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TPS40345: variable voltage output with TPS40345

Part Number: TPS40345
Other Parts Discussed in Thread: LM10011, LM10010

Hi,

I would like to use a TPS40345 buck controller to deliver between 1.12V (5W) and 1.5V (9W) to a 0.6 ohm load.

The buck's high side is connected to a 3.7V battery, the TPS 40345 is powered via a 3.3V VDD.

By connecting the FB pin to a DAC, is it possible to control the TPS 40345's output by changing the DAC output ? 

  •  

    1) The TPS40345 is not intended for split rail operation.  The high-side current limit detects the voltage drop between the switching node and the VDD input during the high-side FET on-time.  With VDD and the drain of the high-side FET separate, the TPS40345 will triggger high-side short circuit protection when the battery voltage drops below the 3.3V input, and when the battery voltage is greater than the 3.3V input, the short circuit current will be much higher than intended, effectively disabled.

    2) Yes, you can adjust VOUT by injecting current into the FB divider from a DAC through a resistor, or from a programmable current DAC.  The change in voltage at the output will be equal to minus the current injected into the FB pin times the FB to VOUT resistance.  As a result of the inversion, VOUT will he highest when the DAC voltage is 0 and sinking current from FB and lowest when the DAC voltage is at its maximum and sourcing current into FB.

    The LM10010 and LM10011 are 4/6 bit parallel input current sink DACs specifically designed for this purpose, but other DACs can be used as well.

    Be careful when rapidly reducing VOUT, as this boosts the excess energy stored in the output capacitors back to the input and can charge the input voltage.

  • Hi,

    Thank you for your reply. That really helps me understand how it works.

    The circuit on my simulation didn't take into account those consideration.

    On another note, is there any chance TI has an integrated buck that could fit this application, easily controllable via a voltage or I2C ?