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LDO与DCDC问题(Some questions about LDO and DCDC)

Other Parts Discussed in Thread: TPS563201, LM1085

大家好:

        DCDC和LDO用作电源芯片时,DCDC和LDO的可调版本(ADJ)都是通过电阻分压来获得反馈引脚的电压,但是为什么两者的计算方式不一样呢。

Vout=Vref*(1+R1/R2)

对于DCDC而言,R2是对地电阻;对于LDO而言,R1是对地电阻。

谢谢。

Hello everyone:

         When DCDC and LDO are used as power chips, the adjustable versions of LDO , DCDC  are all voltage dividers to obtain the feedback pin voltage, but why both are calculated in different ways.

Vout=Vref*(1+R1/R2)

For DCDC, R2 is the resistor connected to GND; for LDO, R1 is the resistor connected to GND.

Thanks.

  • Hi
    这个纯粹是写法上的问题,看你是定义高边电阻为R1,还是低边电阻为R1, 就原理上而言是一样的。
  • 对于TI的TPS563201 DCDC芯片,此时的输出电压计算公式为VOUT=0.768*(1+R1/R2),此时的R1是高边电阻,一端连接5V一端接FB引脚;R2是低端电阻,一端接FB一端接地。且此时R1和R2取值在千欧级别。

    而对于TI的LM1085  LDO芯片,此时输出电压VOUT=1.25*(1+R2/R1),此时的R1是连接在输出端和ADJ引脚的;R2是连接在ADJ引脚和地之间的。

    所以应该不是定义的问题,DCDC是电压输出端电阻/对地端电阻;LDO是对地端电阻/电源输出端电阻,这种不同的原因是什么?

    还有,LDO的输出调节电阻一般是百欧级别,且在数据手册中LDO对于ADJ引脚电流有明确表示,DCDC数据手册中却没有。如果将百欧电阻换为千欧级别,会有其他什么问题吗?