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I am using TPS4H000BQPWPRQ1 in my design. Below is my design. Can you please review my design especially current sense (PIN No 8) and current limit (PIN No 9) design?

enter image description here

In the datasheet page no 27 you can see the detailed design. My nominal current is 700 mA and set current limit to 1 A.

Using the equation 9 I calculated the value of RCS:

RCS = 4*80/0.7 = 457 Ω, I am using 453 Ω in my board.

For finding RCL I am using equation 10:

RCL = 0.8*300/1 = 240 Ω I used the same value in my board.

All the control signals(Left side of IC) are going to uC from NXP.

I have few questions:

May I know is these calculations are fine?

CS is going to uC (S32K148) ADC, R598 is 10 kΩ and C11 is 100nF, are they correct?

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    \$\begingroup\$ Is this for industrial/automotive environements? General review: decoupling caps? I/O protection? Reverse voltage protection? Are you driving coils/valves/motors with this? If so, flyback diodes are highly recommended. \$\endgroup\$
    – Lundin
    Aug 25, 2023 at 8:12
  • \$\begingroup\$ This is for automotive environment. I am not driving any coils \$\endgroup\$
    – Confused
    Aug 25, 2023 at 8:17
  • \$\begingroup\$ I actually believe the part might have some reverse voltage protection internally(?). Not used at working with the TI flavour of these. But depending on requirements, you should probably have automotive rated TVS (typically 1500W peak pulse) on all outputs. A TVS will double as flyback too in case you do eventually find yourself driving a relay or whatever. \$\endgroup\$
    – Lundin
    Aug 25, 2023 at 8:31

1 Answer 1

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Using the equation 9 I calculated the value of RCS

Equation 9 is for a typical application example. You should have used Equations 1 to 3 because there are other considerations that should be taken into account.

Using Eq.1:

$$ \mathrm{ R_{CS}=\frac{K_{CS} \ V_{CS}}{I_{OUTx}}=\frac{80 \cdot 4}{0.7}\approx457\Omega \rightarrow 453\Omega} $$

And also the requirement given with Eq.3 should be met:

$$ \mathrm{ R_{CS}=453\Omega\geq \frac{V_{CS(H-min)}}{I_{CS(H-min)}}=\frac{4.5}{0.015}=300\Omega } $$

No problems here. Note that the first equation is given for a linear change from 0 to 4 V output for the selected current range i.e. 0 to 700 mA. Selected sense resistor will bring that. But 10k-100n filter will bring a delay of ~5-ms (neglecting the chip's internal delays, tCSx and tSEL) i.e. when the load current changes from 0 to 700 mA in, say, 50 microseconds it'll take 5 milliseconds for the SIG_LOADSW_CUR_SENSE lane to hit 4V, and vice versa. So, if your measurements are time-critical so even this 5-ms delay is too long for you then you may want to revise the filter, otherwise leave it as it is.


For adjustable current limit, the calculations seem correct although you should have used Eq.4 (again, Eq.10 is for a typical application example).


One thing worth to note here is that the CS output is not a combined/total output for current sense. It outputs a current-related voltage for the selected output combined with the DIAG_EN input. So, make sure none of your outputs exceeds the linear sense limits.

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  • \$\begingroup\$ May I know how to calculate the power rating of resistor connected to CL pin \$\endgroup\$
    – Confused
    Sep 4, 2023 at 4:41

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