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WEBENCH® Tools/TPS40210: DC/DC boost error

Hariharan Gunasekar37
Prodigy 90 points
Part Number: TPS40210

Tool/software: WEBENCH® Design Tools

Vin min = 7V

Vin max = 8.4V

Current = 500mA

Vout = 50V

I built my circuit using a reference design from webench, the board layout was also made accordingly. According to the circuit calculations it should give 50V output but it seems to only give 22V output. I calculated the feedback resistors manually once and it gives the same value as webench value but still my output is 22V/500mA without connecting any load. I did look for shorts in the circuit but there seems to be no shorts.

Thanks.

  • 0
    Prodigy 90 points
    The link for the webench design: webench.ti.com/.../SDP.cgi
    The EN pin has voltage value 0V.
  • 0 in reply to Hariharan Gunasekar37
    TI__Guru* 78070 points
    Thank you for considering the TPS40210-Q1 in your project. If the design is generated by Webench, it should work. I am afraid there is a mistake somewhere when copied the Webench design to layout your PCB, or a wrong part is used. Please capture a few key waveforms like the switch node voltage, current sense voltage, etc, and we can see if the power stage is set up correctly.

    Best Regards,
    Youhao Xi, System and Applications Engineering, APP-BMC-BCS, TI
  • 0 in reply to Youhao Xi
    Prodigy 90 points

    The BOM, schematic and layout are done according to the webench design. Attached the schematic and layout of the circuit.2017-05-22_14-23-12.pdf2017-05-22_14-23-12.pdf

  • 0 in reply to Hariharan Gunasekar37
    Prodigy 90 points
    The voltage across the sense resistor is zero, the GDRV pin is 4 V and the COUT2 has 22V. This 22V output is only available only when it draws the whole current available from the dc source. IF the DC source is limited to 500mA it withdraws the whole current, if the DC source is 700mA it withdraws 700mA.
  • 0 in reply to Youhao Xi
    Prodigy 90 points

    I would also like to add that the temperature simulation by webench works as same as the board. I would also like to know whether the circuit will withdraw current like 500mA without connecting a load ?

    Thanks

  • 0 in reply to Youhao Xi
    Prodigy 90 points

    I tried changing the RFB1 to 2.2K and got a boost output of 17.3V and 0.01A current without load. But it only works until the input voltage is 7.7V and if i increase the input voltage more than that the circuit gives the input voltage as the output. I calculated the values and 2.2K corresponds to 17.3V

    I tried changing the RFB1 to 1K now and the circuit behaves the same as that when with 732ohm resistor. When the input is below 7.9V(doesn't work if it is increased to 8V)  it draws 5V and 500mA (draws how much ever current is supplied, i limited my circuit to 500mA) under no load condition and the output is 18.9V/500mA. 

    Would be helpful if any help on this weird behavior. Below are the values of voltage on all the pins under different circumstances

    RC - 0.2V
    SS - 2.7V
    EN - 0V
    COMP - 4.1V
    FB - 0.3
    ISNS - 17.8mV
    GDRV - 3.7V
    BP - 4.2V
    VDD - 4.9V ( Even though I supply 7V it draws only this much from the supply) 
    VOUT - 18.9V
    IOUT - 500mA ( Draws current how much ever supplied with no load condition)

    Also if I increase the voltage beyond 8V then the circuit only provides the input voltage as output. 
    When Vin is 10V
    RC - 200mV
    SS - 6V
    EN - 0V
    COMP - 9V
    FB - 200mV
    ISNS - 21.7mV
    GDRV - 0V 0r 0.1 mV ( No switching)
    BP - 8V
    VDD - 10V 
    VOUT - 9.6V
    IOUT - 1mA

    Now I changed the RFB1 to 2.2K according to the calculation I should get 17.3V
    When Vin is below 7.8V
    RC - 0.25V
    SS - 4.43V
    EN - 0V
    COMP - 1.9V
    FB - 0.7V
    ISNS - 19.3mV
    GDRV - 0.37 V 
    BP - 6.9V
    VDD - 7.5V 
    VOUT - 17.26V
    IOUT - 1mA

    Also if I increase the voltage beyond 7.8V then the circuit only provides the input voltage as output. 
    When Vin is 10V

    RC - 0.19V
    SS - 1.1V
    EN - 0V
    COMP - 8.17V
    FB - 0.38V
    ISNS - 21.8mV
    GDRV - 0 V (No switching) 
    BP - 8V
    VDD - 10V 
    VOUT - 9.6V
    IOUT - 1mA

    NOTE : I desoldered and resoldered a new TPS40201-Q1 IC and still the results are same as I have mentioned.