PTN3992 LDOCAP_AUX issue

[markjeffrey]

Hi

I am developing a DP to VGA converter on one of our carrier boards using the PTN3392.

Upon power up nothing seemed to be happening.

When checking the voltages I have found that pin 38 LDOCAP_AUX is sitting at 0.8V not 1.8V.

Pin 30 LDOCAP_CORE is at 1.8V as expected.

Can you have a look at the attached schematic and let me know what I am doing wrong.

[JozefKozon]

Hi Mark Jeffrey,

please refer to the schematic attached. Your schematic seems to be not complete. I don't see pull-up resistors on the SDA and SCL I2C lines and there is also missing the part with the DP connector. Could you please also provide the missing parts of the schematic for review?

With Best Regards,

Jozef

[markjeffrey]

Hi Josef

The Display port interface is connected to a SMARC Computer on Module. There is no display port connector.

(The AUX siugnals ar capacitively coupled on the SMARC module).

The VGA interface does not use the I2C interface so there is nothing connected to these signals.

[markjeffrey]

Hi Josef

Have you had a cahnc to look at the schematic?

[JozefKozon]

Hi Mark Jeffrey,

I have contacted an application engineer for the schematic review. For his answer please see below. Please answer the application engineer questions.

DESCRIPTION

Customer’s schematics looks OK, please check with customer for questions below.

1. Please ask customer to measure VDDA pin (pin 37) to see whether it is 3.3V.
2. Please ask customer to measure HPD pin status to see whether it is high (3.3V) or low (0V).
3. How many boards were built? And How many boards were seeing this issue.

With Best Regards,

Jozef

[markjeffrey]

Hi Jozef

VDDA pin 37 is at 3.3V

HPD is at 0V

We have built 2 prototypes and both are seeing this issue.

[markjeffrey]

Hi Josef

Probing the chip I noticed the JTAG pins didnt look as expected.

I cut the track on pin 5 TCK and the device sprang into life.

Measuring pin 5 at the device the voltage is 3.3V as this is an input I would have expected this to be floating.

Is there an issue with the JTAG interface on this device.

[JozefKozon]

Hi Mark Jeffrey,

please see below an answer from the application engineer.

DESCRIPTION

Where the TCK pin is connected to in customer’s application board originally?

JTAG is only used for programming firmware into internal embedded MCU resided in the PTN3392 in factory ATE test stage, it should not be used in customer’s application.

With Best Regards,

Jozef

[markjeffrey]

Hi Josef

TCK is connected to 3 other devices with JTAG interfaces as per the JTAG specification.

[JozefKozon]

Hi Mark Jeffrey,

please see below an answer from the application engineer.

DESCRIPTION

PTN3392 JTAG interface is only used for ATE test in NXP production line, please ask customer to not connect PTN3392 JTAG pins to the other devices or system JTAG interface.

It will cause application issues if PTN3392 receives random clock/data from its JTAG interface.

We don’t provide command/protocol for PTN3392 JTAG interface, so that customer would not be able to send appropriate commands

to PTN3392 through JTAG interface.

With Best Regards,

Jozef