SC221 Datasheet

SC221 x
20MHz, 650mA, X-EMI™-Enabled
Synchronous Step-Down Regulator
POWER MANAGEMENT
Features
Description
„„
Patented X-EMITM Inductor Technology
„„ Enables Trace Inductors in PC Board Material
„„ Excellent EMI Performance
Efficiency up to 90%
17.5µA Quiescent Current under Very Light Loads
Wide Input Voltage Range — 2.7V to 5.5V
Adjustable Output Voltage Down to 1.0V
Output DC Current — up to 650mA
High Light-load Efficiency via Automatic PSAVE Mode
Ultra-fast Transient Response — <1µs
Temperature Range — -40 to +85°C
Shutdown Current — 0.1µA (typical)
Requires Tiny 220nH Inductor
Requires Only 1μF of Output Capacitance
External Switching Frequency Synchronization
Protection Features Including
„„ Over-Current Protection
„„ Output Short-Circuit Protection
„„ Thermal Shutdown Protection
Offered in MLPD-UT 8 Lead Packages
„„
Lead-free, Halogen-free, and RoHS/WEEE Compliant
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Applications
HDTV, Set Top Boxes, Gaming Consoles
POL Applications
„„ White Goods
„„
The SC221 is a 20MHz X-EMI™(1)-enabled step-down regulator optimized for power low voltage rails from 2.7 to
5.5V input voltage. X-EMI™ inductor technology enables
inductors to be drawn directly on the PC board. This technology meets or exceeds the EMI performance of chip
inductors and eliminates the need for discrete inductors.
The SC221 uses a unique constant frequency, self-oscillating control loop architecture to provide excellent
transient performance. Under light loads, the device
operates in Power Save mode(PSAVE) maintaining a
typical quiescent current of 17.5µA. At moderate to heavy
loads, this part operates in PWM mode with a constant
switching frequency of 20MHz. This high switching frequency offers the advantages of using small and low cost
external components like a 1µF external capacitor and a
small 220nH inductor (including X-EMI TM PCB trace
inductors).
The device provides adjustable output voltages down to
1.0V and an output current up to 650mA. An EN pin can
be used to synchronize to an external source and includes
de-glitching to reduce noise sensitivity.
The SC221 is available in MLPD-UT 8 Lead package.
„„
Note 1: Purchase of SC221 includes royalty-free right to use X-EMITM inductor technology with no additional cost.
Typical Application Circuit
L, 220nH
VIN
SW
PVIN
2.7~5.5V
AVIN
VOUT
CIN
1 µF
R1
SC221
EN
Enable
VOUT=1.8V
up to 650mA
COUT
1 µF
FB
PGND
R2
AGND
Revision 2.0
© 2016 Semtech Corporation
1
SC221 x
Pin Configuration
Ordering Information
SW
PGND
PVIN
AGND
VOUT
AVIN
FB
Device
Package
SC221ULTRT (1)(2)
MLPD-UT 8 Lead
SC221EVB
Evaluation Board
EN
MLPD-UT 8 Lead, θJA = 38 °C/W
Notes:
(1) Available in tape and reel only. A reel contains 3000 devices.
(2) Device is lead-free, halogen-free, and RoHS/WEEE compliant.
Marking Information
2
SC221 x
Absolute Maximum Ratings
Recommended Operating Conditions
AVIN, PVIN (V). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.0
Input Voltage Range (V). . . . . . . . . . . . . . . . . . . . . +2.7 to +5.5
VOUT, FB, EN, SW (V). . . . . . . . . . . . . . . . . . . . . -0.3 to (VIN +0.3)
Output DC Current (mA). . . . . . . . . . . . . . . . . . . . . up to 650
AGND (V). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3
Operating Temperature Range (°C) . . . . . . . . . . -40 to +85
to
+0.3
ESD Protection Level (kV). . . . . . . . . . . . . . . . . . . . . . . . . . 3kV
(1)
Thermal Information
Thermal Resistance, Junction to Ambient(2) (°C/W)....38
Junction Temperature Range (°C). . . . . . . . . . -40 to +150
Storage Temperature Range (°C). . . . . . . . . . . . . -65 to +150
Lead Temperature (soldering 10s (°C). . . . . . . . . . . . . . . . 260
Exceeding the above specifications may result in permanent damage to the device or device malfunction. Operation outside of the parameters
specified in the Electrical Characteristics section is not recommended.
Notes:
(1) All voltage values in this section are with respect to PGND pin voltage.
(2) Tested according to JEDEC standard JESD22-A114-B.
(3) Calculated from package in still air, mounted to 3 x 4.5 (in), 4 layer FR4 PCB with thermal vias under the exposed pad per JESD51 standards.
Electrical Characteristics
Unless otherwise specified: AVIN=PVIN = 3.6V, EN = AVIN = PVIN, CIN=COUT =1.0μF, L=220nH. TA = 25°C for typical values, -40°C < TA = TJ < 85°C for
minimum and maximum values.
Parameter
Symbol
Condition
Min
Typ
Max
Units
5.5
V
60
µA
1.0
µA
POWER SUPPLY
Input Voltage
VIN
2.7
Input Quiescent Current
IVIN_Q
No load, no switching
Shutdown Current
IVIN_SD
EN = 0V
17.5
POWER SWITCH
PMOS On Resistance
400
mΩ
NMOS On Resistance
360
mΩ
OSCILLATOR
Switching Frequency
fOSC
PWM Mode
16
20
24
MHz
REGULATION
Output Voltage Tolerance(1)
Current Limit
VOUT_TOL
-4.0
4.0
%
ILIMIT
800
1300
mA
Soft-Start(1)
tSS
EN pin low to high
Feedback Voltage
VFB
2.7V ≤ VIN ≤ 5.5V
40
0.97
1.00
µs
1.03
V
3
SC221 x
Electrical Characteristics (continued)
Unless otherwise specified: AVIN=PVIN = 3.6V, EN = AVIN = PVIN, CIN=COUT =1.0μF, L=220nH. TA = 25°C for typical values, -40°C < TA = TJ < 85°C for
minimum and maximum values.
Parameter
Feedback Leakage Current
Symbol
Condition
Min
Typ
IFB
Max
Units
1
µA
ENABLE
EN Input High Voltage Threshold
VENH
EN Input “Low” Voltage Threshold
VENL
EN Input High Current
IENH
VEN= VIN
EN Input Low Current
IENL
VEN= AGND
fSYN_MIN
Square wave applied at EN pin
Minimum Synchronization Frequency
1.2
V
0.4
V
-1.0
1.0
µA
-1.0
1.0
µA
3
MHz
PROTECTION
Over Temp Thermal Shutdown(1)
TOT
150
°C
Thermal Shutdown Hysteresis(1)
THYST
15
°C
Notes
(1) Guaranteed by design. Not tested in production.
4
SC221 x
Pin Descriptions
Pin #
Pin Name Pin Function
1
SW
Switching output node — connect to the output LC filter.
2
PVIN
Power input supply voltage (2.7 to 5.5V).
3
VOUT
Input for sensing the output of LC filter.
4
FB
Input for regulation of output LC filter — Using R1 and R2 to set the output voltage, VOUT = VFB x (1+ R1/R2). (Please refer
to the typical application circuit diagram on page 1).
5
EN
Enable Input — when low, circuit draws <1µA. Apply a square wave clock at EN to synchronize the switching frequency
with an external clock. It is recommended that the externally applied clock frequency should not be above 20MHz.
6
AVIN
Input supply voltage
7
AGND
Analog ground
8
PGND
Power ground
Block Diagram
5
SC221 x
Typical Characteristics (Continuous)
Efficiency vs. Load Current
90
VOUT = 1.8V
VIN = 2.7V
80
70
VOUT = 1.8V
90
VIN = 3.3V
80
VIN = 5.5V
70
60
IOUT = 360mA
IOUT = 40mA
IOUT = 650mA
60
Efficiency (%)
Efficiency (%)
Efficiency vs. VIN
50
40
30
50
40
30
20
20
10
10
0
0.00
0
0.10
0.20
0.30
0.40
0.50
2.5
0.60
3
3.5
4
Efficiency vs. Load Current
VOUT = 1.8V
1.81000
VIN = 2.7V
80
5.5
Nominal VOUT = 1.8V
VIN = 3.3V
70
Output Voltage (V)
VIN = 5.5V
60
Efficiency (%)
5
Load Regulation
(Chip Inductor vs. X-EMITM Inductor)
90
4.5
Input Voltage (V)
Load Current (A)
50
40
30
20
1.80000
1.79000
VIN = 5.5V
VIN = 2.7V
1.78000
VIN = 3.3V
10
Solid Lines: Efficiency with X-EMI TM Inductor
Dashed Lines: Efficiency with Chip Inductor
0
0.00
0.10
0.20
0.30
0.40
0.50
1.77000
0.60
0.00
Load Current (A)
0.10
0.20
0.30
0.40
0.50
0.60
Load Current (A)
Switching Frequency vs. VIN
Switching Frequency vs. VIN
18.40
18.00
18.20
Switching Frequency (MHz)
Switching Frequency (MHz)
VOUT = 1.8V
20.00
16.00
14.00
Io=200mA
12.00
10.00
Io=300mA
8.00
Io=450mA
6.00
4.00
Io=650mA
2.00
3.00
3.50
4.00
Input Voltage (V)
4.50
5.00
18.00
17.80
17.60
Io=200mA
17.40
17.20
Io=300mA
17.00
Io=450mA
16.80
0.00
2.50
VOUT = 1V
5.50
Io=650mA
16.60
2.50
3.00
3.50
4.00
4.50
5.00
5.50
Input Voltage (V)
6
SC221 x
Typical Characteristics (Continuous)
Load Transient Response
Load Transient Response
VIN = 3.6V, VOUT = 1.8V, IOUT = 0mA - 500mA
VOUT
VIN = 3.6V, VOUT = 1.8V, IOUT = 80mA - 500mA
VOUT
(ac coupled)
100mV/div
(ac coupled)
50mV/div
200mA/div
200mA/div
200us/div
200us/div
Steady State operation
Steady State Operation
VIN = 3.6V, VOUT = 1.8V, IOUT = 50mA
IOUT
VIN = 3.6V, VOUT = 1.8V, IOUT = 300mA
IOUT
50mA/div
200mA/div
IL
IL
500mA/div
200mA/div
VSW
VSW
2V/div
2V/div
500ns/div
50ns/div
Output Hard Short
Input Quiescent Current vs. Temperature
VIN = 5V, VOUT = 1.8V, IOUT = 650mA
VOUT
18
VIN= 3.6V, EN = High, FB = High
Quiescent Current (µA)
1V/div
IL
500mA/div
17.5
17
16.5
16
-40
0
40
80
Temperature (°C)
120
160
500ns/div
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SC221 x
Typical Characteristics (Continuous)
Start-up Operation
Shutdown Operation
VIN = 3.6V, VOUT = 1.8V, IOUT = 20mA
VIN = 3.6V, VOUT = 1.8V, IOUT = 20mA
EN
EN
2V/div
2V/div
VIN
VIN
2V/div
2V/div
VOUT
VOUT
1V/div
1V/div
IOUT
50mA/div
IOUT
50mA/div
100us/div
200us/div
Start-up Operation
Shutdown Operation
VIN = 3.6V, VOUT = 1.8V, IOUT = 650mA
VIN = 3.6V, VOUT = 1.8V, IOUT = 650mA
EN
EN
2V/div
VIN
2V/div
2V/div
VIN
2V/div
VOUT
VOUT
1V/div
1V/div
IOUT
IOUT
500mA/div
500mA/div
200us/div
200us/div
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SC221 x
Applications Information
General Description
The SC221 is a step-down regulator capable of delivering
a lower voltage from an input supply voltage of 2.7V to
5.5V with high efficiency. Using a unique control architecture, the SC221 is capable of delivering a peak efficiency
upto 90%, while maintaining efficiency over 80% during
light load condition. The converter operates at 20MHz
switching frequency with pulse width modulation (PWM)
at moderate to heavy loads up to 650mA. Under light
load, the converter operates in power save (PSAVE) mode.
Control Scheme
The SC221 operates with a self-oscillating control method
based on the output voltage ripple. This control loop
compares the output voltage to an internal 1V reference
to regulate the output voltage directly, adjusting the
turn-on and turn-off time of the power switches such that
the output voltage at the load is held at a precise value.
This architecture gives a single-cycle response to transient
events.
To maintain constant frequency, a phase locked loop (PLL)
is included to synchronize the switching with an internal
clock. This PLL adjusts the effective upper and lower
thresholds of the comparator, thus maintaining a constant
frequency. Under transient conditions the voltage control
loop determines the required switching pattern to best
maintain the output voltage. After a short transient, the
PLL will bring the switching frequency back to normal. At
extreme duty cycles, where the frequency control loop
may not be able to maintain frequency lock even under
steady-state conditions, frequency may fall, but the
output voltage regulation will be maintained by the main
voltage control loop. This unique architecture helps to
achieve the excellent line and load transient response.
Operating Modes
The SC221 operates in two modes over a wide range of
load currents. At moderate to high load, it operates in
PWM mode with its switching frequency held constant.
Under light loads, the converter enters PSAVE mode automatically. With the typical 220nH inductor, the transition
between PWM and PSAVE mode typically occurs in the
range of 100-200mA, depending on the input and output
voltages. At very light loads, the SC221 maintains high
efficiency by shutting down all but the most essential
circuit blocks, maintaining a typical quiescent current of
about 17.5µA. In this mode, some circuitry used to control
absolute DC accuracy is turned off. In that case, there may
be a small DC shift (tens of mV) between normal operation and this ‘no-load’ state. However, in the case of a load
transient, the system will turn on the high-side FET within
nanoseconds as a discontinuous pulse is issued. The transition to PWM mode can occur within that nominal
on-time, giving superior no load to full load transient
response.
The transition from PWM mode to PSAVE mode is controlled by sensing the minimum value of the ripple
current. When it drops below a threshold level for 32 consecutive cycles, the transition to PSAVE mode is initiated.
Once in PSAVE, the regulation is maintained by modulating the time between fixed current pulses. When a new
pulse is required by the loop before the existing pulse has
terminated, the loop determines that the load cannot be
maintained in PSAVE mode. This prompts an instantaneous switch from PSAVE mode back to PWM mode.
Enable and Start-up
The SC221 is enabled by applying a voltage higher than
1.2V on EN pin pin, and it is disabled when the applied
voltage is pulled below the logic low threshold. The EN
pin can also be used to set the switching frequency: if a
digital clock is fed to EN, the SC221 will sense this as a
valid enable signal and the external clock will be used
rather than the internal 20MHz oscillator.
The SC221 has an internal soft start circuit that limits the
inrush current during start-up with a stepped current
limit. Over the course of about 40μs, the SC221 is stepped
in increments of one quarter of the nominal current limit
to full current limit, thereby reducing the worst-case
surge current that might otherwise be reflected to the
input current.
Current Limit
The SC221 integrates a current limit feature to protect
itself and the external components during over load condition. When the current in the high-side PMOS switch
exceeds the current limit, the PMOS switch is turned off.
9
SC221 x
Applications Information (Cont.)
The high-side switch is then held off for a period sufficient
to allow inductor current to decay. When the output
voltage is close to the nominal regulation point, this will
look similar to constant current limiting. As the output
voltage falls, imposed off-time is such that the frequency
will drop so that the inductor will have appropriate time
to reset. This may cause the average current to reduce,
giving a mild ‘fold-back’ characteristic to the current limit,
where the average load current drops as the output
voltage collapses (although the peak current maintains its
nominal value). In a short-circuit condition, the system
runs continuously at this reduced frequency.
Load Transient Response
The SC221 features excellent regulation during line and
load transients. This is due to the nature of the proprietary
control method and the high di/dt allowed by the use of a
small inductor. This allows for best performance while
providing the benefit of using a small low cost output
capacitor. V OUT shows only tens of milivolts of ripple
voltage during a load current step change of 1mA to
650mA within hundreds of nanoseconds, using a 1μF
output capacitor. (See the typical performance curves on
page 7).
X-EMI™ Inductor Technology
The SC221 is the industry’s first buck regulator that enables
designers to draw their own inductors directly on the PC
board. This patented technology is called as X-EMI™
inductor technology and is different from conventional
PCB trace inductors. Conventional PCB trace inductors can
be used with high-frequency switchers, but they exhibit
significant EMI issues. X-EMI™ inductor technology solves
these EMI problems and can meet or exceed the EMI performance of conventional chip inductors.
X-EMITM technology works by placing two small air-core
inductors adjacent to one another in anti-phase position,
where the magnetic fields of each inductor partially cancel
one another to reduce EMI. The net flux from the two
inductors, partially cancels the wide leakage paths caused
by the wide geometry, while still storing the energy of the
inductors in series. This approach uses multiple air core
inductors implemented using printed circuit traces.
Because these traces may be located on internal layers of
the PCB, inductors can be designed with almost no impact
on the available PCB area for components on the surface
of the board. (See the efficiency curves using X-EMI™
inductor technology on page 6).
External Components
The input and output capacitors used for the operation of
the SC221 should be multilayer ceramic capacitors, preferably with X7R or X5R dielectric. SC221 is optimized to
operate with the input and output capacitance of 1μF
typical. In practice, the self-resonant frequency of surface
mount capacitors of this type is well below 20MHz ripple
frequency, so efforts to minimize output ripple may best
be focused on minimizing the inductance of the output
capacitor and the length of the circuit path to ground
rather than on increasing the capacitance value of the
output capacitor.
The inductor should be a high current inductor rated for
currents at least up to 1A. Typical power inductors may be
too lossy at 20MHz unless specifically designed for high
frequency operation. For inductor value of 220nH, it may
be preferred to use wire-wound RF chokes, many of which
are rated for appropriate currents.
Some Recommended External Components
Value
Manufacturer
Part Number
Package
0.22μH
Coilcraft
XFL2005-221ME
2x2mm
0.24μH
Coilcraft
0603LS-241XJL
0603
0.22μH
Wurth
Elektronik
74479762122
0603
CIN
1μF
Murata
GRM155R61C105KA12
0402
COUT
1μF
Murata
GRM155R61C105KA12
0402
L
Figure 1. Top view of an evaluation board with X-EMI inductor
10
SC221 x
Applications Information (Cont.)
PCB Layout Considerations
Fundamental layout rules must be followed since the
layout is critical for achieving the desirable performance.
Poor layout can degrade the performance of the DC-DC
converter and can contribute to EMI problems, ground
bounce, and resistive voltage losses, and possibly poor
regulation and instability.
The following guidelines are recommended when developing a PCB layout:
1. The input capacitor, CIN should be placed as close to
the PVIN and PGND pins as possible. This capacitor
provides a low impedance loop for the pulsed
currents present at the buck converter’s input. Use
short wide traces to connect this capacitor as close
to the IC as possible. This will minimize EMI and input
voltage ripple by localizing the high frequency current
pulses.
2. Keep the SW pin traces as short as possible to minimize
pickup of high frequency switching edges to other
parts of the circuit. COUT and L should be connected as
close as possible between the SW and GND pins, with
a direct return to the GND pin from COUT.
3. Route the output voltage feedback/sense path away
from the inductor and SW node to minimize noise
and magnetic interference to the output feedback/
sense path.
4. Use a ground plane referenced to the PGND pin,
and the ground connection of the input and output
capacitors should be put on this plane and close to
each other if possible, and as close to the PGND pin as
possible. Use several vias to connect to the component
side ground to further reduce noise and interference
on sensitive circuit nodes.
5. If possible, minimize the resistance from the VOUT
and AGND pin to the load. This will reduce the
voltage drop on the ground plane and improve the
load regulation. And it will also improve the overall
efficiency by reducing the copper losses on the output
and ground planes.
11
SC221 x
Outline Drawing — MLPD-UT 8 Lead
A
B
D
DIM
E
PIN 1
INDICATOR
(LASER MARK)
A
aaa C
A2
A1
SEATING
PLANE
C
A
A1
A2
b
D
D1
E
E1
e
L
N
aaa
bbb
DIMENSIONS
MILLIMETERS
INCHES
MIN NOM MAX MIN NOM MAX
.024
.002
(.006)
.007 .010 .012
.075 .079 .083
.061 .067 .071
.075 .079 .083
.026 .031 .035
.020 BSC
.012 .014 .016
8
.003
.004
.020
.000
0.60
0.50
0.00
0.05
(0.1524)
0.18 0.25 0.30
1.90 2.00 2.10
1.55 1.70 1.80
1.90 2.00 2.10
0.65 0.80 0.90
0.50 BSC
0.30 0.35 0.40
8
0.08
0.10
D1
1
E/2
2
LxN
E1
N
bxN
e
bbb
C A B
e/2
D/2
NOTES:
1. CONTROLLING DIMENSIONS ARE IN MILLIMETERS (ANGLES IN DEGREES).
2. COPLANARITY APPLIES TO THE EXPOSED PAD AS WELL AS THE TERMINALS.
12
SC221 x
Land Pattern —MLPD-UT 8 Lead
H
R
DIM
(C) K
G
Y
X
P
Z
C
G
H
K
P
R
X
Y
Z
DIMENSIONS
INCHES
MILLIMETERS
(.077)
.047
.067
.031
.020
.006
.012
.030
.106
(1.95)
1.20
1.70
0.80
0.50
0.15
0.30
0.75
2.70
NOTES:
1.
CONTROLLING DIMENSIONS ARE IN MILLIMETERS (ANGLES IN DEGREES).
2.
THIS LAND PATTERN IS FOR REFERENCE PURPOSES ONLY.
CONSULT YOUR MANUFACTURING GROUP TO ENSURE YOUR
COMPANY'S MANUFACTURING GUIDELINES ARE MET.
3.
THERMAL VIAS IN THE LAND PATTERN OF THE EXPOSED PAD
SHALL BE CONNECTED TO A SYSTEM GROUND PLANE.
FAILURE TO DO SO MAY COMPROMISE THE THERMAL AND/OR
FUNCTIONAL PERFORMANCE OF THE DEVICE.
13
SC221 x
© Semtech 2016
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Contact Information
Semtech Corporation
Power Management Products Division
200 Flynn Road, Camarillo, CA 93012
Phone: (805) 498-2111 Fax: (805) 498-3804
www.semtech.com
14