一个power问题！

szx841129

有个FPGA的小板，本来应该出来2.5V的电压，但是不知道为什么，出来的一直是2V，为什么呢？ 请看下图：

jackzhang

最好把你的电源部分原理图发上来

szx841129

回复 2# jackzhang

szx841129

我用LTspice对电路做了一个简单的simulation，负载用的是3Ω的电阻，请参看下图：

szx841129

对于fset pin,datasheet里面这样说：The LTM4601 is designed to typically operate at 850kHz
across most input conditions. The fSET pin is normally left
open or decoupled with an optional 1000pF capacitor. The
switching frequency has been optimized for maintaining
constant output ripple noise over most operating ranges.
The 850kHz switching frequency and the 400ns minimum
off time can limit operation at higher duty cycles like 5V to
3.3V, and produce excessive inductor ripple currents for
lower duty cycle applications like 20V to 5V. The 5V and
3.3V drop out curves are modifi ed by adding an external
resistor on the fSET pin to allow for lower input voltage
operation, or higher input voltage operation.


还有，用3Ω的电阻作为负载是否合适？

loopgain

换一家芯片试试。
最好用固定输出的版本。

spx0821

我觉得明显负载拉低了电源输出.负载过大,再小点.

zhang2001

对这不是很懂！

大李飞刀

看来还是带载的问题，引起了反馈环路不正常？

peleGuo

能用实验和仿真诊断问题，方法是不错的！