SEMTECH SC191AEVB

SC191
Low Supply Ripple Synchronous
Buck Conversion Regulator
POWER MANAGEMENT
Description
Features
The SC191 is a synchronous step-down converter with
integrated power devices and an integrated front-end
LDO regulator to minimize input supply ripple. If supply
ripple is not a concern, the front-end LDO regulator can be
bypassed externally to maximize efficiency.
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The internal MOSFET switches provide peak current greater
than 550mA to achieve a DC output of at least 330mA over
the rated input voltage range, making the SC191 ideal for
single-cell Li-ion battery applications as well as fixed 3.3V
and 5V fixed input applications. The output is a fixed 1.2V
- ideal for low-voltage microprocessors. Other voltage
options are available (consult the factory for details).
Less than 1mV Supply Ripple
2.7V to 5.5V Input Range
330mA Guaranteed Output Current
Fixed Frequency 1MHz Operation
No Schottky Diode Required
Over-Current Protection
Over-Voltage Protection
Over-Temperature Protection
Soft-Start
No External Compensation Required
MLPD-8, 2.3mm x 2.3mm Package
WEEE and RoHS Compliant
Applications
Additional features include internal soft-start to limit inrush current, over-current protection, over-temperature
protection, and over-voltage protection.
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The 1MHz switching frequency allows the use of small
surface mount capacitors and inductors, and no other
external compensation components are needed. The
device is available in a low profile (0.8mm max height)
2.3mm x 2.3mm MLPD 8-lead package, minimizing area
without compromising performance.
Cell Phones
Cordless Phones
Notebook and Subnotebook Computers
PDAs and Mobile Communicators
WLAN Peripherals
Wireless Modules
1 Li-Ion or 3 NiMH/NiCd Powered Devices
Patent Pending
Typical Application Circuit
VIN
CIN
4.7μF
3
4
2
VIN
SC191
LX
EN
VOUT
PVIN
BP
7
April 12, 2006
PGND
GND
1
8
L
4.7μH
VOUT
5
COUT
1
6
CBP
4.7μF
4.7μF
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SC191
POWER MANAGEMENT
Absolute Maximum Ratings
Exceeding the specifications below 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.
Parameter
Symbol
Maximum
Units
Input Voltage
VVIN, VPVIN
-0.3 to 7.0
V
Enable Input
VEN
-0.3 to 7.0
V
LX Voltage
VLX
-1 to VBP + 1 (7V max)
V
VVOUT
-0.3 to 7.0
V
BP Voltage
VBP
0.3 to 7.0
V
Thermal Impedance Junction to Ambient1
θJA
135
°C/W
VOUT Short Circuit to GND
tSC
Continuous
s
Storage Temperature
TS
-60 to +160
°C
Junction Temperature
TJC
+150
°C
Peak IR Reflow Temperature
TLEAD
260
°C
ESD Protection Level2
VESD
2
kV
Output Voltage
Notes:
1) Calculated from package in still air, mounted to 3” x 4.5”, 4 layer FR4 PCB with thermal vias under the exposed pad as per JESD51 standards.
2) Tested according to JEDEC standard JESD22-A114-B.
Electrical Characteristics
Unless otherwise noted: VIN = 3.6V , VEN = VIN , TA = -40°C to 85°C . Typical values are at TA = 25°C.
Parameter
Symbol
Conditions
Min
Typ
2.7
Max
Units
5.5
V
Input Voltage Range
VIN
Input Voltage Ripple
VIN (P-P)
CIN = CBP = 10μF
Line Regulation
VLINEREG
IOUT = 150mA
Load Regulation
VLOADREG
0mA < IOUT < 330mA
0.002
%/mA
P-Channel On Resistance
RDSP
ILX = 100mA
0.3
Ω
N-Channel On Resistance
RDSN
ILX = 100mA
0.2
Ω
Start-Up Time
TSTART
IOUT = 150mA
1.25
ms
Output Voltage Accuracy
ΔVOUT
Front End LDO (FELDO)
© 2006 Semtech Corp.
VBP
1
-0.3
mV
0.3
%/V
IOUT = 150mA
-3
3
%
IOUT = 150mA, TA = 25°C
-1.5
1.5
%
325
mV
IBP = 110mA(1)
2
300
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SC191
POWER MANAGEMENT
Electrical Characteristics (Cont.)
Parameter
Symbol
Conditions
Min
Typ
Max
Units
P-Channel Current Limit
ILIM(P)
550
730
940
mA
N-Channel Current Limit
ILIM(N)
-270
-420
-700
mA
Quiescent Current
IQ
Switching mode, IOUT = 100μA
2.5
Shutdown Current
ISD
EN tied to GND
0.1
1
μA
LX Leakage Current PMOS
ILXP
VIN = 5.5V
LX, EN tied to GND
0.1
1
μA
LX Leakage Current NMOS
ILXN
VIN = VLX = 5.5V
EN tied to GND
Oscillator Frequency
UVLO Threshold (Lower)
UVLO Hysteresis
mA
-20
0.1
μA
fOSC
0.87
1.0
1.12
MHz
VUVLO
2.4
2.5
2.6
V
VUVLO-HYS
50
mV
Thermal Shutdown
TSD
145
°C
Thermal Shutdown
Hysteresis
TSD-HYS
10
°C
Logic Input High
VIH
EN pin
1.6
Logic Input Low
VIL
EN pin
Logic Input Current High
IIH
EN pin
-2
Logic Input Current Low
IIL
EN pin
-2
V
0.6
V
0.1
2
μA
0.1
2
μA
Note:
1) FELDO tested at IBP = 110mA. Equivalent to IOUT = 330mA at VOUT= 1.2V.
© 2006 Semtech Corp.
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SC191
POWER MANAGEMENT
Pin Configuration
Ordering Information
TOP VIEW
BP
1
8
LX
PVIN
2
7
PGND
VIN
3
6
GND
EN
4
5
VOUT
DEVICE
PACKAGE
SC191AWLTRT(1)(2)
MLPD-8LD
(2.3mm x 2.3mm BODY SIZE)
SC191AEVB
Evaluation Board
Notes:
1) Available in tape and reel only. A reel contains 3,000 devices.
2) Device is WEEE and RoHS compliant.
MLPD-8 2.3mm x 2.3mm 8-lead
Output Voltage Options
PART
VOUT
SC191A
1.2V*
*Only option currently available - contact Semtech for other voltage options.
Marking Information
91A
yw
nnn = Part Number
yw = Datecode
© 2006 Semtech Corp.
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SC191
POWER MANAGEMENT
Block Diagram
VIN
3
Voltage
References
VREF1
500mV
LDO
Error Amp
Plimit
Amp
2 PVIN
Front-End
LDO
Current
Amp
1
BP
OSC and Slope
Generator
8 LX
Control
Logic
VOUT 5
PWM
Comp
7
500mV
PGND
VREF1
Error
Amp
Nlimit
Comp
6 GND
EN
4
Pin Descriptions
Pin#
Pin Name
1
BP
2
PVIN
3
VIN
Input power supply for the analog functions.
4
EN
Enable (digital input): high input enables the SC191, a low disables and reduces the quiescent
current to < 1μA. In shutdown LX becomes high impedance.
5
VOUT
Regulated output voltage and feedback for the SC191.
6
GND
Ground: this pin should be connected directly to PGND on the user’s PCB.
7
PGND
8
LX
© 2006 Semtech Corp.
Pin Function
Regulated output, with respect to VIN, of the front-end LDO. A 4.7μF decoupling capacitor
should be connected to this pin. This output is connected directly to the internal switching
MOSFETs.
Input power supply for the power devices.
Power Ground: this pin should be connected directly to GND on the user’s PCB and should
be the reference point for the input, output and BP capacitor GND connections. These ground
paths should be separate and as short as possible to minimize circuit noise.
Inductor connection to the switching MOSFETs.
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SC191
POWER MANAGEMENT
Applications Information
SC191 Detailed Description
Current Limit
The part has a number of current limit functions. The
front-end LDO regulator has a current limit set at approximately 500mA, which will protect it in the event of a
pulsed short circuit. The PMOS and NMOS power devices
of the buck switcher stage are also protected by current
limit functions. In the case of a short to ground on the
output, the part enters frequency foldback mode which
causes the switching frequency to divide by a factor determined by the output voltage, which prevents the inductor
current from “stair stepping”.
The SC191 is a step-down, pulse-width-modulated (PWM)
DC-DC converter with a Low Dropout (LDO) pre-regulator.
The device has an internal synchronous rectifier and does
not require a Schottky diode on the LX pin. The device is
designed to operate as a buck converter in PWM mode
with a fixed-frequency of 1MHz. The SC191 operates as
a fixed frequency current mode regulator with the input
supply for the switching regulator pre-regulated by a frontend LDO regulator. This technique reduces the supply
voltage ripple from 10mV, typically seen from a switching
converter, to less than 1mV for the SC191. The supply to
the switcher is regulated to the supply voltage minus approximately 300mV. Current feedback for the switching
regulator is through the PMOS current path, and it is amplified and summed with the internal slope compensation
network and level shifted. The voltage feedback loop is
through an internal feedback divider.
Over-Voltage Protection
Over-voltage protection is provided on the SC191. In the
event of an over-voltage on the output, the PWM drive is
disabled, tri-stating the LX output and disabling the frontend LDO.
Soft-Start
The soft-start mode is enabled after every shutdown cycle
to limit in-rush current. In conjunction with the frequency
foldback this controls the maximum current during startup. The switcher’s PMOS current limit is stepped from
25%, to 50%, to 75%, and then 100% of its typical value
by a timer driven by the internal oscillator. The oscillator
frequency is stepped by 1/8, 1/4, 1/2 and 1 under the
control of 4 output voltage thresholds. As soon as the
part reaches regulation, soft start mode is disabled.
The on-time is determined by comparing the summed current feedback and the output of the error amplifier. The
period is set by the onboard oscillator.
Efficiency at moderate to high loads can be improved by
shorting the VIN and BP pins together. This bypasses the
front-end LDO, reducing voltage drop and improving efficiency at the expense of increasing input supply ripple.
Protection Features
The SC191 provides the following protection features:
Output Filter
The SC191 series of synchronous step-down converters
have internal loop compensation. The internal compensation is designed to work with a certain output filter corner frequency defined by the equation:
• Thermal Shutdown
• Current Limit
• Over-Voltage Protection
• Soft-Start
1
fC = —————
———
2 √ L×C
Thermal Shutdown
The thermal shutdown feature protects the device from
exceeding a junction temperature of 150°C. In thermal
shutdown the PWM drive is disabled, the LX output is tristated, and the front-end LDO is disabled. The device will
not be enabled again until the temperature reduces by
10°C. If during this time the output falls by greater than
60% of its regulation voltage, a soft-start will be invoked.
© 2006 Semtech Corp.
The internal compensation is optimized to operate with
an output filter, L = 4.7μH and COUT = 10μF. When selecting output filter components the LC product should not
vary over a wide range.
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SC191
POWER MANAGEMENT
Applications Information (Cont.)
Table 1: Output Filter Combinations
L (μH)
COUT (μF)
4.7
4.7
4.7
10
10
10
Alternatively, the inductor saturation current should be
greater than the switch current limit. Final inductor selection will depend on various design considerations such
as efficiency, EMI, size and cost (see Table 2 for a list of
practical inductor options).
CIN Selection
To prevent large input voltage ripple caused by discontinuous source input current, a low ESR ceramic capacitor
is required. A minimum value of 4.7μF should be used
for sufficient input voltage filtering, and a 10μF capacitor
is strongly recommended for optimum input voltage filtering. Input voltage ripple of approximately 1mV can be
achieved when CIN = 10μF and the front-end LDO regulator is active and pre-regulating the input supply to the
switching regulator.
The selection of smaller inductor and capacitor values will
move the corner frequency, having an impact on system
stability. Due to this issue the practical lower limit for the
inductor value is 4.7μH.
Inductor Selection
The value of the inductor should be in the range 4.7μH
to 10μH. The magnitude of the inductor current ripple is
dependant on the inductor value and can be determined
by the following equation:
(
COUT Selection
A 10μF ceramic capacitor is recommended for the output filter capacitor. Output voltage ripple is mainly determined by the filter capacitor in the following equation:
)
VOUT
VOUT
ΔIL = ——— 1 + ———
L × fOSC
VIN
ΔVOUT(ESR) = ΔIL(ripple) × ESRCOUT
This equation demonstrates the relationship between VIN,
VOUT and IL. To minimize conduction losses and maximize
efficiency, the inductor should have a low DC resistance.
As a minimum requirement, the DC current rating of the
inductor should be equal to the maximum load current
plus half of the inductor current ripple as described by the
following equation:
X7R or X5R ceramic dielectric capacitors should be used
because of their low ESR and superior temperature and
voltage characteristics. Y5V ceramic capacitors should
be avoided due to their widely-varying temperature coefficients.
ΔIL
IL(PK) = IOUT(MAX) + ——
2
Table 2: Recommended Inductors
Part Number
Value
(μH)
DCR
Ω
Rated Current
(A) (40°C rise)
ISAT (A)
L drop 25%
Tolerance
(± %)
Dimensions
(LxWxH mm)
TDK
LDR655312T-4R7W
4.7
0.206
0.9
-
20
6.5x5.3x1.2
Sumida
CDRH3D16LD
4.7
0.073
0.68
-
30
4x4x1.8
Taiyo Yuden
LMNP04SB100M
10
0.066
0.9
-
20
5x5x2
Coilcraft
LPS3015
10
0.044
-
0.65
20
3x3x1.5
Coilcraft
LP06610-103M
10
0.41
-
0.8
20
6.9x3.8x1.0
Manufacturer
© 2006 Semtech Corp.
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SC191
POWER MANAGEMENT
Applications Information (Cont.)
Table 3: Recommended Capacitors
Manufacturer
Part Number
Value
(μF)
Rated Voltage
(VDC)
Temperature
Coefficient
Package Size
Murata
GRM-188R60J475KE19D
4.7
6.3
X5R
0603
Murata
GRM-188R60G106ME47D
10
4
X5R
0603
TDK
C1608X5R0G106M
10
4
X5R
0603
PCB Layout Considerations
Poor layout can degrade the performance of the DC-DC
converter and can be a contributory factor in EMI problems, ground bounce and resistive voltage losses. Poor
regulation and instability can result. A few simple design
rules can be implemented to ensure good layout:
ductor and LX node to minimize noise and magnetic interference. Use a ground plane to further reduce noise.
3) Maximize ground metal on the component side to
improve the return connection and thermal dissipation.
Separation between the LX node and GND should be
maintained to avoid coupling of switching noise to the
ground plane.
1) Place the inductor and filter capacitors as close to the
device as possible and use short, wide traces between
the power components.
4) To further reduce noise interference on sensitive circuit
nodes, use a ground plane with several vias connecting
all ground planes together.
2) Route the output voltage feedback path away from in-
Suggested Layout
GND
CBP
LX
VIN
SC191
LOUT
CIN
COUT
VOUT
GND
Vias to GND
Plane
© 2006 Semtech Corp.
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SC191
POWER MANAGEMENT
Typical Characteristics
Efficiency vs. Load Current (FELDO Bypassed)
100
100
90
90
80
80
70
70
Efficiency (%)
Efficiency (%)
Efficiency vs. Load Current (FELDO Active)
60
50
VIN=3V
40
VIN=3.6V
30
50
VIN=3V
40
VIN=3.6V
30
VIN=4.2V
20
60
VIN=4.2V
20
10
10
0
0
0.0100
0.1000
1.0000
0.0100
0.1000
IOUT (A)
1.0000
IOUT (A)
Line Regulation (FELDO Bypassed)
Line Regulation (FELDO Active)
1.21
1.21
IOUT=1mA
IOUT=1mA
1.205
IOUT=150mA
IOUT=150mA
IOUT=330mA
IOUT=330mA
1.2
VOUT (V)
VOUT (V)
1.205
1.195
1.2
1.195
1.19
1.19
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
2.5
3.0
3.5
4.0
VIN (V)
4.5
5.0
5.5
6.0
VIN (V)
Load Regulation
Switching Frequency vs. Temperature
1.01
1.21
Switching Frequency (MHz)
1
VOUT (V)
1.205
VIN=4.2V
1.2
VIN=3.6V
VIN=3V
0.98
0.97
0.96
VIN=3.6V
1.195
0.00
0.99
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.95
0.45
-60
IOUT (A)
© 2006 Semtech Corp.
-40
-20
0
20
40
60
80
100
120
140
TJ (°C)
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SC191
POWER MANAGEMENT
Typical Characteristics (Cont.)
Switching Frequency vs. Input Voltage
Quiescent Current vs. Input Voltage
1.005
4
3.5
0.995
Quiescent Current (mA)
Switching Frequency (MHz)
1
0.99
0.985
0.98
0.975
0.97
0.965
TJ=85oC
3
TJ=25 C
o
2.5
TJ=-40oC
2
1.5
1
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
2.7
3.1
3.5
3.9
VIN (V)
4.3
4.7
5.1
5.5
VIN (V)
N-Channel RDSON vs. Temperature
P-Channel RDSON vs. Temperature
400
600
350
500
300
RDSON (mΩ)
RDSON (mΩ)
400
250
200
150
300
200
100
100
50
0
0
-60
-40
-20
0
20
40
60
80
100
120
140
-60
TJ (°C)
-40
-20
0
20
40
60
80
100
120
140
TJ (°C)
Load Transient Response
Start-Up
VIN=3.6V, VOUT=1.2V
VIN=3.6V, IOUT=300mA
IOUT
33 to 330mA
VOUT
100mV/DIV
VOUT
500mV/DIV
ENABLE
5V/DIV
200μs/Div
© 2006 Semtech Corp.
200μs/Div
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SC191
POWER MANAGEMENT
Typical Characteristics (Cont.)
Input Voltage Ripple (FELDO Bypassed)
Input Voltage Ripple (FELDO Active)
VIN =3.6V, IOUT=300mA, CBP=10uF, CIN= not fitted
VIN =3.6V, IOUT=300mA, CBP=10uF, CIN= 10uF
VOUT
5mV/DIV
VOUT
5mV/DIV
VLX
2V/DIV
VLX
2V/DIV
400ns/Div
400ns/Div
Input Voltage Ripple (FELDO Bypassed)
VIN =3.6V, IOUT=300mA, CBP=20uF, CIN= not fitted
VOUT
5mV/DIV
VLX
2V/DIV
400ns/Div
© 2006 Semtech Corp.
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SC191
POWER MANAGEMENT
Outline Drawing - MLPD-8
A
B
D
DIMENSIONS
INCHES
MILLIMETERS
DIM
MIN NOM MAX MIN NOM MAX
E
PIN 1
INDICATOR
(LASER MARK)
A
aaa C
SEATING
PLANE
C
A1
A2
1
A
A1
A2
b
D
E
e
L
L1
N
aaa
bbb
.028 .030 .031
.000 .001 .002
(.008)
.008 .010 .012
.087 .091 .094
.087 .091 .094
.020 BSC
.012 .016 .020
.016 .020 .024
8
.003
.003
0.70 0.75 0.80
0.00 0.02 0.05
(0.20)
0.20 0.25 0.30
2.20 2.30 2.40
2.20 2.30 2.40
0.50 BSC
0.30 0.40 0.50
0.40 0.50 0.60
8
0.08
0.08
2
LxN
L1
0.125 CHAMFER
N
bxN
bbb
e
C A B
e/2
NOTES:
1. CONTROLLING DIMENSIONS ARE IN MILLIMETERS (ANGLES IN DEGREES).
© 2006 Semtech Corp.
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SC191
POWER MANAGEMENT
Land Pattern - MLPD-8
DIM
C
G
C
G
P
X
Y
Z
Z
Y
DIMENSIONS
INCHES
MILLIMETERS
(.083)
.047
.020
.012
.035
.118
(2.10)
1.20
0.50
0.30
0.90
3.00
X
P
NOTES:
1.
THIS LAND PATTERN IS FOR REFERENCE PURPOSES ONLY.
CONSULT YOUR MANUFACTURING GROUP TO ENSURE YOUR
COMPANY'S MANUFACTURING GUIDELINES ARE MET.
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
© 2006 Semtech Corp.
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