TPS53676 provides three layers of overcurrent protection:

• Overcurrent fault (OCF) is a programmable threshold which sets the maximum allowed total current (sum of all phases) for a channel. Detection is based on output current telemetry. When the sensed output current for a channel exceeds this limit, the output overcurrent fault is detected. Program this threshold using the IOUT_OC_FAULT_LIMIT command with the PHASE set to FFh. TPS53676 supports values of 0 to 1023 A per channel.
• Per-phase overcurrent limit (OCL) is a programmable cycle-by-cycle valley current limit for each individual phase current, to protect against inductor saturation. TPS53676 does not pass PWM pulses to phases when their current is above the configured OCL threshold. Other than cycle-by-cycle current limit, no action is taken when the per-phase OCL is engaged. Typically, in the case of a severe overload event, power conversion is disabled when the output voltage reaches the VOUT_UV_FAULT_LIMIT. This is illustrated in the figure below. Program the OCL threshold using the IOUT_OC_FAULT_LIMIT command with the PHASE set to 00h. TPS53676 supports values of 17 A to 130 A per phase.
• Overcurrent warning (OCW) is a programmable warning threshold based on the total current (sum of all phases) for a channel. Detection is based on output current telemetry. When the sensed output current for a channel exceeds this limit, the output overcurrent warning is detected. Program this threshold using the IOUT_OC_WARN_LIMIT. TPS53676 supports values of 0 to 1023 A per channel.

Figure 7-31 Per-phase OCL (2 phase example)

Typically, set the per-phase OCL threshold greater than total peak design current I_PK-CHANNEL to allow margin for transient events, as shown in the equation below. TI recommends 30-50% design margin. Then peak current allowed in any individual phase is given by the equation below. Select output inductor components such that current saturation levels are above this limit, including margin for threshold and current sensing accuracy.

where

• I_OCL(min) is the per-phase overcurrent limit in amperes
• I_OUT(PEAK) is the peak design current in amperes
• N_ϕ is the number of phases assigned to the channel
• K_MARGIN is a factor of safety for design margin

where

• I_PEAK(phase) is the peak current observed in any individual phase
• I_OCL is the per-phase overcurrent limit in amperes
• ΔI_RIPPLE is the peak-to-peak inductor current ripple

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

In response to the overcurrent fault condition, TPS53676 responds according to the programmed IOUT_OC_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_IOUT and asserts the SMB_ALERT# line if these bits are not masked.