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DRV8143-Q1: DRV8143-Q1 OLD Diagnosis

Florens Liang
Prodigy 320 points
Part Number: DRV8143-Q1


Hi team,

For OLD diagnostics for the DRV8143-Q1, could you please help solve these questions? Thanks.

1. Could you explain the working principle of this schematic?

image.png

2.Could you explain why both OPEN and Short are high level under this setting? 

image.png

3. Is the low-side load determined by two tests to be Normal/Open/Short?

Test 1: If OLP_CMP Output is L: Normal / H: Open or Short

Test 2: If OLP_CMP Output is L: Normal or Open / H: Short

image.png

BRs,

Florens

  • 0
    TI__Mastermind 26910 points

    Hi Florens,

    To start, the schematic shows all the components used in the DRV8145's OLP feature. For OLP to function DRVOFF must be high which placed OUTx in Hi-Z. Since the output is Hi-Z the load will pull the output either high or low depending on its configuration. Assuming a low side load (OUT to GND), we can check that the load is connected by enabling the pull-up to an internally generated 5V and compare the value on OUT with a reference voltage to see if the OUT voltage is where we expect it to be. For example, assume the load is 20 ohms, the voltage on OUT should be ~0.09V which is less than VOLP_REFH (~2.9V) so under normal conditions this would make the comparator output low. In this case if an open were present the OUT voltage would be 5V and a VM short would make OUT > 5V so both result in the comparator output being high. Hope this makes sense and helps clear up the table/schematic.

    Florens Liang said:
    3. Is the low-side load determined by two tests to be Normal/Open/Short?

    For a low side load, the first test the first row would be a better option since this setting allows an open to be distinguishable from a loaded condition. In all cases the short is a short to battery and a short to GND is not detectable since it would have the same outputs as the low-side loads normal case. The second row in the table is better for a high side load.

    Regards,

    Joshua

  • 0 in reply to Joshua Horlander Cruz
    TI__Prodigy 320 points

    Hi Joshua,

    Here are some questions regarding your answer. Could you pls help to solve, thanks.

    1. Is it right that low-side load short means OUT = VM and high-side load short means OUT = GND? Why?

    2. According to the datasheet, both lines in Table 7-8 are for low-side load diagnostics. "The second row in the table is better for a high side load." maybe not be right?

    BRs,

    Florens

  • +1 in reply to Florens Liang
    TI__Mastermind 26910 points

    Hi Florens,

    Florens Liang said:
    Is it right that low-side load short means OUT = VM and high-side load short means OUT = GND? Why?

    Correct, this is because with only a half-bride a load to GND and a short to GND are indistinguishable since the Output voltage will be pulled well below 2V, which is the lower reference voltage. If the resistance of the load was >~670 ohms then the load would be able to be distinguishable from a short to GND but motors do not normally have resistances in the hundreds of Ohms. This is the same principle for the high-side loads and a short to VM.

    So, since a short to GND and short to VM appear the same as a load to GND and load to VM respectively, Short in the table indicates a specific type of short.

    Florens Liang said:
    According to the datasheet, both lines in Table 7-8 are for low-side load diagnostics. "The second row in the table is better for a high side load." maybe not be right?

    I should clarify what my intention was, in the case that only one setting can be used, LVL3/LVL4 is "better" for high side loads since normal will be high, and an open or short case will be low. LVL2/LVL6 is "better" for low side loads since a normal is low and the open and short cases will be high.

    Using both LVL3/LVL4 and LVL2/LVL4 with either load configuration will allow an open condition to be distinguished from a short condition.

    When LVL3/LVL4 is set for the DIAG option, the output has the ROLP_PD enabled and the reference voltage to the OLP_CMP is VOLP_REFL and when LVL2/LVL6 is set for the DIAG option, the output has the ROLP_PU enabled and the reference voltage to the OLP_CMP is VOLP_REFH. The voltage reference voltage used in combination with the pullup/pulldown cannot be changed.

    Regards,

    Joshua