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

3 Boost Converter ± Quick Calculator Design

Table 3-1 shows the example of the test condition.

Table 3-1 Test Condition Example
Test condition
Input voltage 12V
Output voltage ± 19V
Output load ± 100mA

And the application note uses TPS61377 to achieve the design. The switching frequency is 650kHz. Table 3-2 shows the preliminary results.

Table 3-2 I/O Condition in Boost Converter ± Quick Calculator Design
I/O condition
System Parameters Value Unit Remark
Vin(typ) 12 V Typical input voltage
VOUT1 19 V Positive power rail voltage
VOUT2 -19 V Negative power rail voltage
Fsw 650 kHz Switching frequency
IOUT1 0.1 A Load current of positive voltage rail
IOUT2 0.1 A Load current of negative voltage rail
Efficiency 90 % Estimated value, used 90% as default
Ripple of VCOUT2 0.19 V 1% of VOUT
CCHG 0.81 µF Recommended CCHG that achieve desired Vout ripple
RCHG 0.32733 Ω Recommended RCHG, by using Ts = RCHG × CCHG

Table 3-3 shows the components selection. The forward voltage of D2 and D3 are better to select the smaller to minimize the power loss of the architecture. In the previous section, the recommendation is to forward voltage of D1 and R3. For the power loss of R3 needs be carefully designed.

Table 3-3 Components Selection in Boost Converter ± Quick Calculator Design
Components selection
System Parameters Value Unit Remark
CCHG 4.70 µF Real CCHG, suggest > recommended value for derating
RCHG 1 Ω Real RCHG, suggest >= 1Ω && recommended value, use 1Ω as first
VD2 0.35 V Real forward voltage of VD2, smaller is good
VD3 0.35 V Real forward voltage of VD3, smaller is good
VD1 0.7 V Recommended forward voltage of VD1=VD2+VD3
VD1 0.7 V Real forward voltage of VD1
R3 2.32 Ω Recommended R3 by using real VD1
R3 2.32 Ω Real VD1 resistor
PR3 0.0408 W Average power of R3

Table 3-4 shows the calculation result after inputting the I/O condition and Component selection. Original gap means that the architecture without using R3 and D1. After R3, the gap can be effectively reduced.

Table 3-4 Calculation Result in Boost Converter ± Quick Calculator Design
Calculation result
System Parameters Value Unit Remark
D 0.43 Duty cycle of boost converter
Ts 1.54 µs Duty time
Ton 0.66 µs Duty on time
ICHG1 0.23 A Averaged ICHG1
ICHG2 0.18 A Averaged ICHG2
ΔVCHG 0.033 V Ripple of the CCHG
VCHG 19.17 V DC voltage of the CCHG
Original -VCOUT2 18.59 V Original negative voltage rail
Original Gap 0.41 V Original gap
Output capacitance 0.4603 µF Cout need for VOUT1
Optimized -VCOUT2 19.0005 V Optimized negative voltage rail
PRCHG 0.0408 W Power of RCHG
Optimized Gap -0.0005 V Optimized gap