Re: problem about LDO!
LvW said:
flying591 said:
hi everyone
In a LDO circuit, I change the value of the ESR resistance, it should only change the zero which is generated by Resr.but at some values it not only change the zero bu also change the pole. moreover,the changed pole has imaginary part.
why??
for this pole,how compensation?
thanks in advance for any response that may help me!
If the load resistance RL across the series connection Resr-Cs is rather low, there is a (slight) influence of Resr also on the pole location beause the sum Resr+RL determines the pole frequency. This can be seen and calculated by a simple equivalent circuitry. Why do you want to compensate this pole ? Do you know the motivation for the output capacitance Cs ?
Sorry! the problem I said is not clearly!
Specifically! when Resr=0.1 simulation result
****** pole/zero analysis tnom= 25.000 temp= 25.000
******
input = 0:v_v3 output = v(111
input = 0:v_v3 output = v(111
poles (rad/sec) poles ( hertz)
**********************************************************************
real imag real imag
-487.7838k -864.8038k -77.6332k -137.6378k
-487.7838k 864.8038k -77.6332k 137.6378k
-10.6519x 0. -1.6953x 0.
-250.3852x 0. -39.8500x 0.
-368.1041x -161.1716x -58.5856x -25.6513x
-368.1041x 161.1716x -58.5856x 25.6513x
-399.9232x 0. -63.6498x 0.
zeros (rad/sec) zeros ( hertz)
**********************************************************************
real imag real imag
-1.0000x 0. -159.1549k 0.
-248.8822x 0. -39.6108x 0.
-365.5345x 251.9861x -58.1766x 40.1048x
-365.5345x -251.9861x -58.1766x -40.1048x
1.4730g 1.7979g 234.4380x 286.1465x
1.4730g -1.7979g 234.4380x -286.1465x
-3.1062g 0. -494.3622x 0.
when Resr=0.2
poles (rad/sec) poles ( hertz)
**********************************************************************
real imag real imag
-791.1464k 0. -125.9149k 0.
-1.4024x 0. -223.2004k 0.
-9.3955x 0. -1.4953x 0.
-250.3834x 0. -39.8498x 0.
-368.0945x -161.1854x -58.5841x -25.6535x
-368.0945x 161.1854x -58.5841x 25.6535x
-399.9812x 0. -63.6590x 0.
zeros (rad/sec) zeros ( hertz)
**********************************************************************
real imag real imag
-500.0000k 0. -79.5775k 0.
-248.8822x 0. -39.6108x 0.
-365.5345x 251.9861x -58.1766x 40.1048x
-365.5345x -251.9861x -58.1766x -40.1048x
1.4730g 1.7979g 234.4380x 286.1465x
1.4730g -1.7979g 234.4380x -286.1465x
-3.1062g 0. -494.3622x 0.
when Resr=0.3
poles (rad/sec) poles ( hertz)
**********************************************************************
real imag real imag
-373.0597k 0. -59.3743k 0.
-3.7192x 0. -591.9233k 0.
-7.4589x 0. -1.1871x 0.
-250.3816x 0. -39.8495x 0.
-368.0851x -161.1990x -58.5826x -25.6556x
-368.0851x 161.1990x -58.5826x 25.6556x
-400.0383x 0. -63.6681x 0.
-925.4669g 0. -147.2926g 0.
zeros (rad/sec) zeros ( hertz)
**********************************************************************
real imag real imag
-333.3333k 0. -53.0516k 0.
-248.8822x 0. -39.6108x 0.
-365.5345x 251.9861x -58.1766x 40.1048x
-365.5345x -251.9861x -58.1766x -40.1048x
1.4730g 1.7979g 234.4380x 286.1465x
1.4730g -1.7979g 234.4380x -286.1465x
-3.1062g 0. -494.3622x 0.
I do not know why, is that my simulation method wrong?
the command of HSPICE is .pz v(111) v_v3