Hi Khalid,
The issue you’re describing is a classic symptom of power supply instability or inadequate instantaneous current delivery during LTE transmission bursts.
Even though you added a 100µF capacitor to the 5V input, the fundamental problem likely lies in the high transient current draw of the EC200U during RF transmission and potential voltage sag on the 5V rail, or limitations in the modem board’s internal power circuitry.
High Current Requirement: The EC200U can draw 500–900 mA during LTE data transmission (depending on band and model, e.g., LTE-FDD B1 at 22.89 dBm draws ~699 mA on EC200U-EU).
Power Supply Recommendation: The external 5V supply should support at least 2 A (LTE only) or 3 A (GSM + LTE).
Voltage Drop Concern: The input voltage (VBAT_BB/VBAT_RF, 3.3–4.3V) must not sag more than ~400 mV. If the voltage dips too much, the baseband may crash, leading to the LEDs turning off and loss of AT/PPP communication.
Recommended Steps to Debug / Fix
A. Power Supply Verification
Use a robust external PSU rated for at least 3 A peak output. Avoid relying solely on USB ports or weak adapters.
Increase input capacitance—100µF may be insufficient. Consider 470µF or more with low ESR, placed close to the modem’s power input.
B. Diagnostics (if issue persists)
Check Module Status: If the module is temporarily responsive, send AT+CFUN? to see if it’s functional (+CFUN: 1).
Monitor Voltage: Use a multimeter or ADC (if exposed) to measure voltage on power rails during data bursts. If voltage drops below 3.3 V on internal VBAT lines, the module will fail. You can use AT+QADC=0 if ADC pins are accessible.
C. LED Behavior & Recovery
Power LED ON, Net LEDs OFF: Confirms the module is powered but core functions have crashed.
Recovery: Use the RESET_N pin (drive low for ≥100 ms) or perform a full power cycle to restore functionality.
In summary, this is almost certainly a power delivery issue during LTE transmission bursts. Improving the power supply’s current capacity and transient response is usually sufficient to resolve it.
Hope this helps!
Have a great day!
Best Regards,
Ananthan