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Regarding application of TPS65381

Dear,

Regarding application of TPS65381, I have several questions and hope to get support from your side:

  1. How to use NRES? Can it be connected directly to MCU? Is there pull-up resistor needed?
  2. As we understand, DIAG_OUT is output of diagnostic signals selected by SPI, is it right? If choosing analog signal as output, how to select low-pass resistor and capacitor, what frequency need to filter out?
  3. Is RSTEXT used to set delay time of NRES by adjusting resistance? How to select the resistor?
  4. If we decide not to use CAN wake up function, how to configure CANWU pin (floating or pull down)?
  5. If we choose 5V as sensor supply voltage, should VSIN be connected to VDD6? Should VTRACK be connected to VDD5? How to choose the resistor for VSOUT1 when we want unity gain feedback?
  6. If we want VDD1 to be 1.2V, how to choose resistor for VDD1_SENCE? How to calculate it?

1 Reply

  • Hello Alan,

    My answers below will be referencing Rev F of the TPS65381-Q1 datasheet: http://www.ti.com/lit/gpn/tps65381-q1

    Additionally, there are other resources such as the design checklist and other application notes at: http://www.ti.com/product/TPS65381-Q1/technicaldocuments

    Q1: How to use NRES? Can it be connected directly to MCU? Is there pull-up resistor needed?

    A1: NRES is the reset output from the TPS65381. It is open drain with integrated pull up. The internal pull up is datasheet parameter 9.2, RNRES_ENDRV_PULLUP. Whether an external one is needed depends on any other loading you may have in your system on the reset line.

    Q2: As we understand, DIAG_OUT is output of diagnostic signals selected by SPI, is it right? If choosing analog signal as output, how to select low-pass resistor and capacitor, what frequency need to filter out?

    A2: Any filtering requirements will be dependent on the MCU ADC. The MCU ADC should specify any filtering needed. The input resistance, and any filter resistance and capacitance will impact the settling time and the voltage level (resistor divider with between the TPS65381 output resistance and any filter or input resistance). The datasheet suggest the order to switch through the analog signals to minimize the settling time in section 5.4.1.9 Analog MUX (AMUX)

    Q3: Is RSTEXT used to set delay time of NRES by adjusting resistance? How to select the resistor?

    A3: Yes, RSTEXT is the pin by changing a resistance will adjust how long NRES is held low after an event that causes reset (or RESET state in TPS65381), reset extension time. Datasheet spec line 9.4, tRSTEXT(22kΩ) and spec line 9.4a, tRSTEXT(0kΩ), give you two specified points for the reset extension time. This is described in section: 5.3.8 Reset Extension and shown in Figure 5-1. Power-Up and Power-Down Behavior.

    Q4: If we decide not to use CAN wake up function, how to configure CANWU pin (floating or pull down)?

    A4: CANWU pin is an input pin. One of two wake up pins, the other wake up pin is IGN. One of the two wake up pins need to be used to wake up the device. If one or the other wake up pins are not used they may be floated (there is an internal pull down) or an additional external pull down can be added.

    Q5: If we choose 5V as sensor supply voltage, should VSIN be connected to VDD6? Should VTRACK be connected to VDD5? How to choose the resistor for VSOUT1 when we want unity gain feedback?

    A5: With 5V sensor supply, VDD6 is likely the best choice since it will be more efficient to use the VDD6 pre-regulated supply into VSIN. For use of VSOUT1 configurations please see the application section of the datasheet where these are all documented. First you should decide if you want to track VDD5 or just have a 5V supply. I think the best application section to look at is: 6.2.2.3 VSOUT1 Tracking Linear Regulator, Configured to Track VDD5

    Q6: If we want VDD1 to be 1.2V, how to choose resistor for VDD1_SENCE? How to calculate it?

    A6: Please see application section: 6.2.2.2 VDD1 Linear Controller for how to calculate resistors for VDD1 and use VDD1.

    Best Regards,

    Scott