Two undervoltage threshold limits are provided:

• Tracking UVF is a fault limit, programmable as an offset from the current VOUT_COMMAND value. Program this threshold through VOUT_UV_FAULT_LIMIT. When the VSP-VSN pin differential voltage falls below this limit during power conversion, the tracking undervoltage fault condition is detected. This fault detection is disabled whenever power conversion is disabled.
• Tracking UVW is a warning limit, programmable as an offset from the current VOUT_COMMAND value. Program this threshold through VOUT_UV_WARN_LIMIT. When the VSP-VSN pin differential voltage exceeds this limit during power conversion, the tracking undervoltage warning condition is detected. This is a warning condition only, and does not cause any interruption to power conversion. The undervoltage warning provides early feedback to they system host allowing it to make adjustments prior a fault triggering.

In response to the undervoltage warning condition, TPS53676 sets the appropriate status bits in STATUS_WORD and STATUS_VOUT and asserts the SMB_ALERT# line if these bits are not masked.

In response to the undervoltage fault condition TPS53676 responds according to the programmed VOUT_UV_FAULT_RESPONSE. When not set to the ignore response, this causes the PWM pins of the rail which experienced a fault to tristate immediately. TPS53676 then sets the appropriate status bits in STATUS_WORD and STATUS_VOUT and asserts the SMB_ALERT# line if these bits are not masked.

Program the tracking undervoltage fault threshold through the VOUT_UV_FAULT_LIMIT command as an absolute voltage. When a new VOUT_UV_FAULT_LIMIT command is received, the device calculates the tracking undervoltage offset value internally according to the equation below. Threshold voltages get scaled with the use of an external voltage sensing divider, and VOUT_SCALE_LOOP. TPS53676 supports tracking undervoltage fault offsets from -32 mV to -448 mV in 32 mV steps.

Program the tracking undervoltage warning through the VOUT_UV_WARN_LIMIT command as an absolute voltage. When a new VOUT_UV_WARN_LIMIT command is received, the device calculates the tracking undervoltage warning offset according to the equation below. Threshold voltages get scaled with the use of an external voltage sensing divider, and VOUT_SCALE_LOOP. TPS53676 supports tracking undervoltage warning offsets from -24 mV to -448 mV in 8 mV steps.

The undervoltage warning and fault trip thresholds include the load-line setting as shown in the equations below.

Example: Programming the UVF and UVW thresholds

Assume the current VOUT_COMMAND is 1.000 V, the VOUT_DROOP setting is equal to 0.5 mΩ, and the load current is equal to 100 A.

• Program the VOUT_UV_WARN_LIMIT to 0.872 V (1.0 V - 128 mV), to select the -128 mV tracking undervoltage warning offset. The VOUT_DROOP is assumed to be zero for calculation purposes. However, the undervoltage warning trip threshold does account for the load-line setting and is equal to 0.872 V - 0.5 mΩ × I_OUT.
• Program the VOUT_UV_FAULT_LIMIT to 0.744 V (1.0 V - 256 mV), to select the -256 mV tracking undervoltage fault offset. The VOUT_DROOP is assumed to be zero for calculation purposes. However, the undervoltage fault trip threshold does account for the load-line setting and is equal to 0.744 V - 0.5 mΩ × I_OUT.

If the VOUT_COMMAND value is changed to is 1.100 V, the TPS53676 reports VOUT_UV_WARN_LIMIT as 0.972 V (1.1 V - 128 mV), and VOUT_UV_FAULT_LIMIT as 0.844 V (1.1 V - 256 mV). The offset values are not changed.