CS5530
24-bit ADC with Ultra-low-noise Amplifier
Features & Description
General Description
Chopper-stabilized
The CS5530 is a highly integrated ΔΣ Analog-to-Digital
Converter (ADC) which uses charge-balance techniques
to achieve 24-bit performance. The ADC is optimized for
measuring low-level unipolar or bipolar signals in weigh
scale, process control, scientific, and medical
applications.
Instrumentation
Amplifier, 64X
• 12 nV/√Hz @ 0.1 Hz (No 1/f noise)
• 1200 pA Input Current
Digital
Gain Scaling up to 40x
Delta-sigma Analog-to-digital Converter
• Linearity Error: 0.0015% FS
• Noise Free Resolution: Up to 19 bits
Scalable
VREF Input: Up to Analog Supply
Simple Three-wire Serial Interface
• SPI™ and Microwire™ Compatible
• Schmitt-trigger on Serial Clock (SCLK)
To ease communication between the ADC and a microcontroller, the converter includes a simple three-wire serial interface which is SPI and Microwire compatible with
a Schmitt-trigger input on the serial clock (SCLK).
Onboard
Offset and Gain Calibration
Registers
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
C2
VREF+
AIN1+
64X
AIN1-
To accommodate these applications, the ADC includes
a very-low-noise, chopper-stabilized instrumentation
amplifier (12 nV/√Hz @ 0.1 Hz) with a gain of 64X. This
device also includes a fourth-order ΔΣ 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).
High dynamic range, programmable output rates, and
flexible power supply options make this device an ideal
solution for weigh scale and process control
applications.
ORDERING INFORMATION
See page 35.
VREF-
VD+
DIFFERENTIAL
4TH ORDER ΔΣ
MODULATOR
PROGRAMMABLE
SINC FIR FILTER
CS
SDI
SERIAL
INTERFACE
SDO
SCLK
CLOCK
GENERATOR
LATCH
VA-
http://www.cirrus.com
A0
A1
OSC1
OSC2
Copyright Cirrus Logic, Inc. 2009
(All Rights Reserved)
CALIBRATION
SRAM/CONTROL
LOGIC
DGND
NOV ‘09
DS742F3
CS5530
TABLE OF CONTENTS
1.
2.
3.
4.
5.
6.
7.
2
CHARACTERISTICS AND SPECIFICATIONS ................................................................. 4
ANALOG CHARACTERISTICS................................................................................ 4
TYPICAL NOISE-FREE RESOLUTION (BITS) ........................................................ 6
5 V DIGITAL CHARACTERISTICS .......................................................................... 7
3 V DIGITAL CHARACTERISTICS .......................................................................... 7
DYNAMIC CHARACTERISTICS .............................................................................. 8
ABSOLUTE MAXIMUM RATINGS ........................................................................... 8
SWITCHING CHARACTERISTICS .......................................................................... 9
GENERAL DESCRIPTION .............................................................................................. 11
2.1. Analog Input ........................................................................................................... 11
2.1.1. Analog Input Span .......................................................................................... 12
2.1.2. Voltage Noise Density Performance ........................................................... 12
2.1.3. No Offset DAC ............................................................................................ 12
2.2. Overview of ADC Register Structure and Operating Modes .................................. 12
2.2.1. System Initialization .................................................................................... 12
2.2.2. Command Register Descriptions ................................................................ 14
2.2.3. Serial Port Interface .................................................................................... 16
2.2.4. Reading/Writing On-Chip Registers ............................................................ 17
2.3. Configuration Register ........................................................................................... 17
2.3.1. Power Consumption ................................................................................... 17
2.3.2. System Reset Sequence ............................................................................ 17
2.3.3. Input Short .................................................................................................. 17
2.3.4. Voltage Reference Select .......................................................................... 17
2.3.5. Output Latch Pins ....................................................................................... 18
2.3.6. Filter Rate Select ........................................................................................ 18
2.3.7. Word Rate Select ........................................................................................ 18
2.3.8. Unipolar/Bipolar Select ............................................................................... 18
2.3.9. Open Circuit Detect .................................................................................... 18
2.3.10. Configuration Register Description ........................................................... 19
2.4. Calibration .............................................................................................................. 21
2.4.1. Calibration Registers .................................................................................. 21
2.4.2. Gain Register ............................................................................................. 21
2.4.3. Offset Register ........................................................................................... 21
2.4.4. Performing Calibrations .............................................................................. 22
2.4.5. System Calibration ...................................................................................... 22
2.4.6. Calibration Tips ........................................................................................... 22
2.4.7. Limitations in Calibration Range ................................................................. 23
2.5. Performing Conversions ........................................................................................ 23
2.5.1. Single Conversion Mode ............................................................................. 23
2.5.2. Continuous Conversion Mode .................................................................... 24
2.6. Using Multiple ADCs Synchronously ..................................................................... 25
2.7. Conversion Output Coding .................................................................................... 25
2.7.1. Conversion Data Output Descriptions ........................................................ 26
2.8. Digital Filter ............................................................................................................ 27
2.9. Clock Generator ..................................................................................................... 28
2.10. Power Supply Arrangements ................................................................................. 28
2.11. Getting Started ....................................................................................................... 31
2.12. PCB Layout ............................................................................................................ 31
PIN DESCRIPTIONS ...................................................................................................... 32
Clock Generator ......................................................................................................32
Control Pins and Serial Data I/O .............................................................................32
Measurement and Reference Inputs ......................................................................33
Power Supply Connections .....................................................................................33
SPECIFICATION DEFINITIONS ..................................................................................... 33
PACKAGE DRAWINGS .................................................................................................. 34
ORDERING INFORMATION .......................................................................................... 35
ENVIRONMENTAL, MANUFACTURING, & HANDLING INFORMATION .................... 35
DS742F3
CS5530
LIST OF FIGURES
Figure 1. SDI Write Timing (Not to Scale)............................................................................... 10
Figure 2. SDO Read Timing (Not to Scale)............................................................................. 10
Figure 3. Front End Configuration........................................................................................... 11
Figure 4. Input Model for AIN+ and AIN- Pins......................................................................... 11
Figure 5. Measured Voltage Noise Density............................................................................. 12
Figure 5. Measured Voltage Noise Density............................................................................. 12
Figure 6. CS5530 Register Diagram ....................................................................................... 13
Figure 7. Command and Data Word Timing ........................................................................... 16
Figure 8. Input Reference Model when VRS = 1 .................................................................... 18
Figure 9. Input Reference Model when VRS = 0 .................................................................... 18
Figure 10. System Calibration of Offset .................................................................................. 22
Figure 11. System Calibration of Gain .................................................................................... 22
Figure 12. Synchronizing Multiple ADCs................................................................................. 25
Figure 13. Digital Filter Response (Word Rate = 60 Sps) ....................................................... 27
Figure 14. 120 Sps Filter Magnitude Plot to 120 Hz ............................................................... 27
Figure 15. 120 Sps Filter Phase Plot to 120 Hz ...................................................................... 27
Figure 16. Z-Transforms of Digital Filters................................................................................ 27
Figure 17. On-chip Oscillator Model........................................................................................ 28
Figure 18. CS5530 Configured with a Single +5 V Supply ..................................................... 29
Figure 19. CS5530 Configured with ±2.5 V Analog Supplies.................................................. 29
Figure 20. CS5530 Configured with ±3 V Analog Supplies..................................................... 30
LIST OF TABLES
Table 1. Conversion Timing for Single Mode .......................................................................... 24
Table 2. Conversion Timing for Continuous Mode.................................................................. 24
Table 3. Output Coding ........................................................................................................... 25
DS742F3
3
CS5530
1. CHARACTERISTICS AND SPECIFICATIONS
ANALOG CHARCTERISTICS
(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)
(See Notes 1 and 2.)
CS5530-CS
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 to +85 °C.
2. Specifications guaranteed by design, characterization, and/or test. LSB is 24 bits.
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
DS742F3
CS5530
ANALOG CHARACTERISTICS
(Continued)
(See Notes 1 and 2.)
Parameter
Min
Analog Input
Common Mode + Signal on AIN+ or AINBipolar/Unipolar Mode (VA-) + 1.6
CVF Current on AIN+ or AINInput Current Noise
Open Circuit Detect Current
100
Common Mode Rejection
DC
50, 60 Hz
Input Capacitance
Voltage Reference Input
Range
(VREF+) - (VREF-)
1
CVF Current
(Note 5, 6)
Common Mode Rejection
DC
50, 60 Hz
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
Typ
Max
Unit
1200
1
300
130
120
10
(VA+) - 1.6
V
pA
pA/√Hz
nA
dB
dB
pF
2.5
50
120
120
-
(VA+)-(VA-)
22
V
nA
dB
dB
pF
-
110
100
90
%FS
%FS
%FS
Notes: 5. See the section of the data sheet which discusses input models.
6. Input current on 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.
DS742F3
5
CS5530
ANALOG CHARACTERISTICS
(Continued)
(See Notes 1 and 2.)
CS5530-CS
Parameter
Min
Typ
Max
Unit
-
6
0.6
8
1.0
mA
mA
-
35
5
500
45
-
mW
mW
µW
-
115
115
-
dB
dB
Power Supplies
DC Power Supply Currents (Normal Mode)
IA+, IAID+
Power Consumption
Normal Mode
Standby
Sleep
(Note 7)
Power Supply Rejection
(Note 8)
DC Positive Supplies
DC Negative Supply
7. All outputs unloaded. All input CMOS levels.
8. Tested with 100 mV change on VA+ or VA-.
TYPICAL NOISE-FREE RESOLUTION (BITS) (See Notes 9 and 10)
Output Word Rate (Sps)
-3 dB Filter Frequency (Hz)
Noise-free Bits
Noise (nVrms)
7.5
1.94
19
17
15
3.88
19
24
30
7.75
18
34
60
15.5
18
48
120
31
17
68
240
62
16
115
480
122
16
163
960
230
15
229
1,920
390
15
344
3,840
780
13
1390
9. 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.
10. “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.
6
DS742F3
CS5530
5 V DIGITAL CHARACTERISTICS
(VA+, VD+ = 5 V ±5%; VA-, DGND = 0 V; See Notes 2 and 11.)
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 3-State Leakage Current
IOZ
-
-
±10
µA
Digital Output Pin Capacitance
Cout
-
9
-
pF
3 V DIGITAL CHARACTERISTICS
(TA = 25 °C; VA+ = 5V ±5%; VD+ = 3.0V±10%; VA-, DGND = 0V; See Notes 2 and 11.)
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 3-State Leakage Current
IOZ
-
-
±10
µA
Digital Output Pin Capacitance
Cout
-
9
-
pF
11. All measurements performed under static conditions.
DS742F3
7
CS5530
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 12, 13, and 14)
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
12. 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.
13. 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.
14. 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 15.)
Parameter
Symbol
Min
Typ
Max
Unit
(Notes 16 and 17)
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 18 and 19)
IIN
-
-
±10
mA
IOUT
-
-
±25
mA
(Note 20)
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: 15.
16.
17.
18.
19.
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.
20. 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.
8
DS742F3
CS5530
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 21)
External Clock or Crystal Oscillator
MCLK
Master Clock Duty Cycle
Rise Times
Fall Times
(Note 22)
Any Digital Input Except SCLK
SCLK
Any Digital Output
trise
(Note 22)
Any Digital Input Except SCLK
SCLK
Any Digital Output
tfall
Start-up
Oscillator Start-up Time
XTAL = 4.9152 MHz
(Note 23)
Serial Port Timing
Serial Clock Frequency
Serial Clock
Pulse Width High
Pulse Width Low
SDI Write Timing
SDO Read Timing
Notes: 21. Device parameters are specified with a 4.9152 MHz clock.
22. Specified using 10% and 90% points on waveform of interest. Output loaded with 50 pF.
23. Oscillator start-up time varies with crystal parameters. This specification does not apply when using an
external clock source.
DS742F3
9
CS5530
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)
10
DS742F3
CS5530
2. GENERAL DESCRIPTION
The CS5530 is a ΔΣ Analog-to-Digital Converter
(ADC) which uses charge-balance techniques to
achieve 24-bit performance. The ADC is optimized
for measuring low-level unipolar or bipolar signals
in weigh scale, process control, scientific, and medical applications.
To accommodate these applications, the ADC includes a very-low-noise, chopper-stabilized instrumentation amplifier (12 nV/√Hz @ 0.1 Hz) with a
gain of 64X. This ADC also includes a fourth-order
ΔΣ 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
micro-controller, 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).
The amplifier is chopper-stabilized and operates with
a chop clock frequency of MCLK/128. The CVF
(sampling) current into the 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-) +
1.6 V to (VA+) - 1.6 V.
Figure 4 illustrates the input model for the 64X amplifier.
AIN
C = 3 .9 pF
Vos ≤ 8 mV
in = fVos C
f=
MCLK
128
Figure 4. Input Model for AIN+ and AIN- Pins
Note:
2.1 Analog Input
Figure 3 illustrates a block diagram of the CS5530.
The front end includes a chopper-stabilized instrumentation amplifier with a gain of 64X.
The C = 3.9 pF capacitor is for input current
modeling only. For physical input capacitance
see ‘Input Capacitance’ specification under
Analog Characteristics.
VREF+ VREFX1
1000 Ω
AIN+
64x
22 nF
C1 PIN
C2 PIN
AIN1000 Ω
X1
Differential
4th Order
ΔΣ
Modulator
5
Sinc
Digital
Filter
Programmable
Sinc 3
Digital Filter
Serial
Port
Figure 3. Front End Configuration
DS742F3
11
CS5530
2.1.1 Analog Input Span
The full-scale input signal that the converter can digitize is a function of the reference voltage connected
between the VREF+ and VREF- pins. The full-scale
input span of the converter is
((VREF+) – (VREF-))/(64Y), where 64 is the gain
of the amplifier and Y is 2 for VRS = 0, or Y is 1 for
VRS = 1. VRS is the Voltage Reference Select bit,
and must be set according to the differential voltage
applied to the VREF+ and VREF- pins on the part.
See section 2.3.4 for more details.
With a 2.5 V reference, the full-scale biploar input
range is equal to ±2.5/64, or about ±39 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). The gain setting in the Gain Register
can be altered to map the digital codes of the converter to set full scales from 1 mV to 40 mV.
2.1.2 Voltage Noise Density Performance
Figure 5 illustrates the measured voltage noise density versus frequency from 0.025 Hz to 10 Hz. The
device was powered with ±2.5 V supplies, using
30 Sps OWR, bipolar mode, and with the input
short bit enabled.
1000
100
0.10
1.00
Frequency (Hz)
10.00
Figure 5. Measured Voltage Noise Density, 64x
2.1.3 No Offset DAC
An offset DAC was not included in the CS5530 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.
12
The converter has 32-bit registers to function as the
offset and the 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 converter includes a 32-bit configuration register which is used for setting options such as the
power down modes, resetting the converter, shorting the analog input, enabling logic outputs, and
other user options.
The following pages document how to initialize the
converter and perform offset and gain calibrations.
Each of the bits of the configuration register is described. 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
10
1
0.025
2.2 Overview of ADC Register Structure
and Operating Modes
The CS5530 ADC has 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.
The CS5530 provide no power-on-reset function.
To initialize the ADC, the user must perform a software reset via the configuration register. Before
accessing the configuration register, the user must
insure serial port synchronization by using the Serial Port Initialization sequence. 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
DS742F3
CS5530
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
8 master clock cycles, then write the RS bit back to
logic 0. Note that the other bits in the configuration register cannot be written on this write cycle
as they are being held in reset until RS is set back
to logic 0. While this involves writing an entire
word into the configuration register to casue the
RS bit to go to logic 0, 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 Register:
Gain Register
00000000(H)
00000000(H)
01000000(H)
After the configuration register has been read to
clear the RV bit, the register can then be written to
set the other function bits or other registers can be
written or read.
Once the system initialization or reset is completed, 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, or perform a conversion
or a calibration. The Command Register Descriptions section lists all valid commands.
Conversion Data
Register (1 x 32)
Offset Register (1 x 32)
Offset (1 x 32)
Read Only
Data (1 x 32)
Gain Register (1 x 32)
Gain (1 x 32)
CS
SDI
SDO
SCLK
Write Only
Serial
Interface
Configuration Register (1 x 32)
Power Save Select
Reset System
Input Short
Voltage Reference Select
Output Latch
Filter Rate Select
Word Rate
Unipolar/Bipolar
Open Circuit Detect
Command
Register (1 × 8)
Figure 6. CS5530 Register Diagram
DS742F3
13
CS5530
2.2.2 Command Register Descriptions
READ/WRITE OFFSET REGISTER
D7(MSB)
0
D6
0
D5
0
D4
0
D3
R/W
D2
0
D1
0
D0
1
D4
0
D3
R/W
D2
0
D1
1
D0
0
D4
0
D3
R/W
D2
0
D1
1
D0
1
R/W (Read/Write)
0
Write offset register.
1
Read offset register.
READ/WRITE GAIN REGISTER
D7(MSB)
0
D6
0
D5
0
R/W (Read/Write)
0
Write gain register.
1
Read gain register.
READ/WRITE CONFIGURATION REGISTER
D7(MSB)
0
Function:
D6
0
D5
0
These commands are used to read from or write to the configuration register.
R/W (Read/Write)
0
Write configuration register.
1
Read configuration register.
PERFORM CONVERSION
D7(MSB)
1
D6
MC
D5
0
D4
0
D3
0
D2
0
D1
0
D0
0
D4
0
D3
0
D2
1
D1
0
D0
1
MC (Multiple Conversions)
0
Perform a single conversion.
1
Perform continuous conversions.
PERFORM SYSTEM OFFSET CALIBRATION
D7(MSB)
1
D6
0
D5
0
PERFORM SYSTEM GAIN CALIBRATION
D7(MSB)
1
D6
0
D5
0
D4
0
D3
0
D2
1
D1
1
D0
0
D6
1
D5
1
D4
1
D3
1
D2
1
D1
1
D0
1
SYNC1
D7(MSB)
1
Function:
14
Part of the serial port re-initialization sequence.
DS742F3
CS5530
SYNC0
D7(MSB)
1
Function:
D6
1
D5
1
D4
1
D3
1
D2
1
D1
1
D0
0
D2
0
D1
0
D0
0
End of the serial port re-initialization sequence.
NULL
D7(MSB)
0
Function:
DS742F3
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.
15
CS5530
2.2.3 Serial Port Interface
The CS5530’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
16
DS742F3
CS5530
2.2.4 Reading/Writing On-Chip Registers
The CS5530’s offset, gain, and configuration registers are readable and writable while the conversion
data register is read only.
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 the 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.
2.3 Configuration Register
To ease the architectural design and simplify the
serial interface, the configuration register is thirtytwo bits long, however, only fifteen of the thirty
two bits are used. The following sections detail the
bits in the configuration register.
2.3.1 Power Consumption
The CS5530 accommodates three power consumption modes: normal, standby, and sleep. The default
mode, “normal mode”, is entered after power is applied. In this mode, the CS5530 typically consumes
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 0. If PSS and PDW are
DS742F3
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.
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 register is read. The on-chip registers are initialized to
the following default states:
Configuration Register:
Offset Register:
Gain Register
00000000(H)
00000000(H)
01000000(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 the inputs of the ADC. 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 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
17
CS5530
φ1 Fine
φ1 Fine
φ2 Coarse
VREF
C = 14pF
Vos ≤ 8 mV
in = fV os C
MCLK
16
VRS = 1; 1 V ≤ VREF ≤ 2.5 V
f=
Figure 8. Input Reference Model when VRS = 1
the magnitude of the reference voltage to achieve
optimal performance. Figures 8 and 9 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 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.
2.3.5 Output Latch Pins
The A1-A0 pins of the ADC mimic the D24-D23
bits of the configuration register. 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 from VA+ and VA-. Their output
voltage will be limited to the VA+ voltage for a
logic 1 and VA- for a logic 0. Note that if the latch
bits are used to modify the analog input signal the
user should delay performing a conversion until he
knows the effects of the A0/A1 bits are fully settled.
18
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 9. Input Reference Model when VRS = 0
2.3.6 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 Configuration Register. Rates
can be 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.
2.3.7 Word Rate Select
The Word Rate Select bits (WR3-WR0) allow slection of the output word rate of the converter as depicted in the Configuration Register Descriptions.
The word rate chosen by the WR3-WR0 bits is
modified by the setting of the FRS bit as presented
in the previous paragraph.
2.3.8 Unipolar/Bipolar Select
The UP/BP Select bit sets the converter to measure
either a unipolar or bipolar input span.
2.3.9 Open Circuit Detect
When the OCD bit is set it activates a current
source as a means to test for open thermocouples.
DS742F3
CS5530
2.3.10 Configuration Register Description
D31(MSB) D30
PSS
PDW
D15
D14
NU
WR3
D29
RS
D13
WR2
D28
RV
D12
WR1
D27
D26
D25
IS
NU
VRS
D11
D10
D9
WR0 UP/BP OCD
D24
A1
D8
NU
D23
A0
D7
NU
D22
NU
D6
NU
D21
NU
D5
NU
D20
NU
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.
NU (Not Used)[26]
0
Must always be logic 0. Reserved for future upgrades.
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 (A1 and A0) will be set to the logic state of these bits when the Configuration register is written.
Note that these logic outputs are powered from VA+ and VA-.
00
A1 = 0, A0 = 0
01
A1 = 0, A0 = 1
10
A1 = 1, A0 = 0
11
A1 = 1, A0 = 1
NU (Not Used)[22:20]
0
Must always be logic 0. Reserved for future upgrades.
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)[18:15]
0
DS742F3
Must always be logic 0. Reserved for future upgrades.
19
CS5530
WR3-WR0 (Word Rate) [14:11]
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.
U/B (Unipolar / Bipolar) [10]
0
Select Bipolar mode.
1
Select Unipolar mode.
OCD (Open Circuit Detect Bit) [9]
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. 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.
NU (Not Used) [8:0]
0
20
Must always be logic 0. Reserved for future upgrades.
DS742F3
CS5530
2.4 Calibration
Calibration is used to set the zero and gain slope of
the ADC’s transfer function. The CS5530 provides
system calibration.
Note:
After the ADC is reset, it is functional and can
perform measurements without being
calibrated (remember that the VRS bit in the
configuration register must be properly
configured). If the converter is operated
without calibraton, the converter will utilize
the initialized values of the on-chip registers
(Offset = 0.0; Gain = 1.0) to calculate output
words. Any initial offset and gain errors in the
internal circuitry of the chip will remain.
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 percent 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
D29
5
2 +b
D28
4
2 +b
D27
3
2 +…+b
D0
2
– 24
bDi 2
) =
( – 24 + i )
i=0
2.4.1 Calibration Registers
The CS5530 converter has an offset register that is
used to set the zero point of the converter’s transfer
function. As shown in Offset Register section, one
LSB in the offset register is 1.835007966 X 2-24
proportion of the input span (bipolar span is 2 times
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.
2.4.2 Gain Register
Decimal Point
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
2-10
2-11
2-12
2-13
2-14
2-15
2-16
2-17
2-18
2-19
2-20
2-21
222
2-23
0
0
0
0
0
0
0
0
0
0
0
0
0
0
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’.
2.4.3 Offset Register
MSB
Sign
D30
-2
D29
-3
D28
-4
D27
-5
D26
-6
0
2
0
2
0
2
0
2
0
2
0
D15
D14
D13
D12
D11
D10
2-17
0
2-18
0
2-19
0
2-20
0
2-21
0
2-22
0
D25
-7
2
0
D24
-8
D23
-9
D22
D21
D20
D19
D18
D17
D16
-10
-11
-12
-13
-14
-15
2
0
2
0
0
0
0
0
2-16
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
0
2
0
2
D9
D8
2-23
0
2-24
0
2
2
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.
DS742F3
21
CS5530
2.4.4 Performing Calibrations
To perform a calibration, the user must send a command byte with its MSB=1, and the appropriate
calibration bits (CC2-CC0) set to choose the type
of calibration to be performed. The calibration will
be performed using the filter rate, and siganl span
(unipolar or bipolar) as set in the configuration register. 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. 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 effects from the previous calibration.
Only one calibration is performed with each command byte.
2.4.5 System Calibration
For the system calibration functions, the user must
supply the converter input calibration signals which
Figure 10. System Calibration of Offset
22
represent ground and full-scale. When a system offset calibration is performed, a ground referenced signal must be applied to the converter. Figure 10
illustrates system offset calibration.
As shown in Figure 11, 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).
2.4.6 Calibration Tips
Calibration steps are performed at the output word
rate selected by the WR3-WR0 bits of the configuration register. To minimize the effects of peak-topeak noise on the accuracy of calibration the converter should be calibrated using the slowest word
rate that is acceptable. It is recommended that
word rates of 240 Sps and higher not be used for
calibration.) 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 microcontroller and the ADC, and may
prematurely halt the calibration cycle.
Figure 11. System Calibration of Gain
DS742F3
CS5530
For maximum accuracy, calibrations should be performed for both offset and gain.
FSCR, margin is again incorporated to accommodate the intrinsic gain error.
When the device is used without calibration, the
uncalibrated gain accuracy is about ±1 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 Performing Conversions
The CS5530 offers two distinctly different conversion modes. The paragraphs that follow detail the
differences in the conversion modes.
2.4.7 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
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
DS742F3
2.5.1 Single Conversion Mode
When the user transmits the perform single conversion command, a single, fully settled conversion is
performed using the word rate and polarity selections set in the configuration register. Once the
command byte is 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 to act as a flag to indicate that
the data is available. 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 the serial port will remain in data mode until SCLK transitions 40 times.
After reading the data, the serial 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.
23
CS5530
Table 1. Conversion Timing for 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
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:
2.5.2 Continuous Conversion Mode
When the user transmits the perform continuous
conversion command, the converter begins continuous conversions using the word rate and polarity
selections set in the configuration register. Once
the command byte is transmitted, the serial port enters data mode where it waits until a conversion is
complete. After the conversion is done, SDO falls
to logic 0 to act as a flag to indicate that the data is
available. 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 using the same word
rate and polarity information. 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
24
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.
Table 2. Conversion Timing for Continuous Mode
FRS (WR3-WR0)
Clock Cycles
Clock Cycles
(First Conversion) (All Other
Conversions)
0
0000
89528 ± 8
40960
0
0001
171448 ± 8
81920
0
0010
335288 ± 8
163840
0
0011
662968 ± 8
327680
0
0100
1318328 ± 8
655360
0
1000
2472 ± 8
1280
0
1001
12728 ± 8
2560
0
1010
17848 ± 8
5120
0
1011
28088 ± 8
10240
0
1100
48568 ± 8
20480
1
0000
107434 ± 10
49152
1
0001
205738 ± 10
98304
1
0010
402346 ± 10
196608
1
0011
795562 ± 10
393216
1
0100
1581994 ± 10
786432
1
1000
2966 ± 10
1536
1
1001
15274 ± 10
3072
1
1010
21418 ± 10
6144
1
1011
33706 ± 10
12288
1
1100
58282 ± 10
24576
DS742F3
CS5530
2.6 Using Multiple ADCs Synchronously
Some applications require synchronous data outputs from multiple ADCs converting different analog channels. Multiple CS5530 devices 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.
An example of a synchronous system using two
CS5530 devices is shown in Figure 12.
2.7 Conversion Output Coding
The CS5530 outputs 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 an overflow flag bit. The overrange
flag (OF) monitors to determine if a valid conversion was performed.
DS742F3
CS5530
SDO
SDI
SCLK
CS
μC
OSC2
CS5530
SDO
SDI
SCLK
CS
OSC2
CLOCK
SOURCE
Figure 12. Synchronizing Multiple ADCs
The CS5530 output data conversions in binary format when operating in unipolar mode and in two's
complement when operating in bipolar mode. Table 3 shows the code mapping for both unipolar and
bipolar modes. 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.
Table 3. Output Coding
Unipolar Input Offset
Voltage
Binary
Bipolar Input
Voltage
>(VFS-1.5 LSB) FFFFFF >(VFS-1.5 LSB)
VFS-1.5 LSB
FFFFFF
-----FFFFFE
VFS/2-0.5 LSB 800000
-----7FFFFF
+0.5 LSB
<(+0.5 LSB)
000001
-----000000
Two's
Complement
7FFFFF
VFS-1.5 LSB
7FFFFF
-----7FFFFE
-0.5 LSB
000000
-----FFFFFF
-VFS+0.5 LSB
800001
-----800000
000000 <(-VFS+0.5 LSB)
800000
25
CS5530
2.7.1 Conversion Data Output Descriptions
CS5530 (24-BIT CONVERSIONS)
D31(MSB) D30
MSB
22
D15
D14
7
6
D29
21
D13
5
D28
20
D12
4
D27
19
D11
3
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
0
D16
8
D0
0
Conversion Data Bits [31:8]
These bits depict the latest output conversion.
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).
Other Bits [7:3], [1:0]
These bits are masked logic zero.
26
DS742F3
CS5530
2.8 Digital Filter
The CS5530 has a linear phase digital filter which
is programmed to achieve a range of output word
rates (OWRs) as stated in the Configuration Register Description section. The ADC uses 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 13 shows the magnitude response of the
60 Sps filter, while Figures 14 and 15 show the
magnitude and phase response of the filter at 120
Sps. The Sinc3 is active for all output word rates
0
FRS = 0
except for the 3200 Sps and 3840 Sps (MCLK =
4.9152 MHz) rate. The Z-transforms of the two filters are shown in Figure 16. 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 percent 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.
Gain (dB)
-40
180
-120
0
60
120
180
240
300
Frequency (Hz)
Phase (Degrees)
-80
-90
0
0
Gain (dB)
0
-180
Figure 13. Digital Filter Response (Word Rate = 60 Sps)
-80
-120
0
30
60
90
120
Frequency (Hz)
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
Figure 15. 120 Sps Filter Phase Plot to 120 Hz
( 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 ) 3Sinc 3 = -----------------------( 1 – z –1 ) 3
40
80
120
Frequency (Hz)
Figure 14. 120 Sps Filter Magnitude Plot to 120 Hz
DS742F3
90
Note:
See the text regarding the Sinc3 filter’s
decimation ratio “D”.
Figure 16. Z-Transforms of Digital Filters
27
CS5530
2.9 Clock Generator
The CS5530 includes an on-chip inverting amplifier which can be connected with an external crystal
to provide the master clock for the chip. Figure 17
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 1/2 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 onchip 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 microampere output
of the on-chip amplifier. This will not harm the onchip circuitry. In this scheme, OSC1 should be left
unconnected.
2.10 Power Supply Arrangements
The CS5530 is designed to operate from single or
dual analog supplies and a single digital supply.
The following power supply connections are possible:
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
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 18 illustrates the CS5530 connected with a
single +5.0 V supply to measure differential inputs
relative to a common mode of 2.5 V. Figure 19 illustrates the CS5530 connected with ±2.5 V bipolar
analog supplies and a +3 V to +5 V digital supply
to measure ground referenced bipolar signals. Figures 20 illustrates the CS5532 connected with ±3 V
analog supplies and a +3 V digital supply to measure ground referenced bipolar signals.
1 MΩ
~60 μA
~
VTH
+
20 pF
OSC1
MCLK
20 pF
OSC2
NOTE: 20 pF capacitors are on chip and
should not be added externally.
Figure 17. On-chip Oscillator Model
28
DS742F3
CS5530
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
CS5530
4
1
2
20
19
7
8
C2
AIN1+
AIN1NC
NC
A0
A1
VA 6
CS
SDI
SDO
SCLK
14
13
Serial
Data
Interface
12
11
DGND
16
Figure 18. CS5530 Configured with a Single +5 V Supply
+2.5 V
Analog
Supply
+3 V ~ +5 V
Digital
0.1 µF Supply
0.1 µF
5
VA+
-
+
18 VREF+
OSC2
17 VREF3 C1
OSC1
Optional
Clock
Source
9
10
4.9152 MHz
22 nF
CS5530
4
1
2
20
19
7
8
-2.5 V
Analog
Supply
15
VD+
C2
AIN1+
AIN1NC
NC
A0
A1
VA 6
CS
SDI
SDO
SCLK
14
13
12
11
Serial
Data
Interface
DGND
16
Figure 19. CS5530 Configured with ±2.5 V Analog Supplies
DS742F3
29
CS5530
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
CS5530
4
1
2
20
19
7
8
-3 V
Analog
Supply
15
VD+
C2
AIN1+
AIN1NC
NC
A0
A1
VA 6
CS
SDI
SDO
SCLK
14
13
12
11
Serial
Data
Interface
DGND
16
Figure 20. CS5530 Configured with ±3 V Analog Supplies
30
DS742F3
CS5530
2.11 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 be inserted
before the start of the processor’s ADC initialization code. Next, since the CS5530 does not provide
a power-on-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
DS742F3
Sequence). After the converter is properly reset,
the configuration register bits should be configured
as appropriate, for example, the voltage reference
selection, word rate, signal polarity(unipolar or bipolar) should be configured.
Calibrations or conversions can then be performed
as appropriate.
2.12 PCB Layout
For optimal performance, the CS5530 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 split-plane
system, place the analog-digital plane split immediately adjacent to the digital portion of the chip.
31
CS5530
3. PIN DESCRIPTIONS
DIFFERENTIAL ANALOG INPUT
AIN1+
1
DIFFERENTIAL ANALOG INPUT
AIN1-
2
AMPLIFIER CAPACITOR CONNECT
C1
AMPLIFIER CAPACITOR CONNECT
20
NC
19
NC
3
18
VREF+
VOLTAGE REFERENCE INPUT
C2
4
17
VREF-
VOLTAGE REFERENCE INPUT
POSITIVE ANALOG POWER
VA+
5
16
DGND
DIGITAL GROUND
NEGATIVE ANALOG POWER
VA-
6
15
VD+
POSITIVE DIGITAL POWER
LOGIC OUTPUT (ANALOG)
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
CS5530
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.
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), A1 – Logic Output (Analog)
The logic states of A1-A0 mimic the A1-A0 bits in the Configuration Register. Logic
Output 0 = VA-, and Logic Output 1 = VA+.
32
DS742F3
CS5530
Measurement and Reference Inputs
AIN1+, AIN1- – 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.
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 fullscale.
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.
DS742F3
33
CS5530
5. 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.
34
DS742F3
CS5530
6. ORDERING INFORMATION
Model Number
Bits
Channels Linearity Error (Max) Temperature Range
Package
CS5530-IS
24
1
±0.003%
-40°C to +85°C
20-pin 0.2" Plastic SSOP
CS5530-ISZ
24
1
±0.003%
-40°C to +85°C
20-pin 0.2" Plastic SSOP, Lead Free
7. ENVIRONMENTAL, MANUFACTURING, & HANDLING INFORMATION
Model Number
Peak Reflow Temp
MSL Rating
Max Floor Life
CS5530-IS
240 °C
2
365 Days
CS5530-ISZ
260 °C
3
7 Days
DS742F3
35
CS5530
Revision History
REVISION
DATE
CHANGES
A1
OCT 2006
Advance Release
A2
NOV 2006
Updated power consumption values.
A3
NOV 2006
Updated noise density plot.
A4
NOV 2006
Updated temperature range specification.
F1
JAN 2007
Corrected input current on p1 to 1200 pA. Changed temp range to -40 to +85.
F2
MAY 2009
Increased input current noise spec. to 1.0 pA / √Hz.
F3
NOV 2009
Minor correction to Figure 4. Input Model for AIN+ and AIN- Pins (page 11).
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
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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
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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
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Microwire is a trademark of National Semiconductor Corporation.
36
DS742F3