SEMTECH SC618_08

SC618
Charge Pump Flash LED
Driver with Safety Timer
POWER MANAGEMENT
Features
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.
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Flash and spotlight — two selectable modes
Flash mode — up to 700mA output
Flash mode — 500mA max output (over rated voltage,
temperature, and load conditions)
Flash mode safety timer shut-off — 1 second
Spotlight mode set to 40% of flash current
Spotlight mode — up to 280mA output
Spotlight mode —1x mode (under most conditions)
for best efficiency
Input range — 3.0V to 5.25V
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
Ultra-thin package MLPD-UT-10 — 3mm x 3mm x
0.6mm
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 overrides the control
input to make sure the flash function is activated .
Applications
The SC618 ultra-thin package provides both a low profile
and high thermal efficiency.
„
Mobile camera phones
„ Digital cameras
„ PDAs with built-in cameras
Typical Application Circuit
SC618
VBAT
VIN
VOUT
C1+
GND
C1-
ISET
C2+
CTRL
C2-
FLASH
10μF
1μF
1μF
1μF
White LED
RSET
FLASH
CTRL
February 6, 2008
1
SC618
Pin Configuration
Ordering Information
10
C2+
9
VOUT
3
8
C1+
C1-
4
7
CTRL
FLASH
5
6
ISET
VIN
1
C2-
2
GND
TOP VIEW
T
Device
Package
SC618ULTRT(1)(2)
MLPD-UT-10 3×3
SC618EVB
Evaluation Board
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.
MLPD-UT-10; 3x3, 10 LEAD
θJA = 40°C/W
Marking Information
618
yyww
xxxx
yyww = Date code
xxxx = Semtech Lot Number
2
SC618
Absolute Maximum Ratings
Recommended Operating Conditions
VIN (V) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3 to +6.5
Ambient Temperature Range (°C) . . . . . . . . . . . . -40 to +85
VOUT (V) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3 to +6.5
C1+, C2+ (V) . . . . . . . . . . . . . . . . . . . . . . . -0.3 to (VOUT + 0.3)
Pin Voltage - All Other Pins (V) . . . . . . -0.3 to (VIN + 0.3)
Thermal Information
Circuit Duration . . . . . . . . . . . . . . . . . . . . . . . . . . . . Continuous
ESD Protection Level(1) (kV) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Thermal Resistance, Junction to Ambient(2) (°C/W) . . . . 40
Junction Temperature Range (°C) . . . . . . . . . . . . -40 to +150
Storage Temperature Range (°C) . . . . . . . . . . . . . -60 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”, 4 layer FR4 PCB with thermal vias under the exposed pad per JESD51 standards.
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;
VOUT = 2.8V to 4.25V; RSET = 0.5Ω (0.1%).
Parameter
Symbol
Conditions
Min
FLASH high, RSET = 0.357Ω
3.7V < VIN < 4.2V, VOUT = 3.7V(1)
Output Current
ISET Reference Voltage
Quiescent Current
IOUT
VISET
IQ
FLASH high, RSET = 0.5Ω
3.3V < VIN < 4.2V
2.8V < VOUT < 4.25V
Typ
Max
Units
700
460
500
540
mA
FLASH low, CTRL high, RSET = 0.357Ω
3.7V < VIN < 4.2V, VOUT = 3.4V(1)
280
FLASH low, CTRL high, RSET = 0.5Ω
3.0V < VIN < 4.5V
2.8V < VOUT < 4.5V
170
200
230
FLASH high, RSET = 0.5Ω
3.3V < VIN < 4.2V
2.8V < VOUT < 4.25V
230
250
270
FLASH low, CTRL high, RSET = 0.5Ω
3.0V < VIN < 4.5V
2.8V < VOUT < 4.5V
85
mV
100
115
FLASH high
3.4
5.0
mA
FLASH low, CTRL high
2.0
4.5
mA
FLASH low, CTRL low
0.1
2.0
μA
3
SC618
Electrical Characteristics (continued)
Parameter
Symbol
Conditions
Flash Mode Pulse Duration(2)
tFLASH
Flash Mode Start-Up Time(2)
Max
Units
3.3V < VIN < 4.2V
IOUT = 500mA, VOUT > 2.8V
500
ms
tF-SU
t = 0 when FLASH goes high to
IOUT = 90% of final value
1
ms
Flash Mode Safety Timer(2)
tSAFE
FLASH high
1.25
s
Spotlight Mode
Start-Up Time(2,3)
tS-SU
VIN = 4.2V, VOUT = 3.2V; t = 0 when CTRL goes high
to IOUT = 90% of final value
1
ms
Oscillator Frequency
fOSC
Device enabled
Oscillator Frequency Accuracy
ΔfOSC
Short-Circuit Output
Current Limit
ISC
Input Current Limit
ILIMIT
Min
Typ
0.90
250
-15
kHz
15
%
Steady State with VOUT shorted to GND
600
mA
2x mode, 3.3V < VIN < 4.2V
2.1
A
2x mode, VIN = 3.7V, VOUT = 3.7V, TA = 25°C
1.38
TOT
Rising threshold
150
TOT -HYS
Hysteresis
10
Logic Input High Threshold
VIH
FLASH, CTRL
1.5
Logic Input Low Threshold
VIL
FLASH, CTRL
Logic Input High Current
IIH
1.53
Over-Temperature Protection(2)
Logic Input Low Current
ISET Ripple Voltage
°C
IIL
V
0.4
FLASH
1
20
35
CTRL
2
40
70
FLASH, CTRL
0.1
2.0
Spotlight mode — IOUT = 200mA
25
FLASH mode — IOUT = 500mA
100
V
μA
VISET(P-P)
μA
mV
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.
4
SC618
Typical Characteristics
Flash Current at 100ms, RISET = 500mΩ, VOUT = 3.68V
515
515
510
510
505
505
LED Current (mA)
LED Current (mA)
Flash Current at 10ms, RISET = 500mΩ, VOUT = 3.75V
500
495
490
500
495
490
485
3.3
3.45
3.6
3.75
3.9
4.05
485
3.3
4.2
3.45
3.75
VIN (V)
3.6
VIN (V)
4.2
220
515
510
212
505
LED Current (mA)
LED Current (mA)
4.05
Spotlight Current, RISET = 500mΩ, VOUT = 3.16V
Flash Current at 500ms, RISET = 500mΩ, VOUT = 3.58V
500
495
Transition to
2x Mode
204
1x Mode
196
188
490
485
3.3
3.45
3.6
3.75
3.9
4.05
180
5.25
4.2
4.8
4.35
3.9
3.45
3
VIN (V)
VIN (V)
Flash Duration, RISET = 350mΩ, VOUT = 3.86V
(start), 3.61V (LED Heated 500ms)
Flash Duration, RISET = 500mΩ, VOUT = 3.75V (start),
3.58V (LED Heated 500ms)
515
755
509
735
VIN=4.2V
LED Current (mA)
LED Current (mA)
3.9
VIN=3.7V
715
VIN=4.2V
VIN=3.7V
503
VIN=3.3V
497
VIN=3.4V
695
491
VIN=3.3V
675
485
0
100
200
300
Pulse Duration (ms)
400
500
0
100
200
300
Pulse Duration (ms)
400
500
5
SC618
Typical Characteristics (continued)
Flash Mode Ripple, RISET = 500mΩ
Start-Up Flash Mode, 500mA
Ch 1: 100mV/DIV
Ch 1: 100mV/DIV
Ch 2: 200mV/DIV
Ch 2: 2V/DIV
Ch 3: 200mV/DIV
Ch 3: 2V/DIV
Time (4μs/div)
Safety Timer Shut-Off
Time (40μs/div)
Spotlight 1x Mode Ripple, RISET = 500mΩ
Ch1: 100mV/DIV
Ch1: 50mV/DIV
Ch2: 2V/DIV
Ch2: 50mV/DIV
Ch3: 5V/DIV
Ch3: 50mV/DIV
Time (200ms/div)
Time (4μs/div)
Spotlight 2x Mode Ripple, RISET = 500mΩ
Short Circuit Current Limiting, VIN = 5.25V, VOUT = 0V
Ch1: 50 mV/DIV
Ch2: 100 mV/DIV
Ch1: 2V/DIV
Ch3: 100 mV/DIV
Ch4: 100mA/DIV
Time (4μs/div)
Time (400ms/div)
6
SC618
Pin Descriptions
Pin#
Pin Name
Pin Function
1
VIN
Input voltage
2
C2-
Negative terminal of bucket capacitor 2
3
GND
Ground— connect to ground plane using multiple vias
4
C1-
Negative terminal of bucket capacitor 1
5
FLASH
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
C1+
Positive terminal of bucket capacitor 1
9
VOUT
10
C2+
T
Thermal Pad
Flash mode enable pin— puts the device in active flash mode when high and also overrides CTRL.
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.
7
SC618
Block Diagram
VIN
1
LDO
250kHz
8
C1+
4
C1-
10 C2+
CTRL
7
FLASH
5
Logic Control
and Flash
Mode Timer
Reference
Voltage
Generator
CHARGE
PUMP
2
C2-
9
VOUT
3
GND
6
ISET
8
SC618
Applications Information
The SC618 is a powerful dual-mode charge pump designed
to drive a high-intensity white LED. A constant current
spotlight mode or a pulsed current with higher intensity is
used for camera flash. The device operates in 2x mode
while operating in flash mode. In spotlight mode it can
operate in either 2x or 1x 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. 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 0.5Ω). 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 0.35Ω 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. 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 350ms. In
flash mode, IOUT = 250mV/RISET. Figure 1 shows maximum
flash mode current for extended duration times.
800
700
Flash Current [mA]
General Operation
600
500
400
300
200
100
0
0
100
200
300
400
500
600
700
800
900 1000
Flash Duration [ms]
Figure 1 — 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 protect 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 0.5Ω 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 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
9
SC618
Applications Information (continued)
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 device remains in 2x mode until the part is
turned off. If the part is re-enabled in spotlight mode, it
will begin operation in 1x mode and determine the
appropriate mode of operation as previously described.
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 from excessive power dissipation. This
feature protects the device when in 1x mode. The current
limit is set lower in the 1x mode due to lower current
requirements.
Protection Circuitry
The SC618 provides several protection features to safeguard the device from catastrophic failures. These features
include:
•
•
•
•
•
Input Over-Voltage Protection (IOVP)
Output Over-Voltage Protection (OVP)
Over-Temperature Protection (OTP)
Over-Current Protection (OCP)
Short-Circuit Current Protection (SCCP)
Input Over-Voltage Protection
IOVP 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 OVP prevents 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.
Over-Temperature Protection
The OTP circuit prevents the device from overheating and
experiencing a catastrophic failure. When the junction
temperature exceeds 150°C the device is disabled. It
remains disabled until the junction temperature drops
below this threshold. Hysteresis is included to prevent
toggling between modes.
Short-Circuit Current Protection
SSCP 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, and 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
uses a 0.5Ω 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.
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.
10
SC618
Applications Information (continued)
PCB Layout Considerations
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 VOUT pin. C4 is the input
decoupling capacitor placed near the 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+.
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.
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 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.
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.
Thermal Resistance Considerations
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 40°C/W, and this rating is dependent on the connection between the thermal pad and the ground plane. The
layout 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
11
SC618
Outline Drawing — MLPD-UT-10
E
A
DIMENSIONS
B
DIM
INCHES
MIN
A
.018
NOM
-
A1
.000
-
MILLIMETERS
MAX
MIN
.024
0.45
.002
0.00
(.006)
A2
NOM
-
MAX
0.60
0.05
(0.1524)
b
.007
.009
.011
0.18
0.23
0.30
C
.074
.079
.083
1.87
2.02
2.12
PIN 1
D
.042
.048
.052
1.06
1.21
1.31
INDICATOR
E
e
.114
.118
.122
2.90
3.00
3.10
L
.012
.020
0.30
E
(LASER MARK)
A
aaa
.020 BSC
.016
10
0.50 BSC
0.40
0.50
10
N
aaa
.003
0.08
bbb
.004
0.10
SEATING
PLANE
C
A1
C
1
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.
12
SC618
Land Pattern — MLPD-UT-10
DIMENSIONS
K
DIM
(C)
G
H
Z
Y
X
INCHES
MILLIMETERS
C
(.112)
(2.85)
G
.075
1.90
H
.055
1.40
K
.087
2.20
P
.020
0.50
X
.012
0.30
Y
.037
0.95
Z
.150
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.
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
www.semtech.com
13