SNVAAB4 January   2026 LM63615-Q1 , LM63625-Q1 , LM63635-Q1

 

  1.   1
  2.   Summary
  3. 1 Profile
  4. 2 Generation of the reverse current
  5. 3 EOS failure case
  6. 4 Potential cause
  7. 5 EVM test
  8. 6 Reverse current generation and failure process
  9. 7 Data validation
  10. 8 Design recommendations
  11. 9 Summary
  12. 10References:

4 Potential cause

VCC is especially important for the logic work of the chip, and the irrational design of VCC can introduce noise. Any noise can affect the logic error of the control, thereby creating a risk of cross-conduction. VCC acts as the charge capacitance for CBOOT, and CBOOT acts as the bias voltage for the upper transistor driver in the half-bridge. This plays a vital role in the control logic.

LM63635-Q1 function block diagram Figure 4-1 LM63635-Q1 function block diagram

It can be seen from Figure 4-1 that VCC is taken from the VIN linear buck, and any noise from VIN can be conducted to VCC. As shown in Figure 4-2, TI recommends avoiding any external circuitry connected to VCC while adding a 1uF high-quality capacitor for decoupling and filtering. Refer to LM63635-Q1EVM for guidance, using X7R MLCC capacitor.

LM63635-Q1 data sheet VCC design recommendations Figure 4-2 LM63635-Q1 data sheet VCC design recommendations

For layout design, TI recommends placing a VCC bypass capacitor close to the VCC pin. This capacitor must be placed as close to the device as possible with short and wide traces to VCC and PGND pins. It is not recommended for thermal dissipation in this area.

Following a rigorous review of the schematic diagram and layout design by TI's product line for this case, the design is found to fully comply with the schematic diagram and layout specifications. This essentially rules out control logic anomalies arising from an unreasonable VCC design. Consequently, the failure will now be analyzed from the perspective of reverse current.