The user can determine the impedance on the
OUT node using off-state diagnostics in the STANDBY state when the power FETs are off.
With this diagnostics, it is possible to detect the following fault conditions passively in
the STANDBY state:
- Output short to VM or GND <
100Ω
- Open load > 1KΩ for low-side load
- Open load > 10KΩ for high-side load,
VM = 13.5V
Note: It is NOT possible to detect a load
short with this diagnostic. However, the user can deduce this logically if an over
current fault (OCP) occurs during ACTIVE operation, but OLP diagnostics do not report any
fault in the STANDBY state. Occurrence of both OCP in the ACTIVE state and OLP in the
STANDBY state would imply a terminal short (short on OUT node).
- The user can configure the following
combinations
- Internal pull up resistor (ROLP_PU) on OUT
- Internal pull down resistor (ROLP_PD) on OUT
- Comparator reference level
- This combination is determined by the controller inputs (pins only for the HW variant)
or equivalent bits in the SPI_IN register for the SPI variant if the SPI_IN register
has been unlocked.
- HW variant - When off-state diagnostics
are enabled, comparator output (OLP_CMP) is available on nFAULT pin.
- SPI variant - The off-state diagnostics comparator output (OLP_CMP) is
available on OLP_CMP bit in STATUS2 register. Additionally, if the SPI_IN register has been
locked, this comparator output is also available on the nFAULT pin when off-state
diagnostics are enabled.
- The user is expected to toggle through all the combinations and record the comparator
output after its output is settled.
- Based on the input combinations and
comparator output, the user can determine if there is a fault on the output.
The OLP
combinations and truth table for a no fault scenario vs. fault scenario for a low-side load
is shown in Table 7-8.
Table 7-8 Off-State Diagnostics Table for a
Low-Side Load
User Inputs |
OLP Set-Up |
OLP_CMP Output |
DIAG Pin |
S_DIAG Bits |
nSLEEP |
DRVOFF |
IN |
OUT |
CMP REF |
Normal |
Open |
Short |
LVL2, LVL6 |
2'b01 |
1 |
1 |
1 |
ROLP_PU |
VOLP_REFH |
L |
H |
H |
LVL3, LVL4 |
2'b11 |
1 |
1 |
1 |
ROLP_PD |
VOLP_REFL |
L |
L |
H |
The OLP combinations and truth table for a no
fault scenario vs. fault scenario for a high-side load is shown in Table 7-9.
Table 7-9 Off-State Diagnostics Table for a
High-Side Load
User Inputs |
OLP Set-Up |
OLP_CMP Output |
DIAG Pin |
S_DIAG Bits |
nSLEEP |
DRVOFF |
IN |
OUT |
CMP REF |
Normal |
Open |
Short |
LVL2, LVL6 |
2'b01 |
1 |
1 |
1 |
ROLP_PU |
VOLP_REFH |
H |
H |
L |
LVL3, LVL4 |
2'b11 |
1 |
1 |
1 |
ROLP_PD |
VOLP_REFL |
H |
L |
L |