background image

AINP

AINN

10000pF

10

10

-

+

+

-

10

10

1k

1k

1k

THS4521 

Vocm =+2.25V

-2.15V

+2.15V

1k

0V

-2.15V

+2.15V

0V

0.1V

4.3V

2.25V

0.1V

4.3V

2.25V

-4.3V

+4.3V

0V

5V 

A0(-)

A0(+)

EVM Analog Interface

www.ti.com

2

EVM Analog Interface

The ADS8881EVM is designed for easy interfacing to multiple analog sources. SMA connectors allow
the EVM to have input signals connected through coaxial cables. In addition, the Samtec connector
provides a convenient 10-pin, dual-row, header/socket combination at J1. Consult Samtec at

http://www.samtec.com

or call 1-800-SAMTEC-9 for a variety of mating connector options. All analog

inputs are buffered by THS4521 high-speed fully differential amplifier in order to properly drive the
ADS8881 ADC inputs.

Use appropriate caution when handling these pins.

Table 1

summarizes the pinout for analog interface J1.

Table 1. J1: Analog Interface Pinout (Samtec 10 x 2)

Pin Number

Signal

Description

CH0 negative differential input. This pin can be

J1.10

A0(-)

grounded for single ended signals.

CH0 positive differential input or input for single

J1.12

A0(+)

ended signals

Table 2

lists the SMA analog inputs.

Table 2. SMA Analog Inputs

Pin Number

Signal

Description

CH0 negative differential input. This pin can be

J4

A0(-)

grounded for single ended signals.

CH0 positive differential input or input for single

J5

A0(+)

ended signals

2.1

Differential Input Signal Configuration

The ADS8881 can only convert differential signals with common mode between 0 V and V

REF

, but the

THS4521 can condition a bipolar signal changing its common mode. This EVM sets the THS4521 output
common mode to 2.25 V, that corresponds to V

REF

/ 2. Thus, a bipolar differential signal with a common

mode of 0 V can be applied at the EVM inputs A0(-) and A0(+). Then, the THS4521 shifts the common
mode to 2.25 V. Although input common mode can be corrected, since the THS4521 is powered by a 5-V
supply, the input signals must limit the differential range from –4.3 V to 4.3 V to avoid saturating the
amplifier output.

Figure 1

illustrates an input signal with 0-V common mode and 8.6-V differential, which

common mode is changed from 0 V to 2.25 V.

Figure 1. Differential Input Example

4

ADS8881EVM-PDK

SBAU211 – June 2013

Submit Documentation Feedback

Copyright © 2013, Texas Instruments Incorporated

Содержание ADS8881EVM-PDK

Страница 1: ...881EVM as a daughter card MMB0 motherboard A to B USB cable and 6 V wall adapter power supply This user s guide covers circuit description schematic diagram and bill of materials for the ADS8881EVM daughter card The following related documents are available through the Texas Instruments website at http www ti com Related Documentation Device Literature Number ADS8881 SBAS547 REF5045 SBOS410 OPA333...

Страница 2: ... Wire Configuration 8 6 Plug In Installer 9 7 MMB0 Motherboard Jumper Configuration 10 8 ADS8881EVM Jumper Configuration 10 9 Loading EVM Plug in 11 10 ADS8881EVM Plug in Device Configuration Tab 12 11 ADCPro Test Plug ins 13 12 ADS8881EVM PCB Top Layer 16 13 ADS8881EVM PCB Ground Layer 16 14 ADS8881EVM PCB Power Layer 17 15 ADS8881EVM PCB Bottom Layer 17 List of Tables 1 J1 Analog Interface Pinou...

Страница 3: ...e literature number SBAU128 available for download from the TI website ADS8881EVM Daughter Board Features Includes support circuitry as a design example to match ADC performance 3 3 V slave serial peripheral interface SPI Serial interface header for easy connection to TI DSP based communication systems Compatible with the TI Modular EVM system Designed for 5 V analog supply Onboard 4 5 V voltage r...

Страница 4: ...nput for single J1 12 A0 ended signals Table 2 lists the SMA analog inputs Table 2 SMA Analog Inputs Pin Number Signal Description CH0 negative differential input This pin can be J4 A0 grounded for single ended signals CH0 positive differential input or input for single J5 A0 ended signals 2 1 Differential Input Signal Configuration The ADS8881 can only convert differential signals with common mod...

Страница 5: ...single ended signals as illustrated in Figure 2 Figure 2 Single Ended Signal Example 2 3 Voltage Reference Since the EVM is powered by a 5 V analog supply the reference should be a value below 5 V This EVM uses a 4 5 V created by the on board REF5045 Then it is filtered by an RC filter of 160 Hz cutoff frequency to minimize its noise contribution Finally the EVM is buffered by the THS4281 which ca...

Страница 6: ... if JP3 is J2 17 CONVST installed J2 4 J2 10 and J2 18 GND Digital ground connections I2 C bus used only used to program the U4 J2 16 J2 20 I2 C bus EEPROM on the EVM board J2 2 J2 5 6 J2 8 9 J2 11 12 J2 14 and Unused Unused J2 19 3 1 Serial Interface SPI The ADS8881 ADC uses SPI serial communication in mode 1 CPOL 0 CPHA 1 with high speed clocks higher than 30 MHz or mode 0 CPOL 0 CPHA 0 for slow...

Страница 7: ... to work with a 5 V analog power supply connected to J3 3 The ADS8881 is limited to 3 6 V as analog supply so the board regulates down the 5 V analog supply with an on board 3 3 V LDO TPS78833 4 2 Digital Power Options The ADS8881EVM connects the digital power supply of the ADS8881 to 3 3 VD J3 10 with a 0 Ω resistor This matches the logic level of the MMB0 motherboard 4 3 Analog and Digital Groun...

Страница 8: ...S8881 digital output out of Tri State and initialize conversions The rising edge of the chip select signal starts a conversion then after conversion time the falling edge of chip select brings the digital output out of Tri State Figure 4 Serial 3 Wire Configuration 5 2 SPI 4 Wire Mode JP2 1 2 and JP3 CLOSED The chip select signal is used to bring the ADS8881 digital output out of Tri State However...

Страница 9: ...ling the ADCPro Software ADCPro is the primary program used to evaluate the ADS8881 It is available from the TI website at www ti com tool adcpro Refer to the ADCPro User s Guide literature number SBAU128 for detailed installing instructions 6 2 Installing ADS8881EVM PDK Plug In Software NOTE ADCPro should be installed before attempting to install the ADS8881EVM PDK plug in software The installati...

Страница 10: ...lows the wall supply to power up the MMB0 and the ADS8880EVM through J2 6 VDC input and regulate down to 5 V 3 3 V J13B must be closed This connects the 5 V analog power supply with the 5 V digital power supply J13A must be opened This setting allows the 5 V analog power supply to be regulated on board Step 3 Set JP1 2 3 JP2 2 3 and JP3 open on the ADS8881EVM as shown in Figure 8 Figure 8 ADS8881E...

Страница 11: ...The MMB0 is not sold as a DSP development board and it is not available separately TI cannot offer support for the MMB0 except as part of an EVM kit For schematics or other information about the MMB0 contact Texas Instruments 7 2 Loading the ADS8881EVM PDK Plug in Step 1 Make sure the PDK kit is configured and powered up as explained in Section 6 Then press the Reset button on the MMB0 in the top ...

Страница 12: ...t should be a value between 70 MHz to 80 MHz for 1 MSPS For slow sampling rates use 10 MHz Do not use SLCK frequencies between 30 MHz and 50 MHz Reference By default it is 4 5 V which matches the on board reference of the EVM The value of this control should always match the reference used by the ADC to read accurate voltages Device Information By default is ADS8881 and it cannot be modified About...

Страница 13: ... displays it in a graph of voltage vs time For further details regarding how to set up and use the various test plug ins refer to the ADCPro User s Guide literature number SBAU128 7 5 Acquiring Data Once the ADS8881EVM is configured for the desired test scenario press the Acquire button to start the data collection process the software collects the number of data points specified in the Test plug ...

Страница 14: ...Ceramic 10 16WV TDK C3216X7R1C106K 1206 9 2 J1 J2 Top Header 20 Pin SMT Plug 100 Gold Samtec TSM 110 01 L DV P 2x10 10 2 J1 J2 Bottom Header 20 Pin SMT Socket 100 Gold Samtec SSW 110 22 F D VS K 2x10 11 1 J3 Top Header 10 Pin SMT Plug 100 Gold Samtec TSM 105 01 L DV P 2x5 12 1 J3 Bottom Header 10 Pin SMT Socket 100 Gold Samtec SSW 105 22 F D VS K 2x5 13 2 J4 J5 CONN SMA JACK STRAIGHT PCB Amphenol ...

Страница 15: ... SOT23 5 Texas THS4281DBV Instruments 28 1 U5 IC OPAMP GP R R CMOS SOT23 5 Texas OPA330AIDBV Instruments 29 1 U6 IC REG LDO 3 3V 15A SOT 23 5 Texas TPS78833DBV Instruments 30 1 U7 IC OPAMP DIFF R R 145MHZ 8MSOP Texas THS4521IDGK Instruments 31 1 U8 IC EEPROM 256KBIT 400KHZ Microchip 24LC256 I ST 8TSSOP 32 2 0 100 Shunt Black Shunts 3M 969102 0000 DA 15 SBAU211 June 2013 ADS8881EVM PDK Submit Docum...

Страница 16: ...Board layouts are not to scale These figures are intended to show how the board is laid out they are not intended to be used for manufacturing ADS8881EVM PCBs Figure 12 ADS8881EVM PCB Top Layer Figure 13 ADS8881EVM PCB Ground Layer 16 ADS8881EVM PDK SBAU211 June 2013 Submit Documentation Feedback Copyright 2013 Texas Instruments Incorporated ...

Страница 17: ... Materials Schematics and Layout Figure 14 ADS8881EVM PCB Power Layer Figure 15 ADS8881EVM PCB Bottom Layer 17 SBAU211 June 2013 ADS8881EVM PDK Submit Documentation Feedback Copyright 2013 Texas Instruments Incorporated ...

Страница 18: ...Bill of Materials Schematics and Layout www ti com 8 3 Schematic 18 ADS8881EVM PDK SBAU211 June 2013 Submit Documentation Feedback Copyright 2013 Texas Instruments Incorporated ...

Страница 19: ...product This notice contains important safety information about temperatures and voltages For additional information on TI s environmental and or safety programs please contact the TI application engineer or visit www ti com esh No license is granted under any patent right or other intellectual property right of TI covering or relating to any machine process or combination in which such TI product...

Страница 20: ...esponsible for compliance with all legal regulatory and safety related requirements concerning its products and any use of TI components in its applications notwithstanding any applications related information or support that may be provided by TI Buyer represents and agrees that it has all the necessary expertise to create and implement safeguards which anticipate dangerous consequences of failur...

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