1 www.semtech.com
POWER MANAGEMENT
SC2434
TriPhase Current Mode Controller
with Power Good
May 18, 2005
Description Features
The SC2434, a tri-phase, current mode controller is
designed to work with Semtech smart synchronous
drivers, such as the SC1205, SC1206, and SC1207 to
provide the DC/DC converter solution for the most
demanding Microprocessor applications. Input current
sensing is used to guarantee precision phase to phase
current matching using a single sense resistor on the
input power line. This topology reduces the power loss
and complexity associated with output current sense
methods. Multi phase operation allows significant
reduction in input/output ripple while enhancing
transient response. Two or three phase operation is
selectable. The DAC step size and range are program-
mable with external components thus allowing compliance
with new and emerging VID ranges. A novel approach
implements active droop to minimize output capacitors
during load transients.
! 12V input
! Input sensing current mode control
! Selectable 2 or 3 phase operation
! Precision, pulse by pulse phase current matching
! Active drooping allows for best transient response
! Programmable internal oscillator to 1.5 MHz
! Programmable DAC step size/offset allows compli-
ance with VRM9.0 and VRM9.2
! VID 11111 Inhibit (No CPU)
! Externally programmable soft-start
! 0% minimum duty cycle improves transient
response
! Cycle by cycle current limiting plus hiccup
! Power good signal
! Intel Pentium-4 microprocessors
!!
!!
! High performance desktop systems
Typical Application Circuit
Applications
+12V
C17
1uF
D1
1N4148
+5V
R2
2R2
R9
2R2
L4
600nH
+5V_ATX
C6
4.7uF
+
C21
1500uF/6.3V
D6
1N4148
+
C2
2200uF/16v
VID0
C24 1uF
R_OS
46.4K
+
C26
1500uF/6.3V
C23
2.2nF
+
C7
1500uF/6.3V
D3
1N4148
C16
4.7uF
M4
+
C10
1500uF/6.3V
U1
SC1205
1
2
3
4 5
6
7
8
DRN
TG
BST
CO EN
VS
BG
PGND
C5
4.7uF
M5
R4
1R
+
C18
1500uF/6.3V
R29
100
VCCVID_PWRGD(Open Collector Input)
+
C32
1500uF/6.3V
+12V
VOUT
C35 1uF
C4
1uF
C9
1nF
M6
Differential
Pair
R_COMP
75K
C15
1uF
+12V
C22
1nF
L1
600nH
U2
SC2434
1
2
3
4
5
6
7
8
9
10 11
12
13
14
15
16
17
18
19
20
VID4
VID3
VID2
VID1
VID0
PGIN
ERROUT
PGOUT
FB
OSCREF DACREF
OC+
OC-
AGND
PC
OUT3
OUT2
OUT1
BGOUT
VCC
D2
1N4148
R10
1R
R5
20
D5
1N4148
C34
2.2nF
+
C28
1500uF/6.3V
R15
1K
R_OSC
31.6K
C27
1uF
L2
600nH
VID4
M3
R17
1
SM/R_1206
Differential
Pair
M2
R14
2R2
R6
1
SM/R_1206
C76 0.33uF
C75 0.33uF
C11
2.2nF
U3
SC1205
1
2
3
4 5
6
7
8
DRN
TG
BST
CO EN
VS
BG
PGND
C33
1nF
+
C30
1500uF/6.3V
+
C14
1500uF/6.3V
R1 3m
R16
1R
M1
+
C1
2200uF/16v
V_PULL_UP
+
C19
1500uF/6.3V
R_FB
10K
+
C20
1500uF/6.3V
C77 0.33uF
R_DRP
187K
D4
1N4148
R3
2R2
C31
470pF
R8
NO POP
+
C3
2200uF/16v
VID3
R13
5.1K
+
C25
1500uF/6.3V
+5V
C12 1uF
AGND
C13
10nF
C_COMP
18pF
+12V_ATX
C29
100nF
VID1
C8
1uF
PWR_GOOD
R19
750
VID2
U4
SC1205
1
2
3
4 5
6
7
8
DRN
TG
BST
CO EN
VS
BG
PGND
PGND
R_DAC
37.4K
L3
600nH
R11
1
SM/R_1206
R20
1K
