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PTN3355

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Product data sheet

Rev. 3.1 — 4 November 2016

10 of 37

NXP Semiconductors

PTN3355

Low power DP to VGA adapter with integrated 1 : 2 VGA switch

7.4 VGA monitor detection

The PTN3355 implements a robust scheme for VGA monitor detection. It senses

presence or absence of VGA monitor load termination (75

) by pulsing the RGB lines.

The load sensing operation is performed periodically to determine the latest VGA

connectivity status. If the VGA monitor is disconnected, then the detection logic informs

the host platform via IRQ_HPD signal.

7.5 EDID handling

Figure 3 shows a DisplayPort-to-analog video converter between the DisplayPort source

and a VGA monitor. The PTN3355 implements a DP I2C-Over-AUX protocol, providing for

DP source access to the monitor’s DDC bus. With this, the monitor’s EDID data is made

available to DP source for access at any time.

It is the responsibility of the source to choose only video modes which are declared in the

EDID and to adjust the DisplayPort link capabilities (link rate and lane count) to provide

the necessary video bandwidth. The PTN3355 does not cache or modify the EDID to

match the capabilities of the DisplayPort link data.

If the DisplayPort source drives display modes that are not specified in the EDID mode

list, the PTN3355 does not detect such conditions, and it depends entirely on the VGA

display on what is being displayed.

7.6 Triple 8-bit video DACs and VGA outputs

The triple 8-bit video DACs output a 700 mV (peak-to-peak) analog video output signal

into 37.5

 load, as is the case of a doubly terminated 75  cable. The DAC is capable of

supporting the maximum pixel rate supported by a two-lane DP link (240 MHz).

7.6.1 DAC reference resistor

An external reference resistor must be connected between pin RSET and ground. This

resistor sets the reference current which determines the analog output level, and is

specified as 1.2 k

 with a 1 % tolerance. This value allows a 0.7 V (peak-to-peak) output

into a 37.5

 load (for example, double-terminated 75  coaxial cable).

Fig 3.

DisplayPort to VGA adapter IC sits between the DisplayPort source and a VGA

monitor with EDID

DP Tx

002aaf640

embedded

DisplayPort

source device

DP Rx

with DPCD

VIDEO DAC

DisplayPort to VGA adapter IC

box-to-box

legacy

VGA DISPLAY

WITH EDID

sink device

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