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TPS65310A-Q1: About Output Capacitor for Boost circuit

user5795039
Prodigy 190 points
Part Number: TPS65310A-Q1
Other Parts Discussed in Thread: TPS65311-Q1

Dear ALL:

In the datasheet, when we  want to chose Output Capacitor for Boost circuit , it said we shoud use "Equation 12 " to calculate the value of Output Capacitor, and we should meet " FLC is in the range 10kHz-15kHz". but if I use the data about L=4.7uH and Cout=57uF which are gived by datasheet, I found that the" FLC is not in the range 10kHZ-15kHz", so I want to konw  why is that? 

Best Regards.

  • 0
    TI__Expert 8730 points
    Hi,

    Datasheet equations are correct. Equations are just the starting point and final values need to be fine tuned based on actual measurements. In the datasheet calculation, F_LC comes to around 7.6 KHz for the given values, but if you consider the output capacitor de rating effects, actual F_LC may be around 10 KHz. Output capacitor de rating depends on the capacitor type you use and hence for your calculations, please consider this and use the value according to capacitor datasheet. I agree that datasheet specified output capacitor value is very conservative and you can use slightly smaller values depending on your ripple and load current requirements.

    Can you please let me know which customer is using this device? We normally recommend TPS65311-Q1 instead of TPS65310A for automotive customers as TPS65311-Q1 BUCK2/3 and BOOST are switching at 2.45 MHz (out side AM Band) and this helps to reduce the output inductance and capacitor size.

    Regards,

    Murthy
  • 0 in reply to Krishnamurthy Hegde
    TI__Expert 8730 points
    Hi,

    Looks like there was some issues with previous answer and hence re sending it..

    Datasheet equations are correct. Equations are just the starting point and final values need to be fine tuned based on actual measurements. In the datasheet calculation, F_LC comes to around 7.6 KHz for the given values, but if you consider the output capacitor de rating effects, actual F_LC may be around 10 KHz. Output capacitor de rating depends on the capacitor type you use and hence for your calculations, please consider this and use the value according to capacitor datasheet. I agree that datasheet specified output capacitor value is very conservative and you can use slightly smaller values depending on your ripple and load current requirements.

    Can you please let me know which customer is using this device? We normally recommend TPS65311-Q1 instead of TPS65310A for automotive customers as TPS65311-Q1 BUCK2/3 and BOOST are switching at 2.45 MHz (out side AM Band) and this helps to reduce the output inductance and capacitor size.

    Regards,

    Murthy
  • 0 in reply to Krishnamurthy Hegde
    Prodigy 190 points
    Dear Murthy:
    What is the price of TPS65311-Q1, is it higher than TPS65310-Q1?
  • 0 in reply to user5795039
    TI__Expert 8730 points
    Hi,

    For the pricing, please contact the local TI sales team and they should be able to help you. On TI.com, both the devices have the same price.

    Can you please let me know more about your project and customer?

    Regards,

    Murthy