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SC1109_04 Datasheet, PDF (1/19 Pages) Semtech Corporation – Synchronous PWM Controller with Dual Low Dropout Regulator Controllers
SC1109
Synchronous PWM Controller with Dual
Low Dropout Regulator Controllers
POWER MANAGEMENT
Description
The SC1109 was designed for the latest high speed
motherboards. It combines a synchronous voltage mode
controller (switching section) with two low-dropout linear
regulator controllers. The voltage mode controller pro-
vides the power supply for the system AGTL bus. The Dual
linear controllers power the chip set and clock circuitry.
The SC1109A switching section features lossless current
sensing, while SC1109C provides programmable over cur-
rent limit. SC1109 also utilizes latched driver outputs for
enhanced noise immunity. SC1109A and SC1109C oper-
ate at a fixed frequency of 200kHz, and the SC1109B is
available at a fixed frequency of 500kHz. The VTT output
voltage is internally fixed at 1.2V
The SC1109 linear sections are low dropout regulators
designed to track the 3.3V power supply when it turns on
or off. The voltage for the linear controllers LDO1, and LDO2
are 1.8V/1.5V.
Typical Application Circuit
Features
‹ Dual linear controllers
‹ LDOs track input voltage within 200mV (function of
the MOSFETs used) until regulation
‹ Integrated drivers
‹ Power good signal (SC1109A, SC1109B)
‹ Soft start
‹ Lossless current sense
‹ Programmable over current limit (SC1109C)
‹ 200kHz (SC1109A, SC1109C), and 500kHz (SC1109B)
fixed frequency.
Applications
‹ Pentium® III Motherboards
‹ Triple power supplies
12V IN
5V STBY
5V IN
POWER GOOD
3.3V IN
C2
C3
2x1500uF + 0.1uF
C9
0.1uF
C5
0.1uF
SC1109ACSTR or SC1109BCSTR
11 VCC
STBY 3
4
C6
0.1uF
5
BCAP+
BCAP-
BST 10
DH 9
PHASE 7
R1 2.2
14 SS/EN
12 PWRGD
DL 8
R2 2.2
13 VOSENSE GND 6
15 GATE2
GATE1 2
16 LDOS2 LDOS1 1
C4
0.1uF
U1
C1
0.1uF
Q1
MOSFET N
L1 4uH
C7
Q2
3x1500uF
MOSFET N
+
1.2V 6A
C8
0.1uF
VTT
+
C10
330uF
Q3
MOSFET N
+
C11
330uF
LDO2 = 1.5V
Q4
MOSFET N
+
C12
330uF
LDO1 = 1.8V
12V IN
5V STBY
5V IN
C2
C3
2x1500uF + 0.1uF
C13
1nF
OCSET
R3
TBD
C9
0.1uF
C5
0.1uF
11 VCC
U1
STBY 3
4
C6
0.1uF
5
14
12
13
15
16
BCAP+
BCAP-
BST 10
DH 9
PHASE 7
SS/EN
OCSET
DL 8
VOSENSE GND 6
GATE2
GATE1 2
LDOS2
LDOS1 1
R1 2.2
R2 2.2
SC1109CCSTR
C4
0.1uF
C1
0.1uF
Q1
MOSFET N
L1 4uH
C7
Q2
3x1500uF
MOSFET N
+
1.2V 6A
C8
0.1uF
VTT
3.3V IN
+
C10
330uF
Q3
MOSFET N
+
C11
330uF
LDO2 = 1.5V
Q4
MOSFET N
+
C12
330uF
LDO1 = 1.8V
Revision: May 13, 2004
1
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