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PDF SC2443 Data sheet ( Hoja de datos )
| Número de pieza | SC2443 | |
| Descripción | Dual-Phase Single or Two Output Synchronous Step-Down Controller | |
| Fabricantes | Semtech Corporation | |
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POWER MANAGEMENT
Features
u Wide input voltage range: 4.7V to 16V
u 0.5V feedback voltage for low-voltage outputs
u Programmable frequency up to 1 MHz per phase
u 2-Phase synchronous continuous conduction mode for
high efficiency step-down converters
u Out-of-phase operation for low input current ripples
u Output source and sink currents
u Fixed frequency peak current-mode control
u 75mV/-110mV maximum current sense voltage
u Inductor DCR current-sensing for low-cost applications
u Dual outputs or 2-phase single output operation
u Excellent current sharing between individual phases
u Individual soft-start, overload shutdown and enable
u External reference input for DDR applications
u External synchronization
u Industrial temperature range
u 4mm X 4mm X1mm 24-lead MLPQ package
Applications
u Telecommunication power supplies
u DDR memory power supplies
u Graphic power supplies
u Servers and base stations
Typical Application Circuit
SC2443
Dual-Phase Single or Two Output
Synchronous Step-Dowwwwn.DaCtaSohenet4tUr.coomller
Description
The SC2443 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-channel MOSFET power
stages. The SC2443 operates in synchronous continuous-con-
duction mode. Both phases are capable of maintaining regula-
tion with sourcing or sinking load currents, making the SC2443
suitable for generating both VDDQ and the tracking VTT for
DDR applications.
The SC2443 employs fixed frequency peak current-mode con-
trol for the ease of frequency compensation and fast transient
response.
The dual-phase step-down controllers of the SC2443 can be
used to produce two individually controlled and regulated out-
puts 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 outputs as low as 0.5V
Individual soft-start and overload shutdown timer is included
in each step-down controller. The SC2443 implements hiccup
overload protection. In single output current share configura-
tion, the master timer controls the soft-start and overload shut-
down functions of both controllers.
VOUT1 VP1
VIN
U1
IN1- 1 IN1-
2 COMP1
3 SYNC
4 AGND
SC2443
5 REF
6 REFIN
GDL1 18
PVCC 17
PGND 16
GDL2 15
GDH2 14
BST2 13
VIN
VP1 VOUT1
IN1-
VIN
VOUT2
IN2-
VIN
IN2-
Dual Independent Outputs
July 09 2007
VOUT1 VP1
VIN
U1
IN1- 1 IN1-
2 COMP1
3 SYNC
4 AGND
SC2443
5 REF
6 REFIN
GDL1 18
PVCC 17
PGND 16
GDL2 15
GDH2 14
BST2 13
VIN
VP1 VOUT1
IN1-
VIN
VIN
Single Output With Current Sharing
1 page  
Electrical Characteristics (continued)
Parameter
Symbol
Gate Drivers
High side Gate Driver
Peak Source Current
High side Gate Driver
Peak Sink Current
Low side Gate Driver
Peak Source Current
Low side Gate Driver
Peak Sink Current
Gate Drive Rise Time
Gate Drive Fall Time
Low side Gate Driver to High side
Gate Driver Non-overlapping delay
High side Gate Driver to Low side
Gate Driver Non-overlapping delay
Minimum On Time
Soft Start, Overload Latchoff and Enable
Soft Start Charging Current
Overload Enabling Soft Start Voltage
Overload IN1- Threshold
Overload IN2- Threshold
Soft Start Discharge Current
Overload Recovery Soft Start Voltage
Gate Driver Disable SS/EN Voltage
Gate Driver Enable SS/EN Voltage
ISS1 , ISS2
I , ISS1 _DIS SS2_DIS
VSSRCV1 ,
VSSRCV2
Internal 0.5V Reference Buffer
Output Voltage
Load Regulation
VREF
Notes:
(1) Guaranteed by design.
Conditions
VBST1, VBST2 = 12V
VBST1, VBST2 = 12V
AVCC = PVCC = 12V
AVCC = PVCC = 12V
CL = 2200pF
CL = 2200pF
CL = 0
CL = 0
TA = 25°C
VSS1 = VSS2 = 1.5V
VSS1 and VSS2 Rising
VSS1 = 3.8V, VIN1- falling
VSS2 = 3.8V, VIN2- falling
VSS1 = VSS2 = 3.8V
VSS1 and VSS2 Falling
IREF = -1mA
0 < IREF <-5mA
SC2443
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Min Typ Max Units
1.5 A
1A
1.5 A
1A
20 ns
20 ns
90 ns
90 ns
150 ns
2
3.2
0.75VREF
0.72 X
1.4
0.3 0.5 0.7
0.7 0.9
1.2 1.5
µA
V
V
V
µA
V
V
V
490 500 510 mV
0.05 %/mA
5 Page 
SC2443
Applications Information
Description
The SC2443 is a constant frequency 2-phase current-mode
step-down PWM switching controller driving all N-channel
MOSFET. The two channels of the controller operate at
180 degrees out-of-phase from each other. Since input
currents are interleaved in a two-phase converter, input
ripple current is lower and smaller input capacitor can
be used for filtering. Also, with lower inductor current
and smaller inductor ripple current per phase, overall I2R
losses are reduced.
The SC2443 operates in synchronous continuous-
conduction mode. It can be configured either as two
independent step-down controllers producing two
separate outputs or as a dual-phase single-output
controller by tying the IN2- pin to VCC. In single output
operation, the channel one error amplifier controls both
channels and the channel two error amplifier is disabled.
Soft-start and overload hiccup of both channels is
synchronized to channel one.
Frequency Setting and Synchronization
The internal oscillator of the SC2443 runs at twice the
phase frequency. The free-running frequency of the
oscillator can be programmed with an external resistor
from the ROSC pin to ground. The step-down controllers
are capable of operating up to 1 MHz. It is necessary to
consider the operating duty-ratio before deciding the
switching frequency. See Applications Information section
for more details.
When synchronized externally, the applied clock frequency
should be twice the desired phase frequency. The
synchronizing clock frequency should also be between 2
- 2.6 times the set free-running channel frequency.
Control Loop
The SC2443 uses peak current-mode control for fast
transient response, ease of compensation and current
sharing in single output operation. The low-side MOSFET
of each channel is turned off at the falling-edge of the
phase timing clock. After a brief non-overlapping time
interval of 90ns, the high-side MOSFET is turned on.
The phase inductor current ramps up. When the sensed
inductor current reaches the threshold determined by
the error amplifier output and compensation ramp, the
high-side MOSFET is turned off. After a non-overlapping
conduction time of 90ns, the low-side MOSFET is turned
on.
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The supply voltages for the high-side gate drivers are
obtained from two diode-capacitor bootstrap circuits. If
the bootstrap capacitor is charged from VCC, the high-
side gate drive voltage swing will be from approximately
2VCC to the ground. The power dissipated in the high-
side gate driver is not higher with higher voltage swing
because the gate-source voltage of the high-side MOSFET
still swing from zero to VCC. The outputs of the low-side
gate drivers swing from VCC to ground.
The SC2443 has internal ramp-compensation to prevent
sub-harmonic oscillation when operating above 50%
duty cycle. There is enough ramp internally for a sensed
voltage ripple between 1/4 to 1/3 of the full-scale sensed
voltage limit of 75mV. The maximum sensed voltage limit
is unaffected by the compensating ramp.
Current-Sensing
There are two ways to sense the inductor current for
current-mode control with the SC2443. Since the peak
inductor current corresponds to 75mV of sensed voltage
(CS+ - CS-), resistor current sensing can be used at the
output without resulting in excessive power dissipation.
Although accurate and far easier to lay out than high-side
resistor sensing, a pair of precision sense resistors adds
cost to the converter.
With proper RC filter, Inductor DCR sensing can also be
used for SC2443 resulting in low cost and without extra
power dissipation.
Error Amplifiers
In closed loop operation, the error amplifier output ranges
from 1.1V to 3.5V. The upper output operating range
of either error amplifier is reserved for positive current-
sense voltage (CS+ - CS-) and corresponds to positive
(sourcing) output current. If the amplifier swings to its
lower operating range, the amplifier will still modulate the
high-side gate drive duty-ratio. However the peak current-
sense voltage (hence the peak inductor current) will be
limited to a negative value. The error amplifier output
is about 2.2V when the peak sense-voltage is zero. The
built-in offset in the current sense amplifier together with
synchronous continuous-conduction mode of operation
allows the SC2443 to regulate the output irrespective of
the direction of the load current.
11
11 Page | ||
| Páginas | Total 20 Páginas | |
| PDF Descargar | [ Datasheet SC2443.PDF ] | |
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