Difference between Reference Design Voltage and Measured Voltage

[agodeau]

Hi,

We are bringing up a board based on the NXP Volansys Modular Gateway Reference Design. We are setting 5.2V on the power supply to achieve 5.0V on the J15 connector.

The current drawn by the board (as shown by the power supply) is almost 1.5A.
The measuremets results are:
* U8_LTC2
- voltage on the R22_LTC2 - 4.29V (should be 5V)
* TP3 (VSYS_5V) - 3.49V (Reference Design Value: 5V)
* R141 (SYS_5V) - 3.6V (Reference Design Value: 5V)
* TP20 (VSYS_5V) - 3.45V (Reference Design Value: 5V)
* R147 (VSYS_5V) - 3.44V (Reference Design Value: 5V)
* TP21 (VCC_3V3) - 0.14V (Reference Design Value: 3.3V)
* TP22 (VDD_3V3) - 0.14V (Reference Design Value:3.3V)

What could be causing the voltage drop between the reference design value and the measured value?

Thanks

[agodeau]

Hi Mrudang,

1. Impedance between SYS_5V and GND: No continuity, Impedance between 3.3V and GND: 0.5 to 0.8 ohms, Impedance between 3.3V and 5V: No continuity, Impedance between VSYS_5V and GND: No continuity
2. I do not think is it a power adapter issue.
3. Still working on this.

Thanks,

Aquiel

[mrudangshelat1]

Hi Aquiel,

Thanks for sharing the test data.

Based on your testing it shows that impedance between 3.3V and GND is <1 ohm (low impedance). It means that the board power is short. And due to that, the complete power rails are getting off/dropdown. Kindly remove L7 and check the which side the 3.3V is getting low impedance with GND. DC-DC Buck side or System load end. 

Regards,

Mrudang

[agodeau]

Hi Mrudang,

I am currently going through these checks right now.

Thanks,

Aquiel

[mrudangshelat1]

Hi Aquiel,

Please check the below data and let us know your findings.

1. There could be some shorting on the board. Please check the Impedance between 5V and GND, 3.3V and GND and 5V and GND.
2. Since SYS_5V and VSYS_5V are low, there might be an issue with the power adapter. Please check the power adapter's load regulation. 
3. Kindly check the SYS_5V and VSYS_5V value while setting the Input voltage from 5V to 5.5V

Regards,

Mrudang

[mrudangshelat1]

Hi Aquiel,

Any update on the above query?

Regards,

Mrudang