600kHz 3A Step-Down Switching Regulator
TJ4519
1
L1
2
5
8
3
6
7
BST
VOUT
IN
SW
FB
EN
N.C
TJ4519
R1
R2
COMP
GND
C2
D2
C4
4
C5
R3
Figure 3. Compensation network provides 2 poles and 1 zero.
The compensation network gives the following characteristics:
s
1+
R2
ωZ
GCOMP(s) = ω1 •
• gm •
s
R1 +R2
s • (1+
)
ωP2
Where:
ω1 =
1
C4 + C5
1
ωZ
=
R3 • C4
C4 + C5
ωP2
=
R3 • C4 • C5
The loop gain will be given by:
s
1+
RL
R2
1
•
ωZ
T(s) = GCOMP(s)• GVD(s) = 2.125 •10-3
•
•
•
s
s
C4 R1 +R2
s
(1+
)•(1+
)
ωP1
ωP2
Where:
ωP1
1
=
RL • C
One integrator is added at origin to increase the DC gain. ωZ is used to cancel the power stage pole ωP1 so that
the loop gain has –20dB/dec rate when it reaches 0dB line. ωP2 is placed at half switching frequency to reject high
frequency switching noises. Figure 4 gives the asymptotic diagrams of the power stage with current loop closed
and its loop gain.
Jul. 2010 – Preliminary
- 10 -
HTC
HTC [ HTC KOREA TAEJIN TECHNOLOGY CO. ]
