SLVAFH1A December   2022  – December 2023 TPS62933 , TPS62933F , TPS62933O , TPS62933P

 

  1.   1
  2.   Create an Inverting Power Supply Using a TPS6293x Buck Converter With Internal Compensation
  3.   Trademarks
  4. 1Configuring the Buck Converter for Inverting Buck-Boost Topology Application
  5. 2Choosing the Correct Buck Converter for Inverting Power Application
    1. 2.1 Output Voltage Range
    2. 2.2 Input Voltage Range
    3. 2.3 Output Current Range
  6. 3Selecting Applicable External Components for Inverting Power Application
    1. 3.1 Resistor Divider
    2. 3.2 Inductor and Output Capacitor Selection
      1. 3.2.1 Inductor Selection
        1. 3.2.1.1 Output Current
        2. 3.2.1.2 Inductor Current Ripple
      2. 3.2.2 Output Capacitor Selection
        1. 3.2.2.1 Large Load Transient
        2. 3.2.2.2 Output Ripple Voltage
    3. 3.3 Input Capacitors
    4. 3.4 Bypass Capacitor
    5. 3.5 Enabling and Adjusting UVLO
  7. 4Experimental Results
  8. 5Summary
  9. 6References
  10. 7Revision History

3.5 Enabling and Adjusting UVLO

The TPS62933 device is enabled when the voltage at the EN pin trips its threshold, and the input voltage is above the UVLO threshold. It stops operation when the voltage on the EN pin falls below its threshold, or the input voltage falls below the UVLO threshold. However, when configured as a Buck-Boost application, the GND pin of the TPS62933 device is tied to the negative output voltage and not the zero voltage (system ground), which can cause difficulties enabling or disabling the device. So, level-shifting circuitry is needed to solve the problem, as shown in Figure 3-2.

GUID-20221212-SS0I-C7H6-VPVT-LD6S0JMHM0NS-low.svg Figure 3-2 Enabling and Adjusting UVLO Circuit

R11 and R12 are used to divide the input voltage into a small one, to ensure the EN pin can take the normal action while not exceeding the maximum pin rating of 5.5 V. Considering the internal pull-up current source of the TPS62933 device, Equation 16 and Equation 17 could be used to get the right value of R11 and R12.

Equation 16. V I N + V O U T × R 12 R 11 + R 12 + R 11 × R 12 R 11 + R 12 I p = V S T A R T × R 12 R 11 + R 12 + R 11 × R 12 R 11 + R 12 I p ≥ V E N _ R I S E ( m a x ) = 1.28 V
Equation 17. V I N + V O U T × R 12 R 11 + R 12 + R 11 × R 12 R 11 + R 12 I p m a x = V I N m a x + V O U T × R 12 R 11 + R 12 + R 11 × R 12 R 11 + R 12 I p ≤ 5.5 V

Here for example, set VSTART = 7.5 V for the 8-V minimum input voltage, you can choose R12 = 13.2 kΩ and R11 = 62.2 kΩ.

R7 and R8 form a voltage divider to set the VSTOP voltage. U1 is an adjustable precision zener hunt regulator, the simplified block diagram of the regulator is shown as Figure 3-3.

GUID-20221213-SS0I-6WSZ-RNQ7-65FL5KCNT1RR-low.svg Figure 3-3 Simplified Block Diagram of the Regulator

When the zener diode turns on, Q2 is turned on as well. Then, the voltage of the EN pin equals the value Equation 16 gets. When the diode turns off, Q2 turns off, and the voltage of the EN pin equals the VOUT voltage. Then, the IC turns off at once. From the LM431BCM3 data sheet, the Vref voltage is 2.5 V. Given this value and the stop voltage, Equation 17 is derived as follow:

Equation 18. V S T O P × R 7 R 7 + R 8 = 2.5 V

Here for example, set VSTOP = 7 V, R7 = 45.3 kΩ and R8 = 24.9 kΩ was chosen.