SEMTECH SC615

SC615
Charge Pump
Flash LED Driver
POWER MANAGEMENT
Description
Features
The SC615 is a high-current charge pump designed specifically for use with white LEDs used in camera flash
applications. Only two small bucket capacitors are required to develop the output drive, providing a low EMI
solution compared to inductive boost regulators.
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The SC615 has two modes of operation: Flash mode
and Spotlight mode. The SC615 is capable of delivering
500mA of peak current for a duration of 500ms in Flash
mode. In Spotlight mode the SC615 outputs 100mA
and can remain enabled continuously.
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A minimum 0.5Ω sense resistor is used to set the current through the LED in both modes. This resistor dissipates up to 0.125W, reducing the power dissipation requirement of the SC615. The flash input (FLASH) overrides the control input (CTRL) to make sure the flash function is activated when called for.
500mA Output Current - Flash Mode
3.0V to 5.25V Input Range
Two Selectable Modes - Flash and Spotlight
External Flash Control Pin for Synchronization to a
Camera Module or Graphics Controller
Spotlight Mode Current Setting - 100mA
Short Circuit, Over-Voltage, and Over-Temperature
Protection
Soft-Start Functionality
Two Control Inputs for Maximum Versatility
Shutdown Current < 2µA
Micro Lead-frame Package MLPD-10, 3mm x 3mm
Applications
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The thermally efficient MLPD-10 package and ceramic
bypass and bucket capacitors help make the SC615 a
high output current driver that requires a minimal amount
of PCB area.
Mobile Camera Phones
Digital Cameras
PDAs with Built-in Cameras
Multi-LED Backlit LCDs
Application Circuit
1
3.0V to 5.25V
10µF
8
1µF
4
10
1µF
2
SC615
VIN
VOUT
C1+
GND
C1-
ISET
C2+
CTRL
C2-
FLASH
9
white LED
3
1µF
6
7
5
0.5Ω
FLASH
CTRL
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SC615
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 implied.
Parameter
Symbol
Maximum
Units
Supply Voltage
VIN
-0.3 to 6.5
V
Output Voltage
VOUT
-0.3 to 6.5
V
-0.3 to VIN + 0.3
V
-0.3 to VOUT + 0.3
V
Pin Voltage - FLASH, CTRL, ISET, C1-, C2Pin Voltage - C1+, C2+
VOUT Short Circuit Duration
SC
Indefinite
Thermal Resistance, Junction to Ambient
(JESD51 Standard Method)(1)
θJA
49
°C/W
Operating Ambient Temperature Range
TA
-40 to +85
°C
Junction Temperature Range
TJC
-40 to +150
°C
Storage Temperature Range
TSTG
-65 to +150
°C
IR Reflow Temperature
TLEAD
260
°C
ESD Protection Level(2)
V ESD
2
kV
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 per JESD51 standards.
2) Tested according to JEDEC standard JESD22-A114-B
Electrical Characteristics
Unless otherwise specified: TA = 25°C for TYP, -40°C to +60°C for MIN and MAX;
CBUCKET = COUT = 1.0µF (ESR < 0.1Ω); CIN = 10.0µF; VIN = 3.0V to 5.25V; RISET = 0.5Ω (0.1%).
Parameter
Output Current
ISET Reference Voltage
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Symbol
IOUT
VISET
Conditions
Min
Typ
Max
FLASH high, RISET = 0.5Ω
3.3V < VIN < 4.2V
2.8V < VOUT < 4.25V
460
500
540
FLASH low, RISET = 0.5Ω
CTRL high, 2.8V < VOUT < 4.5V
3.0V < VIN < 4.5V
75
100
125
FLASH high, RISET = 0.5Ω
3.3V < VIN < 4.2V
2.8V < VOUT < 4.25V
230
250
270
FLASH low, CTRL high,
2.8V < VOUT < 4.5V
3.0V < VIN < 4.5V
37.5
2
Units
mA
mV
50
62.5
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SC615
POWER MANAGEMENT
Electrical Characteristics (Cont.)
Unless otherwise specified: TA = 25°C for TYP, -40°C to +60°C for MIN and MAX;
CBUCKET = COUT = 1.0µF (ESR < 0.1Ω); VIN = 3.0V to 5.25V; CIN = 10.0µF; RISET = 0.5Ω (0.1%).
Parameter
Symbol
Conditions
Typ
Max
Units
FLASH high
3.4
5
mA
FLASH low, CTRL high
2.0
4.5
mA
FLASH low, CTRL low
0.1
2
µA
Quiescent Current
IQ
Min
Flash Mode Pulse Duration(1)
tFLASH
3.3V < VIN < 4.2V
IOUT = 500mA, VOUT > 2.8V
500
ms
Flash Mode Start-Up Time(1)
tF-ST
t = 0 when FLASH goes high to
IOUT = 90% of final value
1
ms
Spotlight Mode Start-Up Time(1)
tS-ST
t = 0 when CTRL goes high to
IOUT = 90% of final value
1
ms
Oscillator Frequency
fOSC
Device Enabled
Oscillator Frequency Accuracy
∆fOSC
250
-15
Short-Circuit Output Current Limit
ISC
VOUT = 0V
Input Current Limit
ILIMIT
VIN = 3.7V, VOUT = 4.0V
1.0
kHz
15
%
465
mA
2.1
A
150
°C
Hysteresis
10
°C
1.5
V
TOT
Over-Temperature Protection
Logic Input High Threshold
VIH
FLASH, CTRL
Logic Input Low Threshold
VIL
FLASH, CTRL
Logic Input High Current
IIH
FLASH, CTRL
Logic Input Low Current
IIL
ISET Ripple Voltage(1)
V PP
0.4
V
20
35
µA
FLASH, CTRL
0.1
2
µA
Spotlight mode - IOUT = 100mA
25
FLASH mode - IOUT = 500mA
100
1
mV
Notes:
(1) Guaranteed by design - not tested in production.
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SC615
POWER MANAGEMENT
Pin Configuration
Ordering Information
DEVICE
SC615IMLTRT (1)
VIN
1
C2-
2
GND
10
C2+
9
VOUT
3
8
C1+
C1-
4
7
CTRL
FLASH
5
6
ISET
TOP VIEW
T
S C 615E V B
PACKAGE
MLPD-10 3x3
(2)
Evaluation Board
Notes:
(1) Available in tape and reel only. A reel contains 3000 devices.
(2) Available in lead-free package only. This product is fully WEEE
and RoHS compliant.
MLP10: 3X3 10 LEAD
Pin Descriptions
Pin
Pin Name
Pin Function
1
VIN
Input voltage.
2
C 2-
Negative terminal of bucket capacitor 2.
3
GND
Ground - connect to ground plane using multiple vias.
4
C 1-
Negative terminal of bucket capacitor 1.
5
F LA S H
6
ISET
Current-setting reference pin - connect to the LED cathode and the current setting resistor.
7
CTRL
Control input bit - used to enable and set the output current in Spotlight mode when high.
8
C 1+
9
VOUT
10
C 2+
T
Thermal
P ad
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Flash mode enable pin - puts the device in active Flash mode when high and also overrides
CTRL.
Positive terminal of bucket capacitor 1.
Output pin.
Positive terminal of bucket capacitor 2 .
Pad for heat sinking purposes -not connected internally. Connect to ground plane using multiple
vias.
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SC615
POWER MANAGEMENT
Applications Information
General Operation
The SC615 is a powerful 2X charge pump designed to
drive a high-intensity white LED with a constant current
(Spotlight mode) or with a pulsed current of higher intensity (Flash mode) used for camera flash.
Spotlight Mode
Spotlight mode is enabled by setting the CTRL pin high
and keeping the FLASH pin low. When in Spotlight mode,
the SC615 can maintain a constant current indefinitely
to drive an LED or bank of LEDs. The ISET reference
voltage is set to 50mV so that the output current is mainIn Flash mode the SC615 output can drive 500mA at tained at 100mA when a 0.5Ω resistor is used.
4.25V into an LED for a minimum duration of 500ms.
The FLASH pin is used to trigger this mode (active high). Protection Circuitry
In spotlight mode the SC615 regulates the output cur- The SC615 also provides protection circuitry that prerent to 100mA when the CTRL pin is pulled high and the vents the device from operating in an unspecified state.
FLASH pin is low. Note that Flash mode has priority over These funtions include Input Over-Voltage Protection
Spotlight mode, i.e., the FLASH pin triggers Flash mode (IOVP), Output Over-Voltage Protection (OVP), Over-Temregardless of the state of the CTRL pin.
perature (OT) Protection, Over-Current Protection (OCP),
and Short-Circuit Current Protection (SCCP).
Output current is regulated by attaching the ISET pin to
the cathode(s) of the LED package and a low resistance Input Over-Voltage Protection
sense resistor (typically 0.5Ω). The ISET pin monitors Input over-voltage protection is included to prevent opthe voltage at the cathode and signals the charge pump eration at high input voltages that could damage the
to increase or decrease the output current until the ISET device. The IOVP circuit senses the input voltage and
voltage reaches the programmed setting. The resistor determines when the supply exceeds 6V. Hysteresis is
value is chosen to set the current through the LED based included in this circuit to avoid chattering between states.
on this reference voltage. The resistor can be chosen to When the voltage rises above this threshold, the device
set either the flash mode current or spotlight mode cur- is disabled until the input voltage drops to a level within
rent, but it should not be less than 0.5Ω due to output the specified range.
current limitations of the device.
Output Over-Voltage Protection
Flash Mode
Output over-voltage protection is included to prevent the
Flash mode is enabled whenever the FLASH pin is pulled SC615 from generating an output voltage that could damhigh and remains active until the FLASH pin is released. age other devices connected to it such as load LEDs and
This mode has higher priority than Spotlight mode, so bypass capacitors. When the output voltage exceeds
the state of the CTRL pin is overridden whenever the 5.5V, the OVP circuit disables the charge pump until the
FLASH pin is activated. While in flash mode the refer- voltage decreases to a level within the acceptable range.
ence voltage on the ISET pin is set to 250mV. The duration of the pulse is limited by the amount of power that This circuit allows the device to drive LEDs with high forcan be dissipated in the SC615 before it exceeds the ward voltages at a reduced level without exceeding the
maximum operating temperature. Note that if an output output voltage limits specified for the device. Note, howcurrent less than the rated 500mA is desired, the dura- ever, that this effect is a consequence of the OVP circuit
tion of the pulse can increase proportionally. However, and is not its intended purpose.
great care should be taken to insure the FLASH pin is
not held high for an extended amount of time so that Over-Temperature Protection
overheating does not occur. Extending flash mode be- The over-temperature circuit helps prevent the device
yond the 500ms pulse limit could adversely affect the from overheating and experiencing a catastrophic faillong term reliability of the SC615.
ure. When the junction temperature exceeds 150°C the
device is disabled. It remains disabled until the junction
temperature drops below this threshold. As with the UVLO
and OVP circuits, hysteresis is included to prevent toggling between modes.
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SC615
POWER MANAGEMENT
Applications Information (Cont.)
through the resistor and back to the ground pins. Resistance in this path adds to the total resistance and has
the effect of reducing the LED current by about 4% per
10mV of DC drop across the return copper trace in flash
mode. For this reason, it is crucial to have a low resistance return path. Place and ground the resistor as close
as possible to the ground pin of the SC615. The trace
from the ISET pin has virtually no current. The ISET trace
should make contact at the pad of the power sense resistor to minimize the effect of voltage drop between
the LED cathode and the resistor.
Over-Current Protection
When the SC615 is in 2X charge pump mode, the input
current will be approximately doubled the required output. When the steady-state load requires the maximum
current available in 2X mode, the OCP circuit prevents
the device from overheating due to excessive power dissipation.
Short-Circuit Current Protection
Short-circuit current protection is provided to limit the
current that can be sourced when the output is shorted
to ground. When a short circuit forces VOUT to drop below
2V, the SCCP detects the condition and limits the output
current.
Capacitor Selection
The SC615 is designed to use low-ESR ceramic capacitors for the input and output bypass capacitors as well
as the charge pump bucket capacitors. Ideal performance is achieved when C1 is exactly equal to C2. It is
recommended that X5R or X7R ceramic capacitors be
used for best performance.
Resistor Selection
The ISET resistor selection is critical in generating the
correct current. The value can be chosen to set the Spotlight mode current or the Flash mode current, but it must
be noted that the two current settings are dependent on
the same resistor. It is recommended that the resistor
be selected to match the desired LED current for Flash
mode. This allows the designer to set the SC615’s maximum current and select the package size necessary for
the power dissipation required in Flash mode. The typical application shown on page 1, uses a 0.5Ω resistor to
set a flash mode current of 500mA and spotlight mode
current of 100mA. A high precision resistor should be
used to ensure the specified accuracy for LED current.
Thermal Resistance
The SC615 package is thermally efficient when the circuit board layout connects the thermal pad though multiple vias to the ground plane. The thermal resistance is
rated at 49°C/W and this rating is dependent on the
connection between the thermal pad and the ground
plane. A layout that is done correctly should keep the
junction temperature below the OT limit while operating
the SC615 within the specified electrical conditions for
IOUT and VISET. A poor layout may allow the junction temperature to reach the OT limit while in Flash or Spotlight
mode. So, it is important to maintain adequate ground
plane around the device to maximize heat transfer to
the PCB.
To avoid malfunction of the charge pump, it is recommended that the resistance seen at the ISET pin remain
constant while the device is active (Flash or Spotlight
mode). Changing the resistance value or the load current while the device is active could cause instability that
would result in non-compliant behavior.
The load current return path is from the ISET sense point
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SC615
POWER MANAGEMENT
Block Diagram
VIN
10µF
C1+
LDO
1µF
250kHz
VBAT
C1C2+
CTRL
1µF
Logic Control
CHARGE
PUMP
FLASH
CTRL
C2VOUT
Reference
Voltage
Generator
white LED
1µF
FLASH
GND
ISET
0.5Ω
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SC615
POWER MANAGEMENT
Typical Characteristics
Flash Duration
Flash Current at 500ms
VOUT = 3.53V(start) to 3.40V(LED heated 500ms)
VOUT = 3.4V
540
520
520
VIN=4.2V
VIN=3.75V
VIN=3.3V
Current [mA]
LED Current [mA]
540
500
480
500
480
460
0
100
200
300
400
460
3.30
500
3.45
3.60
Pulse Duration [ms]
Flash Current at 100ms
3.90
4.05
4.20
Flash Current at 10ms
VOUT = 3.46V
VOUT = 3.53V
540
520
520
Current [mA]
Current [mA]
540
500
500
480
480
460
3.30
3.75
VIN [V]
3.45
3.60
3.75
3.90
4.05
460
3.30
4.20
VIN [V]
3.45
3.60
3.75
3.90
4.05
4.20
VIN [V]
100mA Spotlight Current
VOUT = 2.93V
130.0
Current [mA]
115.0
100.0
85.0
70.0
3.00
3.45
3.90
4.35
4.80
5.25
VIN [V]
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SC615
POWER MANAGEMENT
Typical Characteristics (Cont.)
Flash Mode VISET Ripple
Startup Flash Mode 500mA
Ch1 100mV/div
Ch2 2V/div
Ch3 2V/div
4us/div
Ch1 100mV/div
Ch2 2V/div
Ch3 2V/div
40us/div
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SC615
POWER MANAGEMENT
Layout Guidelines
The following layout is suggested for a two-layer design.
The capacitors C1 and C2 are the bucket capacitors and
each conducts the full load current of up to 500mA
pulsed for one half clock cycle. C3 is the output
decoupling capacitor placed near the SC615 VOUT pin.
C4 is the input decoupling capacitor placed near the
SC615 VIN pin. Multiple vias should be used whenever
it is necessary to change layers on nets connecting to
pins VIN, VOUT, GND, C1-, C1+, C2- and C2+. Resistor
R1 is routed with a very low resistance connection between R1 and GND pin 3. The sense trace between Pin
6 and R1 is routed around the ground vias, allowing the
shortest ground return path possible. The sense trace is
connected to R1 at the positive terminal pad for the most
accurate output possible.
The bottom copper layer is mostly a ground plane with
no obstructions between the ground vias. The smaller
rectangle to the left connects the input power to VIN pin
1 and input capacitor C4. The two traces at the lower
left are for logic inputs FLASH and CTRL. The trace to
the right is the ISET pin "sense" trace. The sense trace is
routed out of the path of the returning ground current.
Bottom Copper
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Top Copper
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SC615
POWER MANAGEMENT
Outline Drawing -MLPD-10 3x3
A
E
DIMENSIONS
INCHES
MILLIMETERS
DIM
MIN NOM MAX MIN NOM MAX
B
A
A1
A2
b
C
D
E
e
L
N
aaa
bbb
E
PIN 1
INDICATOR
(LASER MARK)
A
aaa C
A1
C
1
.039
.031
.000
.002
(.008)
.007 .009 .011
.074 .079 .083
.042 .048 .052
.114 .118 .122
.020 BSC
.012 .016 .020
10
.003
.004
0.80
1.00
0.00
0.05
(0.20)
0.18 0.23 0.30
1.87 2.02 2.12
1.06 1.21 1.31
2.90 3.00 3.10
0.50 BSC
0.30 0.40 0.50
10
0.08
0.10
SEATING
PLANE
C
A2
2
LxN
D
N
e
bxN
bbb
C A B
NOTES:
1. CONTROLLING DIMENSIONS ARE IN MILLIMETERS (ANGLES IN DEGREES).
2. COPLANARITY APPLIES TO THE EXPOSED PAD AS WELL AS TERMINALS.
Marking Diagram
Top Mark
615
yyww
xxxx
yyww = Datecode (Example = 0552)
xxxx = Semtech Lot Number
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SC615
POWER MANAGEMENT
Land Pattern - MLPD-10 pin
K
DIM
(C)
H
G
C
G
H
K
P
X
Y
Z
Z
Y
X
DIMENSIONS
INCHES
MILLIMETERS
(.112)
.075
.055
.087
.020
.012
.037
.150
(2.85)
1.90
1.40
2.20
0.50
0.30
0.95
3.80
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
Visit us at: www.semtech.com
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