BD9A301MUV-LB Datasheet, PDF (24/35 Pages) Rohm – This is the product guarantees long time support in Industrial market

BD9A301MUV-LB
Datasheet
4. Phase Compensation Component
A current mode control buck DC/DC converter is a one-pole, one-zero system. One poles are formed by an error amplifier
and load and the one zero point is added by phase compensation. The phase compensation resistor R_ITH determines the
crossover frequency F_CRS where the total loop gain of the DC/DC converter is 0dB. A high value crossover frequency F_CRS
provides a good load transient response characteristic but inferior stability. Conversely, a low value crossover frequency
F_CRS greatly stabilizes the characteristics but the load transient response characteristic is impaired.
(1) Selection of Phase Compensation Resistor R_ITH
The Phase Compensation Resistance R_ITH can be determined by using the following equation.
R _ITH
2π
V_OUT F_CRS C_OUT
V_FB G _MP G_MA
[_Ω]
　V_OUT : Output Voltage[V　]
　F _CRS: Crossover Frequency[Hz]
　C_OUT : Output Capacitance[F]
　V_FB : Feedback Reference Voltage (0.8V (Typ))
　G_MP : Current Sense Gain (13A/V (Typ))
　G_MA : Error Amplifier Trans conductance (260μA /V(Typ))
(2) Selection of Phase Compensation Capacitance C_ITH
For stable operation of the DC/DC converter, zero for compensation cancels the phase delay due to the pole formed
by the load.
The phase compensation capacitance C_ITH can be determined by using the following equation.
C _ITH
C _OUT
R _ITH
V_OUT
I _OUT
[_F]
(3) Loop stability
To ensure the stability of the DC/DC converter, make sure that a sufficient phase margin is provided. A phase margin
of at least 45º in the worst conditions is recommended.
VOUT
RUP
RDW
FB
ITH
－
＋
0.8V
RITH
CITH
A
Gain [dB]
0
Phase[deg] 0
－90
－180
(a)
GBW(b)
f
FCRS
－90°
PHASE MARGIN
－180°
f
Figure 52. Phase Compensation Circuit
Figure 53. Bode Plot
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20.Aug.2014 Rev.001