TMS570LS3137: TMS570 output driver impedance value

Hello,

It is not good to connect a output pin to ground. If the output value is set to high, the pin is driven high which may damage the part.

Hello Mr. Wang,

Thank you for your reply. I need to verify, If we have a scenario where receiver fails in short to ground, will TMS570 driver impedance (or resistance) be enough to drive it for a short duration of time so asked about the steady state resistance or impedance values (minimum and maximum) for the TMS570 drivers?

Hello，

From the datasheet, the impedance can be calculated by the 0.2*VCCIO drop with Ioma (2mA, 4mA, or 8mA) of current. The estimated resistance value for 2mA pins is:

0.2*3.3V/2mA = 330ohms.

Hello Mr. QJ Wang, 

Thanks for the reply. When simulated the IBIS model of TMS570 in Hyperlynx tool with output shorted to ground of MIBSPI5SOMI[0] driver, i could see that driver is able to source current upto 157.7mA. In this case driver impedance is coming out to be approx. 3.3V/0.157A = 21Ohms which is not matching with the value you mentioned above. Please find the attached snapshots from the simulation. So can we say that TMS driver current can goes upto 157mA in case of short to ground?

The output buffer drive strength of an I/O specifies how much current it can drive and sink while maintaining the minimum Voh and Vol levels. The output drive strength is not the current that the pin will deliver. 

MibSPI5_SOMI[0] (8mA buffer) can drive a current of 8mA and still produce output levels: Voh=0.8*3.3=2.64V, so it can drive a 2.64/8mA=330ohm resistor to GND and still get the guaranteed output level.

I am sorry I think this value (330ohms) is for the external load rather than the internal impedance. I will check with our design team.

Hello Mr. Wang,

Did you receive any reply from the design team, regarding the same?

Thanks and Best regards,

Nilesh

Hello Nilesh,

I will let you know once I get any comments.