SLOA284A january   2020  – may 2023 AFE5832 , AFE5832LP , ISO7741 , ISOW7841 , LM25037 , LM25180 , LM5180 , LM5181 , LM5181-Q1 , TX7316 , TX7332

 

  1.   1
  2.   Designing Bipolar High Voltage SEPIC Supply for Ultrasound Smart Probe
  3.   Trademarks
  4. 1Introduction
    1. 1.1 Key Design Challenges
    2. 1.2 Potential Topologies for Generating High Voltage Supply
  5. 2Design of high voltage circuit using SEPIC topology
    1. 2.1 TI HV Supply Architecture Using SEPIC Topology
  6. 3Test Results
    1. 3.1 Efficiency and Load Regulation
    2. 3.2 Output Ripple Measurement
    3. 3.3 Load Transient Test
    4. 3.4 Noise Measurement
    5. 3.5 Thermal Performance
  7. 4Possible Variants of the Design
    1. 4.1 Option 1: Programmable Output Voltage
    2. 4.2 Option 2: Support Input From 1S Li-Ion Battery
    3. 4.3 Option 3: Output Voltage Up to ±100 V
  8. 5Layout Guidelines
  9. 6Clock Synchronization
  10. 7Summary
  11. 8References
  12. 9Revision History

4.1 Option 1: Programmable Output Voltage

Based on the various ultrasound operating modes, the output of the high voltage circuit should be programmable. This can be implemented as shown in Figure 2-2 by replacing the diode D18 with one resistor R3, joining the feedback resistors (shown in Figure 4-1). Output voltage can be varied through the control voltage (VDAC). Resistors can be set using equations (2), (3), (4) where R1 and R2 are the feedback resistors.

GUID-D3921A05-3A71-4200-9DE4-2AE69A4768E1-low.gifFigure 4-1 Implementation of Programmable Output
Equation 14. GUID-A1482DDB-149C-4AC5-A282-E1F066B1725B-low.gif
Equation 15. GUID-311588CD-F3D2-4CB3-8680-896F4D4F4160-low.gif
Equation 16. GUID-3FC284A4-72F4-492C-8EC6-40B12CC70DEE-low.gif

Figure 4-2 shows linear relationship between the programmed output voltage and the control voltage.

GUID-6C4A13F1-B69F-4999-B104-D213B673E3F3-low.gifFigure 4-2 Linearity of Output Voltage vs Control Voltage (VDAC)

The designer should take care of the saturation current rating of the secondary inductors to take care of increased output current at reduced output voltage. In SEPIC converter the current is provided mainly from secondary inductors during off time. In this design, the secondary inductors are rated for 80 mA.