LMG1210: Schmitt trigger in EVM and propagation delay

Shengnan Li

Part Number: LMG1210

Hi,

I am using LMG1210 for envelope tracking application, the topology is 4 phase synchronous buck at 25MHz. I have a few questions:

1. in EVM there are two Schmitt triggers in the input, and the purpose is 'a precision signal to measure', can you explain more about why it is not precise without the buffer? and what cause it?

2. I have max9111 LVDS interface device to convert the differential PWM to single ended PWM, can it also take the function of the schmitt buffer?

3. there are 4 phase interleaves in our circuit, the phase difference is 10ns since the switching frequency is 25MHz. LGM1210 has a propagation 10ns to 18ns, does this variation add error on our phase delay?

Thanks!

over 1 year ago

0 Daniel W over 1 year ago

TI__Genius 13216 points

Hi,

The purpose of the buffer is to ensure a clean, fast switching input in order to make measurement easier despite what input is given to the EVM. In order to have a precise input it is simply important to have a low noise input that has a short rise/fall time.
It appears this device has a very short rise/fall time so it should be good for this application
Yes, the prop delay difference in each device will add variation to the phase delay. However, the prop delay for each device will be consistent.

Thanks,

Daniel W

0 Shengnan Li over 1 year ago in reply to Daniel W

Expert 1010 points

Daniel,

Thanks for the reply.

One more question: the eval board use this for scope connection, will it cause signal distortion at higher frequency, is there better options?

Thanks!

0 Daniel W over 1 year ago in reply to Shengnan Li

TI__Genius 13216 points

Hi,

The tip and barrel probe will be optimal for low inductance. Keeping the probe points as close to the device as possible will reduce distortion from board parasitics.

Thanks,

Daniel W

0 Shengnan Li over 1 year ago in reply to Daniel W

Expert 1010 points

Is SMA connector better than probe, in low side measurement?

+1 Daniel W over 1 year ago in reply to Shengnan Li

TI__Genius 13216 points

Hi Shengnan,

Either is a viable option as the SMA connector is a common high frequency option.

Thanks,

Daniel W

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LMG1210: Schmitt trigger in EVM and propagation delay