TPS7H2201-SP: TPS7H2201-SP

Hi Rajan,

Both resistors will depend on what load current your design uses.

The IL resistor should be chosen so that the programmable current limit is at least 20% higher than the current limit value that you select (due to the +/-20% accuracy of the current limit). You will also need to make sure the current limit is not set above 7.5A due to the device's maximum current rating of 6A. The minimum current limit you could use will depend on your load current - I've attached an image of the datasheet spec below and linked to the page in the datasheet that shows the specification here.

For CS, the range of resistor values you can use will depend on your load current. The current output from the CS pin is equal to the load current of the switch divided by 41.500. The voltage on this pin must not exceed VIN-0.4V (which is 4.6V for your design), so you should choose the CS resistor that will ensure this requirement is met based on the highest CS current you expect. This pin can also be left floating if you are not using the current sense feature. 

Thanks,

Sarah 

Hi Rajan,

I don’t notice an issues with your schematic once you add the resistor for the IL pin.

I would recommend using equation 8 in section 8.3.3 of the datasheet to obtain a more precise value for the IL pin resistor. Using a 13 kOhm resistor would result in a nominal current limit of 3.75A, but due to the 20% accuracy of the current limit there may be some occasions where the current could reach ~4.5A (3.75 + 20%) before the current limit triggers. This may or may not be an issue for you, but if your design cannot exceed 4A, you will want to set the current limit 20% below this value to guarantee the current limit always goes into effect by the time the current reaches 4A.

Equations 3 and 6 from section 8.3.2 of the datasheet show that Css = 1.3 uF in order to obtain a 100ms soft start time for your system. As you mention, it’s possible for the current limit to experience a false trip when the device is enabled. Equation 4 shows the relationship between the current limit, load current, output capacitance that determines the maximum VOUT slew rate that can be set by Css to safely avoid such false trips.  

Thanks,

Sarah

Hi Rajan,

Yes, any capacitance that is seen at the output node of the load switch should be considered when calculating max slew rate since it will all contribute to the current demanded through the load switch.

There is one more thing I notice about your current limit setting. The datasheet also specifies a minimum current limit setting that is dependent on the load current. For loads larger than 3A, the current limit needs to be set at least 1.5A above the load. If the nominal continuous load for your design is 4A, this means the minimum current limit setting will be 5.5A.

Thanks,

Sarah

Hi Rajan,

Yes, I would still recommend placing at least 10uF as close as possible to the output pins. This recommendation is less about adding an extra 10-uF to your total COUT, and more about the placement of the capacitor. Placing it as close as possible to the output pins helps minimize any effects that parasitic trace inductances may have on the operation of the device. 

Thanks,

Sarah

Hi Rajan,

Thanks for posting your updated schematic. I would recommend updating RIL to 8.87k just to be on the safe side and make sure the current limit is not lower than the 5.5A required by the datasheet. You could also decrease the 0.35 sec soft start time a bit if you wanted to, but that is up to you.

Thanks,

Sarah

Hi Rajan,

You will need to set the current limit to 5.5A to avoid violating the minimum current limit spec, so you should use that value. 

Thanks,

Sarah