Pinouts of LTC4125

I am wondering if PTH1(Pin11) and PHT2(Pin10) of LTC4125 are output or input pin. 

Also is it possible to apply a certain level of voltage to those pins to adjust Vpp across Tx coil?

Thanks,

Jay

  • 0
    •  Analog Employees 
    on Jul 22, 2019 1:45 PM over 1 year ago

    Hi Jay,

    That is a great question. If PTH1 and PTH2 pins are left open or connected with a small cap, they will be charged up by internal source depended on the step count of the optimum power search feature. It will also be pulled down in case a fault is detected. 

    To apply a certain level of voltage to PTH1 and PTH2 pin is possible. However, you need to somehow disable the search feature and connect a pull-up resistor (in case these pins are pulled down in fault). The voltage on this pin decides the duty cycle of each half bridge in the circuit and the change of duty cycle will cause the change at Vpp across Tx coil. 

    Would you let me know what feature you want to achieve with LTC4125. I may be able to help with your design if you can provide more details. 

    Thanks,

    Wenwei. 

  • Hi Wenwei,

    Thanks for your explanation. 

    I have one sensor which allows me to estimate how strong wireless coupling is. Depending on this input, Vpp across Tx coil should be adjusted by using PTH1/2 pins. I am aware that LTC4125 has similar capability, but sometimes it was not accurate and triggered higher transmitting power than expected. 

    So I am evaluating several options to insure more precise Tx power based on coupling.

    BTW, how can I disable the search feature? 

    Thanks

    Jay

  • 0
    •  Analog Employees 
    on Jul 22, 2019 2:50 PM over 1 year ago in reply to JKim172

    Hi Jay,

    The way I usually use to disable the search is to fake the exit condition at the beginning of the search and short the  PTHM pin to ground. This exit condition can be triggered by connecting a 1V reference (ADR510) at IMON pin. Here is an example of the application circuit with search feature disable to achieve fixed duty cycle operation. It can be found at P25 of LTC4124 datasheet 

    As PTHM sets the starting point of the search and 1V at IMON guarantees the exit condition is met right at the beginning, the target voltage for the internal supply to charge up the PTH will be kept at its minimum. As a result, an external voltage source can be applied to PTH pins with a pull up resistor. 

    Thanks,

    Wenwei.