LMX8410L: About power sequence order & layout questions

Ryan Lee TW

Intellectual 506 points

Part Number: LMX8410L

Hi Team,

Q1:

I am wondering about the blue part and red part description in datasheet chapter 7.5.2 as below screenshot.

I think the two descriptions are inconsistent even conflicting, or it is just my misunderstanding.

Is the right power sequence as below steps?

Power On Device.
Reset = 1, R0<D1> to reset register.
Reset = 0, R0<D1> to remove reset.
Program Register R127 to value 0x7F0003.
Program Register R6 to value 0x 060100
Program Register R127 to R0 in reverse order
If using internal LO, wait 10msec.
Program Register R0 <D3> for FCAL_EN = 1 to ensure that the VCO calibration runs from a stable state.

Q2:

For the IF output from LMX8410L, could TI team advise the value of series capacitor to ADC devices?

The IF frequency will be zero frequency, or close to zero frequency.

Will the 0.01uF be right for Zero-IF architecture?

Thanks.

over 2 years ago

0 Jane Pieh over 2 years ago

Prodigy 30 points

Hi Team:

Follow the q2, Because LMX8410L have a large output Vpp, How to attenuator it for our ADC input? our ADC input can handle Vpp 0.8V only. Thank you.

B.R. Jane

0 Dean Banerjee over 2 years ago

TI__Mastermind 27581 points

Jane,

1. Yes, I agree with this that it is best to reset the device, then do R127, then R6 and then R127 to R0. I see that TICSPro does it this way, except for no Reset.

2. For the capacitor value, you might target 1 ohm at the target frequency of interest. So if you say that this can be 1 MHz, that works out to 0.1 uF. So maybe 0.01 uF might be a little small, depending on what you say DC is. Also, on our EVMs, we have used the broadband ATC 520L103KT16T capacitors for this kind of outptus.

Regards,

Dean

0 Ryan Lee TW over 2 years ago in reply to Dean Banerjee

Intellectual 506 points

Hi Dean,

Thanks for answers, it is very helpful.

As mention above, LMX8410L have a large output Vpp, how to attenuator it for our ADC input? our ADC input can handle Vpp 0.8V only.

Thank you.

+1 Noel Fung over 2 years ago in reply to Ryan Lee TW

TI__Guru* 81750 points

Hi Ryan,

We can add a resistive attenuator at the output of LMX to reduce the voltage swing. There are many online calculators available in the web, you can make use of these calculators to find out the resistor values.

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LMX8410L: About power sequence order & layout questions