a****y
发帖数: 255 | 1 NCP1402是一个DC TO DC STEP UP转换器. | a****y
发帖数: 255 | 2 它有LXpin做电压输入, OUTpin做电压输出, CEpin是使能控制.
如果CE接高电平, 芯片工作, Vout就是变换后的电压.
可是如果CE接低电平, 芯片不工作, Vout是多少呢?
在Vin是直流3V左右,
Vout是等于Vin减去二级管的正向导通电压(这个情况 下, 是0.3V) 吗? | a****y
发帖数: 255 | | n****t
发帖数: 170 | 4 你可以认为这时OUT pin通过一个高电阻接地，也就是没有输出电压。 | a****y
发帖数: 255 | 5 多谢. 可是如果看 Vin -- 电感 -- 二级管 -- Vout 这个联线,
这时候(CE disabled), Vout上的电压应该是Vin减二级管的正向导通电压吧. 虽然此时
芯片没有提供输出电压. 我的理解对吗?
【在 n****t 的大作中提到】
: 你可以认为这时OUT pin通过一个高电阻接地，也就是没有输出电压。
| f*****0
发帖数: 489 | 6 if you read the datasheet more carefully, you will know that the Vout pin on
the chip isn't to output voltage. the schottky diode / capacitor is. read a
little bit more about boost converters and you will understand why.
yes, if you the CE pin low, it would disable the chip (which by the way is a
PFM chip, good for low-load or standby situations). When that happens, the
LX pin is left float and the current will flow from Vin to Vout through the
inductor and the schottky diode. So the rough volta | g******u
发帖数: 3060 | 7 同学们。
当chip不工作时，内置FET不工作，外面那个电感saturate,怎么可能还有输出。 | f*****0
发帖数: 489 | 8 "当chip不工作时，内置FET不工作，外面那个电感saturate,怎么可能还有输出。"
when the chip is disabled, the gate goes low, and the drain goes high
impedance. When that happens, the current goes through the inductor and the
diode to the load.
another way to look at it: notice that the Out pin supplies Vdd for the chip
and is connected to Vout? if Vout went low when the chip is disabled, how
would the chip have started?
BTW, the chip can be easily converted to a gated PFM regulator, aka LT1073
style. | a****y
发帖数: 255 | 9 good analysis, thanks.
the
chip
【在 f*****0 的大作中提到】
: "当chip不工作时，内置FET不工作，外面那个电感saturate,怎么可能还有输出。"
: when the chip is disabled, the gate goes low, and the drain goes high
: impedance. When that happens, the current goes through the inductor and the
: diode to the load.
: another way to look at it: notice that the Out pin supplies Vdd for the chip
: and is connected to Vout? if Vout went low when the chip is disabled, how
: would the chip have started?
: BTW, the chip can be easily converted to a gated PFM regulator, aka LT1073
: style.
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