Tool/software:
Team,
My customer developed a prototype with TMS3705 and conducted an actual measurement evaluation of the antenna current. There was a large discrepancy between the current value calculated based on the assumption of drain-source on-resistance (TYP. 7-ohm, MAX. 14-ohm) in the data sheet and the actual measured value. Under the measurement conditions, the RDS(ON) was much lower (around 1-ohm?). They are wondering if there is any possibility and would like to confirm the characteristics.
My customer did do:
- VDD=5V, antenna coil resistance=10.5-ohm, dump resistor 18ohm per side, resonance frequency and drive frequency were almost matched.
- Calculated the antenna current with TYP.7-ohm in the datasheet, and the calculated value is 187 mApp.
- The actual measured value is 216 mApp. If the RDS(ON) is about 1-ohm, the calculated value will be 211 mApp, which is close to the measured value.
The following four requests from my customer, your help is needed.
1) Want to see a characteristic graph regarding the RDS(ON) of MOSFETs.
2) Want to know reason why the difference in ON resistance between TMS3705 and TRF4320 is so large.
TMS3705: TYP. 7-ohm for Pch and Nch total, MAX. 14-ohm @50mA, VDD4.5-5.0V
TRF4320: TYP. 0.9-ohm for Pch and Nch total, MAX. 1.45-ohm @1A, VDD12V
3) Want to see actual measurement data of ON resistance of MOSFET.
4) Is there any calculation tool that can calculate RDS(ON)?
One that can calculate ON resistance by entering preconditions such as VDD, current value, etc...
Could I have your comments on those?
Regards,
Nonaka
