BD9045FV-E2 Rohm Semiconductor, BD9045FV-E2 Datasheet - Page 11

• Manufacturer Part Number: BD9045FV-E2
• Description: IC REG SW STEP DOWN HE 28SSOP
• Manufacturer: Rohm Semiconductor
• Type: Step-Down (Buck)r

Specifications of BD9045FV-E2

• Internal Switch(s): No
• Synchronous Rectifier: Yes
• Number Of Outputs: 2
• Frequency - Switching: 200kHz ~ 750kHz
• Voltage - Input: 4.5 ~ 18 V
• Mounting Type: Surface Mount
• Package / Case: 28-SSOP
• Power - Output: 940mW
• Primary Input Voltage: 12V
• No. Of Outputs: 1
• Output Voltage: 5.5V
• Output Current: 6mA
• Voltage Regulator Case Style: SSOP
• No. Of Pins: 28
• Operating Temperature Range: -40°C To +85°C
• Svhc: No SVHC
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Current - Output: -
• Voltage - Output: -
• Operating Temperature: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant
• Other names: BD9045FV-E2TR

(10) Method to set the phase compensation
lead, please select one of the following.
LC resonance.
・Stable condition of application
Moreover, for DC/DC converter application, because it is sampled by switching frequency, the whole series of GBW are to be set at 1/10 of
switching frequency. To sum up, the features aiming at application are as follows.
Therefore, it is necessary to raise the switching frequency up to higher frequency in order to raise the response by means of limit of GBW.
The key to ensuring the stability by means of phase compensation is that the quadratic phase delay (-180°) produced by LC resonance is
cancelled by quadratic phase lead (i.e. let two phase leads into).
make (enlarge) the capacitor larger when you want to reduce the GBW.
Shown as below are the stable conditions of the feedback system for negative feedback to return.
Moreover, GBW (the frequency at the time of gain=1) is determined by the phase compensation capacitor attached on the error amplifier, so
・If output capacitor is aluminum electrolytic capacitor etc, ESR of which is large
Because of the change of phase characteristic caused by ESR, the phase lead that needs inserting becomes a single one. For this phase
For setting of the frequency inserting the phase lead, please set it near LC resonance frequency for the purpose of canceling the
Feedback
General integrator (low pass filter)
・The phase delay when the gain is 1(0dB) is no more than150°（i.e. phase margin is more than 30°）
・The phase delay when the gain is 1(0dB) is no more than150°（i.e. phase margin is more than 30°）
・GBW（i.e. frequency of 0dB gain）at that time is no more than 1/10 of switching frequency
Error amplifier becomes a low pass filter because such measures of phase compensation as
In case of DC/DC converter application, R becomes the parallel of feedback resistance.
If ESR of output capacitor is large (a few Ω), the phase compensation becomes relatively simple. For DC/DC converter application, there
is always LC resonance circuit, because of which the phase delay is -180°.
However, if ESR component exists, a phase lead of +90° comes into existence, and so the phase delay becomes -90°. Please set the
phase delay within 150°.
It is a very advantageous means according to circumstances, but as a disadvantage, the ripple component in output voltage increases.
Two output high frequency step-down switching regulator
LC resonance circuit
Vcc
Insert C in feedback resistance
Phase lead fz =
Vo
R
L
R1
R2
FB
C
Vo
A
C1
2πC1R1
C
Resonance point phase delay -180 º is at
FB
fr =
1
COMP
C2
A
2π√LC
[Hz]・・・ （16）
Open loop characteristic of integrator
1
Phase
[deg]
Gain
[dB]
-180
[Hz]・ ・ ・ （13）
-18 0
-90
18 0
-9 0
COMP
0
9 0
A
0
0
Phase margin
(a)
11/16
-90°
Vcc
With ESR
-20dB/decade
Phase lead fz =
Vo
L
R1
R2
GBW(b)
C
Insert R3 in integrator
R
-180°
ESR
Vo
(a)点 fa =
(b)点 fa = GBW
2πC2R3
Phase delay -90°
fr =
f
ESR
FB
1
=
&
R3
2π√LC
2πR
A
are taken.
1
C2
[Hz]・・・ （17）
1
2πRCA
ESR
C
[Hz],
1
2πRC
[Hz],
resonance point is at this fr
1
COMP
1.25[Hz]・ ・ ・ （11）
phase lead is at this f
[Hz] ・ ・ ・ （12）
ESR
・ ・ （ 14）
（15）