40960
171448 ± 8
81920
335288 ± 8
163840
662968 ± 8
327680
1318328 ± 8
655360
2472 ± 8
1280
12728 ± 8
2560
17848 ± 8
5120
28088 ± 8
10240
48568 ± 8
20480
107434 ± 10
49152
205738 ± 10
98304
402346 ± 10
196608
795562 ± 10
393216
1581994 ± 10
786432
2966 ± 10
1536
15274 ± 10
3072
21418 ± 10
6144
33706 ± 10
12288
58282 ± 10
24576
2.6.3. Examples of Using CSRs to Perform
Conversions and Calibrations
Any time a calibration or conversion command is
issued (C, MC, and CC2-CC0 bits must be properly
set), the CSRP2-CSRP0 bits in the command byte
are used as pointers to address one of the Setups in
the channel-setup registers (CSRs). Table 3 details
the address decoding of the pointer the bits.
Table 3. Command Byte Pointer
(CSRP2-CSRP0) CSR Location
000
CSR #1
001
010
011
100
101
110
111
DS289F5
CSR #1
CSR #2
CSR #2
CSR #3
CSR #3
CSR#4
CSR #4
Setup
1
2
3
4
5
6
7
8
The examples that follow detail situations that a
user might encounter when acquiring a conversion
or calibrating the converter. These examples assume that the CSRs are programmed with the following physical channel order: 4, 1, 1, 2, 4, 3, 4, 4.
A physical channel is defined as the actual input
channel (AIN1 to AIN4) to which an external signal is connected.
Example 1: Single conversion using Setup 1. The
command issued is ‘10000000’. This instructs the
converter to perform a single conversion referencing Setup 1 (CSRP2 - CSRP0 = ‘000’) In this example, Setup 1 points to physical channel 4. After
the command is received and decoded, the ADC
performs a conversion on physical channel 4 and
SDO falls to indicate that the conversion is complete. To read the conversion, 40 SCLKs are then
required. Once the conversion data has been read,
the serial port returns to the command mode.
Example 2: Continuous conversions using Setup 3.
The command issued is ‘11010000’. This instructs
the converter to perform continuous conversions
referencing Setup 3 (CSRP2 - CSRP0 = ‘010’). In
this example, Setup 3 points to physical channel 1.
After the command is received and decoded, the
ADC performs a conversion on physical channel 1
and SDO falls to indicate that the conversion is
complete. The user now has three options. The user
can acquire the conversion and remain in this
mode, acquire the conversion and exit this mode, or
ignore the conversion and wait for a new conversion at the next update interval, as detailed in the
continuous conversion section.
Example 3: Calibration using Setup 4. This example assumes that the OGS bit in the Configuration
Register is set to ‘0’. The command issued is
‘10011001’. This instructs the converter to perform
a self offset calibration referencing Setup 4
(CSRP2 - CSRP0 = ‘011’). In this example, Setup
4 points to physical channel 2. After the command
is received and decoded, the ADC performs a self
35
CS5531/32/33/34-AS
offset calibration on physical channel 2 and SDO
falls to indicate that the calibration is complete. To
perform additional calibrations, more commands
must be issued.
An example of a synchronous system using two
CS5532 parts is shown in Figure 15.
CS5532
SDO
SDI
Note:
The CSRs need not be written. If they are not
initialized, all the Setups point to their default
settings irrespective of the conversion or
calibration mode (i.e conversions can be
performed, but only physical channel 1 will be
converted). Further note that filter
convolutions are reset (i.e. flushed) if
consecutive conversions are performed on
two different physical channels. If
consecutive conversions are performed on
the same physical channel, the filter is not
reset. This allows the ADCs to more quickly
settle full-scale step inputs.
2.7. Using Multiple ADCs Synchronously
Some applications require synchronous data outputs from multiple ADCs converting different analog channels. Multiple CS5531/32/33/34 parts can
be synchronized in a single system by using the following guidelines:
1) All of the ADCs in the system must be operated
from the same oscillator source.
2) All of the ADCs in the system must share common SCLK and SDI lines.
3) A software reset must be performed at the same
time for all of the ADCs after system power-up (by
selecting all of the ADCs using their respective CS
pins, and writing the reset sequence to all parts, using SDI and SCLK).
4) A start conversion command must be sent to all
of the ADCs in the system at the same time. The ±8
clock cycles of ambiguity for the first conversion
(or for a single conversion) will be the same for all
ADCs, provided that they were all reset at the same
time.
5) Conversions can be obtained by monitoring
SDO on only one ADC, (bring CS high for all but
one part) and reading the data out of each part individually, before the next conversion data words are
ready.
36
SCLK
CS
OSC2
µC
CS5532
SDO
SDI
SCLK
CS
OSC2
CLOCK
SOURCE
Figure 15. Synchronizing Multiple ADCs
2.8. Conversion Output Coding
The CS5531/33 output 16-bit data conversion
words and the CS5532/34 output 24-bit data conversion words. To read a conversion word the user
must read the conversion data register. The conversion data register is 32 bits long and outputs the
conversions MSB first. The last byte of the conversion data register contains data monitoring flags.
The channel indicator (CI) bits keep track of which
physical channel was converted and the overrange
flag (OF) monitors to determine if a valid conversion was performed. Refer to the Conversion Data
Output Descriptions section for more details.
The CS5531/32/33/34 output data conversions in
binary format when operating in unipolar mode and
in two's complement format when operating in bipolar mode. Tables 4 and 5 show the code mapping
for both unipolar and bipolar mode. VFS in the tables refers to the positive full-scale voltage range of
the converter in the specified gain range, and -VFS
refers to the negative full-scale voltage range of the
converter. The total differential input range (between AIN+ and AIN-) is from 0 to VFS in unipolar mode, and from -VFS to VFS in bipolar mode.
DS289F5
CS5531/32/33/34-AS
Table 4. Output Coding for 16-bit CS5531 and CS5533
Table 5. Output Coding for 24-bit CS5532 and CS5534
Unipolar Input Offset
Voltage
Binary
Unipolar Input Offset
Voltage
Binary
>(VFS-1.5 LSB)
VFS-1.5 LSB
VFS/2-0.5 LSB
+0.5 LSB
<(+0.5 LSB)
FFFF
Bipolar Input
Voltage
Two's
Complement
>(VFS-1.5 LSB)
7FFF
Bipolar Input
Voltage
>(VFS-1.5 LSB) FFFFFF >(VFS-1.5 LSB)
VFS-1.5 LSB
FFFF
-----FFFE
VFS-1.5 LSB
7FFF
-----7FFE
8000
-----7FFF
-0.5 LSB
0000
-----FFFF
0001
-----0000
8001
-----8000
+0.5 LSB
-VFS+0.5 LSB
0000
<(-VFS+0.5 LSB)
8000
<(+0.5 LSB)
FFFFFF
-----FFFFFE
7FFFFF
VFS-1.5 LSB
7FFFFF
-----7FFFFE
-0.5 LSB
000000
-----FFFFFF
-VFS+0.5 LSB
800001
-----800000
VFS/2-0.5 LSB 800000
-----7FFFFF
000001
-----000000
Two's
Complement
000000 <(-VFS+0.5 LSB)
800000
2.8.1. Conversion Data Output Descriptions
CS5531/33 (16-BIT CONVERSIONS)
D31(MSB) D30
MSB
14
D15
D14
0
0
D29
13
D13
0
D28
12
D12
0
D27
11
D11
0
D26
10
D10
0
D25
9
D9
0
D24
8
D8
0
D23
7
D7
0
D22
6
D6
0
D21
5
D5
0
D20
4
D4
0
D19
3
D3
0
D18
2
D2
OF
D17
1
D1
CI1
D16
LSB
D0
CI0
D26
18
D10
2
D25
17
D9
1
D24
16
D8
LSB
D23
15
D7
0
D22
14
D6
0
D21
13
D5
0
D20
12
D4
0
D19
11
D3
0
D18
10
D2
OF
D17
9
D1
CI1
D16
8
D0
CI0
CS5532/34 (24-BIT CONVERSIONS)
D31(MSB) D30
MSB
22
D15
D14
7
6
D29
21
D13
5
D28
20
D12
4
D27
19
D11
3
Conversion Data Bits [31:16 for CS5531/33; 31:8 for CS5532/34]
These bits depict the latest output conversion.
NU (Not Used) [15:3 for CS5531/33; 7:3 for CS5532/34]
These bits are masked logic zero.
OF (Over-range Flag Bit) [2]
0
Bit is clear when over-range condition has not occurred.
1
Bit is set when input signal is more positive than the positive full scale, more negative than zero (unipolar
mode) or when the input is more negative than the negative full scale (bipolar mode).
CI (Channel Indicator Bits) [1:0]
These bits indicate which physical input channel was converted.
DS289F5
00
Physical Channel 1
01
Physical Channel 2
10
Physical Channel 3
11
Physical Channel 4
37
CS5531/32/33/34-AS
2.9. Digital Filter
The CS5531/32/33/34 have linear phase digital filters which are programmed to achieve a range of
output word rates (OWRs) as stated in the ChannelSetup Register Descriptions section. The ADCs use
a Sinc5 digital filter to output word rates at 3200
Sps and 3840 Sps (MCLK = 4.9152 MHz). Other
output word rates are achieved by using the Sinc5
filter followed by a Sinc3 filter with a programmable decimation rate. Figure 16 shows the magnitude
response of the 60 Sps filter, while Figures 17 and
18 show the magnitude and phase response of the
filter at 120 Sps. The Sinc3 is active for all output
word rates except for the 3200 Sps and 3840 Sps
(MCLK = 4.9152 MHz) rate. The Z-transforms of
the two filters are shown in Figure 19. For the Sinc3
filter, “D” is the programmable decimation ratio,
which is equal to 3840/OWR when FRS = 0 and
3200/OWR when FRS = 1.
The converter’s digital filters scale with MCLK.
For example, with an output word rate of 120 Sps,
the filter’s corner frequency is at 31 Hz. If MCLK
is increased to 5.0 MHz, the OWR increases by
1.0175% and the filter’s corner frequency moves to
31.54 Hz. Note that the converter is not specified to
run at MCLK clock frequencies greater than
5 MHz.
180
Phase (Degrees)
Gain (dB)
0
-40
-80
-120
90
0
-90
-180
0
60
120
180
240
0
300
30
60
90
120
Frequency (Hz)
Frequency (Hz)
Figure 16. Digital Filter Response (WR = 60 Sps)
Figure 18. 120 Sps Filter Phase Plot to 120 Hz
Gain (dB)
0
Flatness
Frequency
dB
2
-0.01
4
-0.05
6
-0.11
8
-0.19
10
-0.30
12
-0.43
14
-0.59
16
-0.77
19
-1.09
32
-3.13
-40
-80
-120
0
( 1 – z –80 ) 5 ( 1 – z – 16 ) 3- ----------------------( 1 – z –4 ) 2 ----------------------( 1 – z –2 ) 3
Sinc 5 = -------------------------5- × ------------------------×
×
3
2
–
16
–
4
–
2
(1 – z )
(1 – z )
(1 – z )
( 1 – z –1 ) 3
( 1 – z –D ) 3
Sinc 3 = ------------------------3( 1 – z –1 )
40
80
120
Frequency (Hz)
Figure 17. 120 Sps Filter Magnitude Plot to 120 Hz
38
Note:
See the text regarding the Sinc3 filter’s
decimation ratio “D”.
Figure 19. Z-Transforms of Digital Filters
DS289F5
CS5531/32/33/34-AS
2.10. Clock Generator
The CS5531/32/33/34 include an on-chip inverting
amplifier which can be connected with an external
crystal to provide the master clock for the chip. Figure 20 illustrates the on-chip oscillator. It includes
loading capacitors and a feedback resistor to form
a Pierce oscillator configuration. The chips are designed to operate using a 4.9152 MHz crystal;
however, other crystals with frequencies between
1 MHz to 5 MHz can be used. One lead of the crystal should be connected to OSC1 and the other to
OSC2. Lead lengths should be minimized to reduce
stray capacitance. Note that while using the on-chip
oscillator, neither OSC1 or OSC2 is capable of directly driving any off-chip logic. When the on-chip
oscillator is used, the voltage on OSC2 is typically
0.5 V peak-to-peak. This signal is not compatible
with external logic unless additional external circuitry is added. The OSC2 output should be used if
the on-chip oscillator output is used to drive other
circuitry.
The designer can use an external CMOS-compatible oscillator to drive OSC2 with a 1 MHz to
5 MHz clock for the ADC. The external clock into
OSC2 must overdrive the 60 µA output of the onchip amplifier. This will not harm the on-chip circuitry. In this scheme, OSC1 should be left unconnected.
2.11. Power Supply Arrangements
The CS5531/32/33/34 are designed to operate from
single or dual analog supplies and a single digital
supply. The following power supply connections
are possible:
VA+ = +5V; VA- = 0V; VD+ = +3V to +5V
VA+ = +2.5V; VA- = -2.5V; VD+ = +3V to +5V
VA+ = +3V; VA- = -3V; VD+ = +3V
A VA+ supply of +2.5 V, +3.0 V, or +5.0 V should
be maintained at ±5% tolerance. A VA- supply of
-2.5 V or -3.0 V should be maintained at ±5% tolerance. VD+ can extend from +2.7 V to +5.5 V
with the additional restriction that:
[(VD+) - (VA-)] < 7.5 V.
Figure 21 illustrates the CS5532 connected with a
single +5.0 V supply to measure differential inputs
relative to a common mode of 2.5 V. Figure 22 illustrates the CS5532 connected with ±2.5 V bipolar analog supplies and a +3 V to +5 V digital
supply to measure ground referenced bipolar signals. Figures 23 and 24 illustrate the CS5532 connected with ±3 V analog supplies and a +3 V
digital supply to measure ground-referenced bipolar signals.
Figure 25 illustrates alternate bridge configurations
which can be measured with the converter. Voltage
V1 can be measured with the PGIA gain set to 1x
as the input amplifier on this gain setting can go
rail-to-rail. Voltage V2 should be measured with
the PGIA gain set at 2x or higher as the instrumen-
1 MΩ
~~ 60 µA
VTH
+
20 pF
OSC1
20 pF
OSC2
MCLK
NOTE: 20 pF capacitors are on
chip and should not be added
externally.
Figure 20. On-chip Oscillator Model
DS289F5
39
CS5531/32/33/34-AS
tation amplifier used on these gain ranges achieves
lower noise.
10 Ω
+5 V
Analog
Supply
0.1 µF
0.1 µF
5
VA+
18 VREF+
15
VD+
OSC2 9
17 VREF3 C1
-
+
OSC1
10
Optional
Clock
Source
4.9152 MHz
22 nF
CS5532
4
1
2
20
19
7
8
C2
AIN1+
AIN1AIN2+
AIN2A0
A1
VA 6
CS
SDI
SDO
SCLK
14
13
12
11
Serial
Data
Interface
DGND
16
Figure 21. CS5532 Configured with a Single +5 V Supply
40
DS289F5
CS5531/32/33/34-AS
+2.5 V
Analog
Supply
+3 V ~ +5 V
Digital
0.1 µF Supply
0.1 µF
5
VA+
-
+
15
VD+
18 VREF+
OSC2
17 VREF3 C1
OSC1
9
10
Optional
Clock
Source
4.9152 MHz
22 nF
CS5532
4
1
2
20
19
7
8
-2.5 V
Analog
Supply
C2
AIN1+
AIN1AIN2+
AIN2A0
A1
VA 6
CS
SDI
SDO
SCLK
14
13
12
11
Serial
Data
Interface
DGND
16
Figure 22. CS5532 Configured with ±2.5 V Analog Supplies
10 Ω
+3 V
Analog
Supply
0.1 µF
0.1 µF
5
VA+
-
+
18 VREF+
OSC2
17 VREF3 C1
OSC1
9
10
Optional
Clock
Source
4.9152 MHz
22 nF
CS5532
4
1
2
20
19
7
8
-3 V
Analog
Supply
15
VD+
C2
AIN1+
AIN1AIN2+
AIN2A0
A1
VA 6
CS
SDI
SDO
SCLK
14
13
12
11
Serial
Data
Interface
DGND
16
Figure 23. CS5532 Configured with ±3 V Analog Supplies
DS289F5
41
CS5531/32/33/34-AS
10 Ω
+3 V
Analog
Supply
0.1 µF
0.1 µF
5
VA+
1 AIN1+
15
VD+
OSC2
2 AIN13
C1
OSC1
CS5532
4
C2
18 VREF+
22 nF
2.5V
17
20
19
7
8
Cold
Junction
-3 V
Analog
Supply
VREFAIN2+
AIN2A0
A1
VA 6
CS
SDI
SDO
SCLK
9
10
14
13
12
11
Optional
Clock
Source
4.9152 MHz
Serial
Data
Interface
DGND
16
Figure 24. CS5532 Configured for Thermocouple Measurement
V+
V+
V1
V2
V1
V2
(a)
(b)
Figure 25. Bridge with Series Resistors
42
DS289F5
CS5531/32/33/34-AS
2.12. Getting Started
This A/D converter has several features. From a
software programmer’s prospective, what should
be done first? To begin, a 4.9152 MHz or
4.096 MHz crystal takes approximately 20 ms to
start. To accommodate for this, it is recommended
that a software delay of approximately 20 ms start
the processor’s ADC initialization code. Next,
since the CS5531/32/33/34 do not provide a poweron-reset function, the user must first initialize the
ADC to a known state. This is accomplished by resetting the ADC’s serial port with the Serial Port
Initialization sequence. This sequence resets the serial port to the command mode and is accomplished
by transmitting 15 SYNC1 command bytes (0xFF
hexadecimal), followed by one SYNC0 command
(0xFE hexadecimal). Once the serial port of the
ADC is in the command mode, the user must reset
all the internal logic by performing a system reset
sequence (see 2.3.2 System Reset Sequence). The
next action is to initialize the voltage reference
mode. The voltage reference select (VRS) bit in the
configuration register must be set based upon the
DS289F5
magnitude of the reference voltage between the
VREF+ and the VREF- pins.
After this, the channel-setup registers (CSRs) should
be initialized, as these registers determine how calibrations and conversions will be performed. Once
the CSRs are initialized, the user has three options in
calibrating the ADC: 1) don’t calibrate and use the
default settings; 2) perform self or system calibrations; or 3) upload previously saved calibration results to the offset and gain registers. At this point,
the ADC is ready to perform conversions.
2.13. PCB Layout
For optimal performance, the CS5531/32/33/34
should be placed entirely over an analog ground
plane. All grounded pins on the ADC, including the
DGND pin, should be connected to the analog
ground plane that runs beneath the chip. In a splitplane system, place the analog-digital plane split
immediately adjacent to the digital portion of the
chip.
43
CS5531/32/33/34-AS
3. PIN DESCRIPTIONS
DIFFERENTIAL ANALOG INPUT
AIN1+
1
20
AIN2+
19
DIFFERENTIAL ANALOG INPUT
DIFFERENTIAL ANALOG INPUT
AIN1-
2
AIN2-
DIFFERENTIAL ANALOG INPUT
AMPLIFIER CAPACITOR CONNECT
C1
3
18
VREF+
VOLTAGE REFERENCE INPUT
AMPLIFIER CAPACITOR CONNECT
C2
4
17
VREF-
VOLTAGE REFERENCE INPUT
16
CS5531/2
POSITIVE ANALOG POWER
VA+
5
DGND
DIGITAL GROUND
NEGATIVE ANALOG POWER
VA-
6
15
VD+
POSITIVE DIGITAL POWER
LOGIC OUTPUT (ANALOG)/GUARD
A0
7
14
CS
CHIP SELECT
LOGIC OUTPUT (ANALOG)
A1
8
13
SDI
SERIAL DATA INPUT
MASTER CLOCK
OSC2
9
12
SDO
SERIAL DATA OUT
MASTER CLOCK
OSC1
10
11
SCLK
SERIAL CLOCK INPUT
DIFFERENTIAL ANALOG INPUT
AIN1+
1
24
AIN2+
DIFFERENTIAL ANALOG INPUT
DIFFERENTIAL ANALOG INPUT
AIN1-
2
23
AIN2-
DIFFERENTIAL ANALOG INPUT
DIFFERENTIAL ANALOG INPUT
AIN4+
3
22
AIN3+
DIFFERENTIAL ANALOG INPUT
DIFFERENTIAL ANALOG INPUT
AIN4-
4
21
AIN3-
DIFFERENTIAL ANALOG INPUT
AMPLIFIER CAPACITOR CONNECT
C1
5
20
VREF+
VOLTAGE REFERENCE INPUT
AMPLIFIER CAPACITOR CONNECT
C2
6
19
VREF-
VOLTAGE REFERENCE INPUT
18
CS5533/4
POSITIVE ANALOG POWER
VA+
7
DGND
DIGITAL GROUND
NEGATIVE ANALOG POWER
VA-
8
17
VD+
POSITIVE DIGITAL POWER
LOGIC OUTPUT (ANALOG)/GUARD
A0
9
16
CS
CHIP SELECT
LOGIC OUTPUT (ANALOG)
A1
10
15
SDI
SERIAL DATA INPUT
MASTER CLOCK
OSC2
11
14
SDO
SERIAL DATA OUT
MASTER CLOCK
OSC1
12
13
SCLK
SERIAL CLOCK INPUT
Clock Generator
OSC1; OSC2 - Master Clock.
An inverting amplifier inside the chip is connected between these pins and can be used with a
crystal to provide the master clock for the device. Alternatively, an external (CMOS compatible)
clock (powered relative to VD+) can be supplied into the OSC2 pin to provide the master clock
for the device.
Control Pins and Serial Data I/O
CS - Chip Select.
When active low, the port will recognize SCLK. When high the SDO pin will output a high
impedance state. CS should be changed when SCLK = 0.
44
DS289F5
CS5531/32/33/34-AS
SDI - Serial Data Input.
SDI is the input pin of the serial input port. Data will be input at a rate determined by SCLK.
SDO - Serial Data Output.
SDO is the serial data output. It will output a high impedance state if CS = 1.
SCLK - Serial Clock Input.
A clock signal on this pin determines the input/output rate of the data for the SDI/SDO pins
respectively. This input is a Schmitt trigger to allow for slow rise time signals. The SCLK pin
will recognize clocks only when CS is low.
A0 - Logic Output (Analog)/Guard, A1 - Logic Output (Analog).
The logic states of A1-A0 mimic the OL1-OL0 bits in the selected Setup, or the A1-A0 bits in
the Configuration Register, depending on the state of the OLS bit in the Configuration Register.
Logic Output 0 = VA-, and Logic Output 1 = VA+. Alternately, A0 can be used as a guard drive
for the instrumentation amplifier with proper setting of the GB bit in the Configuration Register.
Measurement and Reference Inputs
AIN1+, AIN1-, AIN2+, AIN2- AIN3+, AIN3-, AIN4+, AIN4- - Differential Analog Input.
Differential input pins into the device.
VREF+, VREF- - Voltage Reference Input.
Fully differential inputs which establish the voltage reference for the on-chip modulator.
C1, C2 - Amplifier Capacitor Inputs.
Connections for the instrumentation amplifier’s capacitor.
Power Supply Connections
VA+ - Positive Analog Power.
Positive analog supply voltage.
VD+ - Positive Digital Power.
Positive digital supply voltage (nominally +3.0 V or +5 V).
VA- - Negative Analog Power.
Negative analog supply voltage.
DGND - Digital Ground.
Digital Ground.
DS289F5
45
CS5531/32/33/34-AS
4. SPECIFICATION DEFINITIONS
Linearity Error
The deviation of a code from a straight line which connects the two endpoints of the ADC
transfer function. One endpoint is located 1/2 LSB below the first code transition and the other
endpoint is located 1/2 LSB beyond the code transition to all ones. Units in percent of full
scale.
Differential Nonlinearity
The deviation of a code's width from the ideal width. Units in LSBs.
Full-scale Error
The deviation of the last code transition from the ideal {[(VREF+) - (VREF-)] - 3/2 LSB}. Units
are in LSBs.
Unipolar Offset
The deviation of the first code transition from the ideal (1/2 LSB above the voltage on the AINpin). When in unipolar mode (U/B bit = 1). Units are in LSBs.
Bipolar Offset
The deviation of the mid-scale transition (111...111 to 000...000) from the ideal (1/2 LSB below
the voltage on the AIN- pin). When in bipolar mode (U/B bit = 0). Units are in LSBs.
46
DS289F5
CS5531/32/33/34-AS
5. ORDERING INFORMATION
Model Number
Bits
Channels Linearity Error (Max) Temperature Range
Package
CS5531-AS
16
2
±0.003%
-40°C to +85°C
20-pin 0.2" Plastic SSOP
CS5531-ASZ
16
2
±0.003%
-40°C to +85°C
20-pin 0.2" Plastic SSOP, Lead Free
CS5533-AS
16
4
±0.003%
-40°C to +85°C
24-pin 0.2" Plastic SSOP
CS5533-ASZ
16
4
±0.003%
-40°C to +85°C
24-pin 0.2" Plastic SSOP, Lead Free
CS5532-AS
24
2
±0.003%
-40°C to +85°C
20-pin 0.2" Plastic SSOP
CS5532-ASZ
24
2
±0.003%
-40°C to +85°C
20-pin 0.2" Plastic SSOP, Lead Free
CS5534-AS
24
4
±0.003%
-40°C to +85°C
24-pin 0.2" Plastic SSOP
CS5534-ASZ
24
4
±0.003%
-40°C to +85°C
24-pin 0.2" Plastic SSOP, Lead Free
6. ENVIRONMENTAL, MANUFACTURING, & HANDLING INFORMATION
Model Number
Peak Reflow Temp
MSL Rating*
Max Floor Life
CS5531-AS
240 °C
2
365 Days
CS5531-ASZ
260 °C
3
7 Days
CS5533-AS
240 °C
2
365 Days
CS5533-ASZ
260 °C
3
7 Days
CS5532-AS
240 °C
2
365 Days
CS5532-ASZ
260 °C
3
7 Days
CS5534-AS
240 °C
2
365 Days
CS5534-ASZ
260 °C
3
7 Days
* MSL (Moisture Sensitivity Level) as specified by IPC/JEDEC J-STD-020.
DS289F5
47
CS5531/32/33/34-AS
7. PACKAGE DRAWINGS
20 PIN SSOP PACKAGE DRAWING
N
D
E11
A2
E
e
b2
SIDE VIEW
A1
A
∝
L
END VIEW
SEATING
PLANE
1 2 3
TOP VIEW
INCHES
DIM
A
A1
A2
b
D
E
E1
e
L
∝
MIN
-0.002
0.064
0.009
0.272
0.291
0.197
0.024
0.025
0°
MAX
0.084
0.010
0.074
0.015
0.295
0.323
0.220
0.027
0.040
8°
MILLIMETERS
MIN
MAX
-2.13
0.05
0.25
1.62
1.88
0.22
0.38
6.90
7.50
7.40
8.20
5.00
5.60
0.61
0.69
0.63
1.03
0°
8°
NOTE
2,3
1
1
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.
48
DS289F5
CS5531/32/33/34-AS
24 PIN SSOP PACKAGE DRAWING
N
D
E11
A2
E
e
b2
SIDE VIEW
A1
A
∝
L
END VIEW
SEATING
PLANE
1 2 3
TOP VIEW
INCHES
DIM
A
A1
A2
b
D
E
E1
e
L
∝
MIN
-0.002
0.064
0.009
0.311
0.291
0.197
0.024
0.025
0°
MAX
0.084
0.010
0.074
0.015
0.335
0.323
0.220
0.027
0.040
8°
MILLIMETERS
MIN
MAX
-2.13
0.05
0.25
1.62
1.88
0.22
0.38
7.90
8.50
7.40
8.20
5.00
5.60
0.61
0.69
0.63
1.03
0°
8°
NOTE
2,3
1
1
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.
DS289F5
49
CS5531/32/33/34-AS
Revisions
REVISION
DATE
CHANGES
PP1
Jan 1999
Initial release
PP6
Sep 2004
Added lead-free devices
F1
Jul 2005
Updated with most-current characterization data.
F2
Oct 2005
Updated Input Noise Current spec., Normal Mode Current spec., & note 9.
F3
Nov 2006
Removed -BS devices from the data sheet. Added MSL data.
F4
Apr 2007
Corrected noise spec. on p1 (12 nV/sqrtHz vs 6 nV/sqrtHz).
F5
Oct 2008
Changed Input Current spec to 1200 pA.
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
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
for the use of this information, including use of this information as the basis for manufacture or sale of any items, or for infringement of patents or other rights of third
parties. This document is the property of Cirrus and by furnishing this information, Cirrus grants no license, express or implied under any patents, mask work rights,
copyrights, trademarks, trade secrets or other intellectual property rights. Cirrus owns the copyrights associated with the information contained herein and gives consent for copies to be made of the information only for use within your organization with respect to Cirrus integrated circuits or other products of Cirrus. This consent
does not extend to other copying such as copying for general distribution, advertising or promotional purposes, or for creating any work for resale.
CERTAIN APPLICATIONS USING SEMICONDUCTOR PRODUCTS MAY INVOLVE POTENTIAL RISKS OF DEATH, PERSONAL INJURY, OR SEVERE PROPERTY OR ENVIRONMENTAL DAMAGE ("CRITICAL APPLICATIONS"). CIRRUS PRODUCTS ARE NOT DESIGNED, AUTHORIZED OR WARRANTED FOR USE
IN PRODUCTS SURGICALLY IMPLANTED INTO THE BODY, AUTOMOTIVE SAFETY OR SECURITY DEVICES, LIFE SUPPORT PRODUCTS OR OTHER
CRITICAL APPLICATIONS. INCLUSION OF CIRRUS PRODUCTS IN SUCH APPLICATIONS IS UNDERSTOOD TO BE FULLY AT THE CUSTOMER'S RISK AND
CIRRUS DISCLAIMS AND MAKES NO WARRANTY, EXPRESS, STATUTORY OR IMPLIED, INCLUDING THE IMPLIED WARRANTIES OF MERCHANTABILITY
AND FITNESS FOR PARTICULAR PURPOSE, WITH REGARD TO ANY CIRRUS PRODUCT THAT IS USED IN SUCH A MANNER. IF THE CUSTOMER OR
CUSTOMER'S CUSTOMER USES OR PERMITS THE USE OF CIRRUS PRODUCTS IN CRITICAL APPLICATIONS, CUSTOMER AGREES, BY SUCH USE, TO
FULLY INDEMNIFY CIRRUS, ITS OFFICERS, DIRECTORS, EMPLOYEES, DISTRIBUTORS AND OTHER AGENTS FROM ANY AND ALL LIABILITY, INCLUDING ATTORNEYS' FEES AND COSTS, THAT MAY RESULT FROM OR ARISE IN CONNECTION WITH THESE USES.
Cirrus Logic, Cirrus, and the Cirrus Logic logo designs are trademarks of Cirrus Logic, Inc. All other brand and product names in this document may be trademarks
or service marks of their respective owners.
SPI is a trademark of Motorola, Inc.
Microwire is a trademark of National Semiconductor Corporation.
50
DS289F5