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[FAQ] TPS43330A-Q1: What is the minimum possible duty cycle for the booster?

Phil Yi
Mastermind 49861 points
Part Number: TPS43330A-Q1


  The boost controller allows the device to operate down to 2 V at the input; the duty cycle of Boost converter D = 1 – (input voltage/output voltage); so, it depends on your output voltage selection (7 V, 8.85 V, or 10 V), the minimum possible duty cycle should be: 71%; 77.4% or 80%. The 90% max duty cycle means the input voltage should be > 1/10 of output voltage.

  More detail test results are listed below:

  1.  When apply VBAT in the range of 8.53V to 10.25V (which means 8.53V<VBAT<10.25V), the device can power up WITH the booster switching and booster output is 9.95V. When apply VBAT out of the range above (which means either VBAT<8.53V or VBAT>10.25V), the device powers up WITHOUT the booster switching; the booster works as a bypass switch. For example, if VBAT=8.50V, booster doesn't switching and its output is 8.35V (with about 150mV drop); if VBAT=10.50V, booster doesn't switching and its output is 10.35V (with about 150mV drop). 
  2. When apply VBAT in the range of 8.53V<VBAT<10.25V, the device can power up WITH the booster switching and booster output is 9.95V. From here, I did monitoring the booster switching and lower the VBAT slowly, the booster stopped switching when VBAT=1.99V. 
  3. Yes; please refer to the TPS4333xEVM User Guide for the MOSFETs part number. I found the booster switching waveform on the EVM is not very good ; I suggest to use faster MOSFETs.