SC21150 Datasheet

SC21150
Tiny 1.2A Synchronous
Buck Regulator
POWER MANAGEMENT
Features
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Description
Input voltage range — 2.3V to 5.5V
1.2A continuous output current
4MHz switching frequency
Adjustable Output Voltage
0.8V to VIN
1% output voltage accuracy
Adaptive On-Time architecture
Up to 100% duty cycle
Up to 96% peak efficiency
Power Save mode for efficient light load operation
>90% efficiency 30mA to 75mA
1μA shutdown current
23μA quiescent current
Pre-bias startup protection
Internal or optional external Soft Start
Device options (contact Semtech Marketing)
Automatic output discharge
Power Good indicator
Internal Soft Start
External Programmable Soft Start
Forced PWM Operation Input
0.75mm x 1.11mm, 6-Bump WLCSP Package
WEEE and RoHS compliant and halogen-free
The SC21150 is an ultra high efficiency 1.2A DC/DC buck
regulator available in a tiny CSP package. These features
make the SC21150 family perfect for small form factor
portable applications where long battery life is essential.
SC21150 is an Adaptive On-Time 4MHz switching regulator at full load conditions. Under light load conditions it
seamlessly transitions into Power Save Mode and reduces
switching frequency thus saving energy. High switching
frequency operation allows the use of a very small 0.47μH
inductor along with small input and output capacitors to
minimize overall circuit size. A Forced PWM input allows
continuous switching under all load conditions.
The SC21150 is highly configurable with a wide range of
factory options including internal Soft Start time, fixed or
adjustable output voltage, automatic output discharge,
and a Forced PWM input.
The SC21150 is offered in an ultra small WLCSP 6-Bump
0.75mm x1.11mm package with a bump pitch of 0.35mm.
The SC21150 operating temperature range is -40C to
+85C.
Applications
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Automotive
Smart Phones
Wearable Electronics
Tablet PCs
GPS devices
Battery powered equipment
Portable devices
Typical Application Circuit
Adjustable Output Voltage
2.3V-5.5V Supply
4.7µF
FPWM
EN
Rev 2.0
VIN
LX
FPWM
FB
SC21150
EN
0.47µH
1.2A
Output
10µF
GND
SC21150
Pin Configuration
A2
B2
B1
A1
Marking Information
T O P V IE W
C2
C1
0.7 5x1 .1 1 (m m )
6-B u m p W L C S P
T O P V IE W
XX
0.7 5x1 .1 1
6 -B u m p
W LC SP
6-Bump WLCSP Marking Diagram
XX = Pin A1 and Marking Code
Bump Assignments 0.75x1.11mm 6-Bump WLCSP
Row/Column
1
2
A
GND
VIN
B
LX
FPWM
C
FB
EN
6-Bump WLCSP Device Code
Part Number
Output
Marking
Code
SC21150ACSTRT
Adj
AZ
SC21150
Ordering Information
Options(3)
Device (1)(2)
SC21150ACSTRT
SC21150EVB
Output(3)
Soft-Start(3)
Output Discharge(3)
Adjustable
100μs
Automatic
Package
0.75 x 1.11 mm 6-Bump WLCSP
Evaluation Board 0.75 x 1.11 mm 6-Bump WLCSP
Notes:
(1) Available in tape and reel only. A reel contains 5,000 devices.
(2) Lead-free packaging only. Device is WEEE and RoHS compliant and halogen-free.
(3) For other device combinations contact Semtech Marketing for additional options.
The following options can be made available:
VOUT options : fixed or adjustable versions.
Fixed voltages can be specified, from 0.8V to 3.6V in 50mV increments.
Soft-Start options: Fixed internal 100μs, with options for 200μs/400μs/800μs.
Output Discharge options: Automatic Discharge and No Discharge.
Frequency: The default operating frequency is 4MHz with options of 2.2MHz, 3MHz, or 6MHz.
SC21150
Absolute Maximum Ratings
Recommended Operating Conditions
VIN (V) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3 to +6.0
Input Voltage Range (V) . . . . . . . . . . . . . . . . . . . . . . . . 2.3 to 5.5
EN (V) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.15 to +(VIN+0.3)
Output Voltage Range (V) . . . . . . . . . . . . . . . . . . . . . . . . 0.8 to 3.6
FB, FPWM (V) . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3 to +(VIN+0.3)
Maximum Continuous Current (A). . . . . . . . . . . . . . . . . . . . . 1.2
LX (V). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3 to +(VIN+0.3)
Junction Temperature Range (°C) . . . . . . . . . -40 < TJ < +125
ESD Protection Level (kV)(1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Thermal Information
Thermal Resistance Junction to Ambient(2) (°C/W )
WLCSP package. . . . . . . . . . . . . . . . . . . . . . . . . . . . .100
Maximum Junction Temperature (°C) . . . . . . . . . . . . . . +150
Operating Junction Temperature (°C ). . . . . . . -40 to +125
Storage Temperature Range (°C) . . . . . . . . . . . . -65 to +150
Peak IR Reflow Temperature (10s to 30s) (°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) Tested according to JEDEC standard JESD22-A114-B.
(2) 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 noted VIN = 5.0V, CIN = 4.7μF, COUT = 10μF, L = 0.47μH, EN = VIN, TJ = -40 to +85°C. Typical values are at TA = 25°C.
Parameter
Symbol
Conditions
Min
Typ
Max
Units
5.5
V
Input Supply
Input Supply Voltage Range
VIN
2.3
Shutdown Current
ISD
EN = 0V
0.1
μA
Quiescent Current
IQ
Operating, No Load, Power Save Option
23
μA
Under Voltage Lock Out Threshold
UVLOrise
VIN rising edge
Under Voltage Lock Out Hysteresis
UVLOhyst
2.05
2.16
2.27
V
85
mV
0.80
V
Output Voltage(1)
Feedback Voltage
Feedback Voltage Tolerance
Feedback Input Leakage Current
VFB
Adjustable Vout
VFBtol
Adjustable Vout
IFB
Adjustable Vout
-2
+/- 1
+2
%
1
25
nA
SC21150
Electrical Characteristics (continued)
Parameter
Symbol
Conditions
Min
Vout
Adjustable Vout
0.8
Output Voltage Line Regulation
dVline
5.5V > VIN > (Vout +1), PWM operation
0.17
%/V
Output Voltage Load Regulation
dVload
500mA < ILOAD < 1.2A
-0.13
%/A
IOUT
Continuous current
TSS
FB: from LX rising edge to
95% of final value
100
μs
On Resistance High-side
Rdson_hs
FB = 0V; ILX = 500mA
160
mΩ
On Resistance Low-side
Rdson_ls
FB = VIN; ILX = 500mA
120
mΩ
LX Leakage Current High Side
ILX_hs
FB = VIN = 5.5V; VLX = 0V
-0.1
μA
LX Leakage Current Low Side
ILX_ls
FB = 0V; VLX = VIN = 5.5V;
Vout Automatic Discharge disabled
0.1
LX Pulldown Current(1)
ILX_pd
EN = 0V; VLX = 1V;
Vout Automatic Discharge enabled
20
Switching Frequency(1)
Fsw
4MHz option, PWM operation, 500mA load,
adjustable output, Vout = 2.5V
3.6
4.0
4.4
MHz
High Side Current Limit
ILIMhs
Current from VIN to LX
1.5
2.2
3.0
A
Low Side Current Limit
ILIMls
Current from LX to GND
-0.8
A
Ithzcpfm
Power Save Mode and DC Test condition
0
mA
Over-Temperature Shutdown
Tts_rise
Rising temperature
160
°C
Over-Temperature Hysteresis
Tts_hyst
10
°C
Output Voltage Range
Maximum Output Current
Typ
Max
Units
VIN
V
1.2
A
Soft Start
Soft Start Time (1)
LX Switching Node
-1.5
1
μA
mA
Current Sense
Zero Cross Detector Threshold
Thermal Protection
EN Input
EN Input High Threshhold
VIHen
1.2
EN Input Low Threshhold
VILen
EN Input High Current
IIHen
VEN = VIN
EN Input Low Current
IILen
VEN = 0V
V
0.4
-1
V
μA
1
μA
SC21150
Electrical Characteristics (continued)
Parameter
Symbol
Conditions
Min
Typ
Max
Units
Forced PWM Input(1)
FPWM Input High Threshhold
VIHfpwm
1.2
FPWM Input Low Threshhold
VILfpwm
FPWM Input High Current
IIHfpwm
FPWM pin = VIN
FPWM Input Low Current
IILfpwm
FPWM pin = 0V
V
0.4
-1
V
μA
1
μA
Notes:
(1) The following options can be made available:
VOUT options : fixed or adjustable versions.
Fixed voltage options are as shown in the Ordering Information Table.
Additional fixed voltages can be specified, from 0.8V to 3.6V in 50mV increments.
Soft-Start options: Fixed internal 100μs, with options for 200μs/400μs/800μs.
Output Discharge options: Automatic Discharge and No Discharge.
Frequency: The default operating frequency is 4MHz with options of 2.2MHz, 3MHz, or 6MHz.
SC21150
Typical Characteristics
Efficiency vs. Load - 5VIN
VIN = 5.0V, VOUT as shown, Load = 0 to 1.2A
100
95
95
90
90
85
85
Efficiency (%)
Efficiency (%)
100
Efficiency vs. Load - 4.2VIN
80
75
70
65
80
75
70
65
1.0V PSAVE
1.0V FPWM
1.5V FPWM
60
1.5V PSAVE
1.5V FPWM
2.2V FPWM
55
2.2V PSAVE
2.2V FPWM
3.3V PSAVE
3.3V FPWM
1.0V PSAVE
1.0V FPWM
60
1.5V PSAVE
55
2.2V PSAVE
3.3V PSAVE
3.3V FPWM
50
0.01
VIN = 4.2V, VOUT as shown, Load = 0 to 1.2A
0.10
Load (A)
50
0.01
1.00
100
95
95
90
90
85
85
Efficiency (%)
Efficiency (%)
VIN = 3.3V, VOUT as shown, Load = 0 to 1.2A
80
75
70
65
60
55
1.0V PSAVE
1.0V FPWM
1.5V PSAVE
1.5V FPWM
2.2V PSAVE
50
0.01
VIN = 2.3V, VOUT as shown, Load = 0 to 1.2A
80
75
70
65
60
55
2.2V FPWM
0.10
Load (A)
50
0.01
1.00
VIN as shown, VOUT = 1.0V, Load = 0 to 1.2A
95
2.3VIN PSAVE
2.3VIN FPWM
3.3VIN PSAVE
3.3VIN FPWM
4.2VIN PSAVE
4.2VIN PFWM
5.0VIN PSAVE
5.0VIN FPWM
100
1.5V FPWM
0.10
Load (A)
1.00
VIN as shown, VOUT = 1.8V, Load = 0 to 1.2A
90
85
80
75
70
65
85
80
75
70
60
55
55
50
0.01
50
0.01
1.00
3.3VIN PSAVE
65
60
0.10
Load (A)
1V FPWM
1.5V PSAVE
95
Efficiency (%)
Efficiency (%)
90
1V PSAVE
Efficiency vs. Load - VOUT 1.8V
Efficiency vs. Load - VOUT 1.0V
100
1.00
Efficiency vs. Load - 2.3VIN
Efficiency vs. Load - 3.3VIN
100
0.10
Load (A)
3.3VIN FPWM
5VIN PSAVE
5VIN FPWM
0.10
Load (A)
1.00
SC21150
Typical Characteristics
Frequency vs load - 5VIN, FPWM operation
VIN = 5.0V, VOUT as shown, Load = 0A to 1.2A, FPWM = GND
4.4
4.3
4.3
4.2
4.2
Frequency (MHz)
Frequency (MHz)
4.4
Frequency vs load - 3.3VIN, FPWM operation
4.1
4.0
3.9
3.8
3.7
3.6
0.0
0.2
1.0V FPWM
1.5V FPWM
2.2 FPWM
3.3V FPWM
0.4
0.6
Load (A)
0.8
1.0
VIN = 3.3V, VOUT as shown, Load = 0A to 1.2A, FPWM = GND
4.1
4.0
3.9
3.8
3.7
3.6
1.2
0.0
VIN = 2.3V, VOUT as shown, Load = 0A to 1.2A, FPWM = GND
32
4.3
0.6
Load (A)
4.1
4.0
3.9
3.8
3.7
1V FPWM
0.0
0.2
0.4
0.6
Load (A)
1.5V FPWM
0.8
1.0
1.2
24
22
20
0.8
1.2
1.6
2.3Vin
3.3Vin
4.2Vin
5.0Vin
2.0
2.4
VOUT (V)
2.8
3.2
RDSON vs. Temperature
270
High-side
Low-side
VIN = 5.0V, ILX = 500mA
High-side
Low-side
250
230
RDSON (mŸ)
280
RDSON (mŸ)
1.0
26
18
1.2
VIN as shown, ILX = 500mA
320
240
200
210
190
170
150
130
160
110
120
80
0.8
VIN as shown, VOUT as shown, no load, Rbot = 100kΩ, FPWM = VIN
RDSON vs. Input Voltage
360
0.4
28
Quiescent Current (uA)
Frequency (MHz)
0.2
1.8V FPWM
30
4.2
3.6
1.5V FPWM
Quiescent Current vs Output Voltage
Frequency vs load - 2.3VIN, FPWM operation
4.4
1V FPWM
90
2.3
2.7
3.1
3.5
3.9
VIN (V)
4.3
4.7
5.1
5.5
70
-40
-25
-10
5
20 35 50 65 80
Junction Temperature (°C)
95
110 125
SC21150
Typical Characteristics (continued)
Power Save Operation — no load
Power Save Operation — 50mA load
VIN = 5V, VOUT = 3.3V, 0mA load, FPWM = GND
VIN = 5V, VOUT = 3.3V, 50mA load, FPWM = GND
VOUT (50mV/div)
VOUT (50mV/div)
LX (5V/div)
LX (5V/div)
Time (10ms/div)
Time (2µs/div)
FPWM Operation — no load
FPWM Operation — 1.2A load
VIN = 5V, VOUT = 3.3V, 0mA load, FPWM = VIN
VOUT (50mV/div)
VIN = 5V, VOUT = 3.3V, 1.2A load
VOUT (50mV/div)
LX (5V/div)
LX (5V/div)
Time (200ns/div)
Time (100µs/div)
Startup — VIN Ramp
Startup - EN Control
VIN = 5V, VOUT = 1.2V, 1.2A Load
VIN = EN = 2.3V ramp, VOUT = 1.2V, no load
VIN (2V/div)
EN (2V/div)
VOUT (500mV/div)
VOUT (500mV/div)
LX (5V/div)
LX (5V/div)
Time (200ns/div)
Time (100µs/div)
SC21150
Typical Characteristics (continued)
Load Transient - Power Save PFM to PWM
Load Transient - PWM to PWM
VIN = 3.3V, VOUT = 1.0V, Load 0A to 1.2A to 0A, FPWM = GND
VOUT (50mV/div)
VIN = 3.3V, VOUT = 1.0V, Load 0A to 1.2A to 0A, FPWM = GND
VOUT (50mV/div)
LOAD (1A/div)
LOAD (1A/div)
LX (5V/div)
LX (5V/div)
Time (100μs/div)
Time (100µs/div)
Load Transient - Power Save PFM to PWM
Load Transient - PWM to PWM
VIN = 5V, VOUT = 3.3V, Load 0A to 1.2A to 0A, FPWM = VIN
VIN = 5V, VOUT = 3.3V, Load 0A to 1.2A to 0A, FPWM = VIN
VOUT (100mV/div)
VOUT (100mV/div)
LOAD (1A/div)
LOAD (1A/div)
LX (5V/div)
LX (5V/div)
Time (100μs/div)
PWM Minimum Off Operation
Time (100µs/div)
Overcurrent Shutdown and Recovery
VIN = 5V, VOUT = 1.0V, Load 0A to 2.0A to 0A, FPWM = GND
VIN = 3.7V, VOUT = 3.3V, 800mA Load
VOUT (1V/div)
VOUT (50mV/div)
LOAD (2A/div)
LX (5V/div)
LX (5V/div)
Time (2µs/div)
Time (400µs/div)
10
SC21150
Detailed Application Circuit
Adjustable Output Voltage
2.3V-5.5V Supply
4.7µF
FPWM
EN
VIN
LX
FPWM
FB
SC21150
EN
0.47µH
1.2A
Output
10µF
GND
11
SC21150
Bump Descriptions - 0.75 x 1.11mm 6-bump WLCSP
Bump
Bump Name Bump Description
A1
GND
Ground connection.
A2
VIN
Input Supply Voltage for the device and sense point for the input Under Voltage Lock Out.
B1
LX
Switching node connection to inductor.
B2
FPWM
Forced PWM input A logic low enables the automatic Power Save feature. A logic high disables the Power
Save feature to ensure Forced PWM operation.
C1
FB
Feedback input (Output Voltage sense). To adjust the output voltage, connect to the midpoint of a resistor
divider between the output voltage and GND.
C2
EN
Enable input. Connect to logic high or VIN to enable the device. Connect to logic low or GND to disable the
device.
12
SC21150
Block Diagram
F ixe d /
A d ju sta b le
V o u t S e le ct
EN
E rro r A m p
FPW M
D e vice E n a b le
and UVLO
B1
LX
A1
GND
IC O M P
PW M Com p
P W M /P o w e r S a ve
C o n tro lle r
C1
C2
V IN
PMOS
Ref
FB
A2
G a te
D rive
IC O M P
Ram p
G en
NMOS
B2
13
SC21150
Applications Information
Synchronous Buck Converter
The SC21150 is a synchronous buck regulator that employs
an adaptive on-time architecture to provide fast transient
response and very small circuit area. The SC21150 operates over an input voltage range of 2.3 to 5.5V.
Operating Modes
The SC21150 operates in one of four different modes
depending on the status of VIN, VOUT, and load.
PWM Adaptive On-time operation (AOT)
PWM Minimum Off-time operation (Min Off )
PFM (Pulse Frequency Modulation for Power Saving)
Drop-Out operation (LDO mode)
PWM AOT Mode Operation
During PWM AOT operation the controller uses adaptive
on-time control. The FB ripple signal is routed to a gain
stage and then to the internal comparator and reference
which trigger the high-side pulses. The reference includes
a compensation ramp which emulates the inductor
current to provide stable switching.
AOT operation is used when the low-side pulse-width (offtime) is greater than the minimum 60nsec.
A switching cycle in AOT mode is as follows:
•
On-time: the cycle starts with the high-side
mosfet turn-on. The pulse width is set by the
following formula where fsw is 4MHz:
7 21
•
9 287
9 ,10$; u I 6:
Off-time: after the high-side on-time is completed, the low-side mosfet turns on to begin
the off-time. The off-time pulse width is set by
the internal compensation ramp and under
static conditions results in typically 4MHz switching frequency.
Note that the SC21150 enters AOT operation if VIN is less
than VOUT/0.88. Also note that connecting the FPWM to
a logic high will disable the Power Save feature and lead
to constant switching even under light load conditions.
PWM Min Off Operation
The device will enter Minimum Off-time operation (Min
Off ) when VIN, VOUT, and load conditions force the offtime (time between high-side pulses) to the minimum
value, typically 60nsec. This indicates that the controller
has reached maximum duty cycle for AOT operation and
longer duty cycles are needed.
In Min Off operation the SC21150 uses constant off-time
control. As in AOT operation, the FB ripple signal is routed
to a gain stage and then to the internal AOT comparator
and reference. In Min Off mode, the FB ripple triggers
the low-side turn-on. Min Off switching cycle operation
is as follows:
•
•
Off-time: The low-side mosfet is on for a fixed
Minimum Off time of 60nsec. This draws current
from the output capacitor through the inductor
via the LX pin and causes the output to fall.
On-time: after the Min Off time of 60nsec has
elapsed, the high-side mosfet turns on. This
helps recharge the output capacitor and bring
the output voltage up. The on-time pulse width
is determined by the internal compensation
ramp.
Drop-out Operation
When operating in Min Off mode, the off-time is constant
and the high-side on-time varies in order to regulate the
output. For cases where VIN is near VOUT, the high-side
will remain on continually with 100% duty cycle. The
output voltage will then be limited by the input voltage,
high-side RDSON and inductor DCR as shown in the following equation:
9287
9,1 ,/2$' u 5'621 '&5
Note that RDSON is a function of input voltage and temperature. Inductor DC resistance also increases with
temperature.
14
SC21150
Applications Information (continued)
Power Save (PFM) Operation
Pre-bias Start-up
PFM operation is enabled when the FPWM input is a logic
low. Under this condition, the IC automatically reduces
switching frequency under light load conditions to conserve power. In PFM operation, the FB ripple signal is
routed to a gain stage and compared to an internal reference. A switching cycle is as follows.
During start-up, the low-side mosfet turns off if the inductor current falls negative (into the LX pin) on any cycle.
This prevents discharge of the output capacitor during
the soft-start cycle. Note that if the output is loaded
during a Pre-Bias start-up, the output voltage may fall
until the internal Soft-start ramp rises above the voltage
seen at the FB pin.
•
•
•
On-time: The high-side mosfet turns on, as triggered by the FB signal falling to the internal reference. The high-side stays on for a
predetermined time based on VIN and VOUT,
then turns off.
Off-time: the low-side mosfet turns on. Inductor
current is monitored via the low-side switch.
When the current falls to zero, the low-side
mosfet turns off.
Dead-time: both mosfets are off. If the FB signal
is higher than the internal reference, both
mosfets remain off. During the dead-time the
load current is supplied by the output capacitor,
causing the output and the FB signal to fall.
When the FB signal falls to the 800mV threshold,
the next high-side pulse begins.
As load current increases, the dead-time between pulses
reduces. On any cycle, if the minimum off-time (60nsec)
has elapsed and the FB signal is calling for another highside on-time, the controller exits PFM and enters PWM
operation.
Once the controller is in PWM operation, the inductor
current must go below zero (go negative) for 16 switching cycles before the controller will return to PFM
operation.
Soft start
The SC21150 contains an internal soft start to reduce
inrush current during start-up. During start-up, the FB
signal is compared to an internal ramp, providing a
gradual ramp on VOUT. The timing to move VOUT from
0V to 95% of final value is typically 100usec. Optional soft
start times of 200usec, 400usec, and 800usec can be
provided.
VIN Under-Voltage Lockout
The SC21150 includes an under-voltage lockout (UVLO)
to inhibit switching until the input voltage exceeds 2.16V.
The VIN UVLO threshold has 85mV hysteresis to prevent
chatter during start-up.
EN Input
The EN input is a logic level input. When EN is set to logic
high, the SC21150 goes through an internal reset to
prepare for operation. The soft-start ramp and mosfet
switching begin typically 50μsec after EN is driven high.
When EN is low (grounded), the power mosfets are off
and the SC21150 is its lowest power state. The automatic
discharge mosfet connected to LX is on to discharge the
output before the next start-up cycle.
FPWM Input
The FPWM input is a logic level input that enables or disables the Power Save feature. Connect the FPWM input
to a logic low or GND to enable Power Save operation. To
disable Power Save operation and provide continuous
switching at all loads, connect the FPWM input to a logic
high or VIN.
Automatic Discharge
When the EN pin is pulled low (grounded), the power
mosfets are tri-stated and the LX pin is connected to GND
through an internal mosfet to discharge the output
capacitors. Typical mosfet RDSON is 40 ohms at 5V and
25°C. Note that RDSON is a function of both VIN and
temperature.
The automatic discharge feature can optionally be disabled from the device.
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SC21150
Applications Information (continued)
Over-current Protection
The SC21150 provides overload protection through pulse
by pulse current limiting. During the high-side on-time,
the high-side switches off if the inductor current exceeds
2.2A typically. The low-side turns on briefly, followed by
the next high-side on-time. Switching continues while
the output overload exists. When the overload is removed,
the SC21150 will resume normal operation. If the overload causes high junction temperature, the SC21150 will
go into Over-temperature protection.
Over-temperature Protection
The SC21150 will shut down if the junction temperature
exceeds typically 160 °C. The device will automatically
restart after the junction temperature has dropped typically 10 °C.
The FB regulation setpoint is 800mV. The output voltage
can be calculated as shown.
9287
§ 5WRS ·
u ¨
¸
© 5ERW ¹
The FB resistor values can be calculated as shown. It is
recommended to use 100kΩ for Rbot to minimize power
loss in the FB network.
5WRS
9287 9 u 5ERW
9
The optimum value for Ctop is 22pF.
Component Selection
The SC21150 is optimized for use with components as
shown in the Detailed Applications Circuit, page 11.
Inductor: the inductor should be 0.47uH and capable of
supporting a minimum current of 1.2A.
Input capacitor: ceramic capacitor, minimum 4.7uF, X5R
or X7R or better dielectric.
Output capacitor: ceramic capacitor, minimum 10uF, X5R
or X7R or better dielectric.
Note when operating in Min Off mode, higher output
capacitance may needed to reduce output ripple when
VIN approaches VOUT.
The FB components provide output voltage sensing and
feedback compensation to regulate the output. The
output voltage is programmed using two resistor along
with a compensation capacitor.
VOUT
T o F B p in
R to p
C to p
T o F B p in
R bot
16
SC21150
The input capacitor must be located as close as possible to
the IC and directly connected to pins A2 (VIN) and A1
(GND).
The FB trace should be short and not routed near noise
signals. Do not route the FB trace under the inductor; the
high impedance of the FB circuit can pick up noise from
the inductor’s magnetic field.
FPWM
The LX trace from pin B1 to the inductor should be as
short as possible, and wide to reduce IR loss and improve
heat dissipation.
The output capacitor should be close to the inductor. The
feedback components (Rtop, Ctop, Rbot, for adjustable
VOUT) should be located as close as possible to the FB pin.
For the ground connection to Rbot, use a via to a ground
plane and place another via near the A1 (GND) pin of the
IC.
VIN
GND
FB
SC21150
Rtop
LX
Rbot
CIN
Ctop
An optimum layout for the SC21150 is shown below.
When doing the PCB layout the following guidelines
should be used:
EN
PCB Layout Guidelines
L1
COUT
VOUT
SC21150 PCB Layout
17
SC21150
Outline Drawing — 0.75 x 1.11mm 6-Bump WLCSP
18
SC21150
Land Pattern — 0.75x1.11 6-Bump WLCSP
19
SC21150
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Contact Information
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Power Management Products Division
200 Flynn Road, Camarillo, CA 93012
Phone: (805) 498-2111 Fax: (805) 498-3804
www.semtech.com
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