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ZHCSN24A August 2019 – May 2021 TPS53676

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7.7.4.1 Overvoltage fault (OVF) and warning (OVW)

TPS53676 supports several forms of overvoltage protection. The figure below describes the overvoltage protection scheme in more detail.

Pre-Bias OVF protects the converter while initialization runs. This protection is active t_INIT-PBOV, 350 μs maximum after the VCC pin voltage is established, until initialization is complete. The threshold is hard-coded to 3.7 V. In response to this condition, all PWM pins (regardless of channel assignment) pull low, regardless of the overvoltage response setting. This fault cannot be cleared without a power cycle of the VCC pin. The fixed overvoltage protection becomes active after t_INIT-LOGIC , up to 20 ms after the VCC pin voltage is established. This fault detection cannot be disabled.
Fixed OVF is a programmable limit based on the VSP pin voltage, above which it is not safe to operate the load device. Program the threshold through the MFR_PROTECTION_CONFIG command. This fault detection is active regardless of power conversion. If triggered while power conversion is disabled, this fault is treated as potentially catastrophic, and cannot be cleared without a power cycle of the VCC pin.
Tracking OVF is a fault limit, programmable as an offset from the current VOUT_COMMAND value. Program this threshold through VOUT_OV_FAULT_LIMIT. When the VSP-VSN pin differential voltage exceeds this limit during power conversion, the tracking overvoltage fault condition is detected. This fault detection is disabled whenever power conversion is disabled.
Tracking OVW is a warning limit, programmable as an offset from the current VOUT_COMMAND value. Program this threshold through VOUT_OV_WARN_LIMIT. When the VSP-VSN pin differential voltage exceeds this limit during power conversion, the tracking overvoltage warning condition is detected. This is a warning condition only, and does not cause any interruption to power conversion. The overvoltage warning provides early feedback to they system host allowing it to make adjustments prior a fault triggering.

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

Figure 7-28 Overvoltage Protection

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

Program the tracking overvoltage warning through the VOUT_OV_WARN_LIMIT command as an absolute voltage. Similarly, when a new VOUT_OV_WARN_LIMIT command is received, the device calculates the tracking overvoltage warning offset according to the equation below. The threshold voltages get scaled with the use of an external voltage sensing divider and VOUT_SCALE_LOOP. TPS53676 supports tracking overvoltage warning offsets from +24 mV to +448 mV in 8 mV steps.

Program the fixed overvoltage fault threshold through MFR_PROTECTION_CONFIG. TPS53676 supports values from 0.6 V to 3.7 V, in 100 mV steps.

Equation 36.

V_{OFS(OVF TRK)} = \frac{VOUT_OV_FAULT_LIMIT - VOUT_COMMAND}{VOUT_SCALE_LOOP}

Equation 37.

V_{OFS(OVW TRK)} = \frac{VOUT_OV_WARN_LIMIT - VOUT_COMMAND}{VOUT_SCALE_LOOP}

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

Equation 38.

V_{OVW(trip)} = VOUT_COMMAND + V_{OFS(OVW TRK)} - VOUT_DROOP \times I_{OUT}

Equation 39.

V_{OVF(trip)} = Min (V_{OVFIX}, VOUT_COMMAND + V_{OFS(OVF TRK)} - VOUT_DROOP \times I_{OUT})

Updates to VOUT_COMMAND do not cause these the overvoltage offsets to be recalculated. After the output voltage target has been changed, TPS53676 reports the fault and warning thresholds by adding the previously select offset value to the current VOUT_COMMAND.

Example: Programming the OVF and OVW offsets

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_OV_WARN_LIMIT to 1.128 V (1.0 V + 128 mV), to select the +128 mV tracking overvoltage warning offset. The VOUT_DROOP is assumed to be zero for calculation purposes. However, the over-voltage warning trip threshold does account for the load-line setting and is equal to 1.128 V - 0.5 mΩ × I_OUT.
Program the VOUT_OV_FAULT_LIMIT to 1.256 V (1.0 V + 256 mV) , to select the +256 mV tracking overvoltage fault offset. The VOUT_DROOP is assumed to be zero for calculation purposes. However, the over-voltage fault trip threshold does account for the load-line setting and is equal to 1.256 V - 0.5 mΩ × I_OUT.

If the VOUT_COMMAND value is changed to is 1.100 V, the TPS53676 reports VOUT_OV_WARN_LIMIT as 1.228 V (1.1 V + 128 mV), and VOUT_OV_FAULT_LIMIT as 1.356 V (1.1 V + 256 mV). The offset values are not changed.

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7.7.4.1 Overvoltage fault (OVF) and warning (OVW)