sc4612b Semtech Corporation, sc4612b Datasheet - Page 11

• Manufacturer Part Number: sc4612b
• Description: 40v Synchronous Buck Controller
• Manufacturer: Semtech Corporation

OVERVOLTAGE PROTECTION
If the FB pin ever exceeds 600mV, the top side driver is
latched OFF, and the low side driver is latched ON. This
mode can only be reset by power supply cycling.
ERROR AMPLIFIER DESIGN
The SC4612B is a voltage mode buck controller that utilizes
an externally compensated high bandwidth error amplifier
to regulate output voltage. The power stage of the
synchronous rectified buck converter control-to-output
transfer function is as shown below:
POWER MANAGEMENT
Applications Information (Cont.)
2007 Semtech Corp.
G
VD
(
) s
V
V
IN
S
1
1
s
sESR
R
L
L
s
C
2
C
LC
11
where,
V
L – Output inductance
ESR
V
The classical Type III compensation network can be built
around the error amplifier as shown below:
Figure 1. Voltage mode buck converter compensation
network
The transfer function of the compensation network is as
follows:
where,
IN
S
– Peak to peak ramp voltage
– Input voltage
C
I
Z
– Output capacitor ESR
1
R
C2
R
1
(
C
2
1
R1
C
1
1
1
G
,
R3
C
COMP
3
)
Z
,
2
Vref
(
) s
R (
1
P
s
1
-
+
I
1
R
1 (
1 (
R2
R
3
C )
C3
3
1
C
R
C – Output capacitance
2
2
s
s
L
Z
P
,
,
1
1
– Load resistance
)(
)(
C1
1
1
o
PRELIMINARY
P
SC4612B
s
s
2
P
Z
2
2
Lout
www.semtech.com
)
)
R
2
1
C
Cout
C
1
1
1
C
C
3
3