LDCCOILEVM: the formula for the appropriate capacitor value

Hirotaka Matsumoto

Part Number: LDCCOILEVM
Other Parts Discussed in Thread: LDC1101

Hi all

Would you mind if we ask LDCCOILEVM?

"The appropriate capacitor value should be chosen according to the following formula Fo=1/(2π×√LC)"
->We would like to calculate capacitor value the coil which is "Coil S: 10mm, 16 turns, 4mil trace, 4mil spacing, 2 layers"
   We think the formula is C=1/(4*π^2*L*Fo^2).
   In this case, how much of the value of Fo and L should we use?
   Fo=1MHz, L=300uH?(at the point which the value Q is the highest)

Kind regards,

Hirotaka Matsumoto

over 7 years ago

0 Ben Kasemsadeh over 7 years ago

TI__Genius 13650 points

Hello Matsumoto-san,

yes, the formula is correct. Sensor design considerations and capacitor choices are explained in this apps note: http://www.ti.com/lit/an/snoa930/snoa930.pdf . There is also a spreadsheet calculation tool for the LDCs here: http://www.ti.com/lit/zip/slyc137

0 Hirotaka Matsumoto over 7 years ago in reply to Ben Kasemsadeh

Guru 27565 points

Ben san

Thank you for your reply always!

We would like to confirm one point.
->We would like to calculate capacitor value the coil which is "Coil S: 10mm, 16 turns, 4mil trace, 4mil spacing, 2 layers"
   We think the formula is C=1/(4*π^2*L*Fo^2).
   In this case, how much of the value of Fo and L should we use?
   Fo=1MHz, L=300uH?(at the point which the value Q is the highest)

The value of sensor cpacitance will be 89pF.

On the LDC1101's datasheet P34, there are following descriptions.
1. Ensure that the sensor characteristics are within the Sensor boundary conditions:
(a) 500 kHz < ƒ SENSOR < 10 MHz
(b) 100 pF < C SENSOR < 10 nF
(c) 1 µH < L SENSOR < 500 µH

So, should we use Csensor=100pF or 200pF?

We appreciate your help always.

Kind regards,

Hirotaka Matsumoto

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LDCCOILEVM: the formula for the appropriate capacitor value