JAJSHS0C March 2019 – March 2021 TPS92682-Q1
PRODUCTION DATA
Figure 7-9 shows that the cycle-by-cycle switch current limit is achieved by comparing the sensed switch current with a programmable ILIM threshold and terminating the duty cycle when VISPx ≥ VILIM(THR). The ILIMTHR can be set using a 2-bit value in the ILIM Register. If CHxILIMEN is set to zero in the FEN2 Register, the ILIM fault is disabled. However, the cycle-by-cycle current limit is always active as long as the sensed switch current exceeds ILIMTHR.
If CHxILIMEN is set to "1", the ILIM fault is enabled, and it can be set as a latched or non-latched fault. There is an ILIM event counter for each channel that counts the number of ILIM fault events. When the ILIM event counter reaches a programmed value, the associated channel is turned off. The maximum number of ILIM fault events can be set using a 2-bit CHxILIMCNT in ILIM Register. The ILIM event counter is reset every 100-CHxCLK cycles to prevent transients and non-real faults, resulting in an unwanted channel disable.
If CHxILIMFL is set to "1" in the FLATEN Register, the ILIM event is set to a latched fault. The associated channel is turned off and remains off when the ILIM event counter reaches the programmed value. The channel can be turned on again only by re-setting the CHxEN bit to "1" in the EN Register.
For CHxILIMFL = 0, the ILIM fault is a non-latched fault. When the ILIM event counter reaches the programmed value, the associated channel is turned off and an ILIM fault timer, IFT, is triggered. The associated channel is turned back on by a soft-start ramp when the ILIM fault timer count is completed and the output of the ILIM event counter is cleared. The ILIM fault timer can be programmed using a 2-bit value CHxIFT in the IFT Register. The IFT time can be set to a value between four and 32 cycles of the input clock. The input clock of the IFT is the channel clock, CHxCLK (the switching frequency fSW). For example, for a channel with a switching frequency of fSW = 400 kHz, the timer can be programmed from 10 to 80 µs.
Figure 7-17 shows the simplified functional block diagram of the ILIM fault. Figure 7-18 shows the progress of the cycle by cycle current limit, the ILIM event counter (IFEC), the ILIM Fault Timer (IFT), and the restart of the channel for a non-latched ILIM fault.
The ILIM fault in CV mode is disabled during the soft-start ramp if the CHxRFEN bit is set to "0" in the FEN1 Register.
As stated before, it is important to note that the cycle-by-cycle switch current limit is always active even if the ILIM fault is disabled.