SNLA491 August   2025 DP83826AE , DP83826AI

 

  1.   1
  2.   Trademarks
  3. 1DP83826A Application Overview
  4. 2Troubleshooting the Application
    1. 2.1 Schematic and Layout Checklist
    2. 2.2 Device Health Checks
      1. 2.2.1 Voltage Checks
      2. 2.2.2 Probe the RESET_N Signal
      3. 2.2.3 Probe RBIAS and CEXT
      4. 2.2.4 Probe the XI Clock
      5. 2.2.5 Probe the Strap Pins During Initialization
      6. 2.2.6 Probe the Serial Management Interface Signals (MDC, MDIO)
        1. 2.2.6.1 Read and Check Register Values
          1. 2.2.6.1.1 Extended Register Access
    3. 2.3 MDI Health Checks
      1. 2.3.1 Magnetics
      2. 2.3.2 Probe the MDI Signals
      3. 2.3.3 Link Quality Check
      4. 2.3.4 Compliance
    4. 2.4 MII Health Checks
      1. 2.4.1 MII Check
      2. 2.4.2 RMII Check
    5. 2.5 Loopback and PRBS
      1. 2.5.1 Loopback Modes
      2. 2.5.2 Transmitting and Receiving Packets With the MAC
      3. 2.5.3 Transmitting and Receiving Packets With BIST
  5. 3Summary
  6. 4References

2.2.3 Probe RBIAS and CEXT

The RBIAS pin is critical to PHY operation. This component is used to set the internal reference current within the device. The guidance for component selection is a single 6.49kΩ component that has a 1% tolerance for RBIAS. The preference is to have a single component over multiple in series as the tolerance range can increase.

If properly powered, a 1V signal can appear when probing the RBIAS pin for approximately 60us after power ramp before going back to 0V. CEXT needs to present a 1.7V signal while device is active.

CH 1 (3.3V Supply), CH 2 (CEXT)

DP83826A CEXT RampFigure 2-2 DP83826A CEXT Ramp

CH 1 (3.3V Supply), CH 2 (RBIAS). Notice pulse at trigger point

DP83826A RBIAS Pulse Delay vs VDDA3V3 RampFigure 2-3 DP83826A RBIAS Pulse Delay vs VDDA3V3 Ramp

CH 1 (3.3V Supply), CH 2 (RBIAS)

DP83826A RBIAS Pulse WidthFigure 2-4 DP83826A RBIAS Pulse Width