Other Parts Discussed in Thread: LM5148, LM25190, LM25149, TL494,
Tool/software:
Hi,
We are currently supporting a customer who is designing a non-isolated buck converter with the following conditions:
・Input voltage: 18V to 50V
・Output voltage: 15.2V to 16.8V (adjustable)
・Output current: 0.9A
・Inductor: 100µH (external)
・No transformer (non-isolated)
・High-side switch: external PNP bipolar transistor (2SA1577: https://fscdn.rohm.com/en/products/databook/datasheet/discrete/transistor/bipolar/2sa1577t106q-e.pdf)
The customer is considering using a PNP transistor as the high-side switch to simplify their driver stage, and they are seeking a suitable TI controller that can support this topology.
We have reviewed several synchronous buck controllers such as LM25149, LM5148, and LM25190. However, we understand that these devices utilize bootstrap-based high-side gate drivers designed for N-channel MOSFETs, making them unsuitable for directly driving a high-side PNP transistor (which requires a base voltage lower than VIN).
Given the use of a high-side PNP transistor, could you please advise:
1. Whether there is any TI controller that can support this type of configuration (i.e., directly driving a high-side PNP BJT in a buck topology)?
2. If not, do you have any recommended workaround or reference circuit using TI products that could enable PNP-based buck conversion under these conditions?
If any older analog controllers (such as UC384x family) or low-side PWM controllers are still applicable for this purpose, we would appreciate your guidance as well.
We look forward to your suggestions.
Best regards,
Conor
