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PDF SC475A Data sheet ( Hoja de datos )

Número de pieza SC475A
Descripción Synchronous Buck Controller
Fabricantes Semtech Corporation 
Logotipo Semtech Corporation Logotipo



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Description
SC475A
Synchronous Buck Controller with
Dual-Level VOUT Transition Support
Features
The SC475A is a versatile, constant on-time synchronous
buck, pseudo-xed-frequency, PWM controller intended for
notebook computers and other battery operated portable
devices. The SC475A contains all the features needed to
provide cost-effective control of system elements needing
voltage slewing. An integrated switch provides two resistor-
programmable DC output voltages controlled by the G0
input.
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The output voltage is adjustable from 0.75V to 5V.
Additional features include cycle-by-cycle current limit,
voltage soft-start, under-voltage protection, programmable
over-current protection, soft shutdown, automatic power
save and non-overlapping gate drive. The SC475A
provides an enable input and a power good output which is
automatically blanked during output voltage transitions.
The constant on-time topology provides fast dynamic
response. The excellent transient response means that
SC475A based solutions require less output capacitance
than competing xed-frequency converters. Switching
frequency is constant until a step in load or line voltage
occurs, at which time the pulse density and frequency
will increase or decrease to counter the change in
output voltage. After the transient event, the controller
frequency returns to steady state operation. At light loads,
the automatic power save mode reduces the SC475A
frequency for improved efciency.
VOUT Programmable 0.75V to 5.25V with Integrated
Transition Support
VBAT Range 3V to 25V
Soft Shutoff at Output
Current Sense Using Low-side RDS(ON) or Resistor
Sensing
Adjustable Cycle-by-Cycle Valley Current Limit
325kHz Fixed-Frequency
Constant On-Time for Fast Dynamic Response and
Reduced Output Capacitance
Automatic Smart Power Save
Internal Soft-Start
Over-Voltage/Under-Voltage Fault Protection
Power Good Output with Transition Blanking
1μA Typical Shutdown Current
500μA Typical Operating Current
Tiny 3×3mm, 16 Pin MLP Package
Low External Part Count
Industrial Temperature Range
0.85% Internal Reference
1A/3A Non-Overlapping Gate Drive with
SmartDriver™ Technology
High Efciency > 90%
Device is Fully WEEE and RoHS Compliant
Patent Pending
Applications
Notebook/Sub-Notebook Graphics Voltage
Controllers
Tablet PCs
Embedded Applications
September 25, 2006
1
www.semtech.com

1 page




SC475A pdf
SC475A
POWER MANAGEMENT
Electrical Characteristics (continued)
Parameter
Conditions
25°C
Min Typ Max
-40° to 85°C
Min Max
Units
Fault Protection (continued)
Steady-State
Over-Voltage Fault
Steady-State
www.DataSOheveet4rU-V.coolmtage Fault Delay
G0 Transition
Over-Voltage Fault
FB with Respect to Nominal
FB Forced 50mV Above
Over-Voltage Fault Threshold
FB with Respect to Nominal;
Valid for 32 cycles after G0
Transition
Smart Power Save Threshold FB with Respect to Nominal
Over-Temperature Shutdown(1) Latching, >10°C Hysteresis
+20
5
+50
+8
160
+17 +23 %
μs
%
%
°C
Logic Inputs/Outputs
Logic Input High Voltage
Logic Input Low Voltage
EN Input Bias Current
G0 Input Bias Current
Power Good Output
Low Voltage
EN, G0
EN, G0
EN = 5V
G0 = 5V
RPWRGD = 10kΩ to VCC
1.2 V
0.4 V
-1 +1 μA
5 0 10 μA
0.4 V
Gate Drivers
Shoot-Through
Protection Delay(1)
DH or DL Rising
30
ns
DL Pull-Down Resistance
0.8 1.6 Ω
DL Sink Current
DL Pull-Up Resistance
VDL = 2.5V
3.1
2
A
4Ω
DL Source Current
DH Pull-Down Resistance
VDL = 2.5V
BST - LX = 5V
1.3
2
A
4Ω
DH Pull-Up Resistance(2)
BST - LX = 5V
2
4Ω
DH Sink/Source Current
VDH = 2.5V
1.3
A
Notes:
1) Guaranteed by design.
2) Semtech’s SmartDriver™ FET drive rst pulls DH high with a pull-up resistance of 10Ω (typical) until LX = 1.5V (typical). At this point,
an additional pull-up device is activated, reducing the resistance to 2Ω (typical). This negates the need for an external gate or boost resistor.
© 2006 Semtech Corp.
5
www.semtech.com

5 Page





SC475A arduino
SC475A
POWER MANAGEMENT
Applications Information (continued)
VOUT Voltage Selection
VOUT voltage is regulated through the FB pin via resistors
R1 through R3 as shown in Figure 4.
R1
the output capacitor via the inductor. DL will remain on
until FB falls to 0.75V, at which point a normal DH switch-
ing cycle begins, see Figure 5. This causes the output to
transition to the new voltage level quickly, typically 10~20
usec. Refer to the Smart Power Save Protection section
for a full description.
FB
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TON
0.75V
G0
Logic
Control
R3
D0
R2
SC475A
VOUT A rapid downward change in VOUT also occurs for downward
+ changes less than 8%, provided the load is high enough
such that power-save is not active. In this case, after D0
opens and FB rises above the 0.75V trip point, DL will drive
high and stay high until FB drops to the trip point.
VOUT
Figure 4
The following table shows the equations for VOUT as a
function of control input G0:
VOUT Equation
0.75 • (1 + R1/R2)
0.75 • (1 + R1/R2 + R1/R3)
G0
1
0
R1
R3
D0
R2
FB
D0
RTN
(Smart Psave threshold)
810mV
FB
750mV
(FB threshold)
DL
Note that the RDSON of the internal D0 mosfet is in series with
R3, which adds typically 15 ohms in series.
Voltage Transitioning
The G0 pin allows VOUT to transition to both higher
and lower values. The two directions have differing
responses.
DL
VOUT
Initial VOUT
Final VOUT
When doing a down transition, the sudden release of R3
will cause FB to go above the 0.75V threshold. Depending
on the level of VOUT change and the load, the IC responds
in different ways.
At light load conditions when power-save is active, and
when the downward change is 8% or greater, the rapid
change of D0 is large enough to cause FB to rise up to the
Smart Power Save threshold (810mV). DL will then drive
high to turn on the low-side MOSFET and draw current from
Figure 5
For the case where the down transition is less than
8%, and the load is light such that power-save is active,
the Smart Power Save detector will not activate. In this
case, with FB already above the 0.75V reference there
is no switching activity. DL and DH will remain off, and
the output voltage will slowly fall as the output capacitors
discharge into the load, see Figure 6.
© 2006 Semtech Corp.
11
www.semtech.com

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