DS90C189-Q1: RGB INPUT 50 OHM TERMINATION RESISTOR

kaan kayabasi

Part Number: DS90C189-Q1

Hi Team,

I designed a board which is included Analog Devices ADV7842, TI DS90C189. ADV7842 has 36-bit RGB outputs data but I use 24-bit RGB data output of ADV7842. 24-bit RGB data inputs DS90C189 after 3.3v to 1.8v level shifter. When I looked at DS90C189-Q1EVM, it have 50 ohm termination resistors(do not install) on RGB inputs. What is the cause of the 50 ohm resistors usage ? Should I use 50 ohm resistors on DS90C189 RGB inputs in my design ?

over 4 years ago

0 Aaron Heng over 4 years ago

TI__Mastermind 38930 points

Hi Kaan,

As far as I remember the 50Ω termination is the pad spacing for probing in case such as measuring the VOD in single or differential measurement. I can't find the schematic for the EVM in TI.com. I will need more time to look into this. I will get back with you by 3/24.

Aaron

0 kaan kayabasi over 4 years ago in reply to Aaron Heng

Prodigy 35 points

Aaron Heng said:
for

Hi Aaron,

DS90C189-Q1EVM board schematic

+1 Casey McCrea over 4 years ago in reply to kaan kayabasi

TI__Guru** 103215 points

Hello Kaan,

The 50 ohms are placeholders to allow for passive translation of 3.3V LVCMOS to 1.8V LVCMOS. If you place a series 50 ohm resistor between the source and DS90C189-Q1, then a 50 ohm to GND, you have effectively created a resistor divider to half the voltage going to the DS90C189-Q1 inputs and translate from 3.3V to ~1.8V logic. That is a rudimentary method and does not really take into account VOH/VOL level variation from the source. It is not required to populate these when using 1.8V logic to the DS90C189-Q1 inputs directly.

Best Regards,

Casey

0 kaan kayabasi over 4 years ago in reply to Casey McCrea

Prodigy 35 points

Casey McCrea said:
ohms

Hello Casey,

Thank you for reply.

I will connect ADV7842 RGB datas to DS90C189-Q1 inputs after 3.3v to 1.8v level shifter directly.

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DS90C189-Q1: RGB INPUT 50 OHM TERMINATION RESISTOR