LayerscapeのトピックRe: LS1028A DisplayPort Voltage Levels

LS1028A DisplayPort Voltage Levels

jimmymm — Wed, 25 Nov 2020 00:07:52 GMT

I am working to interface the LS1028A's DisplayPort, and have questions surrounding the voltage level and limits for DisplayPort.

Described in the LS1028A datasheet, the power domain for DisplayPort is "DP_SVDD". This supply is based on a filtered VDD (1.0V). I have found several references to DisplayPort's physical interface being upwards of 3.3V. The DisplayPort lanes are outputs, but the DisplayPort Aux can be an input. I am concerned with a 3.3V signal on these pins if the domain is VDD. I found no reference to protection against this scenario.

Is there any input protection against receiving 3.3V on the DisplayPort Aux input? Can they accept this voltage?

Re: LS1028A DisplayPort Voltage Levels

Bulat — Wed, 25 Nov 2020 06:22:42 GMT

I am not sure what are "several references to DisplayPort's physical interface being upwards of 3.3V", please clarify.
From our side, the user must not exceed specifications listed in the LS1028A data sheet.

Regards,

Bulat

Re: LS1028A DisplayPort Voltage Levels

jimmymm — Wed, 25 Nov 2020 15:11:06 GMT

According to the VESA DisplayPort 1.2 standard, Hot Plug Detect has a voltage range of 2.25V minimum to 3.6V maximum. This is an input to the LS1028A with a OVDD (1.8V) power domain.

The LS1028A's AUX channel is an Input/Output and has peak-to-peak differential voltages ranging up to 1.38V with a max common mode voltage of 2.0V. The power domain for these pins are DP_SVDD (1.0V).

Many protection circuitry components targeted for DisplayPort applications include a working voltage of 3.3V. This includes the Nexperia PUSB3FR4 utilized on the LS1028A's Reference Design Board.

Re: LS1028A DisplayPort Voltage Levels

Bulat — Thu, 26 Nov 2020 09:39:37 GMT

DP_HPD signal of the LS1028A is 3.3V tolerant.

AUX signal path consists of two segments, first is DP bus itself (covered by VESA specifcations) and AC coupled connection to the LS1028A pins.
Max common mode voltage of 2.0V is a DP 1.3 specification. This DC voltage is removed from the LS1028A due to AC coupling. So in fact 1V supply is enough to be compliant with VESA specifications.

Protection device is used for high-level ESD protection. It is connected to DP bus where the voltage can be as high as a sum of common mode voltage (DC) plus dynamic voltage of differential signals.

Regards,

Bulat