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Número de pieza | SC416 | |
Descripción | Dual Synchronous Buck Controller | |
Fabricantes | Semtech Corporation | |
Logotipo | ||
Hay una vista previa y un enlace de descarga de SC416 (archivo pdf) en la parte inferior de esta página. Total 34 Páginas | ||
No Preview Available ! SC416
POWER MANAGEMENT
Features
Dual Synchronous Buck Controller
with Tracking Start-up/Shutdown
Description
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
Proportional or Coincident Tracked Start-up and Shut-
down of Both Outputs
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Adjustable Soft-start Rates for Each Output
Regulated Shutdown for Each Output
Low Shutdown Power
Constant On-Time for Fast Dynamic Response
Adjustable Switching Frequency
Separated Frequencies for Minimal Switching Interac-
tion:
• VOUT1 = up to 600kHz
• VOUT2 = up to 720kHz
Power Save or Continuous Operation at Light Load
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 Lead-free Package
Industrial Temperature Range
WEEE and RoHS Compliant
Applications
Notebook and Sub-Notebook Graphics
Voltage Controllers
Tablet PCs
Embedded Applications
The SC416 is a versatile, constant on-time, pseudo-
fixed-frequency, dual synchronous buck PWM control-
ler intended for notebook computers and other battery
operated portable devices. The SC416 contains all the
features needed to provide cost-effective control of two
independent switchmode power supplies.
The SC416 provides adjustable voltage tracking during
start-up and shut-down, making it an effective solution
for a variety of applications where the voltage differen-
tial between supply rails must meet defined limits dur-
ing all operating conditions including start-up and shut-
down. The SC416 supports proportional tracking which
gives equal start-up and shut-down times for both out-
puts, and can also provide coincident tracking where the
two output voltages are equal during the lower voltage’s
start-up and shut-down ramp.
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, regulated shutdown, selectable power save
and non-overlapping gate drive. The SC416 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
SC416 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 SC416 reduces switching frequency for im-
proved efficiency.
May 17, 2007
© 2007 Semtech Corporation
1
1 page SC416
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
Shutdown SSx Current Sink
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
FB2 = 5V; 0 to 85°C
FB2 = 5V; -40 to 85°C
FB2 = RTN; 0 to 85°C
FB2 = 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 %
400 320 480
330 260 400
nsec
200
167
50 ns
330 ns
5 3.5 6.5 μA
5 3.5 6.5 μA
700 μsec
16 Ω
16 Ω
120 kΩ
90 kΩ
-1 +1 μA
10 9 11 μA
-10 +10 mV
80 60 100 mV
-7 +7 mV
-12 -9 -15 %
5 μs
5
5 Page SC416
Applications Information (continued)
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
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an internal 1.5Meg/1Meg resistor divider from +5V 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 inde-
pendently.
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 ca-
pacitance 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 nor-
mal Psave operation as shown in Figure 3.
VIN
For tracking operation during startup, the two EN pins
are typically tied together; see the Voltage Tracking sec-
tion.
DH Q1
CQ1
L
VOUT
If both EN1 and EN2 are grounded, the device is placed
into the lowest-power state, drawing typically 7μA from
the +5V supply.
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 con-
secutive switching cycles. Once observed, the control-
ler enters psave mode and turns off the low-side MOS-
FET on each subsequent cycle when the current crosses
zero. To add hysteresis, the on-time is also increased by
25% in Psave, for that converter only; it does not affect
the other converter’s on-time. The efficiency improve-
ment 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
DL
LX
VIN
VOUT
Typical ringing at LX
Figure 3
11
11 Page |
Páginas | Total 34 Páginas | |
PDF Descargar | [ Datasheet SC416.PDF ] |
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