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TPS1HC100-Q1: TPS1HC100-Q1

Part Number: TPS1HC100-Q1

Hello, 

I'm considering using the TPS1HC100BQPWPRQ1 to power supply of  LED driver.

The external load conditions are as follows.

- Nominal current : 250~350mA

- Inrush current : 5A, 50us

- The purpose of current sensor is to detect low current

     → 1st low current threshold : 230mA, 2nd low current threshold :45mA

Please check the below question.

Q1)  

I/O voltage is 3.3V and ADC reference voltage is 5V. 

If the input voltage of the DIAG_EN pin is 3.3V, Is the ADC full scale range available up to 3.3V ?

 → If so, Can I extend the full range of ADC to 5V by connecting a 5V pull-up to DIAG_EN pin  ?

Q2)

Is it available if i set "Measurable current(by Rsns) < Icl(current limit threshold)" ?

Q3)

Can you provide a  recommended circuit for maximizing the current accuracy of 40~300mA under upper load condition ?

My concern --> The current sensing range of 0~500mA is sufficient, but considering the 5A inrush current.

Q4)

Is the current sense accuracy the same as the datasheet below regardless of the Rsns value?

Thanks.

  • Hello Mo-Rang,

    Welcome to E2E!

    Q1) The main concern here is the "fault" voltage that the SNS pin sees when there is a fault condition in the part (signified by VSNSFH in the datasheet). The way that this works is that when there is a fault in the system such as an overcurrent event or short-to-battery/open load, the SNS pin is "pulled up" to VSNSFH so that the microcontroller/ADC can detect the fault and take action. The fault voltage is automatically configured on TPS1HC100-Q1 to the voltage that is on DIAG_EN. Therefore you are correct- if DIAG_EN is 3.3V then your ADC range is 0V to 3.3V. You are able to tie DIAG_EN to 5V however (and keeping all other IOs to 3.3V) and this would enable you to have the full 0V to 5V ADC range.

    Q2) The only thing you would have to worry about here is that when the device goes into a current limiting mode, the SNS pin is pulled up to the fault voltage VSNSFH. If the device is not in current limiting mode (and does not have any other short-to-battery/open load faults) then the SNS pin will have a current representative of the actual load current.

    Q3) The recommendation here is to take your minimum VSNSFH value from the datasheet, add approximately a ~10% "buffer" and then use that as your maximum measurable value for the load current. For example with a 5V reference you would have a minimum VSNSFH value of 4.75V and a measurable voltage range of 0V to 4.25V (I used 11.5% buffer, but this can be adjusted depending on your resistor tolerance/ADC accuracy).

    If you wanted a maximum measured load current of 300mA, for example, the calculations would essentially be like this:

    You would calculate the SNS resistor using the worst case values like this:

    So at 15.4kΩ if you plugged in the minimum/maximum KSNS values for 300mA using the following formula:

    ... you would get a corresponding voltage on your ADC pin of a minimum of 4.19V and a maximum of 4.63V. Note the resistor tolerance and ADC accuracy will also have some impact here.

    Q4) The actual resistor on the SNS pin itself does not affect the accuracy of the current sense directly. The purpose of this resistor is to convert the current that is coming out of the SNS pin to a voltage value that the microcontroller's ADC can sample. The tolerance rating of this resistor will indirectly affect the accuracy. A ±5% tolerant resistor, for example, will result in less overall accuracy compared to a ±1% resistor as the converted voltage will be affected.