TPS65235: Bypass FET issue

Ben Kuo

Part Number: TPS65235

Dear expert,

We face to below issue from customer side.

For Diseqc 2.0, we cannot receive the 22K tone when TPS65235 GDR pin connects to N-Mosfet even we set the Tone_Auto to 1.

After we change the Mosfet to P-channel, we can receive the 22K tone from the Diseqc 2.0 device, we also found the same issue with Paul’s project, he also has the P-Mosfet at GDR pin.

We have tried different 22KHz tone receiver mode, but it can not work. Could you give me your commend about this issue?

-Ben

over 6 years ago

0 Sam(MPAA) Zhang over 6 years ago

TI__Mastermind 19080 points

Hi Ben,

Could you post your schematic here? Or send it to my email sam.zhang@ti.com?

Regards,
Hao

0 Ben Kuo over 6 years ago in reply to Sam(MPAA) Zhang

TI__Expert 7550 points

Hi Sam,

Please find in attachment.

BTW, I also attached P FET and N FET datasheet they have tried in their system, only PFET can receive 22K tone.

-Ben

DMN3051LDITR-N-Channel.pdf FDN360P-P-Channel.pdf TPS65235-Schematic.pdf

0 Sam(MPAA) Zhang over 6 years ago in reply to Ben Kuo

TI__Mastermind 19080 points

Hi,

It should work with N-FET. Please set the Tone_Auto to 1, and pull EXTM to logic high. During the test, could you measure the voltage on Gate and Source of the MOSFET, and make sure the NMOS is turned on?
Thanks!

Regards,
Hao

0 Ben Kuo over 6 years ago in reply to Sam(MPAA) Zhang

TI__Expert 7550 points

Hi ,

Customer use external 22KHz tone and connect it to EXTM pin. Is this possible to cause this issue?
Thanks!

Ben

0 Sam(MPAA) Zhang over 6 years ago in reply to Ben Kuo

TI__Mastermind 19080 points

Hi Ben,

TPS65235 can support external 22/44kHz tone. You can refer to page 11 on the datasheet. When you have external 22kHz Tone on EXTM pin, you also need to set the EXTM _Tone bit to 0(in Control Register 1), then you can have the tone signal superposed on VLNB. Leave the TONE_AUTO=1.
For this issue, please check the items below,
1. Measure the gate and source voltage on the NMOS, make sure Vgs meet the turn on requirement. Also, do the same with PMOS.
2. Remove the external 22kHz tone on EXTM pin, just pull it to GND, and see if there is tone signal on VLNB.

Regards,
Hao

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TPS65235: Bypass FET issue