SLVAFB4 July   2022 TPS62902-Q1 , TPS62903 , TPS62903-Q1

 

  1.   Abstract
  2.   Trademarks
  3. 1Inverting Buck – Boost Topology
    1. 1.1 Concept
    2. 1.2 Output Current Calculations
    3. 1.3 VIN and VOUT Range
  4. 2Digital Pin Configurations
    1. 2.1 Enable Pin
    2. 2.2 MODE/S-CONF Pin
    3. 2.3 Power Good Pin
  5. 3Design Considerations
    1. 3.1 Input Capacitor Selection
    2. 3.2 Output Inductor Selection
    3. 3.3 Stability Limits and Output Capacitor Selection
  6. 4Typical Performance and Waveforms
  7. 5Conclusion
  8. 6References

2.2 MODE/S-CONF Pin

TPS62903 has a MODE/S-CONF pin which can be used to customize the device behavior. Refer to schematic in Figure 2-2 and Figure 2-3

  • Selects device configuration (switching frequency, internal or external feedback, output discharge, Forced PWM and Auto PFM/PWM mode) by connecting a single resistor between this pin and -VOUT (IC GND pin) or connecting directly to VIN or -VOUT (IC GND pin).
    • A 2.5 MHz switching frequency setting is recommended for inverting buck-boost application due to lower inductor ripple current. The design example selects MODE/S-CONF resistor as 26.1 k which configures internal feedback, 2.5 MHz switching frequency, Auto PFM/PWM with AEE and output discharge enabled.
    • Note that the maximum output current will be reduced while using 1uH inductor and 1MHz switching frequency. 2.2uH or larger inductance is strongly recommended for 1 MHz switching frequency configuration, otherwise special care has to be taken to make sure the half ripple current doesn't trip the negative current limit under no load condition.
  • Dynamic MODE option is an advance feature which allows MODE/S-CONF pin to actively switch between Forced PWM and Auto PFM/PWM during operation. This feature provides user with the option of controlling when/if the device enters power save mode (DCM). In the inverting buck-boost topology, VIN is HIGH and -VOUT is LOW, but this is only possible by driving the MODE/S-CONF pin between VIN and -VOUT. This can be done with the same type of circuit used to drive the EN pin HIGH and LOW as shown in Figure 2-1
  • The external feedback configuration shown in Figure 2-3 , where the MODE/S-CONF pin can be tied to -VOUT directly to configure as 2.5 MHz switching frequency, Auto PFM/PWM with AEE and output discharge enabled.
GUID-BB4E57D2-B5B1-4E22-B11B-B7FCD46D9944-low.pngFigure 2-3 External Feedback with 2.5 MHz Switching Frequency and Auto PFM/PWM