Question, i.MX25 unused pin handling

[Aemj]

Dear team,

I would like to ask about unused pin handling of i.MX25.

(1)

As for JTAG related pins of i.MX253, the following handling is done on my customer’s board. Are these correct when JTAG is not used?

- RTCK/TCK/TMS/TDI/TDO/TRSTB/DE_B : NC

- SJC_MOD : Pull-down through 10K ohm register.

TDO pad will be INPUT pad after reset, then it may need some external pull-up. Is it true?

(2)

As for USBPHY1 related pins of i.MX253, the following handling is done on my customer’s board. Are these correct when USBPHY1 is not used?

- USBPHY1_VBUS/USBPHY1_UID/USBPHY1_DP/USBPHY1_DM : NC

- USBPHY1_RREF : Pull-up through 10K ohm register

- USBPHY1_VDDA/USBPHY1_UPLLVDD/USBPHY1_VDDA_BIAS : connected to 3.3V

- USBPHY1_VSSA/USBPHY1_UPLLVSS/USBPHY1_VSSA_BIAS : Connected to GND

(3)

As for USBPHY2 related pins of i.MX253, the following handling is done on my customer’s board. Are these correct when USBPHY2 is not used?

- USBPHY2_DP/USBPHY2_DM : NC

- USBPHY2_VDD : Connected to 3.3V

- USBPHY2_VSS : Connected to GND

Thanks in advance.

Miyamoto

[Yuri]

Hello,

1.

 JTAG configuration is correct. TDO may be left free.

2.
it is possible to pull down the USBPHY1_VBUS, USBPHY1_DP, USBPHY1_DM,

USBPHY1_UID, USBPHY1_RREF, USBPHY2_DM and USBPHY2_DP signals with

10kOhm pull-down resistors, when not used in the design.

  As for power supply and GND - correct :

USBPHY1_VDDA/USBPHY1_UPLLVDD/USBPHY1_VDDA_BIAS : to 3.3V

USBPHY1_VSSA/USBPHY1_UPLLVSS/USBPHY1_VSSA_BIAS : to GND

3.

  Perhaps it would be better to pull down data signals DP, DM .

As for power supply and GND - correct :

 USBPHY2_VDD : to 3.3V

 USBPHY2_VSS : to GND

Have a great day,
Yuri

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[Aemj]

Hi Yuri,

Sorry for my late response and thanks for your kindly explanation.

Actually, those pads are configured as I mentioned now on my customer's board.

And they do not want to change the current pads configuration.

Is it possible?

Thanks,

Miyamoto

[Yuri]

Hello,

  unused signal termination is applied 1) for noise-immunity, 2) to avoid additional consumption.   

Also, if some pins are left floating, system software should be very accurate, say, to avoid  

spurious USB interrupts by floating D+/D- lines.

Regards,

Yuri.