An INPUT_OFF warning is detected because the VIN_SNS pin voltage is below the VIN_OFF setting. The device will also typically hold SHARE_CLK low preventing other devices from turning on.
Device Behavior for VIN and SHARE_CLK
This section provides background information for a deeper understanding of how devices behave and coordinate when VIN is lost or applied.
The example waveform above illustrates how a device behaves when its VIN is lost. It also describes how devices communicate this condition to each other via the SHARE_CLK signal to insure coordinated behavior. The example starts with the device in normal operating mode with no faults. Typically the SHARE_CLK signal is connected between PSM devices to insure coherent sequencing. Let's take the scenario where VIN for the system is removed and then re-applied. The behavior of the system is as describe in the following sequence points highlighted above:
- a – The system is operating normally, with VIN good and no faults. SHARE_CLK is toggling normally to provide a common arbitrated timebase across devices for sequencing.
- b -- A device in the system detects that its VIN voltage drops below its programmed VIN_OFF threshold.
- c – The first such device to see VIN drop below VIN_OFF immediately holds SHARE_CLK low to signal to the system that VIN was lost, and a normal power down should occur
- d -- When a channel (of any device connected to the common SHARE_CLK) detects that the SHARE_CLK has stopped, it immediately disables its output
- For PSM Controllers, power deliver is stopped by the controller itself
- For PSM Managers, the output enable (VOEN) pin is de-asserted to disable the managed power supply
- e -- VIN ramps back up. Devices detect when VIN rises above their programmed VIN_ON threshold, and release the common SHARE_CLK.
- f – When the last such device in the system detects VIN rising above its programmed VIN_ON threshold, it releases the common SHARE_CLK signal and the SHARE_CLK starts toggling again. Devices connected to SHARE_CLK detect that SHARE_CLK has started, and initiate a coordinated re-sequence (the start of SHARE_CLK marks time=zero).
- f – During the coordinated re-sequence, each channel, after waiting its programmed on delay (TON_DELAY) will start ramping its voltage up
- Controllers have the ability to ramp the voltage directly, and will ramp the output consistent with the programmed TON_RISE setting.
- Managers will assert the assert the VOEN pin to enable the managed supply at this time
This coordination feature insures that as power is applied (or lost) the system remains coordinated in its sequencing behavior, and all devices agree on time=zero for up sequencing, and turn off immediately when VIN is lost.
Possible Causes:
- VIN not applied
- VIN_ON setting is too high
- Board or assembly error between the VIN_SENSE pins of the device and the VIN sensed (missing or cracked resistor, etc)
Remedies and Workarounds
Here are some things you can try to narrow things down:
- Apply sufficient VIN voltage (as seen by VIN_SNS pin)
- Change VIN_ON and VIN_OFF settings to lower values
Other Debugging Tips
- Even if VIN is applied and > VIN_ON, all channels may be Off due to SHARE_CLK pin being held low
- If this is the case, check that other PSM devices that use SHARE_CLK are not detecting a VIN problem
