TPS3808G09DBVR Circuit Design Flaws That Can Lead to Unexpected Resets

Title: Circuit Design Flaws in TPS3808G09DBVR That Can Lead to Unexpected Resets and How to Fix Them

The TPS3808G09DBVR is a popular voltage supervisor IC, commonly used to monitor the Power supply voltage levels and reset systems when those levels are outside the desired range. However, improper circuit design can lead to unexpected resets, which can affect system performance and reliability. In this article, we will discuss potential design flaws that may cause this issue and provide step-by-step solutions to fix them.

Common Causes of Unexpected Resets

Incorrect capacitor Selection for the Reset Pin: The TPS3808G09DBVR typically requires a capacitor (often between 0.1µF to 10µF) on its reset pin to stabilize the reset signal. Flaw: If the wrong value capacitor is used, the reset signal may become unstable, leading to unexpected resets. Too large a capacitor may delay the reset response, while too small a capacitor might not filter noise effectively, causing the IC to reset erroneously. Solution: Ensure you select the correct capacitor value according to the datasheet recommendations (usually 0.1µF to 1µF) and choose a capacitor with low equivalent series resistance (ESR) to prevent instability. Improper Grounding and Layout Issues: Flaw: If the grounding is poor or if the layout causes noisy signals or voltage spikes, the TPS3808G09DBVR can mistakenly detect these as voltage drops, triggering a reset. Solution: Ensure a solid, low-resistance ground plane, and minimize noise coupling by placing the reset circuitry away from high-power traces or noisy components. Also, consider using ground planes and decoupling capacitors near sensitive pins. Incorrect Threshold Voltage Settings: Flaw: The TPS3808G09DBVR offers adjustable threshold settings for triggering a reset (through the reference pins or external resistors). Incorrect resistor values or improper voltage reference can cause the reset threshold to be too sensitive, causing frequent resets. Solution: Check and adjust the resistors connected to the threshold pins (typically the A and B pins). Make sure the threshold voltage corresponds to your system’s nominal operating voltage and does not trigger false resets. Supply Voltage Fluctuations: Flaw: Unexpected resets can occur if there are fluctuations or transients in the power supply voltage that the TPS3808G09DBVR interprets as falling below the set threshold. Power supply instability can lead to frequent or random resets. Solution: Use high-quality voltage regulators or power supplies with low ripple. Additionally, place decoupling capacitors (typically 0.1µF and 10µF) close to the power input pins of the TPS3808G09DBVR to stabilize the supply voltage. Overvoltage and Undervoltage Detection Errors: Flaw: The TPS3808G09DBVR monitors the supply voltage and asserts a reset when it falls outside of the configured voltage window. Incorrect detection can occur if the IC's voltage detection window is too narrow or too wide, potentially causing unnecessary resets. Solution: Carefully configure the overvoltage and undervoltage thresholds to match your system's specifications. Use precision resistors for setting these thresholds and ensure that the power supply is stable and well within these limits.

Step-by-Step Troubleshooting and Solutions

Step 1: Check Capacitor Placement and Value

Review the datasheet for the recommended capacitor value for the reset pin. Replace any overly large or small capacitors with values in the range specified (0.1µF to 1µF). Verify that the capacitor is placed as close as possible to the reset pin to minimize noise interference.

Step 2: Improve Grounding and Layout

Inspect your PCB layout for ground noise and poor signal integrity. Ensure that all ground traces are wide and low-resistance. Use a separate ground plane for sensitive components like the TPS3808G09DBVR to prevent interference from noisy signals. Avoid running high-power traces near the reset circuitry to reduce the chances of false resets due to noise.

Step 3: Validate Threshold Voltage Settings

Double-check the resistor values connected to the reference pins (A and B) to ensure the voltage thresholds are set appropriately. Use a multimeter or oscilloscope to verify that the voltage being monitored by the TPS3808G09DBVR is within the expected range.

Step 4: Check the Power Supply

Measure the voltage levels coming into the TPS3808G09DBVR to ensure there are no dips or spikes. If you observe any power supply fluctuations, consider using a more stable regulator or adding more decoupling capacitors to smooth out voltage irregularities.

Step 5: Monitor the Overvoltage and Undervoltage Settings

Confirm that the TPS3808G09DBVR’s detection window is appropriate for your application. If the reset triggers unnecessarily, widen the detection window. Adjust the resistors connected to the A and B pins to modify the threshold window, ensuring it fits your system’s voltage specifications.

Conclusion

Unexpected resets in systems using the TPS3808G09DBVR can usually be traced back to issues with capacitors, layout, threshold settings, or power supply stability. By carefully following the troubleshooting steps outlined above, you can ensure that the voltage supervisor operates reliably and prevents false resets. Always follow the manufacturer’s datasheet and application notes for best practices in selecting components and designing your circuit to avoid these common pitfalls.