2 Vsense Waveform

In practical applications, the device’s Vsense pin can be used to sense the current flowing through the LDO. This pin may be left floating to simplify the design if the feature is not needed. However, this pin can also characterize the failure type when an issue occurs. Therefore, customers often measure the voltage on this pin to identify the failure type when troubleshooting.

When this pin is left floating, oscillation on the Vsense voltage is observed at power-up. This behavior is normal. The datasheet specifies that a 1uF capacitor connected to ground is required on this pin for frequency compensation. In other words, the current sensing circuit needs an external capacitor to ensure a stable output and proper operation within the specified bandwidth. The oscillation observed is sinusoidal, which is caused by insufficient loop stability. Even if SENSE_EN and SENSE_SEL are both pulled low and the current sense function is disabled, the Vsense pin may still oscillate if no external capacitor is connected. Therefore, it is not available for diagnosing the failure in this state. However, the oscillation does not affect device reliability as long as the pin voltage is within the recommended range.