TLK105L MLED polarity

g.f.

Guru 15520 points

Other Parts Discussed in Thread: TLK105L

Hi,

I have questions about TLK105L MLED pin polarity.

I'm going to route the MLED to pin 29.

In TLK105L datasheet(rev.c) page. 75 Table 7-40,

bit9 of MLEDCR register is written as following:

//////////////////////////////////////////////////////////////

The polarity of MLED depends on the routing configuration and the strap in use on the selected pin.

If the pin is (strap) PU then polarity is low, if the pin is (strap) PD the polarity is high. /

/////////////////////////////////////////////////////////////

1. Is this means that if PHYAD0 is High at POR, MLED polarity will be active "Low" and

if PHYAD0 is Low at POR, MLED polarity will be active "High" ?

2. After POR, if I invert the value of MLEDCR bit9, does logic be reversed?

What I meant is, if MLED polarity is Low by strap, does MLED polarity be active High logic

if I write "1" to the MLEDCR bit9?

best regards,

g.f.

over 10 years ago

0 Ross Pimentel over 10 years ago

TI__Mastermind 23675 points

Hi g.f.,

If you pull the line high at POR then the polarity is active LOW, which means that the pin will be configured as a current sink. A good example of a pull-up with an LED on the pin is on page #33 in the datasheet.

If you pull the line low at POR then the polarity is active HIGH, which means that the pin will be configured as a current source. The LED will need to be flipped compared to the example on page #33.

If you reverse switch the value in Register 0x0025 (MLEDCR) bit[9] from a '1' to a '0' or from a '0' to a '1', you will switch the polarity for this pin (i.e. from a sink to source or vice verse).

This will give you flexibility if you would prefer to have the PHY act as the current source or sink but want to have a specific PHYID.

Regards,

Ross

0 g.f. over 10 years ago in reply to Ross Pimentel

Guru 15520 points

Hi Ross,

Thank you for the reply.

I understood but I have one more question.

If reverse switch the value in Register(MLEDCR) bit[9] after POR,
I guess I need to modify the hardware to let LED works, is it correct?
(Modify Pullup to Pulldown, or Pulldown to Pullup)

I refer to TLK110EVM User guide page.9, it seem that EVM can switch Pulldown or Pullup by jumper.
www.ti.com/.../sllu155.pdf

So, PHY Address and MLED polarity are selected at bootstrap.
If user want to change the MLED polarity after POR,
change the value of MLEDCR but need a hardware modification to let LED works as in TLK110EVM.
Is it correct?

best regards,
g.f.

0 Ross Pimentel over 10 years ago in reply to g.f.

TI__Mastermind 23675 points

Hi g.f.,

You are correct if you want the same operation, here is what I mean by that:

Lets say that on page 9 you set the jumper as a pull-up. On POR the register will latch to an active LOW since the pin will be a current sink. When the device is linked, the pin will go low and the LED will light. If you were to switch the polarity without switching the hardware what would happen is this....

When link is established, the pin will now go HIGH since you flipped the polarity. You will have 3.3V at the pin and 3.3V at the pull-up, which means the LED will not be light. When link is not established, the pin will go LOW and the LED will light (thus changing the operation).

If you still want the LED to light when the Link is established what you will need to do is change the jumper, or flip the diode so that when Link is established the pin will go HIGH as expected, but will sink the current to ground connection since you are connecting it through a pull-down.

Regards,
Ross

0 g.f. over 10 years ago in reply to Ross Pimentel

Guru 15520 points

Hi Ross,

Thank you for the reply.
I understood.

best regards,
g.f.

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TLK105L MLED polarity