SLVAFU0 April   2024 TPS61377

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2Analysis of Dual Polarity Voltage Rails Design With Boost Converter
    1. 2.1 Analysis of Factors Affecting Negative Voltage Rail
    2. 2.2 Improvement of Gap Between Negative Voltage Rail and Positive Voltage Rail
  6. 3Boost Converter ± Quick Calculator Design
  7. 4Demo and Test
    1. 4.1 Simulation Results
    2. 4.2 Demo Board Example
  8. 5Summary
  9. 6References

2.1 Analysis of Factors Affecting Negative Voltage Rail

Negative voltage rail DC voltage can be estimated through Equation 1. The negative voltage rail can have a gap comparing with positive voltage rail. Main factors causing negative voltage gap are RCHG and forward voltage of D2 and D3.

Equation 1. - V O U T 2 = V O U T 1 + V D 1 - I C H G 1 + I C H G 2 × R C H G - V D 2 - V D 3
Equation 2. I C H G 1 = 1 D × I O U T 2
Equation 3. I C H G 2 = 1 1 - D × I O U T 2

But forward voltage of D1 helps the voltage gap. Normally, selecting higher forward voltage of D1 to cover the gap is the common method and the higher forward voltage can help the gap in full load, but in light load condition, the higher forward voltage can generate the extra voltage on the negative voltage rail if we select higher forward voltage of D1.

Equation 4. N e g a t i v e   v o l t a g e   d r o p =   1 D ( 1 - D ) × I O U T 2 × R C H G + V D 2 + V D 3 - V D 1