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, TPS281C100 implements a high accuracy sense mode that enables customers to achieve ±12.5% at 4mA 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 20 mA. 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. TPS281C100 senses the load flowing through the VS to VOUT path to be less than 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 FAULT 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 6 mA I_Load will be represented as ~7.5 mV using RSNS=1kOhm with a current sense ratio of 800. For a 10-bit 5 V ADC the 7.5 mV output is just over 1 LSB (4.88 mV). 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, TPS281C100 decreases its current sense ratio to 24. With a sense ratio of 24, the 6 mA I_Load will be represented as 250 mV using RSNS=1kOhm when operating in high accuracy sense mode. This equals to 51 LSBs of margin for the same 10-bit ADC or even for an 8-bit ADC the output would still provide > 12 LSBs of headroom.

Full Protection and Diagnostics for full device states.

Figure 8-4 High Accuracy Sensing FAULT Indication