l Simple Four-wire Serial Interface
l Charge Pump Driver output generates
negative power supply.
l Ground-Referenced Bipolar Inputs
VA+
GAIN
IIN1+
IIN1-
VIN1+
VIN1-
x1, 20
x1
4th Order∆ΣModulator
2nd Order∆ΣModulator
Description
The CS5451 is a highly integrated Delta-Sigma (∆Σ) Analog-to-Digital Converter (ADC) developed for the Power
Measurement Industry. The CS5451 combines six ∆Σ
ADCs, decimation filters, and a serial interface on a single chip. The CS5451 interfaces directly to a current
transformer or shunt to measure current, and resistive
divider or transformer to measure voltage. The product
features a serial interface for communication with a micro-controller or DSP. The product is initialized and fully
functional upon reset, and includes a Voltage Reference.
Figure 3. Serial Port Data Transfer ................................................................................................. 8
Figure 4. Close-up of One Data Frame ........................................................................................... 9
Figure 5. Generating VA- with a Charge Pump ............................................................................. 10
Contacting Cirrus Logic Support
For a complete listing of Direct Sales, Distributor, and Sales Representative contacts, visit the Cirrus Logic web site at:
http://www.cirrus.com/corporate/contacts/
Preliminary product information describes products which are in production, but for which full characterization data is not yet available. Advance product information describes products which are in development and subject to development changes. Cirrus Logic, Inc. has made best efforts to ensure 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). No responsibility is assumed by Cirrus Logic, Inc. for the use of this information, nor for infringements of patents or other rights
of third parties. This document is the property of Cirrus Logic, Inc. and implies no license under patents, copyrights, trademarks, or trade secrets. No part of
this publication may be copied, reproduced, stored in a retrieval system, or transmitted, in any form or by any means (electronic, mechanical, photographic, or
otherwise) without the prior written consent of Cirrus Logic, Inc. Items from any Cirrus Logic website or disk may be printed for use by the user. However, no
part of the printout or electronic files may be copied, reproduced, stored in a retrieval system, or transmitted, in any form or by any means (electronic, mechanical,
photographic, or otherwise) without the prior written consent of Cirrus Logic, Inc.Furthermore, no part of this publication may be used as a basis for manufacture
or sale of any items without the prior written consent of Cirrus Logic, Inc. The names of products of Cirrus Logic, Inc. or other vendors and suppliers appearing
in this document may be trademarks or service marks of their respective owners which may be registered in some jurisdictions. A list of Cirrus Logic, Inc. trademarks and service marks can be found at http://www.cirrus.com.
2DS458PP4
1.CHARACTERISTICS AND SPECIFICATIONS
CS5451
ANALOG CHARACTERISTICS (T
= -40 °C to +85 °C; +2.7V < VA+ < +3.5V; +2.7V < VD+ < +3.5V;
Notes: 1. Specifications guaranteed by design, characterization, and/or test.
2. Analog signals are relative to AGND and digital signals to DGND unless otherwise noted.
3. Effective Input Impedance (EII) varies with clock frequency (XIN) and Input Capacitance (IC)
EII = 1/(IC*XIN/4)
DS458PP43
CS5451
ANALOG CHARACTERISITCS (continued)
ParameterSymbol Min TypMaxUnit
Reference Output
Output VoltageREFOUT1.15-1.25V
Temperature Coefficient-2050ppm/°C
Load Regulation(Output Current 1µA Source or Sink)∆V
R
Power Supply RejectionPSRR60--dB
Reference Input
Input Voltage RangeVREF+1.151.21.25V
Input Capacitance--10pF
Input CVF Current--1µA
Power Supplies
Power Supply CurrentsI
I
A+
D+
PSCA
PSCD
Power Consumption(Note 4)PC--27mW
Power Supply Rejection(DC)
(see Note 5)(50, 60 Hz)
PSRR
PSRR
-610mV
-
-
50
60
-
-
-
-
3
4
-
-
mA
mA
dB
dB
Notes: 4. All outputs unloaded. All inputs CMOS level.
5. Definition for PSRR: VREFIN tied to VREFOUT, VA+ = VD+ = 3V, AGND = DGND = 0V, VA- = -2V
(using charge-pump circuit with CPD). In addition, a 106.07 mV rms (60 Hz) sinewave is imposed onto
the VA+ and VD+ pins. The “+” and “-” input pins of both input channels are shorted to VA-. 2048
instantaneous digital output data words are collected for the channel under test. The rms value of the
digital sinusoidal output signal is calculated, and this rms value is converted into the rms value of the
sinusoidal voltage (measured in mV) that would need to be applied at the channel’s inputs, in order to
cause the same digital sinusoidal output. This voltage is then defined as Veq. PSRR is then (in dB):
106.07
------------- ---
log⋅=
V
eq
DIGITAL CHARACTERISTICS (T
PSRR20
= -40 °C to +85 °C; +2.7V < VA+ < +3.5V; +2.7V < VD+ < +3.5V;
A
VA- = -2 V ±10%; AGND, DGND = 0.0 V) (See Note 6)
ParameterSymbol Min TypMaxUnit
High-Level Input VoltageV
Low-Level Input VoltageV
High-Level Output VoltageI
Low-Level Output VoltageI
= -5.0 mAV
out
= 5.0 mAV
out
Input Leakage Current(Note 7)I
3-State Leakage CurrentI
Digital Output Pin CapacitanceC
OH
OL
in
OZ
out
IH
0.6 VD+-VD+V
IL
0.0-0.8V
(VD+) - 1.0--V
--0.4V
-±1±10µA
--±10µA
-9-pF
Notes: 6. All measurements performed under static conditions.
Notes: 12. Device parameters are specified with a 4.000 MHz clock, OWRS = 1.
13. Specified using 10% and 90% points on wave-form of interest. Output loaded with 50 pF.
SDO
SCLK
FSO
SE
t
5
t
6
MSB(V1) MSB(V1) - 1LSB(I3)
t
3
t
t
1
2
t
4
t
6
Figure 1. Serial Port Timing
6DS458PP4
CS5451
2. GENERAL DESCRIPTION
The CS5451 is designed for 3-phase power meter
applications and interfaces to a current transformers or shunt to measure current, and a resistive divider or transformer to measure voltage.
The CS5451 combines six ∆Σ modulators and decimation filters, three channels assigned for current
input that have programmable input gain amplifiers, and three channels assigned for voltage input.
The CS5451 includes six decimation filters that
output data at a 2000 Hz or 4000 Hz output word
rate (OWR) when the input frequency at XIN =
4.096 MHz.
+3 V
The device outputs data on a serial output port.
2.1Theory of Operation
The CS5451 is designed to operate from a single
+3V supply and provides a ±40 mV and ±800 mV
input range for the current channels and ±800 mV
range for the voltage channels. These voltages represent the maximum zero-to-peak voltage levels
that can be presented to the inputs. The CS5451 is
designed to accommodate common mode + signal
levels from VA- to VA+. Figure 2 illustrates the
CS5451 typical inputs and power supply connections.
VA+
REFIN
VD+
V
PHASE
I
PHASE
Optional
External
Reference
+
1.2 V
-2 V
REFOUT
VIN1+, VIN2+, or VIN3+
VIN1-, VI N2-, or VIN3-
IIN1+, IIN2+, or IIN3+
NOTE:
Current input channels
actually measure voltage.
IIN1-, IIN2-, or IIN3-
AGND
VA-
DGND
Figure 2. Typical Connection Diagram
DS458PP47
CS5451
2.2Performing Measurements
The converter outputs are transferred in 16-bit
signed (two’s complement) data formats as a percentage of full scale. Table 1 below illustrates the
ideal relationship between the differential voltage
presented any one of the input channels and the
corresponding output code. Note that for the current channels, the state of the GAIN input pin is assumed to driven low such that the PGA gain on the
current channels is 1x. If the PGA gain of the current channels is set to 20x, a +40 mV differential
voltage is presented across any pair of “IINk+” and
“IINk-” pins (k = 1, 2, 3) would cause a (nominal)
output code of 32767.
Differential Input
Voltage (mV)
+8007FFF32767
0.0122 to 0.036600011
-0.0122 to 0.012200000
-0.0122 to -0.0366FFFF-1
-8008000-32768
Table 1. Nominal Relationship for Differential Input
Voltage vs. Output Code, for all channels. (Assume PGA
Output Code
(hexadecimal)
gain is set to 1x.)
Output Code
(decimal)
2.3High Rate Digital Filters
If the OWRS pin is set to logic low, the high-rate
filters are implemented as fixed sinc3 filters with
the following transfer function:
3
256–
–
1z
–
1–
Hz()
1z
--------------- -------
=
This filter samples the modulator bit stream at
XIN/8 Hz and decimates to XIN/2048 Hz.
If the OWRS pin is set to logic high, then the transfer function is
3
128–
–
1z
–
1–
Hz()
1z
--------------- -------
=
The above filter samples the modulator bit stream
at XIN/8 Hz and decimates to XIN/1024 Hz.
2.4Serial Interface
The CS5451 communicates with a target device via
a master serial data output port. Output data is provided on the SDO output synchronous with the
SCLK output. A third output, FSO, is a framing
signal used to signal the start of output data. These
three outputs will be driven as long as the SE (serial
SCLK
96 SCLKs
FSO
Each data segment
is 16 bits long.
SDO
Channel 1 V
Channel 1 I
Channel 2 V
8DS458PP4
Channel 2 I
Channel 3 I
Channel 3 V
Figure 3. Serial Port Data Transfer
SCLK
96 SCLKs
. . .
CS5451
. . .
FSO
3
012
151413 12 11 10 9 8 7654321
Figure 4. Close-up of One Data Frame
SDO
[ Undefined ]
12151413
1011
Channel 1 ( V )
enable) input is held high. Otherwise, these outputs
will be high impedance.
Data out (SDO) changes as a result of SCLK falling, and always outputs valid data with SCLK rising. When data is being transferred, the SCLK
frequency is either 1/8 of the XIN input frequency
(when OWRS is held low) or 1/4 of the XIN input
frequency (when OWRS is held high). Any other
time, SCLK is held low. (See Figures 3 and 4.)
The framing signal (FSO) output is normally low,
but produces a high level pulse lasting one SCLK
period when the instantaneous voltage/current data
samples are about to be transmitted out of the serial
interface (after each A/D conversion cycle). Note:
SCLK is not active during FSO high.
For 96 SCLK periods after FSO falls, SCLK is active and SDO produces valid output. Six channels
of 16 bit data are output, MSB first. Voltage and
current measurements are output (in that order) for
three phases. SCLK will then be held low until the
next sample period.
2.5System Initialization
When power to the CS5451 is applied, the chip
must be held in a reset condition using the RESET
input.
A hardware reset is initiated when the RESET pin
is forced low with a minimum pulse width of 50 ns.
. . .
01514
. . .
0123456789
. . .
Channel 1 (I )
.........
Ch. 2 ( V ) Ch. 2 ( I )
Ch. 3 ( V ) Ch. 3 ( I )
[ Undefined ]
2.6Analog Inputs
The analog inputs of the CS5451 are bipolar voltage inputs: Three voltage channel inputs VIN(1-3)
and three current channel inputs IIN(1-3). The
CS5451 accommodates a full scale range of
±40 mV or ±800 mV on the Current Channels and
±800 mV on the Voltage Channels.
2.7Voltage Reference
The CS5451 is specified for operation with a +1.2
V reference between the VREFIN and AGND pins.
The converter includes an internal 1.2 V reference
(50 ppm/°C drift) that can be used by connecting
the VREFOUT pin to the VREFIN pin of the device. If higher accuracy/stability is required, an external reference can be used.
2.8Power Supply
The low, stable analog power consumption and superior supply rejection of the CS5451 allow for the
use of a simple charge-pump negative supply generator. The use of a negative supply alleviates the
need for level shifting of the analog inputs. The
CPD pin and capacitor C1 provide the necessary
analog supply current as shown in Figure 5. The
Schottky diodes D1 and D2 are chosen for their low
forward voltages and high-speed capabilities. The
capacitor C2 provides the required charge storage
and bypassing of the negative supply. The CPD
output signal provides the charge pump driver sig-
. . .
. . .
DS458PP49
CS5451
AGND
BAT 85
D1
C1
40 nF
C2
CPD
VA-
BAT 85
1µF
D2
Figure 5. Generating VA- with a Charge Pump
nal. The frequency of the charge pump driver signal is synchronous to XIN. The nominal average
frequency is 1 Mhz. The level on the VA- pin is fed
back internally so that the CPD output will regulate
the VA- level to -2/3 of VA+ level.
Note the value of C1 in Figure 5. The 40 nF value
is recommended when the input frequency presented to the XIN pin is 4.00 MHz. If the user decides
to use an XIN frequency that is significantly different than 4.00 MHz (if the XIN frequency is increased/decreased by more than 5% of 4.00 MHz,
then it is recommended that the user should alter
the value of C1. The percentage change in the value
of C1 (with respect to a reference value of 40 nF)
should be inversely proportional to the percentage
change in the XIN frequency. For example, if the
XIN frequency is increased from 4.00 MHz to 4.5
MHz, this represents a percentage increase of
12.5%. Therefore, the value of C1 should be reduced by 12.5%, making the new value for C1 to be
35 nF. For more information about the operation of
this type of charge pump circuit, the reader can refer to Cirrus Logic, Inc.’s application note AN152:
Using the CS5521/24/28, and CS5525/26 Charge
Pump Drive for External Loads.
2.9PCB Layout
For optimal performance, the CS5460A should be
placed entirely over an analog ground plane with
both the VA- and DGND pins of the device connected to the analog plane. Place the analog-digital
plane split immediately adjacent to the digital portion of the chip.
Note: Refer to the CDB5460A Evaluation Board for
suggested layout details and Applications Note
18 for more detailed layout guidelines. Before
layout, please call for our Free Schematic
Review Service.
10DS458PP4
3.PIN DESCRIPTION
CS5451
Serial Clock OutputSCLKVD+Digital Supply
Serial Data OutputSDODGNDDigital Ground
Frame SyncFSOCPDCharge Pump Drive
Serial Port EnableSEXINMaster Clock
Current Input GainGAINRESETReset
Analog GroundAGNDOWRSOutput Word Rate Select
Reference InputVREFINVIN1+Differential Voltage Input 1
Reference Output VREFOUTVIN1-Differential Voltage Input 1
Positive Analog SupplyVA+IIN1+Differential Current Input 1
Negative Analog SupplyVA-IIN1-Differential Current Input 1
Differential Voltage Input 3VIN3+VIN2+Differential Voltage Input 2
Differential Voltage Input 3VIN3-VIN2-Differential Voltage Input 2
Differential Current Input 3IIN3+IIN2+Differential Current Input 2
Differential Current Input 3IIN3-IIN2-Differential Current Input 2
Clock Generator
XIN - Master Clock Input
Control Pins and Serial Data I/O
1
2
3
4
5
6
7
8
9
10
11
12
13
14
28
27
26
25
24
23
22
21
20
19
18
17
16
15
SE - Serial Port Enable
When SE is low, the output pins of the serial port are 3-stated.
SDO - Serial Port Output
Data will be at a rate determined by SCLK.
FSO - Frame Signal Output
Framing signal output for data transfer from SDO pin.
SCLK - Serial Clock Output
A clock signal on this pin determines the output rate of data for SDO pin. Rate of SCLK is determined
by XIN frequency and state of OWRS input pin.
RESET - Reset
When reset is taken low, all internal registers are set to their default states.
GAIN - Input Gain Control
Sets input gain for current channels. A logic high sets internal gain to 1, a logic low level sets the gain
to 20. If no connection is made to this pin, it will default to logic low level (through internal 200K
resistor to DGND).
OWRS - Output Word Rate Select
When OWRS is set to logic low, the output word rate (OWR) at SDO pin is XIN/2048 (Hz). When set to
logic high, the OWR at SDO pin is XIN/1024 (Hz). If no connection is made to this pin, then OWRS will
default to logic low level (through internal 200K resistor to DGND).
DS458PP411
Measurement and Reference Input
IIN(1-3)+, IIN(1-3)- - Differential Current Inputs
Differential analog input pins for current channels.
VIN(1-3)+, VIN(1-3)- - Differential Voltage Inputs
Differential analog input pins for voltage channels.
VREFOUT - Voltage Reference Output
The on-chip voltage reference is output from this pin. The voltage reference has a nominal magnitude of
1.2 V and is referenced to the AGND pin on the converter.
VREFIN - Voltage Reference Input
The voltage input to this pin establishes the voltage reference for the on-chip modulator.
Power Supply Connections
VA+ - Positive Analog Supply
The positive analog supply is nominally +3 V ±10% relative to AGND.
CS5451
VA- - Negative Analog Supply
The negative analog supply is nominally -2 V ±10% relative to AGND.
AGND - Analog Ground
The analog ground pin for input signals.
VD+ - Positive Digital Supply
The positive digital supply is nominally +3 V ±10% relative to DGND.
DGND - Digital Ground
The digital ground is typically at the same level as AGND.
CPD - Charge Pump Drive
This output pin drives the external charge pump circuitry to create a negative supply voltage.
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.
DS458PP413
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