SC2446 Datasheet, PDF (1/38 Pages) Semtech Corporation – Dual-Phase Single or Two Output Synchronous Step-Down Controllers

SC2446
Dual-Phase Single or Two Output
Synchronous Step-Down Controllers
POWER MANAGEMENT
Description
The SC2446 is a high-frequency dual synchronous step-
down switching power supply controller. It provides out-
of-phase high-current output gate drives to all N-chan-
nel MOSFET power stages. The SC2446 operates in syn-
chronous continuous-conduction mode. Both phases are
capable of maintaining regulation with sourcing or sink-
ing load currents, making the SC2446 suitable for gen-
erating both V_DDQ and the tracking V_TT for DDR applica-
tions.
The SC2446 employs fixed frequency peak current-mode
control for the ease of frequency compensation and fast
transient response.
The dual-phase step-down controllers of the SC2446 can
be configured to provide two individually controlled and
regulated outputs or a single output with shared current
in each phase. The Step-down controllers operate from an
input of at least 4.7V and are capable of regulating out-
puts as low as 0.5V
The step-down controllers in the SC2446 have the pro-
vision to sense a synthesized MOSFET R_DS(ON) for cur-
rent-mode control. This sensing scheme (U.S. patent
6,441,597) eliminates the need of the current-sense re-
sistor and is more noise-immune than direct sensing of
the high-side or the low-side MOSFET voltage. Precise cur-
rent-sensing with sense resistor is optional.
Individual soft-start and overload shutdown timer is in-
cluded in each step-down controller. The SC2446 imple-
ments hiccup overload protection. In two-phase single-
output configuration, the master timer controls the soft-
start and overload shutdown functions of both control-
lers.
Typical Application Circuit
Features
‹ 2-Phase synchronous continuous conduction mode
for high efficiency step-down converters
‹ Out of phase operation for low input current ripples
‹ Output source and sink currents
‹ Fixed frequency peak current-mode control
‹ 75mV/-110mV maximum current sense voltage
‹ Synthesized MOSFET R_DS(ON) current-sensing for
low-cost applications
‹ Optional resistor current-sensing for precise current-
limit
‹ Dual outputs or 2-phase single output operation
‹ Excellent current sharing between individual phases
‹ Wide input voltage range: 4.7V to 16V
‹ Individual soft-start, overload shutdown and enable
‹ Duty cycle up to 88%
‹ 0.5V feedback voltage for low-voltage outputs
‹ External reference input for DDR applications
‹ Buffered V_DDQ/2 output
‹ Programmable frequency up to 1 MHz per phase
‹ External synchronization
‹ Industrial temperature range
‹ 28-lead TSSOP - EDP package
Applications
‹ Telecommunication power supplies
‹ DDR memory power supplies
‹ Graphic power supplies
‹ Servers and base stations
VIN
Figure 1
VO2
C99
C95
+
R79
R81
L11
C96 R75
RCS+
Q21
Q23
CFILTER
RFILTER
C101
R83
C103
C92
D11
D12
PVCC
R73
BST2
BST1
Q22
R74
C93
GDH2
GDH1
C94
L12
R77
RCS-
REF
VIN
SYNC
C106
GDL2
GDL1
PGND
Q24
R78
CFILTER
R76
RFILTER
VPN2
VPN1
CS2+
CS2-
CS1+
CS1-
RCS-
IN2-
COMP2
REFIN
IN1-
COMP1
REF
C104
C102
C105
R84
VIN2
AGND
SYNC
Rosc
R85
SS1/EN1
AVCC
VIN
SS2/EN2 REFOUT
C107
C108
U1
SC2446
C109
C97
RCS+
Dual Independant Outputs
VO1
C98
+
R80
C100
R82
Revision: September 9, 2004
1
U.S. Patent No. 6,441,597, www.semtech.com