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PDF SC415 Data sheet ( Hoja de datos )
| Número de pieza | SC415 | |
| Descripción | Dual Synchronous Buck Controller | |
| Fabricantes | Semtech Corporation | |
| Logotipo |  |
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SC415
Dual Synchronous Buck Controller
POWER MANAGEMENT
Features
VIN Range 3-25V
Outputs Adjustable from 0.75 to 5.25V,
or Preset Output Voltages:
• VOUT1 = 1.8 or 1.5V
• VOUT2 = 1.25 or 1.05V
Low Shutdown Power
Constant On-Time for Fast Dynamic Response
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Adjustable Switching Frequency
Separated Frequencies for Minimal Switching
Interaction:
• VOUT1 = up to 600kHz
• VOUT2 = up to 720kHz
Power Save or Continuous Operation at Light Load
Adjustable Soft-start Rates for Each Output
Soft-Shutdown for Each Output
Over-Voltage and Under-Voltage Fault Protection
Cycle-by-Cycle Valley Current Limit
DC Current Sense Using Low-Side RDSON Sensing,
or RSENSE in Source of Low-Side MOSFET for Greater
Accuracy
Separate Power Good Outputs
Separate Enable/Power Save Inputs
3.1A Non-Overlapping Gate Drive
SmartDriveTM for High-Side MOSFET
MLP 4x4 24 Pin Package
Industrial Temperature Range
Applications
Notebook and Sub-Notebook Graphics
Voltage Controllers
Tablet PCs
Embedded Applications
Description
The SC415 is a versatile, constant on-time, pseudo fixed-
frequency, dual synchronous buck PWM controller
intended for notebook computers and other battery
operated portable devices. The SC415 contains all the
features needed to provide cost-effective control of two
independent switchmode power supplies.
The two DC outputs are adjustable from 0.75V to 5.25V.
Additional features for each output include cycle-by-
cycle current limit, voltage soft-start, under-voltage and
over-voltage protection, programmable over-current
protection, soft shutdown, selectable power save and
non-overlapping gate drive. The SC415 provides two
enable/power save inputs, two soft-start inputs, two
power good outputs and an on-time adjust input.
The constant on-time topology provides fast dynamic
response. The excellent transient response means that
SC415 based solutions require less output capacitance
than competing fixed-frequency converters. Switching
frequency is constant until a step in load or line voltage
occurs, at which time the pulse density and frequency
moves to counter the change in output voltage. After the
transient event, the controller frequency returns to steady
state operation. At light loads with power save enabled,
the SC415 reduces switching frequency for improved
efficiency.
Oct 08, 2007
© 2007 Semtech Corporation
1
1 page  
SC415
Electrical Characteristics (continued)
Parameter
Regulation (Continued)
VOUT2 On-Time Threshold
www.DataSVhOeeUtT4xUL.cinome Regulation Error
VOUTx Load Regulation Error
Timing
VOUTx On-Time(1)
VOUTx Set to 1.5V
Minimum On-Time
Minimum Off-Time
Soft-Start/Shutdown
Soft-Start SSx Current Source
Soft-Start Ramp Time
SSx Shutdown
Discharge Resistance
VOUTx Shutdown
Discharge Resistance
Analog Inputs/Outputs
VOUT1 Input Resistance
VOUT2 Input Resistance
FBx Input Bias Current
Current Sense
ILIMx Source Current
ILIMx Comparator Offset
Current Limit (Negative)
Zero Crossing Detector Threshold
Power Good
PGDx Threshold
PGDx Threshold Delay Time (2)
Conditions
FB1 = 5V; 0 to 85°C
FB1 = 5V; -40 to 85°C
FB1 = RTN; 0 to 85°C
FB1 = RTN; -40 to 85°C
VOUT1; RTON = 1Meg
VOUT2; RTON = 1Meg
VOUT1; RTON = 499K
VOUT2; RTON = 499K
DH1, DH2
DL1, DL2
CSSx = 4.7nF
ENx = RTN,
VOUTx < 300mV
ENx = RTN,
VOUTx < 300mV
EN1 = VDD1
EN2 = VDD2
ILIMx - GND
LXx - GND
LXx - GND
1% Hysteresis Typical,
with Respect to
Regulation Point
25°C
Min Typ Max
-40° to 85°C
Min Max
Units
1.25 1.2343 1.2656
V
1.25 1.2281 1.2718
1.05 1.0368 1.0631
1.05
1.0316 1.0684
V
0.04 %/V
0.3 %
400
330
200
167
50
330
5
1500
16
16
320 480
260 400
nsec
nsec
nsec
3.5 6.5 μA
μsec
Ω
Ω
120 kΩ
90 kΩ
-1 +1 μA
10 9 11 μA
-10 +10 mV
80 60 100 mV
0 -7 +7 mV
-12%
5
-9% -15%
μsec
5
5 Page 
SC415
Applications Information (continued)
The voltages available are shown:
FB Internal Voltage Selection
Side1
Side2
FB = RTN
1.5V
1.05V
FB = +5V
1.8V
1.25V
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Enable/Psave Inputs
Each converter has a separate Enable pin. Each EN input
operates as follows:
EN = GND. This turns the converter off.
EN = open (float). This turns the converter on with psave
mode disabled (continuous conduction mode). In this
case, the EN pin will float to approximately 2V due to
an internal 1.5Meg/1Meg resistor divider from the +5V
supply at VDDx to ground.
EN = high (3.1V min). This turns the converter on with
psave mode enabled. At light loads, the converter will
operate in psave mode.
Note that the two EN pins are separate, so each output
can be disabled or operated with or without psave
independently.
If both EN1 and EN2 are grounded, the device is placed
into the lowest-power state, drawing typically 10μA from
the +5V supply.
efficiency improvement at light loads more than offsets
the disadvantage of slightly higher output ripple. If the
inductor current does not cross zero on any switching
cycle, the controller immediately exits PSAVE. Once PSAVE
is exited, it requires 8 switching cycles at light load to re-
enter PSAVE. Since the controller counts zero crossings,
the converter can sink current as long as the current does
not cross zero on eight consecutive cycles. This allows the
output voltage to recover quickly in response to negative
load steps.
When operating in PSAVE mode at light loads, the LX
waveform will not have the typical square wave shape
seen when operating in continuous conduction mode.
Shortly after DL drives low, and both MOSFETs are off, the
LX voltage will show ringing. This ringing is caused by the
LC circuit formed by the inductor and device capacitance
of the MOSFETs and low-side diode. When the low-
side MOSFET turns off the inductor current falls toward
zero. When it reaches zero, the inductance and MOSFET
capacitances will tend to ring freely. This is normal PSAVE
operation as shown in Figure 3:
VIN
DH Q1
CQ1
L
VOUT
DL Q2
COUT
CQ2
PSAVE Operation
Each output provides automatic PSAVE operation at
light loads if the ENx pin is set high. The internal Zero-
Cross comparator looks for inductor current (via the
voltage across the lower MOSFET) to fall to zero on
eight consecutive switching cycles. Once observed,
the controller enters PSAVE mode and turns off the
low-side MOSFET on each subsequent cycle when the
current crosses zero. To add hysteresis, the on-time is also
increased by 25% when PSAVE mode is active, for that
output only; it does not affect the other converter. The
DL
VIN
VOUT
LX Typical ringing at LX
Figure 3
11
11 Page | ||
| Páginas | Total 30 Páginas | |
| PDF Descargar | [ Datasheet SC415.PDF ] | |
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