LMH1981 output resistors

Jaden Ghylin102047

Expert 1140 points

Other Parts Discussed in Thread: LMH1982

The datasheet says to add 100ohm series resistors for current limiting.

The lmh1982 eval kit has 50ohm resistors on these lines.

Which is correct and why are the resistors spec'd on these lines? How much different is the drive of HSOUT vs VSout?

Regards,

-Jaden

over 10 years ago

0 Jeffery Pfarr over 10 years ago

TI__Genius 14317 points

The Rs resistors on these outputs are specified to protect the device in the event that the outputs are momentarily "shorted" to GND. 50 - 100 ohms is generally enough resistance to protect the device as long as the duration of the "short" event isn't too long. The HSOUT and VSOUT are both CMOS or LVCMOS outputs depending upon the Vcc supply being used (3.3 V or 5 V).

0 Jaden Ghylin102047 over 10 years ago in reply to Jeffery Pfarr

Expert 1140 points

We are running this at 3.3v, so what is their drive? Why would they be “momentarily” be shorted to GND?

-Jaden

0 Jeffery Pfarr over 10 years ago in reply to Jaden Ghylin102047

TI__Genius 14317 points

- For Q1: See pg. 16 of the attached .pdf.

- For Q2: Perhaps a technician drags a scope ground probe across the board or the output goes to a connector. Its alway good form to provide at least minimal "short to GND" protection at connector I/O.

scba011.pdf

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LMH1981 output resistors