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8-Channel, Software Selectable True bipolar Input, 12-Bit Plus Sign ADC Preliminary Technical Data AD7328*
FEATURES
* 12-Bit plus Sign SAR ADC * True Bipolar Input Ranges * Software Selectable Input Ranges 10V, 5V, 2.5V, 0 to 10V * 1 MSPS Throughput Rate * Eight Analog Input Channels with Channel Sequencer * Single Ended, True Differential and Pseudo Differential Analog Input Capability * High Analog Input Impedance * Low Power:- 26 mW max * Full Power Signal Bandwidth: 7 MHz * Internal 2.5 V Reference * High Speed Serial Interface * Power Down Modes * 20-Lead TSSOP package * iCMOSTM Process Technology * For four and two channel equivalent devices see AD7324 and AD7322 respectively.
FUNCTIONAL BLOCK DIAGRAM
VDD REFIN/OUT VCC
Vin0 Vin1 Vin2 Vin3 Vin4 Vin5 Vin6 Vin7 I/P MUX T/H
2.5V VREF 13-BIT SUCCESSIVE APPROXIMATION ADC
CHANNEL SEQUENCER
CONTROL LOGIC & REGISTERS
DOUT SCLK +5 DIN
VDRIVE
AGND
VSS
DGND
Figure 1.
GENERAL DESCRIPTION
The AD7328 is an 8-Channel, 12-Bit plus Sign Successive Approximation ADC. The ADC has a high speed serial interface that can operate at throughput rates up to 1 Msps. The AD7328 can accept true bipolar Analog Input signals. The AD7328 has four software selectable inputs Ranges, 10V, 5V, 2.5V and 0 to 10V. Each analog input channel can be independently programmed to one of the four input ranges. The Analog input channels on the AD7328 can be programmed to be Single-Ended, true Differential or Pseudo Differential. The ADC contains a 2.5V Internal reference. The AD7328 also allows for external Reference operation. If a 3V reference is applied the REF IN/OUT pin the AD7328 can accept a true Bipolar 12V Analog Input. VDD and VSS supplies of 12V are required for the 12V Input Range.
PRODUCT HIGHLIGHTS
1. The AD7328 can accept True Bipolar Analog Input signals, 10V, 5V, 2.5V and 0 to 10V unipolar signals. 2. The Eight Analog Inputs can be configured as 8 Single-Ended inputs, 4 True Differential, 4 Pseudo Differential or 7 Pseudo Differential Inputs. 3. The AD7328 features a High Speed Serial Interface. Throughput Rates up to 1 MSPS can be achieved. 4. Low Power, 26 mW at maximum throughput rate of 1 MSPS. 5. Channel Sequencer..
Device Number AD7324 AD7322
Number of bits 12 bit + Sign 12 bit + Sign
Number of Channels 4 2
* Protected by U.S. Patent No. 6,731,232
iCMOSTM Process Technology For analog systems designers within industrial/instrumentation equipment OEMs who need high performance ICs at higher-voltage levels, iCMOS is a technology platform that enables the development of analog ICs capable of 30V and operating at +/- 15V supplies while allowing dramatic reductions in power consumption and package size, and increased AC and DC performance.
Rev. PrK
Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Specifications subject to change without notice. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Trademarks and registered trademarks are the property of their respective companies.
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Preliminary Technical Data
TABLE OF CONTENTS
AD7328--SPECIFICATIONS ............................ 3 ABSOLUTE MAXIMUM RATINGS ................. 7 PIN FUNCTIONAL DESCRIPTIONS........................... 8 TERMINOLOGY ................................................ 9 THEORY OF OPERATION....................................... 10 AD7328 REGISTERS........................................ 14
REVISION HISTORY
Revision PrK: Preliminary Version
AD7328
SEQUENCER OPERATION............................. 18 MODES OF OPERATION ................................ 22 SERIAL INTERFACE ....................................... 23 OUTLINE DIMENSIONS................................. 24
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Preliminary Technical Data
AD7328--SPECIFICATIONS1
AD7328
Table 1. Unless otherwise noted, VDD = + 12V to +16.5V, VSS = -12V to -16.5V, VCC = 2.7V to 5.25V, VDRIVE = 2.7V to 5.25V, VREF = 2.5V Internal/External, fSCLK = 20 MHz, fS = 1 MSPS TA = TMAX to TMIN
Parameter DYNAMIC PERFORMANCE Signal to Noise Ratio (SNR) 2 Signal to Noise + Distortion (SINAD)2 Total Harmonic Distortion (THD)2 Peak Harmonic or Spurious Noise (SFDR) 2 Intermodulation Distortion (IMD) 2 Second Order Terms Third Order Terms Aperature Delay Aperature Jitter Common Mode Rejection (CMRR) Channel-to-Channel Isolation Full Power Bandwidth DC ACCURACY Resolution Integral Nonlinearity2 Differential Nonlinearity2 Offset Error2 Offset Error Match Gain Error2 Gain Error Match Positive Full-Scale Error2 Positive Full Scale Error Match Bipolar Zero Error2 Bipolar Zero Error Match Negative Full Scale Error2 Negative Full Scale Error Match ANALOG INPUT Input Voltage Ranges (Programmed via Range Register) Specification 76 72 75 71.5 -80 -80 -88 -88 10 50 TBD -80 7 1.5 12 + Sign 1.5 0.95 8 0.5 6 0.6 3 0.6 8 0.5 4 0.5 10V 5V 2.5V 0 to 10V 10 12 15 20 3 Units dB min dB min dB min dB min dB max dB max Fa = 40.1 kHz, Fb = 41.5 kHz dB typ dB typ ns max ps typ dB typ dB typ MHz typ MHz typ Bits LSB max LSB max LSB max LSB max LSB max LSB max LSB max LSB max LSB max LSB max LSB max LSB max Volts Test Conditions/Comments FIN = 50 kHz Sine Wave Differential Mode Single-Ended/Pesudo Differential Mode Differential Mode Single-Ended/Pseudo Differential Mode
FIN = 400 kHz @ 3 dB @ 0.1 dB
Guaranteed No missing Codes to 13-Bits Unipolar Range with Straight Binary output coding
Bipolar Range with Twos Complement Output Coding
VDD = +10V min , VSS = -10V min, VCC = 2.7V to 5.25V VDD = +5V min, VSS = -5V min, VCC = 2.7V to 5.25V VDD = +5V min, VSS = - 5V min, VCC = 2.7V to 5.25V VDD = +10V min, VSS = AGND min, VCC = 2.7V to 5.25V See Table 5 When in Track, 10V Range When in Track, 5V, 0 to 10V Range When in Track, 2.5V Range When in Hold
DC Leakage Current Input Capacitance
nA max pF typ pF typ pF typ pF typ
REFERENCE INPUT/OUTPUT Input Voltage Range Input DC Leakage Current Input Capactiance Reference Output Voltage
Rev. PrK | Page 3 of 24
+2.5 to +3V 1 20 2.49/2.51
V min to max A max pF typ Vmin/max
AD328
Parameter Reference Temperature Coefficient Reference Output Impedance LOGIC INPUTS Input High Voltage, VINH Input Low Voltage, VINL Input Current, IIN Input Capacitance, CIN3 LOGIC OUTPUTS Output High Voltage, VOH Output Low Voltage, VOL Floating State Leakage Current Floating State Output Capacitance3 Output Coding Specification 25 10 25 2.4 0.8 0.4 1 10 Units ppm/C max ppm/C typ typ V min V max V max A max pF max
Preliminary Technical Data
Test Conditions/Comments
VCC = 4.75 to 5.25 V VCC = 2.7 to 3.6 V VIN = 0V or VCC
VDRIVE- 0.2V 0.4 1 10 Straight Natural Binary Two's Complement 800 200 200 1
V min V max A max pF max
ISOURCE = 200 A ISINK = 200 A
Coding bit set to 1 in Control Register
Coding bit set to 0 in Control Register
CONVERSION RATE Conversion Time Track-and-Hold Acquisition Time Throughput Rate POWER REQUIREMENTS VDD4 VSS4 VCC VDRIVE Normal Mode IDD ISS ICC Auto-Standby Mode IDD ISS ICC Auto-Standby Mode IDD ISS ICC Full Shutdown Mode IDD ISS ICC POWER DISSIPATION Normal Mode Full Shutdown Mode
ns max ns max ns max MSPS max
16 SCLK Cycles with SCLK = 20 MHz Sine Wave Input Full Scale Step input See Serial Interface section Digital Inputs = 0V or VCC See Table 5 See Table 5 See Table 5
12V/+16.5V -12V/16.5V 2.7V / 5.25V 2.7V/5.25V
V min/max V min/max V min/max V min/max
300 370 2 TBD TBD 1.6 TBD TBD 1 0.9 0.9 0.9
A max A max mA max A max A max mA typ
VDD = +16.5V VSS = -16.5V VCC = 5.25V FSAMPLE = TBD
FSAMPLE = TBD A max A max mA typ A max A max A max
SCLK On or Off
26 35
mW max W max
VDD = +16.5V, VSS = -16.5V, VCC = 5.25V, VDD = +16.5V, VSS = -16.5V, VCC = 5.25V,
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Preliminary Technical Data
AD7328
NOTES 1 Temperature ranges as follows: -40C to +85C 2 See Terminology 3 Guaranteed by initial Characterization 4 Functional from VDD = +4.75V and VSS = -4.75 Specifications subject to change without notice.
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Preliminary Technical Data
TIMING SPECIFICATIONS
2.5V Internal/External, TA = TMAX to TMIN
Parameter fSCLK tCONVERT tQUIET t1 t2 t3 t4 t5 t6 t7 t8 t9 t10 Limit at TMIN, TMAX 10 20 16xtSCLK 50 10 10 20 TBD 0.4tSCLK 0.4tSCLK 10 25 10 TBD 5 1 TBD Unit kHz min MHz max ns max ns max ns min ns min ns max ns max ns min ns min ns min ns max ns min ns min ns min s max s max Description
AD7328
Table 2. Unless otherwise noted, VDD = +12V to + 16.5V, VSS = -12 to -16.5V, VCC =2.7V to 5.25, VDRIVE=2.7V to 5.25, VREF =
TSCLK = 1/fSCLK Minimum Time between End of Serial Read and Next Falling Edge of CS Minimum CS pulse width CS to SCLK Setup Time Delay from CS until DOUT Three-State Disabled Data Access Time after SCLK Falling Edge. SCLK Low Pulsewidth SCLK High Pulsewidth SCLK to Data Valid Hold Time SCLK Falling Edge to DOUT High Impedance SCLK Falling Edge to DOUT High Impedance DIN set-up time prior to SCLK falling edge DIN hold time after SCLK falling edge Power up from Auto Standby Power up from Full Shutdown/Auto Shutdown Mode
Figure 2. Serial Interface timing Diagram
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Preliminary Technical Data
ABSOLUTE MAXIMUM RATINGS
Table 3. TA = 25C, unless otherwise noted
VDD to AGND, DGND VSS to AGND, DGND VCC to AGND, DGND VDRIVE to VCC AGND to DGND Analog Input Voltage to AGND Digital Input Voltage to DGND Digital Output Voltage to GND REFIN to AGND Input Current to Any Pin Except Supplies2 Operating Temperature Range Storage Temperature Range Junction Temperature TSSOP Package JA Thermal Impedance JC Thermal Impedance Pb/SN Temperature, Soldering Reflow (10 s to 30 s) Pb-free Temperature, Soldering Reflow ESD -0.3 V to +16.5 V +0.3 V to -16.5 V -0.3V to +7V -0.3 V to VCC + 0.3V -0.3 V to +0.3 V VSS -0.5V to +VDD + 0.5V -0.3 V to +7 V -0.3 V to VDRIVE +0.3V -0.3 V to VCC +0.3V 10mA -40C to +85C -65C to +150C +150C 143 C/W 45 C/W 240(+0/-5)C 260(+0)C TBD
AD7328
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Preliminary Technical Data
Pin Functional Descriptions
CS 1 DIN 2 DGND 3 AGND 4 REFIN/OUT 5 VSS 6 VIN0 7 VIN1 8 VIN4 9 VIN5 10 20 SCLK 19 DGND
AD7328
AD7328
18 DOUT 17 VDRIVE 16 VCC
DD TOP VIEW 14 VIN2 (Not to Scale) 13 VIN3 12 VIN6 11 VIN7
15 V
Figure 3. AD7328 Pin Configuration TSSOP
Table 4. AD7328 Pin Function Descriptions Pin Mnemonic SCLK DOUT Pin Number 20 18 Description Serial Clock. Logic Input. A serial clock input provides the SCLK used for accessing the data from the AD7328. This clock is also used as the clock source for the conversion process. Serial Data Output. The conversion output data is supplied to this pin as a serial data stream. The bits are clocked out on the falling edge of the SCLK input and 16 SCLKs are required to access the data. The data stream consists of three channel identification bits, followed by the sign bit followed by the 12 bits of conversion data. The data is provided MSB first. See the Serial Interface section. Chip Select. Active low logic input. This input provides the dual function of initiating conversions on the AD7328 and frames the serial data transfer. Data In. Data to be written to the on-chip registers is provided on this input and is clocked into the register on the falling edge of SCLK. See Register section. Logic power supply input. The voltage supplied at this pin determines at what voltage the interface will operate. This pin should be decoupled to DGND. The voltage at this pin may be different to that at VCC but should never exceed VCC by more than 0.3V. Digital Ground. Ground reference point for all digital circuitry on the AD7328. The DGND and AGND voltages ideally should be at the same potential and must not be more than 0.3 V apart even on a transient basis. Analog Ground. Ground reference point for all analog circuitry on the AD7328. All analog input signals and any external reference signal should be referred to this AGND voltage. The AGND and DGND voltages ideally should be at the same potential and must not be more than 0.3 V apart, even on a transient basis. Reference Input/ Reference Output pin. The on-chip reference is available on this pin for use external to the AD7328. Alternativley, the internal reference can be disabled and an external reference applied to this input. On power up this is the default condition. The nominal internal reference voltage is 2.5 V, which appears at the pin. A 470 nF capacitor should be placed on the Reference pin. (See Reference Section) Analog Supply Voltage, 2.7 V to 5.25 V. This is the supply voltage for the ADC core on the AD7328. This supply should be decoupled to AGND. Positive power supply voltage. This is the positive supply voltage for the Analog Input section. Negative power supply voltage. This is the negavtive supply voltage for the Analog Input section. Analog input 0 through Analog Input 7. The analog inputs are multiplexed into the on-chip track-and-hold. The analog input channel for conversion is selected by programming the channel address bits, ADD2 through ADD0, in the control register. The inputs can be configured as 8 Single-Ended Inputs, 4 True Differential Input pairs, 4 Pseudo differential inputs or 7 pseudo differential inputs. The configuration of the Analog inputs is selected by programming the Mode bits, Mode1 and Mode0, in the Control Register. The input range on each input channel is controlled by programming the range registers. Inputs ranges of 10V, 5V, 2.5V and 0 to 10V can be selected on each analog input channel. See Register section.
CS DIN VDRIVE
1 2 17
DGND
3, 19
AGND
4
REF IN/REFOUT
5
VCC VDD VSS Vin0-Vin7
16 15 6 7,8,9,10,11,12,13,14
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Preliminary Technical Data
TERMINOLOGY
Differential Nonlinearity This is the difference between the measured and the ideal 1 LSB change between any two adjacent codes in the ADC. Integral Nonlinearity This is the maximum deviation from a straight line passing through the endpoints of the ADC transfer function. The endpoints of the transfer function are zero scale, a point 1 LSB below the first code transition, and full scale, a point 1 LSB above the last code transition. Offset Code Error This applies to Straight Binary output coding. It is the deviation of the first code transition (00 . . . 000) to (00 . . . 001) from the ideal, i.e., AGND + 1 LSB. Offset Error Match This is the difference in Offset Error between any two input channels. Gain Error This applies to Straight Binary output coding. It is the deviation of the last code transition (111 . . . 110) to (111 . . . 111) from the ideal (i.e., 4 x VRef - 1 LSB, 2 x VREF -1 LSB, VREF -1 LSB) after the offset error has been adjusted out. Gain Error Match This is the difference in Gain Error between any two input channels channels. Bipolar Zero Code Error This applies when using twos complement output coding and a bipolar Analog Input. It is the deviation of the midscale transition (all 1s to all 0s) from the ideal VIN voltage, i.e., AGND - 1 LSB. Bipolar Zero Code Error Match This refers to the difference in Bipolar Zero Code Error between any two input channels. Positive Full Scale Error This applies when using twos complement output coding and any of the bipolar Analog Input ranges. It is the deviation of the last code transition (011...110) to (011...111) from the ideal ( +4 x VREF - 1 LSB, + 2 x VREF - 1 LSB, + VREF - 1 LSB) after the bipolar Zero Code Error has been adjusted out. Positive Full Scale Error Match This is the difference in Positive Full Scale error between any two input channels. Negative Full Scale Error This applies when using twos complement output coding and any of the bipolar Analog Input ranges. This is the deviation of the first code transition (10...000) to (10...001) from the ideal
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AD7328
(i.e., - 4 x VREF + 1 LSB, - 2 x VREF + 1 LSB, - VREF + 1 LSB) after the Bipolar Zero Code Error has been adjusted out. Negative Full Scale Error Match This is the difference in Negative Full Scale error between any two input channels. Track-and-Hold Acquisition Time The track-and-hold amplifier returns into track mode after the fifteenth SCLK falling edge. Track-and-hold acquisition time is the time required for the output of the track-and-hold amplifier to reach its final value, within 1/2 LSB, after the end of conversion. Signal to (Noise + Distortion) Ratio This is the measured ratio of signal to (noise + distortion) at the output of the A/D converter. The signal is the rms amplitude of the fundamental. Noise is the sum of all non-fundamental signals up to half the sampling frequency (fS/2), excluding dc. The ratio is dependent on the number of quantization levels in the digitization process; the more levels, the smaller the quantization noise. The theoretical signal to (noise + distortion) ratio for an ideal N-bit converter with a sine wave input is given by: Signal to (Noise + Distortion) = (6.02N + 1.76) dB Thus for a 13-bit converter, this is 80.02 dB. Total Harmonic Distortion Total harmonic distortion (THD) is the ratio of the rms sum of harmonics to the fundamental. For the AD7328 it is defined as:
V + V3 + V4 + V5 + V6 THD(dB) = 20 log 2 V1
2 2 2 2
2
where V1 is the rms amplitude of the fundamental and V2, V3, V4, V5 and V6 are the rms amplitudes of the second through the sixth harmonics. Peak Harmonic or Spurious Noise Peak harmonic or spurious noise is defined as the ratio of the rms value of the next largest component in the ADC output spectrum (up to fS/2 and excluding dc) to the rms value of the fundamental. Normally, the value of this specification is determined by the largest harmonic in the spectrum, but for ADCs where the harmonics are buried in the noise floor, it will be a noise peak. Channel-to-Channel Isolation Channel-to-channel isolation is a measure of the level of crosstalk between any two channels. It is measured by applying a full-scale, 400 kHz sine wave signal to all unselected input channels and determining how much that signal is attenuated in
AD7328
the selected channel with a 50 kHz signal. The figure given is the worst-case across all eight channels for the AD7328. Intermodulation Distortion With inputs consisting of sine waves at two frequencies, fa and fb, any active device with non-linearities will create distortion products at sum and difference frequencies of mfa nfb where m, n = 0, 1, 2, 3, etc. Intermodulation distortion terms are those for which neither m nor n are equal to zero. For example, the second order terms include (fa + fb) and (fa - fb), while the third order terms include (2fa + fb), (2fa - fb), (fa + 2fb) and (fa - 2fb). The AD7328 is tested using the CCIF standard where two input frequencies near the top end of the input bandwidth are used. In this case, the second order terms are usually distanced in frequency from the original sine waves while the third order terms are usually at a frequency close to the input frequencies. As a result, the second and third order terms are specified separately. The calculation of the intermodulation distortion is as per the THD specification where it is the ratio of the rms sum of the individual distortion products to the rms amplitude of the sum of the fundamentals expressed in dBs. PSR (Power Supply Rejection) Variations in power supply will affect the full-scale transition but not the converter's linearity. Power supply rejection is the maximum change in full-scale transition point due to a change in power supply voltage from the nominal value. See Typical Performance Curves.
Selected Analog Input Range (V) 10 5 2.5 0 to 10
Preliminary Technical Data
Reference Voltage (V) 2.5 3.0 2.5 3.0 2.5 3.0 2.5 3.0 Full Scale Input Range(V) 10 12 5 6 2.5 3 0 to 10 0 to 12 AVCC (V) Minimum VDD/VSS (V)
3/5 3/5 3/5 3/5 3/5 3/5 3/5 3/5
10 12 5 6 5 5 +10/AGND +12/AGND
Table 5. Reference and Supply Requirements for each Analog Input Range
In order to meet the specified performance specifications when the AD7328 is configured with the minimum VDD and VSS supplies for a chosen Analog input range the throughput rate should be decreased from the maximum throughput range. See typical performance curves. The Analog Inputs can be configured as either 8 Single-Ended inputs, 4 True Differential Inputs, 4 Pseudo Differential Inputs or 7 Pseudo Differential Inputs. Selection can be made by programming the Mode bits, Mode0 and Mode1, in the Control Register. The serial clock input accesses data from the part but also provides the clock source for each successive approximation ADC. The AD7328 has an on-chip 2.5 V reference. However the AD7328 can also work with an external Reference. On power up the external reference operation is the default option. If the internal Reference is the preferred option the user must write to the reference bit in the control register to select the internal Reference operation. The AD7328 also features power-down options to allow power saving between conversions. The power-down modes are selected by programming the on-chip Control Register, as described in the Modes of Operation section.
Theory of Operation
CIRCUIT INFORMATION The AD7328 is a fast, 8-Channel, 12-bit plus sign, bipolar Input, serial A/D converter. The AD7328 can accept bipolar input ranges that include 10V, 5V, 2.5V, it can also accept 0 to 10V unipolar input range. A different Analog input range can be programmed on each analog input channel via the on-chip registers. The AD7328 has a high speed serial interface that can operate at throughput rates up to 1 MSPS. The AD7328 requires VDD and VSS dual supplies for the high voltage Analog input structures. These supplies must be equal to or greater than the Analog input range. See Table 5 for the requirements on these supplies for each Analog Input Range. The AD7328 requires a low voltage 2.7V to 5.25 V VCC supply to power the ADC core.
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Preliminary Technical Data
CONVERTER OPERATION The AD7328 is a successive approximation analog-to-digital converter, based around two capacitive DACs. Figure 4 and Figure 5 show simplified schematics of the ADCs in Single Ended Mode during the acquisition and conversion phase, respectively. Figure 6 and Figure 7 show simplified schematics of the ADCs in Differential Mode during acquisition and conversion phase, respectively. The ADC is comprised of control logic, a SAR, and a capacitive DAC. In Figure 4 (the acquisition phase), SW2 is closed and SW1 is in position A, the comparator is held in a balanced condition, and the sampling capacitor array acquires the signal on the input.
B A SW1 A SW2 CS B VREF CS SW3 COMPARATOR CAPACITIVE DAC CONTROL LOGIC
AD7328
Vin+ Vin-
CAPACITIVE DAC
Figure 7. ADC Differential Configuration during Conversion Phase
Vin0
B A SW1 AGND
CS SW2
COMPARATOR
CAPACITIVE DAC CONTROL LOGIC
Output Coding The AD7328 default output coding is set to two's complement. The output coding is controlled by the Coding bit in the Control Register. To change the output coding to Straight Binary Coding the Coding bit in the Control Register must be set. When operating in Sequence mode the output coding for each channel in the sequence will be the value written to the coding bit during the last write to the Control Register. Transfer Functions The designed code transitions occur at successive integer LSB values (i.e., 1 LSB, 2 LSB, and so on). The LSB size is dependant on the Analog input Range selected.
Figure 4. ADC Acquisition Phase(Single Ended)
When the ADC starts a conversion (Figure 5), SW2 will open and SW1 will move to position B, causing the comparator to become unbalanced. The control logic and the charge redistribution DAC is used to add and subtract fixed amounts of charge from the capacitive DAC to bring the comparator back into a balanced condition. When the comparator is rebalanced, the conversion is complete. The Control Logic generates the ADC output code
CAPACITIVE DAC CONTROL LOGIC
Input Range 10V 5V 2.5V 0 to 10V
Full Scale Range/8192 20V/8192 10V/8192 5V/8192 10V/8192
LSB Size 2.441 mV 1.22 mV 0.61 mV 1.22 mV
Vin0
B A SW1 AGND
CS SW2
COMPARATOR
Table 6. LSB sizes for each Analog Input Range
Figure 5. ADC Conversion Phase(Single Ended)
Figure 6 shows the differential configuration during the Acquisition phase. For the Conversion Phase, SW3 will open, SW1 and SW2 will move to position B, Figure 7. The output impedances of the source driving the Vin+ and Vin- pins must be matched; otherwise the two inputs will have different settling times, resulting in errors.
CAPACITIVE DAC CONTROL LOGIC
The ideal transfer characteristic for the AD7328 when Twos Complement coding is selected is shown in Figure 8, and the ideal transfer characteristic for the AD7328 when Straight Binary coding is selected is shown in Figure 9.
Vin+ Vin-
B A SW1 A SW2
CS SW3
COMPARATOR
Figure 8 Twos Complement Transfer Characteristic (Bipolar Ranges)
CS B VREF
CAPACITIVE DAC
Figure 6. ADC Differential Configuration during Acquisition Phase
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AD7328
Preliminary Technical Data
lumped component made up of the on-resistance of the input multiplexer and the track-and-hold switch. The Capacitor C2, is the sampling capacitor, its capacitance will vary depending on the Analog input range selected. (See specifications section) Track-and-Hold Section The Track-and-Hold on the Analog Input of the AD7328 allows the ADC to accurately convert an input sine wave of full scale amplitude to 13-Bit accuracy. The input bandwidth of the Track-and-Hold is greater than the Nyquist rate of the ADC , the AD7328 can handle frequencies up to 7 MHz. The Track-and-Hold enters its tracking mode on the 15th SCLK falling edge after the CS falling edge. The time required to acquire an input signal will depend on how quickly the sampling capacitor is charged. With zero source impedance 200 ns will be sufficient to acquire the signal to the 13-bit level. The acquisition time required is calculated using the following formula: tACQ = 10 x ((RSOURCE + R) C) where C is the Sampling Capacitance and R is the resistance seen by the track-and-hold amplifier looking back on the input. For the AD7328, the value of R will include the on-resistance of the input multiplexer. The value of R is typically 300 . RSOURCE should include any extra source impedance on the Analog input. The AD7328 enters track on the fifteenth SCLK falling edge. When running the AD7328 at a throughput rate of 1 MSPS with a 20 MHz SCLK signal the ADC will have approx. 1 SCLK period plus t8 plus the quiet time, TQUIET, in order to acquire the analog input signal. The ADC goes back into hold on the CS falling edge.
Figure 9. Straight Binary Transfer Characteristic (Bipolar Ranges)
ANALOG INPUT
The analog inputs of the AD7328 may be configured as SingleEnded, True differential or Pseudo Differential via the Control Register Mode Bits as shown in Table 3 of the Register Section. The AD7328 can accept True bipolar input signals. On power up the Analog inputs will operate as 8 Single-Ended Analog Input Channels. If True Differential or Pseudo Differential is required, a write to the Control register is necessary to change this configuration after power up. Figure 10 shows the equivalent Analog input circuit of the AD7328 in Single-Ended Mode. Figure 11 shows the equivalent Analog input structure in Differential mode. The Two Diodes provide ESD protection for the Analog Inputs.
VDD D Vin0 C1 D VSS R1 C2
Figure 10. Equivalent Analog Input Circuit-(Single Ended)
VDD D Vin+ C1 D VSS VDD D VinC1 D VSS R1 C2 R1 C2
TYPICAL CONNECTION DIAGRAM
Figure 12 shows a typical connection diagram for the AD7328. In this configuration the AGND pin is connected to the Analog ground plane of the system. The DGND pin is connected to the Digital ground plane of the system. The Analog Inputs on the AD7328 can be configured to operate in Single Ended, True Differential or Pseudo Differential Mode. The AD7328 can operate with either the internal or an external reference. In Figure 12, the AD7328 is configured to operate with the internal 2.5V reference. A 470 nF decoupling capacitor is required when operating with the internal reference. The VCC pin can be connected to either a 3V or a 5V supply voltage. The VDD and VSS are the dual supplies for the high voltage analog input structures. The voltage on these pins must be equal to or greater than the highest analog input range selected on the analog input channels, see Table 5 for more information. The VDRIVE pin is connected to the supply voltage
Figure 11. Equivalent Analog Input Circuit-(Differential)
Care should be taken to ensure the Analog Input never exceeds the VDD and VSS supply rails by more than 300 mV. This will cause the diodes to become forward biased and start conducting into either the VDD or VSS rails. These diodes can conduct up to 10 mA without causing irreversible damage to the part. The Capacitor C1, in figure 10 and 11 is typically 4 pF and can primarily be attributed to pin capacitance. The resistor R1, is a
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Preliminary Technical Data
of the microprocessor. The voltage applied to the VDRIVE input controls the voltage of the serial interface.
AD7328
Figure 12. Typical Connection Diagram
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Preliminary Technical Data
AD7328 REGISTERS
AD7328
The AD7328 has four-programmable registers, the Control Register, Sequence Register, Range Register1 and Range Register2. These registers are write only registers. Addressing these Registers A serial transfer on the AD7328 consists of 16 SCLK cycles. The three MSBs on the DIN line during this 16 SCLK transfer are decoded to determine which register is addressed. The three MSBs consists of the Write bit, Register Select 1 bit and Register Select 2 bit. The Register Select bits are used to determine which of the four on-board registers is selected. The Write bit will determine if the Data on the DIN line following the Register select bits will be loaded into the addressed register or not. If the Write bit is 1 the bits will be loaded into the register addressed by the Register Select bits. If the Write Bit is a 0 the data on the DIN will not be loaded into any register.
Table 7. Decoding Register Select bits and Write bit. Write 0 1 1 1 1 Register Select1 0 0 0 1 1 Register Select2 0 0 1 0 1 Comment Data on the DIN line during this serial transfer will be ignored This combination selects the Control Register. The subsequent 12 bits will be loaded into the Control Register. This combination selects the Range Register 1 . The subsequent 8 bits will be loaded into the Range Register1. This combination selects the Range Register 2. The subsequent 8 bits will be loaded into the Range Register 2. This combination selects the Sequence Register. The subsequent 8 bits will be loaded into the Sequence Register.
CONTROL REGISTER The Control Register is used to select the Analog Input Channel for conversion, Analog Input configuration, Reference, Coding, Power mode etc. The Control Register is a write only 12-bit register. Data loaded on the DIN line corresponds to the AD7328 configuration for the next conversion. Data should be loaded into the Control Register after the Range Registers and the Sequence Register has been initialized, that is if the Sequence register is being used. The bit functions of the Control Register are outlined in Table 8.
Control Register (The Power-up status of all bits is 0)
MSB Write Register Select 1 Register Select 2 ADD2 ADD1 ADD0 Mode1 Mode0 PM1 PM0 Coding Ref Seq1 Seq2 Weak/Tri-State
LSB 0
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Preliminary Technical Data
Table 8. Control Register Bit 12,11,10 Mnemonic ADD2, ADD1, ADD0 Mode1, Mode0
AD7328
9, 8
7,6 5
PM1, PM0 Coding
4
Ref
Comment These three Channel Address bits are used to select the analog input channel for the next conversion if the Sequencer is not being used. If the Sequencer is being used, these three Channel Address bits are used to select the final channel in a consecutive sequence. These two mode bits are used to select the configuation on the eight Analog Input Pins. They are used in conjunction with the channel Address bits. On the AD7328 the analog inputs can be configured as either 8 Single Ended Inputs, 4 Fully Differential Inputs, 4 Pseudo Differential inputs or 7 Pseudo Differential Inputs. See Table 9. Power Management Bits. These two bits are used to select different power mode options on the AD7328. See Table 10. This bit is used to select the type of output coding the AD7328 will use for the next conversion result. If the Coding = 0 then the output coding will be 2s Complement. If Coding = 1, then the output coding will be Straight Binary. When operating in Sequence mode the output coding for each channel will be the value written to the coding bit during the last write to the Control Register. Reference bit. This bit is used to enable or disable the internal reference. If this Ref = 0 then the External Reference will be enable and used for the next conversion and the internal reference will be disabled. If ref = 1 then the Internal Reference will be used for the next conversion. When operating in Sequence mode the Reference used for each channel will be the value written to the Ref bit during the last write to the Control Register. The Sequence 1 and Sequence 2 bits are used to control the operation of the Sequencer. See
3,2
Seq1/Seq2 Table 11. This bit selects the state of the DOUT line at the end of the current serial transfer. If it is set to 1, the DOUT line will be weakly driven to the channel address bit ADD2 of the ensuing conversion. If this bit is set to 0, then DOUT will return to three-state at the end of the serial transfer. See the Serial Interface section for more details.
1
Weak/Tri-State
The 8 Analog Input channels can be configured as either, 7 Pseudo Differential Analog Inputs, 4 Pseudo Differential Inputs, 4 True Differential Inputs or 8 Single Ended Analog Inputs.
Table 9. Analog Input Configuration Selection Channel Address Bits ADD2 0 0 0 0 1 1 1 1 ADD1 0 0 1 1 0 0 1 1 ADD0 0 1 0 1 0 1 0 1 Mode1 =1, Mode0 = 1 7 Pseudo Differential I/ps Vin+ VinVin0 Vin7 Vin1 Vin7 Vin2 Vin7 Vin3 Vin7 Vin4 Vin7 Vin5 Vin7 Vin6 Vin7 Not Allowed Mode1 = 1, Mode0 =0 4 Fully Differential i/ps Vin+ VinVin0 Vin1 Vin0 Vin1 Vin2 Vin3 Vin2 Vin3 Vin4 Vin5 Vin4 Vin5 Vin6 Vin7 Vin6 Vin7 Mode1 = 0, Mode0 =1 4 Pseudo Differential i/ps Vin+ VinVin0 Vin1 Vin0 Vin1 Vin2 Vin3 Vin2 Vin3 Vin4 Vin5 Vin4 Vin5 Vin6 Vin7 Vin6 Vin7 Mode1 =0, Mode0 =0 Eight-Single Ended i/ps Vin+ VinVin0 AGND Vin1 AGND Vin2 AGND Vin3 AGND Vin4 AGND Vin5 AGND Vin6 AGND Vin7 AGND
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AD7328
Table 10. Power Mode Selection
Preliminary Technical Data
PM1 1
PM0 1
Description Full Shutdown Mode, In this mode all internal circuitry on the AD7328 is powered down. Information in the Control register is retained when the AD7328 is in Full Shutdown Mode. Auto Shutdown Mode, The AD7328 will enter Full Shut down at the end of each conversion when the control register is updated. All internal circuitry is powered down in Full Shutdown. Auto Standby Mode, In this mode all internal circuitry is powered down excluding the internal Reference. The AD7328 will enter Auto Standby Mode at the end of the Conversion after the control register is updated. Normal Mode, All internal Circuitry is powered up at all times.
1
0
0
1
0
0
Table 11. Sequencer Selection
Seq1 0 0
Seq2 0 1
1
0
1
1
Sequence type The Channel Sequencer is not used. The Analog Channel selected by programming the ADD2 to ADD0 bits in the Control Register selects the next channel for conversion. This selects the Sequence of Channels as previously programmed in the Sequence register for conversion. The AD7328 will start converting on the lowest channel in the sequence. It converts the channels in ascending order. If uninterrupted the AD7328 will keep converting the sequence. The range for each channel will default to the Ranges previously written into the Range Registers. This Configuration is used in conjunction with the Channel Address Bits in the Control Register. It allows continuous conversions on a consecutive sequence of channels, from channel 0, up to and including, a final channel selected by the Channel Address Bits in the control register. The range for each channel will default to the Ranges previously written into the Range Registers. The Channel Sequencer is not used. The Analog Channel selected by programming the ADD2 to ADD0 bits in the Control Register selects the next channel for conversion.
THE SEQUENCE REGISTER The Sequence Register on the AD7328 is an 8-Bit Write only register. Each of the eight Analog input channels has one corresponding bit in the Sequence Register. To select a channel for inclusion in the sequence set the corresponding channel bit to 1 in the Sequence Register. Sequence Register
MSB Write Register Select 1 Register Select 2 Vin0 Vin1 Vin2 Vin3 Vin4 Vin5 Vin6 Vin7 0 0 0 0
LSB 0
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Preliminary Technical Data
THE RANGE REGISTERS
AD7328
The Range register to used to select one Analog input Range per Analog input channel. Range Register 1 is used to set the Ranges for Channels 0 to 3. It is an 8-Bit write only Register, with two dedicated Range bits for each of the Analog Input Channels from Channel 0 to Channel3 . There are four Analog input Ranges to choose from, 10V, 5V, 2.5V, 0 to 10V. A write to the Range Register1 is selected by setting the Write bit to 1 and the Range Select bits to 0, 1. Once the initial write to the Range Register1 occurs the AD7328 automatically configure the Analog inputs from Channel 0 to Channel 3 to the appropriate range, as indicated by the Range register1, each time any ones of these analog input channels is selected. The 10V input Range is selected by default on each analog input channel. See Table 12. Range Register 1
MSB Write Reg Select 1 Reg Select2 Vin0A Vin0B Vin1A Vin1B Vin2A Vin2B Vin3A Vin3B 0 0 0 0 LSB 0
Range Register 2 is used to set the Ranges for Channels 4 to 7. It is an 8-Bit write only Register, with two dedicated Range bits for each of the Analog Input Channels from Channel 4 to Channel7 . There are four Analog input Ranges to choose from, 10V, 5V, 2.5V, 0 to 10V. A write to the Range Register2 is selected by setting the Write bit to 1 and the Range Select bits to 1, 0. Once the initial write to the Range Register2 occurs the AD7328 automatically configure the Analog inputs from Channel 4 to Channel 7 to the appropriate range, as indicated by the Range register2, each time any of these analog input channels is selected. The 10V input Range is selected by default on each analog input channel. See Table 12. Range Register 2
MSB Write Reg Select1 Reg Select 2 Vin4A Vin4B Vin5A Vin5B Vin6A Vin6B Vin7A Vin7B 0 0 0 0 LSB 0
Table 12. Range Selection VinXA 0 0 1 1 VinXB 0 1 0 1 Description This combination selects the 10V Input Range on Analog Input X. This combination selects the 5V Input Range on Analog Input X. This combination selects the 2.5V Input Range on Analog Input X. This combination selects the 0 to 10V Input Range on Analog Input X.
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Preliminary Technical Data
SEQUENCER OPERATION
POWER ON
AD7328
CS
DIN:- WRITE TO RANGE REGISTER 1 TO SELECT THE RANGE FOR EACH ANALOG INPUT CHANNEL DOUT:- CONVERSION RESULT FROM CHANNEL O, 10V RANGE, SINGLE-ENDED MODE.
CS
DIN:- WRITE TO RANGE REGISTER 2 TO SELECT THE RANGE FOR EACH ANALOG INPUT CHANNEL DOUT:- CONVERSION RESULT FROM CHANNEL O, SINGLE-ENDED MODE, RANGE SELECTED IN RANGE REGISTER 1
CS
DIN:- WRITE TO SEQUENCE REGISTER TO SELECT THE ANALOG INPUT CHANNELS TO BE INCLUDED IN THE SEQUENCE DOUT:- CONVERSION RESULT FROM CHANNEL O, SINGLE-ENDED MODE, RANGE SELECTED IN RANGE REGISTER 1
CS
DIN:- WRITE TO CONTROL REGISTER TO START THE SEQUENCE, SEQ1 = 0, SEQ2 = 1. DOUT:- CONVERSION RESULT FROM CHANNEL O, SINGLE-ENDED MODE, RANGE SELECTED IN RANGE REGISTER 1
CS
DIN:- TIE DIN LOW/WRITE BIT = 0 TO CONTINUE TO CONVERT THROUGH THE SEQUENCE OF CHANNELS DOUT:- CONVERSION RESULT FROM FIRST CHANNEL IN THE SEQUENCE
DIN TIED LOW/WRITE BIT = 0
CS
DIN:- WRITE TO CONTROL REGISTER TO STOP THE SEQUENCE, SEQ1 = 0, SEQ2 = 0. DOUT:- CONVERSION RESULT FROM CHANNEL IN SEQUENCE STOPPING A SEQUENCE
CONTINUOUSLY CONVERT ON THE SELECTED SEQUENCE OF CHANNELS
SELECTING A NEW SEQUENCE
CS
DIN:- WRITE TO SEQUENCE REGISTER TO SELECT THE NEW SEQUENCE DOUT:- CONVERSION RESULT FROM CHANNEL X IN THE FIRST SEQUENCE
Figure 13. Programmable sequence Flow Chart
The AD7328 can be configured to automatically cycle through a number of selected channels using the on-chip sequence register and the SEQ1 and SEQ2 bits in the control register. Figure 13 shows how to program the AD7328 register in order to operate in sequence mode. After power up all of the four on-chip registers will contain default values. Each analog input will have a default input range of 10V. If different Analog input ranges are required then a write to the range registers is required, this is shown in the first two serial transfers in Figure 13. These two initial serial transfers are only necessary if Input ranges other than the
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default Ranges are required. After the Analog Input ranges are configured a write to the Sequence register is necessary to select the channels to be included in the sequence. Once the channels for the sequence have been selected, the sequence can be initiated by writing to the control register and setting the SEQ1 =0, SEQ2 = 1. The AD7328 will continue to convert through the selected sequence uninterrupted provided the Sequence Register remains unchanged and SEQ1 = 0 and SEQ2 = 1 in the Control Register. If during a sequence a change to one of the range registers is required, it is first necessary to stop the sequence by writing to
Preliminary Technical Data
the Control Register and setting SEQ1 = 0 and SEQ2 = 0. Next the write to the range register can be completed to change the required range. Then the previously selected sequence can be initiated again by writing to the Control Register and setting SEQ1 = 0 and SEQ2 = 1, the ADC will then convert on the first channel in the sequence. The AD7328 can be configured to convert a sequence of consecutive channels, See Figure 14. This sequence will begin by converting on channel 0 and end with a final channel as selected by bits ADD2 to ADD0 in the Control Register. In this configuration there is no need for a write to the Sequence register. To operate the AD7328 in this mode set SEQ1 = 1 and SEQ2 = 0 and select the final channel in the sequence by programming bits ADD2 to ADD0 in the Control Register.
AD7328
Once the control register is configured to operate the ad7328 in this mode the DIN line can be held low or the WRITE bit can be set to 0 in order to keep the AD7328 operating in this mode. To return to traditional multichannel operation a write to the Control Register is necessary, setting SEQ1 = 0 and SEQ2 =0. When the SEQ1 and SEQ2 are both set to 0 or when both are set to 1 the AD7328 is configured to operate in traditional multichannel mode where a write to the channel Address bits, ADD2 to ADD0, in the Control Register selects the next channel for conversion.
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Preliminary Technical Data
POWER ON
AD7328
CS
DIN:- WRITE TO RANGE REGISTER 1 TO SELECT THE RANGE FOR ANALOG INPUT CHANNELS DOUT:- CONVERSION RESULT FROM CHANNEL O, 10V RANGE, SINGLE-ENDED MODE.
CS
DIN:- WRITE TO RANGE REGISTER 2 TO SELECT THE RANGE FOR ANALOG INPUT CHANNELS DOUT:- CONVERSION RESULT FROM CHANNEL O, RANGE SELECTED IN RANGE REGISTER 1, SINGLE-ENDED MODE.
CS
DIN:- WRITE TO CONTROL REGISTER TO SELECT THE FINAL CHANNEL IN THE CONSECUTIVE SEQUENCE, SET SEQ1 = 1 AND SEQ2 = 0. SELECT OUTPUT CODING FOR SEQUENCE. DOUT;- CONVERSION RESULT FROM CHANNEL 0, RANGE SELECTED IN RANGE REG 1, SINGLE-ENDED MODE
CS
DIN:- WRITE BIT = 0 OR DIN LINE HELD LOW TO CONTINUE THROUGH SEQUENCE OF CONSECUTIVE CHANNELS DOUT;- CONVERSION RESULT FROM CHANNEL 0, RANGE SELECTED IN RANGE REG 1, SINGLE-ENDED MODE
CS
DIN:- WRITE BIT = 0 OR DIN LINE HELD LOW TO CONTINUE THROUGH SEQUENCE OF CONSECUTIVE CHANNELS DOUT;- CONVERSION RESULT FROM CHANNEL 1, RANGE SELECTED IN RANGE REG 1, SINGLE-ENDED MODE CONTINUOUSLY CONVERT ON CONSECUTIVE SEQUENCE OF CHANNELS
DIN TIED LOW/WRITE BIT = 0
STOPPING A SEQUENCE
CS
DIN:- WRITE TO CONTROL REGISTER TO STOP THE SEQUENCE, SEQ1 = 0, SEQ2 = 0. DOUT:- CONVERSION RESULT FROM CHANNEL IN SEQUENCE
Figure 14 Flow Chart for Consecutive Sequence of Channels
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Preliminary Technical Data
REFERENCE The AD7328 can operate with either the internal 2.5V on-chip reference or an externally applied reference. The internal reference is selected by setting the REF bit in the Control Register to 1. On power up the REF bit will be 0, selecting the external Reference for the AD7328 conversion. For external reference operation the REFIN/REFOUT pin should be decoupled to AGND with a 470 nF capacitor. The internal Reference circuitry consists of a 2.5V band gap reference and a reference buffer. When operating the AD7328 in internal Reference mode the 2.5V internal reference is available at the REFIN/REFOUT pin. When using the AD7328 with the internal reference the REFIN/REFOUT pin should be decoupled to AGND using a 470 nF cap. It is recommended that the Internal Reference be buffered before applying it else where in the system. The AD7328 is specified for a 2.5V to 3V reference range. When a 3V reference is selected the ranges will be, 12V, 6V, 3V and 0 to 12V. For these ranges the VDD and VSS supply must be equal to or greater than the max Analog Input Range selected. On power up if the internal reference operation is required for the ADC conversion a write to the control register is necessary to set the REF bit to 1. During the Control Register write the conversion result from the first initial conversion will be invalid. The reference buffer will require TBD us to power up and charge the 470 nF decoupling cap, during the power up time the conversion result from the ADC will be invalid.
AD7328
Rev. PrK | Page 21 of 24
AD7328
MODES OF OPERATION
The AD7328 has a number of different modes of operation. These modes are designed to provide flexible power management options. These options can be chosen to optimize the power dissipation/throughput rate ratio for the differing application requirements. The mode of operation of the AD7328 is controlled by the Power Management bits, PM1 and PM0, in the Control register as detailed in Table 10.The default mode is Normal Mode, where all internal circuitry is fully powered up. Normal Mode (PM1 = PM0 = 0) This mode is intended for the fastest throughput rate performance, the AD7328 is fully powered up at all times. Figure 15 shows the general diagram of operation of the AD7328 in Normal Mode. The Conversion is initiated on the falling edge of CS and the track and hold will enter hold mode as described in the Serial Interface Section. The Data on the DIN line during the 16 SCLK transfer will be loaded into one of the on-chip registers, provided the Write bit is set. The register is selected by programming the Register select bits, see Table 1 of the Register section.
Preliminary Technical Data
If a write to the control register occurs while the part is in Full Shut down mode, with the power management bits, PM1 and PM0 set to 0, normal mode, the part will begin to power up on the CS rising edge. To ensure the AD7328 is fully powered up, tPOWER UP, should elapse before the next CS falling edge. Auto Shutdown Mode (PM1 = 1, PM0 = 0) Once the Auto Shutdown mode is selected the AD7328 will automatically enter shutdown at the end of each conversion. The AD7328 retains information in the registers during Shutdown. The track-and-hold is in hold during shutdown. On the falling CS edge, the track-and-hold that was in hold during shutdown will return to track. The power-up from Auto Shutdown is TBD s In this mode the power consumption of the AD7328 is greatly reduced with the part entering shutdown at the end of each conversion. When the control registers is programmed to move into Auto Shutdown mode, it does so at the end of the conversion. Auto Standby Mode (PM1 = 0, PM0 =1) In Auto Standby mode portions of the AD7328 are powered down but the on-chip reference remains powered up. The reference bit in the Control register should be 0 to ensure the on-chip reference is enabled. This mode is similar to Auto Shutdown but allows the AD7328 to power up much faster, allowing faster throughput rates to be achieved. The AD7328 will enter standby at the end of the conversion. The part retains information in the Registers during Standby. The AD7328 will remain in standby until it receives a CS falling edge. The ADC will begin to power up on the CS falling edge. On this CS falling edge the track-and-hold that was in hold mode while the part was in Standby will return to track. Wakeup time from Standby is 1 s. The user should ensure that 1 s has elapsed before attempting a valid conversion. When running the AD7328 with the maximum 20 MHz SCLK, one dummy conversion of 16 x SCLKs is sufficient to power up the ADC. This dummy conversion effectively halves the throughput rate of the AD7328, with every second conversion result being a valid result. Once Auto Standby mode is selected, the ADC can move in and out of the low power state by controlling the CS signal.
Figure 15. Normal Mode
The AD7328 will remain fully powered up at the end of the conversion provided both PM1 and PM0 contain 0 in the control Register. Sixteen serial clock cycles are required to complete the conversion and access the conversion result. At the end of the conversion CS may idle high until the next conversion or may idle low until sometime prior to the next conversion. Once the data transfer is complete, another conversion can be initiated after the quiet time, tQUIET, has elapsed. Full Shutdown Mode (PM1 = PM0 = 1) In this mode all internal circuitry on the AD7328 is powered down. The part retains information in the Registers during Full Shut down. The AD7328 remains in Full shutdown mode until the power managements bits in the Control Register, PM1 and PM0, are changed.
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Preliminary Technical Data
SERIAL INTERFACE
Figure 16 shows the timing diagram for the serial interface of the AD7328. The serial clock applied to the SCLK pin provides the conversion clock and also controls the transfer of information to and from the AD7328 during a conversion. The CS signal initiates the data transfer and the conversion process. The falling edge of CS puts the track-and-hold into hold mode, take the bus out of three-state and the analog input signal is sampled at this point. Once the conversion is initiated it will require 16 SCLK cycles to complete. The track-and-hold will go back into track on the 15th SCLK falling edge. On the sixteenth SCLK falling edge, the DOUT line will return to three-state. If the rising edge of CS occurs before 16 SCLK cycles have elapsed, the conversion will be terminated, the DOUT line will return to three-state, and depending on
AD7328
where the CS signal is brought high the addressed register may or may not be updated. Data is clocked into the AD7328 on the SCLK falling edge. The three MSBs on the DIN line are decoded to select which register is being addressed. The Control Register is a twelve bit register, if the control register is addressed by the three MSB, the data on the DIN line will be loaded into the Control on the 15th SCLK falling edge. If the Sequence register or either of the Range registers is addressed the data on the DIN line will be loaded into the addressed register on the 11th SCLK falling edge. Conversion data is clocked out of the AD7328 on each SCLK falling edge. Data on the DOUT line will consist of three channel identifier bits, a Sign bit and a 12-bit conversion result. The channel identifier bits are used to indicate which channel the conversion result corresponds to.
Figure 16. Serial Interface timing Diagram (Control register write)
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Preliminary Technical Data
OUTLINE DIMENSIONS
20-Lead Thin Shrink Small Outline (TSSOP)
(RU-20)
AD7328
Ordering Guide
AD7328 Products AD7328BRUZ EVAL-AD7328CB1 EVAL-CONTROL BRD22 Temperature Package -40C to +85C Package Description TSSOP Evaluation Board Controller Board Package Outline RU-20
NOTES 1 This can be used as a stand-alone evaluation board or in conjunction with the EVAL-CONTROL Board for evaluation/demonstration purposes. 2 This board is a complete unit allowing a PC to control and communicate with all Analog Devices evaluation boards ending in the CB designators. To order a complete evaluation kit, the particular ADC evaluation board, e.g., EVAL-AD7328CB, the EVAL-CONTROL BRD2, and a 12V transformer must be ordered. See relevant Evaluation Board Technical note for more information.
ESD CAUTION
ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on the human body and test equipment and can discharge without detection. Although this product features proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance degradation or loss of functionality.
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PR04852-0-11/04(PrK)
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