原帖由 icsb 于 2009-4-24 23:20 发表
我觉得这样回答比较好
Regulator的主要目的是提供一个恒定的电压源,所以希望输出电阻比较小,这样考虑的话当然是选NMOS
如果从电压考虑,用PMOS所需的电源电压比较低,如果不是高压的DC-DC,还是选PMOS比较好
You are completely wrong. In term of close loop, the output impedance is mainly determined by loop gain regardless NMOS or PMOS output stage.
Of course if your same loop gain, NMOS output have lower impedance but frequency compensation more complex to keep same loop gain than PMOS type.
NMOS can also work for low power supply voltage although PMOS is more convenient especially for higher efficiency power stage.
Generally, both PMOS and NMOS used a lot in different type DC-DC regulator(converter) and LDOs. It must be tradeoff among power efficiency, current driving ability, stability, frequency compensation, PSRR, process, external component etc. |