LMP91000: Keeping sensor polarized in Standby mode

Hi Frederic,

We're looking into this and will get back to you shortly.

thanks,

Ren

Hi Ren,

Just to illustrate the issue, I attach the herebelow curves showing the voltage between C1 and C2 (C1 is taken after an OPAMP follower buffer).

1. In blue you have 1.5s measurements at 5s interval (50s total) duration. You can clearly see the spikes when transitionning from STANDBY mode to 3-LEAD mode. I had to limit the scale of the Y axis but the spike goes up to 1.2V correspopnding to saturation. After the spike you can see the signal going down.

2. In Orange the LMP is kept in 3-LEAD mode all the time for the same 50s. You can see the same spike on the first measurement then the stabilization phase which takes about 10s.

So you could answer that I should wait for 10s in 3-LEAD mode after the transition from STANDBY but for I guess this would not be optimized for 30s measurement period.

I guess that the STANDBY mode was designed so that the sensor is kept polarized by A1 and all its pin should see the same conditions in both modes (same voltage and same impedance).

However it seems that some glitches happen during the transition phase which modifies the conditions (on the Working electrode I guess) and destabilize the sensor due to its highly capacitive nature.

Thanks for your support.

The standby mode is supposed to keep the sensor polarized so that when the TAI is powered back on, the sensor does not spend too much time to stabilize (as opposed to the deep sleep mode).

But when comparing the permanent 3-LEAD mode and STANDBY mode (see curves) this is not the case. The sensor is being disturbed and takes about 10s to reach a stable value.

I am try to find a solution to minimize this disturbance and therefore optimize sensor stabilization time and reduce energy consumption.

On the datasheet is is written that  "For power savings, the transimpedance amplifier can be turned off and instead a load impedance equivalent to the TIA’s inputs impedance is switched in."

Could you provide some more details on the transition process to STANDBY mode.

Kind regards.

Frederic

Hello Ren,

I plan indeed to have the sensor biased at all time.

There are two solutions for that : permanent 3-LEAD mode (TIA on all time) or STANDBY mode to turn off TIA in between  measurement.

As already explained I am trying to use the STANDBY mode and minimize the disturnances on the sensor when transitionning from STANDBY to 3-LEAD mode. ie ; having the blue plot meet the orange plot sooner. 

To be able to do that it would be very helpful to know what is connected to what inside the LMP91000 while in STANDBY mode. Could you please provide such information. 

Thanks for your support.

Frederic