Other Parts Discussed in Thread: LM5088, LM25148
I would like to utilise the buck controller to realize the negative boost converter (Negative input voltage to Negative output voltage non isolated DC-DC converter).
I found some of the references from TI that discuss about the design of a negative boost converter - https://www.ti.com/lit/an/slyt516/slyt516.pdf?ts=1698300559105
I can not copy the exact solution described in the link since the requirements are somewhat different as mentioned below:
Key specs
- Vin(nom) = -2 V
- Vout(nom) = -4 V up to -15 V
- Pout = 15 W
Based on above requirements, considering the output power requirement I will need a buck controller IC with external switch. Another challenge is the nominal input voltage of -2 V which is lower the minimum input voltage for the most buck controller IC 4.5 V.
In the case of negative boost converter utilizing buck controller IC the IC GND reference is referenced to output voltage. At the start Vin = Vout i.e in the presented case Vout = -2 V. This can be resolved if the IC Vin or Vcc is biased with a positive voltage with reference to GND i.e > 3 V thus the voltage difference between the Vin or Vcc to GND is greater than minimum required input voltage of 4.5 V.
Most of the buck controller ICs I have come across (considering the specific application mentioned here) require that the drain of the external N channel MOS and Vin or Vcc tied together for several reasons as below.
- Buck controller IC with short circuit protection that is based on N-MOS drain-source voltage measurement (If Vin and drain of the external N-MOS is biased with different voltage potential which is higher the threshold for the protection this will prevent from adopting this)
- Buck controller ICs that utilizes DC-level plus current ramp for diode current or N-MOS current (synchronous buck) in the case. The ramp current generation circuit within the IC dependent on the input voltage. (again if Vin is biased with different voltage potential than the external N-MOS drain then the current ramp is not accurate - may be this can be worked out but introduces more complexity)
The LM5088 here is just an example but I am looking for the buck controller IC that I can utilize to realize the negative boost converter with specs. mentioned above.
Looking forward to TI expert/community suggestions.
