SC4605 データシートの表示（PDF） - Semtech Corporation
部品番号
コンポーネント説明
一致するリスト
SC4605 Datasheet PDF : 19 Pages
| |||
SC4605
POWER MANAGEMENT
Applications Information (Cont.)
Loop Compensation Design
For a DC/DC converter, it is usually required that the
converter has a loop gain of a high cross-over frequency
for fast load response, high DC and low frequency gain
for low steady state error, and enough phase margin for
its operating stability. Often one can not have all these
properties at the same time. The purpose of the loop
compensation is to arrange the poles and zeros of the
compensation network to meet the requirements for a
specific application.
The SC4605 has an internal error amplifier and requires
the compensation network to connect among the COMP
pin and VSENSE pin, GND, and the output as shown in
Figure 3. The compensation network includes C1, C2,
R1, R7, R8 and C9. R9 is used to program the output
voltage according to:
VO
=
0.8 ⋅ (1+
R7
R9
)
Where:
R = load resistance and
RC = C4’s ESR.
The compensation network will have the characteristic
as follows:
1+ s 1+ s
GCOMP (s) =
ωI
s
⋅
1+
ωZ1
s
⋅
⋅1+
ωZ2
s
ωP1
ωP2
Where;
1
ωI = R7 ⋅ (C1 + C2 )
1
ωZ1 = R1 ⋅ C2
1
ωZ2 = (R7 + R8 ) ⋅ C9
C1 C2
SC4605
1 BST
DRVH 10
2 VCC
3 ISET
PHASE 9
DRVL 8
4 COMP
GND 7
5 FSET
VSENSE 6
R1
L1
+VO
C4
C9
R7
R8
ωP1
=
C1 + C2
R1 ⋅ C1 ⋅ C2
1
ωP2 = R8 ⋅ C9
After the compensation, the converter will have the
following loop gain:
R9
Figure 3. Compensation network provides 3
poles and 2 zeros.
For voltage mode step down applications as shown in
Figure 3, the power stage transfer function is:
1+
s
1
GVD (s)
=
VI
1+
s
RC
L1
R
+
⋅ C4
s2L1C4
T(s) = GPWM ⋅ GCOMP (s) ⋅ GVD (s) =
1
VM
⋅ ωI
s
⋅
VI
⋅
1+
1+
s
ωZ1
s
ωP1
1+ s
⋅
⋅
1
+
ωZ2
s
ωP2
1+
s
1
⋅
1
+
s
RC ⋅ C4
L
R
+
s2LC
Where:
GPWM = PWM gain
VM = 1.5V, ramp peak to valley voltage of SC4605
2004 Semtech Corp.
10
www.semtech.com
Share Link: 