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POWER MANAGEMENT Description
The SC615A 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. The SC615A has two modes of operation: Flash mode and Spotlight mode. In Flash mode, the SC615A is capable of delivering 500mA of regulated current for a duration of 500ms or up to 700mA for a reduced duration. In Spotlight mode the SC615A outputs 40% of the Flash mode current and can remain enabled continuously. An external resistor is connected in series with the LED to set the current. In Flash mode, this resistor can dissipate up to 175mW, reducing the power dissipation requirement of the SC615A. The flash input (FLASH) overrides the control input (CTRL) to make sure the flash function is activated when called for. The thermally efficient MLPD-10 package and ceramic bypass and bucket capacitors make the SC615A a high output current driver that requires minimal PCB area.
SC615A Charge Pump Flash LED Driver
Features
Two Selectable Modes - Flash and Spotlight Up to 700mA Output - Flash Mode Up to 280mA Output - Spotlight Mode 500mA Over Temperature Range and Voltage Range - Flash Mode Spotlight mode set to 40% of Flash Current 3.0V to 5.25V Input Range External Flash Control Pin for Synchronization to a Camera Module or Graphics Controller Short Circuit, Over-Voltage, and Over-Temperature Protection Soft-Start Functionality Two Control Inputs for Maximum Versatility Shutdown Current < 2A Micro Lead Package MLPD-10, 3mm x 3mm
Applications
Mobile Camera Phones Digital Cameras PDAs with Built-in Cameras
Typical Application Circuit
1
SC615A
VIN C1+ C1C2+ C2VOUT GND ISET CTRL FLASH
9 3 6 7 5
3.0V to 5.25V
10F 1F
8 4 10
1F
white LED
1F
2
0.5
FLASH CTRL
March 5, 2008 1
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SC615A
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 Supply Voltage Output Voltage Pin Voltage - FLASH, CTRL, ISET, C1-, C2Pin Voltage - C1+, C2+ VOUT Short Circuit Duration Thermal Resistance, Junction to Ambient (JESD51 Standard Method)(1) Operating Ambient Temperature Range Junction Temperature Range Storage Temperature Range IR Reflow Temperature ESD Protection Level(2)
Symbol VIN VOUT
Maximum -0.3 to 6.5 -0.3 to 6.5 -0.3 to VIN + 0.3 -0.3 to VOUT + 0.3
Units V V V V
SC JA TA TJC TSTG TPKG VESD
Indefinite 49 -40 to +85 -40 to +150 -65 to +150 260 2 C/W C C C C 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 = 25C for TYP, -40C to +60C for MIN and MAX; CBUCKET = COUT = 1.0F (ESR < 0.1); CIN = 10.0F; VIN = 3.0V to 5.25V; VOUT = 2.8V to 4.25V; RISET = 0.5 (0.1%).
Parameter
Symbol
Conditions FLASH high, RISET = 0.357W 3.7V < VIN < 4.2V, VOUT = 3.7V (1)
Min
Typ 700
Max
Units mA
IOUT Output Current
FLASH high, RISET = 0.5W 3.3V < VIN < 4.2V 2.8V < VOUT < 4.25V FLASH low, CTRL high, RISET = 0.357W 3.7V < VIN < 4.2V, VOUT = 3.4V (1) FLASH low, CTRL high, RISET = 0.5W 2.8V < VOUT < 4.5V 3.0V < VIN < 4.5V
460
500 280
540 mA
170
200
230
ISET Reference Voltage ISET Reference Voltage
VISET VISET
FLASH high, RISET = 0.5W 3.3V < VIN < 4.2V 2.8V < VOUT < 4.25V FLASH low, CTRL high, RISET = 0.5 2.8V < VOUT < 4.5V, 3.0V < VIN < 4.5V
230 85
250 100
270 115
mV mV
(c) 2008 Semtech Corp. 2
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SC615A
POWER MANAGEMENT Electrical Characteristics (Cont.)
Parameter Symbol Conditions FLASH high Quiescent Current IQ FLASH low, CTRL high FLASH low, CTRL low Flash Mode Pulse Duration(2) Flash Mode Start-Up Time(2) Spotlight Mode Start-Up Time(2) Oscillator Frequency Oscillator Frequency Accuracy Short-Circuit Output Current Limit tFLASH tF-ST tS-ST fOSC fOSC ISC ILIMIT VOUT = 0V 3.3V < VIN < 4.2V VIN = 3.7V, VOUT = 3.7V, TA = 25C Over-Temperature Protection(2) Logic Input High Threshold Logic Input Low Threshold Logic Input High Current Logic Input Low Current ISET Ripple Voltage(2) TOT Hysteresis VIH VIL IIH IIL VPP FLASH, CTRL FLASH, CTRL FLASH CTRL FLASH, CTRL Spotlight mode - IOUT = 200mA FLASH mode - IOUT = 500mA 1 2 20 40 0.1 25 mV 100 1.38 150 10 1.5 0.4 35 70 2 1.53 C C V V A A A 3.3V < VIN < 4.2V IOUT = 500mA, VOUT > 2.8V t = 0 when FLASH goes high to IOUT = 90% of final value t = 0 when CTRL goes high to IOUT = 90% of final value Device Enabled -15 250 15 465 2.1 A Min Typ 3.4 2.0 0.1 Max 5 4.5 2 500 1 1 Units mA mA A ms ms ms kHz % mA
Input Current Limit
Notes: (1) VOUT required by the typical LED at this current. (2) Guaranteed by design - not tested in production.
(c) 2008 Semtech Corp. 3
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SC615A
POWER MANAGEMENT Pin Configuration Ordering Information
DEVICE
VIN C2GND C1FLASH
1 2 3 4 5 T 10
PACKAGE MLPD-10 3x3 (2) Evaluation Board
C2+ VOUT C1+ CTRL ISET
SC615AMLTRT (1) SC615AEVB
TOP VIEW
9 8 7 6
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 1 2 3 4 5 6 7 8 9 10 T Pin Name VIN C2GND C1FLASH ISET CTRL C1+ VOUT C2+ Thermal Pad Pin Function Input voltage. Negative terminal of bucket capacitor 2. Ground - connect to ground plane using multiple vias. Negative terminal of bucket capacitor 1. Flash mode enable pin - puts the device in active Flash mode when high and also overrides CTRL. Current-setting reference pin - connect to the LED cathode and the current setting resistor. Control input bit - used to enable and set the output current in Spotlight mode when high. 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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SC615A
POWER MANAGEMENT Block Diagram
VIN
LDO
C1+
10F VBAT
250 kHz C1C2+ CTRL Logic Control FLASH
1F
1F
CHARGE PUMP
C2VOUT
CTRL
Reference Voltage Generator 1F white LED
FLASH
GND
ISET
0.5
(c) 2008 Semtech Corp. 5
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SC615A
POWER MANAGEMENT Applications Information
General Operation Flash mode, IOUT = 250mV/RISET. The plot below shows The SC615A is a powerful 2X charge pump designed to drive maximum Flash mode current for extended duration times. a high-intensity white LED with a constant current (Spotlight 800 mode) or with a pulsed current of higher intensity (Flash 700 mode) used for camera flash. In Flash mode the SC615A output can drive 500mA at 4.25V into an LED for a minimum duration of 500ms under all temperature and input conditions. The FLASH pin is used to trigger this mode (active high). In spotlight mode the SC615A regulates the output current to 40% of the Flash mode current setting when the CTRL pin is pulled high and the FLASH pin is low. Note that Flash mode has priority over Spotlight mode, i.e., the FLASH pin triggers Flash mode regardless of the state of the CTRL pin.
Flash Current [mA]
600 500 400 300 200 100 0 0 100 200 300 400 500 600 700 800 900 1000
Flash Duration [ms]
Output current is regulated by attaching the ISET pin to the cathode(s) of the LED package and a low resistance sense resistor (typically 0.5). The ISET pin monitors the voltage at the cathode and signals the charge pump to increase or decrease the output current until the ISET voltage reaches the programmed setting. The resistor value is chosen to set the current through the LED based on this reference voltage. The resistor can be chosen to set either the flash mode current or spotlight mode current, but it should not In spotlight mode, IOUT = 100mV/RISET. be less than 0.35 due to output current limitations of Protection Circuitry the device. The SC615A also provides protection circuitry that prevents the device from operating in an unspecified state. These Flash Mode Flash mode is enabled whenever the FLASH pin is pulled funtions include Input Over-Voltage Protection (IOVP), Outhigh and remains active until the FLASH pin is released. put Over-Voltage Protection (OVP), Over-Temperature (OT) This mode has higher priority than Spotlight mode, so the Protection, Over-Current Protection (OCP), and Short-Circuit state of the CTRL pin is overridden whenever the FLASH Current Protection (SCCP). pin is activated. While in Flash mode the reference voltage on the ISET pin is set to 250mV. The duration of the pulse Input Over-Voltage Protection is limited by the amount of power that can be dissipated Input over-voltage protection is included to prevent operain the SC615A before it exceeds the maximum operating tion at high input voltages that could damage the device. temperature. Note that if an output current less than the The IOVP circuit senses the input voltage and determines rated 500mA is desired, the duration of the pulse can when the supply exceeds 6V. Hysteresis is included in this circuit to avoid chattering between states. When the increase proportionally. voltage rises above this threshold, the device is disabled Extending Flash mode beyond the 500ms pulse limit could until the input voltage drops to a level within the specified adversely affect the long term reliability of the SC615A. range. Flash duration must be derated at higher currents. For example, 700mA derates to a maximum of 350ms. In
Spotlight Mode Spotlight mode is enabled by setting the CTRL pin high and keeping the FLASH pin low. When in Spotlight mode, the SC615A can maintain a constant current indefinitely to drive an LED or bank of LEDs. The ISET reference voltage is set to 100mV so that the output current is maintained at 200mA when a 0.5 resistor is used. Spotlight current is always 40% of flash current for any given value of RISET.
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SC615A
POWER MANAGEMENT Applications Information (Cont.)
Output Over-Voltage Protection Output over-voltage protection is included to prevent the SC615A from generating an output voltage that could damage other devices connected to it such as load LEDs and bypass capacitors. When the output voltage exceeds 5.5V, the OVP circuit disables the charge pump until the voltage decreases to a level within the acceptable range. This circuit allows the device to drive LEDs with high forward voltages at a reduced level without exceeding the output voltage limits specified for the device. Note, however, that this effect is a consequence of the OVP circuit and is not its intended purpose. Over-Temperature Protection The over-temperature circuit helps prevent the device from overheating and experiencing a catastrophic failure. When the junction temperature exceeds 150C 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. Over-Current Protection When the SC615A is in 2X charge pump mode, the input current will be approximately double 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. 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 SC615A'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 0.5 resistor to set a flash mode current of 500mA and spotlight mode current of 200mA. A high precision resistor should be used to ensure the specified accuracy for LED current. 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 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 SC615A. 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. Capacitor Selection The SC615A 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. Thermal Resistance The SC615A 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 49C/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 SC615A 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 critical to maintain adequate ground plane around the device to maximize heat transfer and avoid over-temperature shutdown.
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SC615A
POWER MANAGEMENT Typical Characteristics
Flash Duration, RISET=500m, VOUT = 3.52V(start) to 3.38V (LED heated 500ms)
510
540
Flash Current at 500ms, RISET = 500m, VOUT = 3.38V
505
520
VIN = 4.2V
LED Current [mA]
Current [mA]
VIN = 3.3V
500
500
VIN = 3.7V
495
480
490 0 100 200 300 400 500
460 3.30
3.45
3.60
3.75
3.90
4.05
4.20
Pulse Duration [ms]
VIN [V]
Flash Duration, RISET = 350m, VOUT = 3.62V (start) to 3.40V (LED heated 500ms)
755
Flash Current at 100ms, RISET = 500m, VOUT = 3.46V
540
VIN = 4.2V
735
520
Current [mA]
715
VIN = 3.7V
Current [mA]
400 500
500
VIN = 3.3V
695
480
675 0 100 200 300
460 3.30
3.45
3.60
3.75
3.90
4.05
4.20
Time [ms]
VIN [V]
200mA Spotlight Current, RISET = 500m, VOUT = 3.0V
212.5
Flash Current at 10ms, RISET = 500m, VOUT = 3.52V
540
207.5
520
Current [mA]
Current [mA]
202.5
500
197.5
480
192.5
187.5 3.00
3.45
3.90
4.35
4.80
5.25
460 3.30
3.45
3.60
3.75
3.90
4.05
4.20
VIN [V]
(c) 2008 Semtech Corp. 8
VIN [V]
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SC615A
POWER MANAGEMENT Typical Characteristics (Cont.)
Flash Current at 350ms, RISET = 350m, VOUT = 3.45V
755
Flash Mode VISET Ripple
735
Current [mA]
715
695
675 3.30
3.45
3.60
3.75
3.90
4.05
4.20
VIN [V]
Ch1 100mV/div Ch2 2V/div Ch3 2V/div 4us/div
755
Flash Current at 100ms, RISET = 350m, VOUT = 3.53V
Startup Flash Mode 500mA
735
Current [mA]
715
695
675 3.30
3.45
3.60
3.75
3.90
4.05
4.20
VIN [V]
Ch1 100mV/div Ch2 2V/div Ch3 2V/div 40us/div
755
Flash Current at 10ms, RISET = 350m, VOUT = 3.62V
735
Current [mA]
715
695
675 3.30
3.45
3.60
3.75
3.90
4.05
4.20
VIN [V]
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SC615A
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 SC615A VOUT pin. C4 is the input decoupling capacitor placed near the SC615A 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 Bottom Copper 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.
Top Copper
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SC615A
POWER MANAGEMENT Outline Drawing -MLPD-10 3x3
A
E
B
DIM
A A1 A2 b C D E e L N aaa bbb
DIMENSIONS INCHES MILLIMETERS MIN NOM MAX MIN NOM MAX
.031 .039 .000 .002 (.008) .007 .009 .011 .074 .079 .083 .042 .048 .052 .114 .118 .122 .020 BSC .012 .016 .020 10 .003 .004 1.00 0.80 0.05 0.00 (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
E PIN 1 INDICATOR (LASER MARK)
A aaa C C 1 LxN 2 A1 A2 C
SEATING PLANE
D
N e bxN bbb CAB
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
615A yyww xxxx
yyww = Datecode (Example = 0552) xxxx = Semtech Lot Number
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SC615A
POWER MANAGEMENT Land Pattern -MLPD-10 3x3
K
DIM
(C) H G C G H K P X Y Z
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
Z
Y 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
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