bd9132muv ROHM Co. Ltd., bd9132muv Datasheet - Page 10

• Manufacturer Part Number: bd9132muv
• Description: Step-down Switching Regulator
• Manufacturer: ROHM Co. Ltd.

Phase
Phase
[deg]
[deg]
Gain
Gain
[dB]
[dB]
3. Selection of input capacitor (Cin)
A low ESR 22μF/10V ceramic capacitor is recommended to reduce ESR dissipation of input capacitor for better efficiency.
4. Determination of RITH, CITH that works as a phase compensator
V
As the Current Mode Control is designed to limit a inductor current, a pole (phase lag) appears in the low frequency area due to
a CR filter consisting of a output capacitor and a load resistance, while a zero (phase lead) appears in the high frequency area
due to the output capacitor and its ESR. So, the phases are easily compensated by adding a zero to the power amplifier output
with C and R as described below to cancel a pole at the power amplifier.
-90
-90
CC
A
A
0
0
0
0
Fig.29 Input capacitor
Fig.31 Error amp phase compensation characteristics
I
L
OUT
fp(Min.)
fz(Amp.)
Cin
Min.
Fig.30 Open loop gain characteristics
Co
fp(Max.)
I
OUT
Max.
V
OUT
fz(ESR)
Input capacitor to select must be a low ESR capacitor of the capacitance
sufficient to cope with high ripple current to prevent high transient voltage. The
ripple current IRMS is given by the equation (5):
If V
I
< Worst case > I
When Vcc=2×V
I
RMS
RMS
CC
=I
=2×
=3.3V, V
OUT
×
fp=
fz
Pole at power amplifier
Zero at power amplifier
√
√
OUT
10/15
(ESR)
V
1.8(3.3-1.8)
RMS(max.)
When the output current decreases, the load resistance Ro
increases and the pole frequency lowers.
OUT
Increasing capacitance of the output capacitor lowers the pole
frequency while the zero frequency does not change. (This
is because when the capacitance is doubled, the capacitor
ESR reduces to half.)
OUT
=1.8V, and I
3.3
2π×R
=
, I
(V
V
RMS
CC
2π×E
CC
1
-V
O
=
fp
fp
fz
×C
OUT
=1.49[A
1
(Min.)
(Max.)
(Amp.)
I
OUTmax.=
SR
OUT
2
O
)
×C
=
=
=
[A]・・・(5)
RMS
O
2π×R
2π×R
2π×R
3A, (BD9132MUV)
]
OMax.
OMin.
ITH
1
1
1
×C
×C
×C
ITH
O
O
[Hz]←with lighter load
[Hz] ←with heavier load