ADS1298R Power Consumption

Hey Mihir,

From which datasheet specifications did you get the 600 uA current? The digital current alone is specified as 500 uA when DVDD = 3 V.

How are you measuring current? To get an accurate depiction of current, you should be measuring the current after the power management devices.

I'd recommend tying the unused analog inputs high instead of low. That is sure to reduce the amount of current that is consumed by the device quiescently.

Regards,
Brian Pisani

I have been informed as following,

he current consumption and power dissipation specs in the datasheet are given on page 16. This assumes that the device is using an external clock oscillator input. The internal oscillator will add approximately 120uW to the total device consumption. All ECG features are turned off, including RLD, WCT, and PACE amplifiers. I believe the RESP modulation/demodulation feature is disabled as well in the ‘R’ devices.

If the user is using LP Mode and running the data rate at 250 SPS, the total expected power dissipation for ADS1294 is around 4.1mW with a 3-V analog supply and 8.3mW with a 5-V analog supply. Each channel consumes approximately 818uW, so they will save about 2.454mW of power in Case 1 when 3 channels are powered-down.

This helps me to calculate 600uA.

Measurement on EVM is after power management, I have actually bypassed the power management by giving direct 3V external supply

Let me follow up and get back to you.

Thanks Brian, will wait for update from you.

BTW, if DVDD 3V takes 500uA on ADS1298R. What will be the current if we change DVDD to 1.8V? Does the ADS1294R or ADS1194 also take similar current on DVDD rail as ADS1298R ? 

Hey Mihir,

I think I have uncovered the discrepancy. The number you use for single channel power was measured when the device was in HR mode. Therefore when you subtract it from the total power consumption of the device, it takes a disproportionate amount from that total power to make the power look very low. If you go to page 16 in the datasheet where this power is specified, look at the very top of the page where it lists conditions. When not otherwise mentioned, all specifications were taken when the device is in HR mode.

Actually the LP mode single channel power is not listed in the datasheet but can be estimated from the other numbers. We can take the power of the ADS1298, subtract the ADS1296 power, and divide that quantity in half to get the per channel power in LP mode. It ends up being 350 uW.

Now do a similar calculation to what you were doing before. For the AD1298 the total power is 6 mW. Subtract 7*0.35 mW to get a power of 3.55 mW when only one channel is active. Then divide by the voltage to get 1.18 mA which is very close to the measured value.

Regarding your question about DVDD voltage. The power listed on page 16 in the datasheet was taken when DVDD = 1.8 V since this is in the listed conditions at the top of the page. You can then calculate the power "overhead" difference for each device (ADS1298, 6, 4) by taking the total power and subtracting all the per channel power. The difference in overhead is actually very small between devices.

Regards,
Brian Pisani

Thanks Brian, It clarifies a lot. 

It means using 1 channel only in LP Mode from ADS1294, 6, 8, 8R will take the same power. And that will be around 1.18mA...   Per Channel power consumption is ~350uW for all these chipset.   (Datasheet page-1 it says 750uW / Channel, seems conflicting)

The ADS1292/R datasheet page-1 says 335uW per channel and overall total power in page-6 is 670uW only. Does that mean 1 Channel @ 250SPS will take very very less current compare to 1.18mA? Can you help me know what that will be? 

Regards,

Mihir

Hey Mihir,

The power dissipation for the ADs1292 will be total power (670 uW) - per channel power (335 uW) = 335 uW. The current drawn at 3 V will be 112 uA.

Regards,

Brian Pisani

Thanks Brian,

ADS1294 Datasheet page-1 says 750uW / Channel, while the calculation we did based on page16 table, it comes to 350uW/channel. Can you pls. help us know which one is correct ?

Mihir

Hey Mihir,

For HR mode it comes out a lot closer to 750 uW (it's about 800 uW). I can find out where the number on page 1 of the datasheet comes from exactly, though. I will follow up.

Regards,
Brian

Hello Mihir,

It seems like the number on the front page of the datasheet is an error. You should look to the numbers in the spec table for how the device performs definitively. I will make sure we change that number on page 1 when we revise the datasheet.

Regards,
Brian Pisani

Thanks Brian.

It is clear that ADS1298R used in 1-lead ECG and 1-channel for respiration will take ~1.18mA compare to ADS1292R in same configuration will take ~300uA. This is a huge difference when it comes to battery life. 

Thanks for your help.

Regards,

Mihir

Hey Mihir,

Yes the ADS1292 is our biopotential AFE for battery powered applications whereas the ADS1294/6/8 have a larger feature set and are targeted more towards clinical systems that draw power from the line.

Brian