5 How to Modify a Buck to Inverting Buck-Boost?

To achieve the inverting function, the output terminals are swapped such that V_OUT becomes GND and the GND terminal becomes -V_OUT. Everything was GND is now labeled - V_OUT. The modification shown in .Figure 5-1

• The reference designators are identical between buck and inverting buck boost, except for the input capacitors C1, C2 and C3 whose connections need to be changed
• Remove input capacitor C1, C2 and C3 from the EVM, but save them to re-install later
• Install 2 pcs 22 μF, 10V ceramic output capacitors at C6 and C7. Might add more to reduce output ripple and improve loop stability.
• Change the value of R1 and R2 to set the appropriate output voltage

Installing the input capacitor C1, C2 and C3 guidance shown in Figure 5-2

• Because existing input GND pads of input capacitors C3 are not the correct electrical location on existing EVM. So put a electrical tape to cover that GND pad of C3 to avoid wrong connection.
• The existing pad for V_IN connection of C3 is used and a wire is added to complete the connection to GND, which is Vout on the PCB
• Re-install C1, C2 and C3 as highlighted in red square area
• Input supply can be applied between VIN and GND, which is V_OUT on the PCB
• Load can be applied between -V_OUT and GND