The device is able to detect an open load or a short-to-battery event when the channel output is disabled (FET is off). These will be referred to below as off state open load detection and off state short-to-battery detection. Whhen the channel output is disabled, the device is able to distinguish between an open load event and a short-to-battery event through a defined sequence that will be discussed below. A block diagram for the off-state open load and off-state short-to-battery detection is shown in Figure 8-36.

Figure 8-36 Open Load and Short-to-battery Detection

Off-state Open Load Detection

The device integrates a pull-up current source, OL_PU, for each channel which can be used to pull-up the output to determine if there is an open load or short-to-battery event. The pull-up current source is enabled when OL_SVBB_EN_CHx [1:0] = 10 along with an internal comparator which is used to detect when the output voltage rises above the V_{OL_OFF_TH}. The strength of the internal pull-up can be programmed through the OL_PU_STR_CHx bits for each channel in the CHx_CONFIG registers. The device also offers a programmable blanking timer per channel to allow the output to settle before determining if there is an open load or a short-to-battery event. The blanking time can be programmed through the OL_SVBB_BLANK_CHx bits in the CHx_CONFIG registers.

When OL_SVBB_EN_CHx [1:0] = 10, the device is only able to report if there is either an open load or a short-to-battery event, it is not able to distinguish between the two with this setting alone. If either an open load or a short-to-battery fault has occurred, then the OL_OFF_CHx bit in the FLT_STAT_CHx register for the corresponding channel will be set to 1. The OL_OFF_CHx bit is a read clear bit which will clear when the FLT_STAT_CHx register is read and the fault no longer exists, either from the removal of the fault or from the open load circuitry being disabled. To distinguish between an open load and short-to-battery faults, a certain procedure needs to be followed. This is detailed below in the Distinguishing Between Open Load and Short-to-battery Faults section.

If OL_SVBB_EN_CHx [1:0] = 10 and the output is enabled, the device will disable the pull-up current source and internal comparator before turning on the output. If OL_SVBB_EN_CHx [1:0] = 10 and the channel is enabled and then is disabled, the device will automatically enable the pull-up source and internal comparator.

Off-state Short-to-battery Detection

The device also integrates a pull-down resistor for each channel which can be used to help distinguish between an open load and a short-to-battery fault when the channel is disabled. The pull-down resistor is enabled when OL_SVBB_EN_CHx [1:0] = 01 along with an internal comparator which is used to detect when the output voltage rises above the V_{OL_OFF_TH}. The pull-down resistor is specified by the R_{SHRT_VBB} parameter in the electrical characteristics. The device offers a programmable blanking timer per channel to allow the output to settle before determining if there is a short-to-battery event. The blanking time can be programmed through the OL_SVBB_BLANK_CHx bits in the CHx_CONFIG registers.

When OL_SVBB_EN_CHx [1:0] = 01, the device is only able to report if there is a short-to-battery event. The device is not able to detect if an open load fault has occurred. If a short-to-battery fault has occurred, then the SHRT_VBB_CHx bit in the FLT_STAT_CHx register for the corresponding channel will be set to 1. The SHRT_VBB_CHx bit is a read clear bit which will clear when the FLT_STAT_CHx register is read and the fault no longer exists, either from the removal of the fault or from the short-to-battery detection circuitry being disabled. To distinguish between an open load and short-to-battery faults, a certain procedure needs to be followed. This is detailed below in the Distinguishing Between Open Load and Short-to-battery Faults section.

If OL_SVBB_EN_CHx [1:0] = 01 and the output is enabled, the device will disable the pull-down resistor and internal comparator before turning on the output. If OL_SVBB_EN_CHx [1:0] = 01 and the channel is enabled and then is disabled the device will automatically enable the pull-down resistor and the internal comparator.

Distinguishing Between Open Load and Short-to-battery Faults

The TPS2HCS08-Q1 device is able to distinguish between an open load and a short-to-battery fault through a defined procedure. Figure 8-37 highlights the procedure that is recommended to distinguish between an open load and a short-to-battery fault.

When reading the OL_OFF_CHx bits and SHRT_VBB_CHx bits to determine if there is an open load fault or a short-to-battery fault, three read command should be used to determine which fault has occurred. The first read command is to set which register to read, the second read command is to see if a fault has occurred and a third read command is to see if the fault has persisted. After these three successive reads, then the determination of the fault can be done.

Figure 8-37 Logic Flow Chart to Distinguish Between Open Load and Short-to-battery Faults