bd8311nuv-e2 ROHM Co. Ltd., bd8311nuv-e2 Datasheet - Page 10

• Manufacturer Part Number: bd8311nuv-e2
• Description: High-efficiency Step-up Switching Regulator With Built-in Power Mosfet
• Manufacturer: ROHM Co. Ltd.

(4) DC/DC converter frequency response adjustment system
Condition for stable application
[1] R
Primary pole point frequency
DC/DC converter DC Gain
By Equations (1) and (2), the frequency f
pole point is as shown below.
It is recommended that f
By this setting, R
an appropriate resistance value is not available and routing may cause noise, the use of R
The condition for feedback system stability under negative feedback is that the phase delay is 135 °or less when gain
is 1 (0 dB).
Since DC/DC converter application is sampled according to the switching frequency, the bandwidth GBW of the whole
system (frequency at which gain is 0 dB) must be controlled to be equal to or lower than 1/10 of the switching
frequency.
In summary, the conditions necessary for the DC/DC converter are:
- Phase delay must be 135°or lower when gain is 1 (0 dB).
- Bandwidth GBW (frequency when gain is 0 dB) must be equal to or lower than 1/10 of the switching frequency.
To satisfy above two items, R
R4=62 kΩ and C2=200pF. These C2 and R
values decide the prim ary pole that determines the
bandwidth of DC/DC converter.
BD8311NUV incorporates phase compensation devices of
1
, R
2
, R
fp=
f
SW
DC Gain =A×
3
= fp×DC Gain =
2π A×(
1
and R
sw
2
R
, which determine the voltage value, will be in the order of several hundred kΩ. Therefore, if
R
1
B
should be approx.10 kHz. When load response is difficult, it may be set at approx. 20 kHz.
1
1
・R
+R
×
1
1
, R
2
2
V
2πC2×(
+R
2
OUT
V
, R
OUT
3
)×C
-V
3
, D
IN
sw
S
2
and R
of point 0 dB under limitation of the bandwidth of the DC gain at the primary
1
(R
(R
1 ・
1+
R
R
2
S
1
2
)
, R
)
in Fig. 34 should be set as follows.
10/14
+R
2
, and R
················ (1)
················ (2)
3
)
×
3
1
B
VOUT
×
R1
R2
Fig.34 Example of phase compensation setting
V
OUT
A: ERROR AMP Gain
B: Oscillator amplification = 0.5
V
V
V
IN:
OUT
OUT
R3
-V
Rs
About 100dB = 10
Cs
: Output voltage
IN
Input voltage
················ (3)
Inside of IC
3
enables easy setting.
R4
5
C2
FB