Precision Data Converters Forum - Recent Threads

Min Vref spec of dac088s085 = 0.5v

john filipetti — Wed, 19 Jun 2013 09:29:05 GMT

Device: dac088s085

Application: Considering dac088s085 for application. Wish to set all outputs near ground (to within output offset of on chip output buffer amps) without changing DAC codes but rather by dropping Vref to near ground. Near ground is sufficient since these outputs will be driving NMOS gate with Vgsth ~ 0.5v and just wish to turn off NMOS. Once Vref is released from ground the DAC outputs should return to their set values. This will occur at a repetition rate of ~ 100Hz from a 10 bit PWM signal or for more accuracy, from a voltage reference enabled by said PWM signal.

Questions: Data Sheet indicates that Vref cannot be below .5 V but this may only be for linearity, SFDR, test, spec considerations. If Vref input is an unbuffered R2R then this should be possible yes? Any glaring issues doing this with the specified part with 10 bit PWM at 100Hz (Min pulse width of 10 bit PWM at smallest duty cycle = 1/1024/100Hz =~ 9.8 uS). Settling time spec of DAC listed as 4.5 uS which I assume is mostly due to the output buffers?

Thank you for any help that you may provide,

--john filipetti--

ADS1293 Evaluation Board Firmware Source Code

Akib Uddin — Fri, 07 Dec 2012 16:30:42 GMT

Hello,

I am wondering if the ADS1293 Eval Board comes with source code for the firmware? If so, where would it be?

Our ADS1292 eval board had the source code in a folder when the software was installed, but this is missing with the ADS1293 software.

Thanks,

Akib

ADS1241 Registers

Hamid Naseri — Tue, 21 May 2013 21:48:58 GMT

Hi All,

I am testing ADS1241 chip and would like to simply write to its registers and read the register back to confirm . I am using the following code based on RREG description on page 19 of the data sheet. The data timing shows a 4nS delay time between write and read register command. I'm not getting 0 back instead of 33 from the register. I would appreciate your feedback.

Thanks,

Hamid

int MUX0REG; spi.write(0x51); // write to MUX regiter spi.write(0x00); // number of regs - 1 spi.write(0x33); // Ain0 (write 0 so we can read ch0 back) spi.write(0x11); // read mux register back spi.write(0x00); // number of regs - 1 wait(0.004); MUX0REG = spi.write(0x00); // number of reg - 1 pc.printf("\r\nmux0reg = %x \r\n", MUX0REG);

ADS1118 Single Ended Input Impedance

John Araujo — Tue, 18 Jun 2013 20:46:41 GMT

Hello,

What is the input bias current/input impedance of the ADS1118 when configured in single ended input mode? I didn't see that info in the datasheet.

Thank you very much!

Information an Radiation Testing on the DAC9881

Stewart Hansen — Tue, 18 Jun 2013 21:07:58 GMT

I am doing work with a very low noise controller, and need a rad hard DAC that has very low noise characteristics. The DAC9881 is used in a design that is not rad hard and we need to either replace it with a rad hard DAC or find documentation on the DAC9881 radiation testing. I have found parts to replace this DAC but the noise is as low as we would like. Does anyone know of any radiation testing on the DAC9881?

Any information would be great thanks.

Questions about ADS1258

Bailin Cao — Mon, 17 Jun 2013 10:32:32 GMT

On page 18 of ADS1258 data sheets, in Equations (2) and (3), does 11b mean 3 in decimal? How do you evaluate CHOP(4.265625+TD)? On page 21, footnote(1) of Table 8, what are t1, t2, ...? (they should be in Greek but they can't be typed in here). How and where can they be obtained? To use its sensor, temperature and other internal features, the external CHOP has to be turned off. However, to reduce external noise and offset, the CHOP feature has to be enabled. How long does it take to switch on and switch off CHOP? If I only use 12 of 16 channels, should I use auto-scan or fixed mode? In each case, what is the maximum realistic sampling rate I can get for all 12 channels on the average? Many thanks ]

ADS1299 internal clock

Julian Grisales — Thu, 06 Jun 2013 02:25:35 GMT

Hello,

What should be the connection of CLK and CLK_SEL pins if i'm using the internal clock of the device?

Unusual application of ADS1281EVM-PDK

Perry Frogge — Thu, 13 Jun 2013 21:01:25 GMT

I am attempting to use the evaluation board and software to talk to my board that has the 1281 installed, but not all its signals exposed.

I removed the 1281 from an EVM daughter board and with jumpers on the headers, I have wired the following over to my board:

GND

SCLK

DRDY#

DIN

DOUT

SYNC

RESET#

On my board I have PINMOD pulled to GND, M0,M1, PWRDN pulled high, MCLK pulled low, CLK tied to 4.096MHZ .

On a working setup with an original daughter board, i monitored for activity on PWRDN, MO, M1, MFLAG, and saw nothing.

When attempting to run with my board,

the ADCpro software comes up, seems to load normally, the LED on main board does the same as with an original board . The LED reads b (minus the left bottom leg) then the dot appears, then 1. 2. 8. 1. The messages about loading firm ware, reseting/conecting to the DSP all seem fine. But past that, if I try to change a setting on the 1281, like the sampling rate, I no longer get any SCLK activity.

As best I can I have monitored activity on sclk, din, dout during the ADCpro startup. Even on the working original board, dout seems inconsistent the first 8 or so sclk burst. Signal integrity seems good on my board.

While using the original board that works, I connected the cables, but left my board unconnected at other end, and ADCpro still worked, so it seems it can drive the cables fine.

I have seen my board work fine in PINMOD in another environment, good ADC data was read over the spi interface.

Any thought on why ADCpro stops issuing any commands or what I should focus on?

thanks

ADS1294 Test Signal Amplitude Issue

Mark Newcomb — Sat, 20 Apr 2013 18:51:39 GMT

Hello,

I am having some trouble with the amplitude of the internal test signal generated by the ads1294, which is a part of a custom board.

The image below is the raw data that I am reading back from the device. The PGA gain for each channel is set to 6, and the amplitude of the test signal should be 1 mV (I have measured the reference voltage (VREFP - VREFN) = 2.4 V and set CONFIG2 to 0x10).

As seen on the image, the amplitude of each channel varies somewhat - the discrepancy is most clearly seen between the blue signal and the rest.

When I scale the command (in MATLAB: square_scaled = square*400/(2^23-1);) the following is my result:

Clearly, I am misunderstanding something about how to scale the values...but I can't figure out what. Am I correct in using 400 instead of 2400 in the scaling since my PGA gain is 6? Why are the amplitudes different on different channels?

I don't have access to the standard on which the test signals were based, but from screenshots I have seen on E2E, my results don't seem right. Does anyone have suggestions?

Thank you,

Mark

ads1299 and msp code?

hulusi kececi — Thu, 08 Nov 2012 20:06:16 GMT

Hi,

there are code for ads1298 and msp430 on your site. but, I dont see open code for ads1299. whether there are open code for ads1298 and msp430.

and is software of ADS1299EEGFE-PDK including open code source?

Thank you

What determines ADS1299 tCLK (Master clock period) Range?

Conor Russomanno — Tue, 18 Jun 2013 15:58:26 GMT

Hi there,

I'm working with the ADS1299 chip and trying to interface it with an Arduino library that I'm building. I've been searching through the datasheet for what determines the tCLK master clock period, but can't seem to find it. I see that the range is from 444 ns to 666ns. Is that range linearly mapped to the DVDD supply (2.7 V < DVDD < 3.6 V) shown at the top of the column of Figure 1 (Timing Requirements) on pg. 8 of the datasheet?

If somebody could help me with this one, that would be great.

Thanks in advance.

Conor

ADS1147 EVM

Max Tibbetts — Tue, 18 Jun 2013 14:22:02 GMT

Hi all,

I am studying the input RC filters on the ADS1147 EVM reference design and noticed the capacitors C7 and C8. What are the function of the capacitors for?

DAC7821 Positive Voltage Supply

Junheng Zhu — Thu, 13 Jun 2013 04:03:22 GMT

I am planning to use the circuit provided in the application section to provide positive voltage supply (Figure 28 in the datasheet). Regarding this circuit I have a couple of questions. Firstly, for the -2.5V reference is it coming via the inverting connection of the first OPA227? And for achieving this what supply should be provided for this opamp? Secondly, could someone list a good recommendation for the voltage reference? I am having a hard time searching for the information about the power consumption for both the DAC and opamp. Thanks in advance.

What is the reference value used to calculate dBFS by the ADS1299ECG-FE analysis software's Fourier power spectrum?

Claire Christensen — Mon, 17 Jun 2013 16:09:10 GMT

Hello.

I am using the ADS1299ECG-FE development kit and associated software. My question is a basic one regarding reference values for the analysis software's calculation of a Fourier power spectrum. Specifically, I am looking at Figures 44-45 on pages 38-39 of the development kit instruction manual. In Figure 45, the power spectrum associated with a 31.25Hz, 6uA (gain=12) signal is shown in dBFS. My question is twofold:

1) Does the analysis software use dBFS=10*log_10(P_obs/P_ref), where P_ref is the power of a full-scale signal, to calculate values for the power spectrum?

2) If so, what is P_ref and does it change depending on gain? In the case outlined above, is it the power we would observe for a 750mV peak-to-peak signal (since 750mV p2p is the full-scale voltage range at gain=12)?

If you could please be as specific as possible with numbers and equations in your reply, that would be great!

Thank you,

Claire

ADS1672EVM-PDK Problem

Herwig Van Dooren — Tue, 02 Apr 2013 14:26:40 GMT

Hello,

I experience exactly the same problems with the ADS1672EVM-PDK.

It also usses the MMB0 motherboard and ADCPro.

I also tried different revisions of the software and two PC's (both XP with SP3. One laptop and one desktop)

Apart from the problems Evginiy describes, I noticed that plugging or unplugging a small load (40W pump) on the mains may hang ADCPro

(Even when it is not collecting, after plugging or unplugging the load, it will hang when pushing the Acquire button)

Is a solution for this problem found already?

Please feedback.

Herwig.

ADS1299 Evaluation Module Setup

Greg Jackson1 — Mon, 22 Oct 2012 20:44:40 GMT

Hi,

I am using the ADS1299 Evaluation Module, and am trying to figure out how to best set it up with an EEG cap for simple readings, blink test, etc.

I am trying to figure out the simplest way to get things up and running with an existing EEG cap, and to be honest am having trouble making complete sense of the manual. Can somebody suggest the quickest setup for pins to use, particularly for bias and reference, as well as the settings? I've been playing around with them with so far minimal success. I do have some experience with EEG data using NeuroScan hardware, etc.

Thanks.

ADS1259 SPI

David V — Mon, 17 Jun 2013 09:55:42 GMT

Hi,

I'm trying to program ADS1259 with MSP430f5508 through SPI.

Is there any application note or example code how to do this in CCS5?

Regards David.

Pros and cons of Unipolar/Bipolar power supplies for ADS1299?

Alexander Zorn — Mon, 17 Jun 2013 19:14:37 GMT

Is there any reason that the ADS1299 can be powered with a unipolar supply, AVDD = 5V & AVSS = 0 V, or a bipolar supply, AVDD = 2.5V, AVSS = -2.5V?

Why would one pick one method of supplying power over the other? Thanks!

Alex

Problem communicating with ADS1259 using MSP430 SPI

UTB — Mon, 01 Nov 2010 18:57:20 GMT

Hi,

I am using the MSP430 in the ez430-RF2500 development kit to communicate with an ADS1259 via SPI.

I am trying to initialize the ADC with the following Code Composer code, but it doesn't seem to work. The MSP430 gets stuck during "while (!(IFG2 & UCB0RXIFG));" as if it can't receive anything.

Notes:

-The SPI is shared with the CC2500 radio, so it has to be disabled first as shown in the code.

-The ADC's SPI CS pin is connected to MSP430's P4.4 GPIO.

-After the communication, the ADC SPI is disabled and the radio SPI is re-enabled.

-I am assuming that "UCB0CTL0 = b10101001" for the ADC.

=======

char junk;

    P3OUT |= b00000001; // turn off radio SPI
    UCB0CTL1 |= UCSWRST; // set SPI to ADC's SPI protocol
    UCB0CTL0 = b10101001;
    UCB0CTL1 &= ~UCSWRST;
    P4OUT = b11101111; // P4.4 is set low, ADC SPI is on

// stop read data continuous mode
while((IFG2 & UCB0TXIFG) == 0);
UCB0TXBUF = b00010001;
while (!(IFG2 & UCB0RXIFG)); //MSP430 seems to get stuck here
junk = UCB0RXBUF;

// specify address to be CONFIG1
while((IFG2 & UCB0TXIFG) == 0);
UCB0TXBUF = b01000001;
while (!(IFG2 & UCB0RXIFG));
junk = UCB0RXBUF;

// write to only 1 register
while((IFG2 & UCB0TXIFG) == 0);
UCB0TXBUF = b00000000;
while (!(IFG2 & UCB0RXIFG));
junk = UCB0RXBUF;

// write register, set to use internal reference
while((IFG2 & UCB0TXIFG) == 0);
UCB0TXBUF = b00000000;
while (!(IFG2 & UCB0RXIFG));
junk = UCB0RXBUF;

P4OUT = b00010000; // P4.4 is set high, ADC SPI is off
UCB0CTL1 |= UCSWRST; // set SPI to radio's SPI protocol
UCB0CTL0 = b10101001;
UCB0CTL1 &= ~UCSWRST;
P3OUT &= b11111110; // turn on radio SPI

======

Thank you very much for your help!

David

ADS1298 test signal

Sebastian Loer — Wed, 17 Oct 2012 08:27:51 GMT

Hello,

i followed exactly the initial flow at power-up as seen in figure 62 in the datasheet to check if the device is working properly.

But when im reading out the conversion results, i get always 0x000000 for each channel.

Previoulsy i configured the device so that only channel 1 is active and routed the RLD signal out on channel 2.

With this configuration i get conversion results like seen in the following picture. (electrodes are not connected to the inputs)

But even when i connect the electrodes and touch them , the signal always looks like this.

Because of that i wanted to test the device with the internal test signal.

But why i always get zeros for each channel?

ADS1294R analog output error

Lingfeng Liu — Wed, 12 Jun 2013 03:35:05 GMT

Hi,

We are developing a 3-channels ECG board using the ADS1294R. We design our own board by incorporating several reference designs, as shown in this file:(Please visit the site to view this file)

The chip is configured as:

Unipolar supply: AVDD=3.3V(Instead of 3V), DVDD=3.3V(Instead of 1.8V)
Baud rate = 2 M
CONFIG1=0x06 //LP mode, 250 sps
CONFIG2=0x13 //Internal test signal, At dc
CONFIG3=0xC0 //Internal reference 2.4V
RLD, WCT, LOFF are off, LOFF is on

The digital part of the chip works properly (read ID=0xD0, registers read ok), but the analog conversion is almost random. We then test the internal signals on all the 4 channels (1-4, PGA=1). The header of the data of each reading is ok (start with C0 00 00), but the conversion is abnormal:

MUX=011 for MVDD measurement: always ouput 7F FF FF

MUX=100 for temperature sensor: always output 7F FF FF

MUX=101 for test signal: channel 1, 4 always output 80 00 00, channel 2, 3 output randomly

MUX=001 for internally shorted input: always output 80 00 00

Seems like the analog supply is not properly feed to the chip, but we have verified the voltage level of AVDD on the board. How could this happened? Could the analog part of the chip fails while the digital part unaffected?

ADS1294R HIGH DC OFFSET WHILE CONNECTING PATIENTS

vrinda harisankar1 — Fri, 07 Jun 2013 12:11:17 GMT

hi,

Im using ADS1294R for acquiring ECG and respiration signals. I have almost completed the development and had used a patient simulator through my development stage. i had set ADS gain as 6. Now when im trying my module with real patients, there is a high DC offset and ADS is going into saturation. When i reduce the gain to 2 this problem get solved but the baseband noise is more at lower gains no matter i do proper filtering .I have a RLD nd proper analog biasing.Any suggestions on how this issue can be solved?

ADS1293 crystal or clock

Tommy Jacobsen — Mon, 13 May 2013 10:38:13 GMT

Hi,

The ADS1293 needs either a 4.096MHz crystal or an external 409.6kHz clock. We have a problem finding the right solution as we have restrictions in our design which limits the possibilities:

Limited space (e.g. max. component height 1.1mm).
Limited power (max. 1-2 mA for ADS1293 frontend including clock).
30ppm precission.

We have not been able to identify any crystals in that frequency range smaller than 8x4.5x1.7mm so because of the heigth restriction crystals is not the solution.

Potentially we can generate the clock in our host processor, but because of other limitations we wont be able to optimize it for a low power mode as processor crystal frequency is to high and we would need to keep it active continuosly.

The best solution seems to be an external oscillator running at a small sized crystal (above 10MHz) but current consumption is an issue.

Other solutions have been considered like ceramic resonator (precission to low) and discrete crystal oscillator (current consumption to high).

Do you have any suggestions for a good solution within the given restrictions?

BR Tommy

DRDYB interrupt ADS1293

Javi Redondo — Mon, 17 Jun 2013 12:10:15 GMT

Hello,

I am trying to connect with ADS1293. I have used the example code demo-app03. I can write and read all registers of ADS1293 but the PORT2 interrupt never occurs. The pin DRDYB is to 3.3V, but when I connect this pin to MSP430F2274 this line goes to 0V.

I have modified the code including "TI_ADS1293_DRDYB_PxREN |=TI_ADS1293_DRDYB_PIN;" to enable pull-up resistor, and the pin goes to 3V but the interrupt doesn't ocurr.

Could you help me?

Thanks.

ADS1298 vs ADS1299

Greg Jackson1 — Wed, 05 Dec 2012 20:13:09 GMT

For building out an EEG system, can somebody explain the key differences between the ADS1298 and the ADS1299? The data sheet for the ADS1298 suggests it can be used for EEG. I realize it's SNR is slightly lower than the 1299, but its power consumption is also significantly lower (an important consideration for a wireless system).

Any help / feedback / etc would be greatly appreciated.