In some applications, having accurate current sensing at lower load currents can be critical to distinguish between a real load and a fault scenario such as an open load condition(Wire-Break). To address this challenge, TPS281C30x implements a high accuracy sense mode that enables customers to achieve ±30% @6mA load. This mode will be activated when diagnostics are enabled(DIAG_EN=HI), OL_ON = HI and I_Load<I_{Ksns2_EN} . To achieve this high accuracy , the device increases its main path resistance to improve its sense accuracy while high accuracy sensing is active. TI recommends users to disable this accuracy sense mode by setting OL_ON=LO if the load starts to increase beyond 40mA. This will proactively prevent any higher power dissipation states.

In other scenarios such as a sudden load step where the system might not be fast enough to react to the change in SNS output current. For this case, in order to prevent a high-power dissipation state given by the increased resistance. TPS281C30x senses the load flowing through the VS-VOUT path to remain < I_{Ksns2_DIS}. If the load increases beyond I_{KSNS2_DIS} the FET resistance will revert back to its lowest resistance and high accuracy sense mode will be disabled. This will result in nFAULT being asserted to signal that high accuracy sense mode has been disabled. This will ensure the lowest power dissipation when higher loads are being driven. In addition to this, the user can PWM the OL_ON pin to disable the high resistance mode and minimize power losses further.

However, even if accuracy is achieved by the device; Depending on the current sense ratio, system ADCs can struggle to measure lower load currents accurately due to the low voltages that would need to be read by the ADC. As an example, a 6mA I_Load will be represented as ~5mV using RSNS=1kOhm with a current sense ratio of 1200. For a 10-bit 5V-ADC the 5mV output is just over 1LSB(4.88mV). This does not provide enough margin to accurately measure this current for the ADC and likely a higher resolution would need to be used.

Therefore, in order to enable lower ADC resolution requirements and to accurately sense low load currents when operating in high accuracy sense mode, TPS281C30x decreases its current sense ratio to 24. With a sense ratio of 24, the 6mA I_Load will be represented as 250mV using RSNS=1kOhm when operating in high accuracy sense mode. This equals to 51LSBs of margin for the same 10-bit ADC or even for an 8-bit ADC the output would still provide >12LSBs of headroom.

Full Protection and Diagnostics for full device states.

Figure 9-4 High Accuracy Sensing FAULT Indication