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Charge Pump Flash LED Driver with Safety Timer
POWER MANAGEMENT Description
The SC618 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 SC618 has two modes of operation: Flash mode and Spotlight mode. In Flash mode, the SC618 is capable of delivering 500mA of regulated current for a duration of 500ms or up to 700mA for a reduced duration. A safety timer is also included to ensure the LED cannot be left on indefinitely and overheat. In Spotlight mode the SC618 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 SC618. The flash input (FLASH) overrides the control input (CTRL) to make sure the flash function is activated when called for. The SC618 is packaged in the ultra-thin MLPD-UT-10 package - a low-profile version of the thermally efficient MLPD-10 package - making ideal for use in applications Typical Application Circuit where component height is critical.
SC618
Features
Ultra-thin Package MLPD-UT-10 - only 0.6mm high! (3mm x 3mm x 0.6mm) Two selectable modes - Flash and Spotlight Up to 700mA output - Flash Mode 500mA max output - Flash Mode (over rated voltage, temperature, and load conditions) 1 second safety timer shut-off - Flash Mode Spotlight Mode set to 40% of flash current Up to 280mA output - Spotlight Mode 1x mode in Spotlight Mode under most conditions for best efficiency (2x mode only when needed) 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 Separate Flash and Spotlight control inputs for maximum versatility
Applications
Mobile Camera Phones Digital Cameras PDAs with Built-in Cameras
Typical Application Circuit
1
SC618
VIN C1+ C1C2+ C2VOUT GND ISET CTRL FLASH
9
VBAT
10F 1F
white LED
3 6 7 5
8 4 10
1F
1F
2
RSET
FLASH CTRL
January 20, 2006 1
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SC618
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 Input Supply Voltage Output Voltage Pin Voltage - FLASH, CTRL, ISET, C1-, C2Pin Voltage - C1+, C2+ Thermal Resistance, Junction to Ambient (JESD51 Standard Method)(1) VOUT Short-Circuit Duration Operating Ambient Temperature Range Junction Temperature Range Storage Temperature Range Peak IR Flow Temperature ESD Protection Level(2)
Symbol VIN VOUT
Maximum -0.3 to +6.5 -0.3 to +6.5 -0.3 to VVIN + 0.3 -0.3 to VVOUT + 0.3
Units V V V V C/W s C C C C kV
JA
SC TA TJ TSTG TLEAD VESD
49 Indefinite -40 to +85 -40 to +150 -60 to +150 260 2
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 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; RSET = 0.5 (0.1%).
Parameter
Symbol
Conditions FLASH high, RSET = 0.357 3.7V < VIN < 4.2V, VOUT = 3.7V(1) FLASH high, RSET = 0.5 3.3V < VIN < 4.2V 2.8V < VOUT = 4.25V FLASH low, CTRL high, RSET = 0.357 3.7V < VIN < 4.2V, VOUT = 3.4V(1) FLASH low, CTRL high, RSET = 0.5 3.0V < VIN < 4.5V 2.8V < VOUT < 4.5V FLASH high, RSET = 0.5 3.3V < VIN < 4.2V 2.8V < VOUT < 4.25V FLASH low, CTRL high, RSET = 0.5 3.0V < VIN < 4.5V 2.8V < VOUT < 4.5V
Min
Typ 700
Max
Units
460
500 280
540 mA
Output Current
IOUT
170
200
230
230
250
270 mV
ISET Reference Voltage
VISET
85
100
115
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SC618
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) Flash Mode Safety Timer(2) Spotlight Mode Start-Up Time(2,3) Oscillator Frequency Oscillator Frequency Accuracy Short-Circuit Output Current Limit Input Current Limit tFLASH tF-SU tSAFE tS-SU fOSC fOSC ISC ILIMIT TOT TOT -HYS Logic Input High Threshold Logic Input Low Threshold Logic Input High Current Logic Input Low Current VIH VIL IIH IIL Hysteresis FLASH, CTRL FLASH, CTRL FLASH CTRL FLASH, CTRL 1 2 20 40 0.1 Steady State with VOUT shorted to GND 2x mode, 3.3V < VIN < 4.2V 2x mode, VIN = 3.7V, VOUT = 3.7V, TA = 25C 1.0 1.38 150 C 10 1.5 0.4 35 A 70 2.0 A V V 1.53 3.3V < VIN < 4.2V IOUT = 500mA, VOUT > 2.8V t = 0 when FLASH goes high to IOUT = 90% of final value FLASH high VIN = 4.2V, VOUT = 3.2V; t = 0 when CTRL goes high to IOUT = 90% of final value Device enabled -15 250 15 600 2.1 A 0.90 Min Typ 3.4 2.0 0.1 Max 5.0 4.5 2.0 500 1 1.25 1 Units mA mA A ms ms s ms kHz % mA
Over-Temperature Protection(2)
Notes: 1) VOUT required by the typical LED at this current. 2) Guaranteed by design - not tested in production. 3) If conditions force 2x mode operation, this start-up time will increase by approximately 32ms due to the timer that is enabled to ensure 2x mode is needed.
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SC618
POWER MANAGEMENT
Pin Configuration
Ordering Information
DEVICE SC618ULTRT((1,2)
2)(1)
PACKAGE(
1)
MLPD-UT-10 3x3 Evaluation Board
VIN C2GND C1FLASH
1 2 3 4 5 T
10
C2+ VOUT C1+ CTRL ISET
TOP VIEW
SC618EVB
9 8 7 6
Notes: 1) Available in tape and reel only. A reel contains 3,000 devices. 2) Lead-free package only. Device is WEEE and RoHS compliant.
MLP10: 3X3 10 LEAD
Marking Information
Top Mark
618 yyww xxxx
yyww = Datecode (Example = 0552) xxxx = Semtech Lot Number
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SC618
POWER MANAGEMENT
Block Diagram
VIN
1
LDO
8
C1+
250kHz
4
C1-
10 C2+ CTRL FLASH 7 5 Logic Control and Flash Mode Timer
CHARGE PUMP
2
C2-
Reference Voltage Generator
9
VOUT
3
GND
6
ISET
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 - connect to the LED anode. 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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(c) 2006 Semtech Corp.
SC618
POWER MANAGEMENT Pin Configuration Applications Information
General Operation The SC618 is a powerful dual-mode 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. The device operates in 2x (doubler) mode while operating in Flash mode, and in Spotlight mode it can operate in either 2x or 1x (LDO) mode depending on the load current, load voltage, and input voltage levels. In Flash mode the SC618 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 SC618 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. 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 be less than 0.35 due to output current limitations of the device. Flash Mode Flash mode is enabled whenever the FLASH pin is pulled high and remains active until the FLASH pin is released. This mode has higher priority than Spotlight mode, so the state of the CTRL pin is overridden whenever the FLASH pin is activated. While in Flash mode the reference voltage on the ISET pin is set to 250mV. The duration of the pulse is limited by the amount of power that can be dissipated in the SC618 before it exceeds the maximum operating temperature. Note that if an output current less than the rated 500mA is desired, the duration of the pulse can increase proportionally. Extending Flash mode beyond the 500ms pulse limit could adversely affect the long term reliability of the SC618. Flash duration must be derated at higher currents. For example, 700mA derates to a maximum of
(c) 2006 Semtech Corp. 6
The plot 350ms. In Flash mode, IOUT = 250mV/RISET. below shows maximum Flash mode current for extended duration times.
800 700
Flash Current [mA]
600 500 400 300 200 100 0
0
100
200
300
400
500
600
700
800
900
1000
Flash Duration [ms]
Maximum Flash Duration Flash Mode Safety Timer The SC618 provides a time-out protection function when in Flash mode. The output is disabled if the FLASH pin is held high for longer than 1 second to prevent extended exposure to high current by the LED. Once this time-out has occurred, the output will stay disabled until the FLASH pin has been pulled low and then re-enabled. Spotlight Mode Spotlight mode is enabled by setting the CTRL pin high and keeping the FLASH pin low. When in Spotlight mode, the SC618 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. In Spotlight mode, IOUT = 100mV/RISET. To maximize power efficiency, the SC618 has been designed to operate in 1x (LDO) mode when conditions do not require the charge pump to be active. When first enabled the SC618 attempts to regulate the voltage on the ISET pin in 1x mode. If the voltage on the ISET pin cannot be maintained and this condition persists for longer than 32ms, then the charge pump will change to 2x mode operation. In a typical application, the SC618 will operate in 1x mode until the supply voltage decreases sufficiently that the voltage on the ISET pin can no longer be maintained. After a 32ms delay (included to prevent false transitions) the charge pump will convert to 2x mode. After the charge pump switches from 1x mode to 2x mode, the
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SC618
POWER MANAGEMENT
Applications Information (Cont.)
device remains in 2x mode while the part is enabled. If the part is disabled and then enabled again in Spotlight mode, it will again begin operation in 1x mode and determine the appropriate mode of operation as described above. As the input voltage decreases and the device approaches drop out, the charge pump is then activated in 2x mode to maintain the output at the required current level. This mode then stays active regardless of the input voltage until the CTRL pin is forced low and Spotlight mode is reset. Protection Circuitry The SC618 also provides protection circuitry that prevents the device from operating in an unspecified state. These functions include Input Over-Voltage Protection (IOVP), Output Over-Voltage Protection (OVP), Over-Temperature Protection (OTP), Over-Current Protection (OCP), and Short-Circuit Current Protection (SCCP). Input Over-Voltage Protection Input over-voltage protection is included to prevent operation at high input voltages that could damage the device. The IOVP circuit senses the input voltage and determines when the supply exceeds 6V. Hysteresis is included in this circuit to avoid chattering between states. When the voltage rises above this threshold, the device is disabled until the input voltage drops to a level within the specified range. Output Over-Voltage Protection Output over-voltage protection is included to prevent the SC618 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
(c) 2006 Semtech Corp. 7
and OVP circuits, hysteresis is included to prevent toggling between modes. Over-Current Protection When the SC618 is in 2x 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. The same mechanism protects the device when in 1x mode, but the limit is set somewhat lower than for 2x mode due to this modes lower current requirements. 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 SC618's maximum current and select the resistor 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
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SC618
POWER MANAGEMENT
Applications Information (Cont.)
to the ground pin of the SC618. 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 SC618 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 SC618 package is thermally efficient when the circuit board layout connects the thermal pad through 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 OTP limit while operating the SC618 within the specified electrical conditions for IOUT and VISET. A poor layout may allow the junction temperature to reach the OTP limit while in Flash or Spotlight mode. It is critical to maintain adequate ground plane around the device to maximize heat transfer and avoid over-temperature shutdown. 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 SC618 VOUT pin. C4 is the input decoupling capacitor placed near the SC618 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.
Top Copper
Bottom Copper
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SC618
POWER MANAGEMENT
Typical Characteristics
Flash Current at 10ms, RISET = 500m, VOUT = 3.75V
515 510
Flash Current at 100ms, RISET = 500m, VOUT = 3.68V
515 510
LED Current [mA]
505 500 495 490 485 3.3 3.45 3.6 3.75 3.9 4.05 4.2
LED Current [mA]
505 500 495 490 485 3.3 3.45 3.6 3.75 3.9 4.05 4.2
VIN [V]
VIN [V]
Flash Current at 500ms, RISET = 500m, VOUT = 3.58V
515 510
Spotlight Current, RISET = 500m, VOUT = 3.16V
220
212
LED Current [mA]
505 500 495 490 485 3.3 3.45 3.6 3.75 3.9 4.05 4.2
LED Current [mA]
transition to 2x Mode
204
1x Mode
196
188
180 5.25
4.8
4.35
3.9
3.45
3
VIN [V]
VIN [V]
Flash Duration, RISET = 350m, VOUT = 3.86V (start), 3.61V (LED Heated 500ms)
755
Flash Duration, RISET = 500m, VOUT = 3.75V (start), 3.58V (LED Heated 500ms)
515
LED Current [mA]
VIN=4.2V VIN=3.7V
LED Current [mA]
735
509 VIN=3.7V VIN=4.2V
503
715
497
VIN=3.3V
695
VIN=3.4V
491 VIN=3.3V
675 0 100 200 300 400 500
485 0 100 200 300 400 500
Pulse Duration [ms]
Pulse Duration [ms]
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SC618
POWER MANAGEMENT
Typical Characteristics (Cont.)
Flash Mode Ripple, RISET = 500m Start-Up Flash Mode, 500mA
Ch 1: Ch 2: Ch 3: time:
100mV/DIV 200mV/DIV 200mV/DIV 4s/DIV
Ch1: Ch2: Ch3: time:
100mV/DIV 2V/DIV 2V/DIV 40s/DIV
Safety Timer Shut-Off
Spotlight 1x Mode Ripple, RISET = 500m
Ch1: Ch2: Ch3: time:
100mV/DIV 2V/DIV 5V/DIV 200ms/DIV
Ch1: Ch2: Ch3: time:
50mV/DIV 50mV/DIV 50mV/DIV 4s/DIV
Spotlight 2x Mode Ripple, RISET = 500m
Short Circuit Current Limiting, VIN = 5.25V, VOUT = 0V
Ch1: Ch2: Ch3: time:
50 mV/DIV 100 mV/DIV 100 mV/DIV 4s/DIV
Ch1: 2V/DIV Ch4: 100mA/DIV time: 400ms/DIV
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SC618
POWER MANAGEMENT
Outline Drawing - MLPD-UT-10
A E B
DIMENSIONS INCHES MILLIMETERS DIM MIN NOM MAX MIN NOM MAX
A A1 A2 b C D E e L N aaa bbb .024 .002 (.006) .007 .009 .011 .074 .079 .083 .042 .048 .052 .114 .118 .122 .020 BSC .012 .016 .020 10 .003 .004 .018 .000 0.60 0.05 (0.1524) 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 0.45 0.00
E PIN 1 INDICATOR (LASER MARK)
aaa C C 1 LxN 2
A SEATING PLANE A1 A2 C
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.
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SC618
POWER MANAGEMENT
Land Pattern - MLPD-UT-10
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.
2. 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.
Contact Information
Semtech Corporation Power Management Products Division 200 Flynn Road, Camarillo, CA 93012 Phone: (805) 498-2111 FAX (805)498-3804
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