LMP91300: LMP91300 for the measurements question

Mickey Zhang

Genius 12080 points

Part Number: LMP91300
Other Parts Discussed in Thread: LDC1101, LDC1101EVM

Hi team,

The customer is using LMP91300SWIFEVM with the capacitance 68uH, ±25% and the inductance 390pF, ±5%.

The capacitance number is 23680C and the inductance number is GRM1885C1H391JA01D. They are made by Murata company.

He uses the EVM to measure the RP value that is the LC parallel circuit. Then he uses the impedance analyzer

(the number is KEYSIGHT E4990A) to measure the RP value. He found the RP values between the EVM and the impedance analyzer

are very different. Their maximum difference is 3K ohm.

Q1: For the different RP value, would you provide some suggestions?

Q2: Does a register of LMP91300 stores the digital value that is the RP value converts. If it does, which is the register of LMP91300?

Best Wishes,
Mickey Zhang
Asia Customer Support Center
Texas Instruments

over 7 years ago

0 Luke LaPointe over 7 years ago

TI__Genius 13335 points

Hello Mickey,
The LMP91300 does not directly store the value of RP. It has the value called "Proximity Data", which is a ratio of the RP settings that represents the actual RP of the circuit. You can convert this data to RP using Step 8 of section "8.2.2.2 Determining The RP of an LC Tank". We also make a note that this value may be ±25% different than the value you measure with an impedance analyzer. Now, if you are trying to make an RP measurement and since your oscillation frequency is above 500kHz, then we would suggest to use the LDC1101 which has a much tighter tolerance on RP readings.
Regards,
Luke