In addition to temperature sense
information, the TPS53676 and TI smart power stage devices use the TAO lines to
communicate fault information:
- Powerstage fault
(TAO_HIGH) is a fault condition detected when any of the connected
powerstage devices pulls its TAO line high (> 2.5 V). This occurs for any
fault conditions detected inside the smart powerstage itself. Refer to the
individual powerstage datasheets for a complete list of conditions which cause
the powerstage fault. Program the controller response to a powerstage fault with
MFR_PROTECTION_CONFIG.
- Powerstage not ready
(TAO_LOW) is a fault condition detected when the TAO line is low (160 mV
falling, 245 mV rising) for any reason. At power-on, the TI smart power stages
hold their TSEN/TAO lines low, until their internal logic is valid, and their
state is known (TAO_LOW condition). Once each device is in a valid state, it's
pull-down of the shared TSEN/TAO line is released, and the TAO/TSEN lines are
driven by the power-stage devices, based on temperature sense telemetry. The
start-up of TPS53676 is blocked while the TAO_LOW condition exists, such that
the controller does not attempt to begin conversion, until the TAO/TSEN line is
released by all power stages. During the initial power-on, no status bit or
alerts are set if the controller is commanded to enable with one of its TSEN/TAO
pins low. This is done to accomodate power sequences which have the power stage
5V rail being enabled after the controller 3.3V. The TAO_LOW fault is a
hysteretic-type response. When the TSEN/TAO pin is released, if the VR enable
condition is still active, power conversion starts immediately.
In response to the powerstage fault,
the TPS53676 responds according to the configured fault response in
MFR_PROTECTION_CONFIG. When not set to the ignore response, this causes the PWM pins
for that channel to tristate immediately. TPS53676 then sets the appropriate status
bits in STATUS_WORD and STATUS_MFR_SPECIFIC and asserts the SMB_ALERT# line if these
bits are not masked.
In response to the TAO_LOW condition,
TPS53676 tristates the PWM pins for that channel. TPS53676 then sets the appropriate
status bits in STATUS_WORD and STATUS_MFR_SPECIFIC and asserts the SMB_ALERT# line
if these bits are not masked. TAO_LOW is a hysteretic fault and cannot be configured
otherwise.