SC635 Datasheet

SC635
Charge Pump
Flash LED Driver
POWER MANAGEMENT
Description
Features
The SC635 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.
Two selectable modes - Flash and Spotlight
200mA max output - Flash Mode
Spotlight mode set to 40% of Flash Current
3.0V to 5.25V Input Range
External pins for control of flash and spotlight modes
for synchronization to a camera module or graphics
controller
u Short circuit, over-voltage, and over-temperature
protection
u Soft-start functionality
u Micro Lead Package MLPD-10, 3mm x 3mm
u
u
u
u
u
The SC635 has two modes of operation: Flash mode and
Spotlight mode. In Flash mode, the SC635 is capable of
delivering 200mA to a high-intensity LED during image
capture. In Spotlight mode the SC635 outputs 40% of the
Flash mode current for general purpose lighting or status
indication.
An external resistor is connected in series with the LED to
set the current. In Flash mode, this resistor can dissipate
up to 50mW, reducing the power dissipation requirement
of the SC635. The flash input (FLASH) overrides the control input (CTRL) to make sure the flash function is activated when called for.
Applications
u Mobile Camera Phones
u Digital Cameras
u PDAs with Built-in Cameras
The thermally efficient MLPD-10 package and ceramic bypass and bucket capacitors make the SC635 a high output current driver that requires minimal PCB area.
Typical Application Circuit
Typical Application Circuit
1
VBAT
10µF
8
1µF
4
10
1µF
2
VIN
SC635
VOUT
C1+
GND
C1-
ISET
C2+
CTRL
C2-
FLASH
9
3
white LED
1µF
6
7
5
RSET
FLASH
CTRL
December 2, 2005
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SC635
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
Symbol
Maximum
Units
VVIN
-0.3 to +6.5
V
VVOUT
-0.3 to +6.5
V
-0.3 to VVIN + 0.3
V
-0.3 to VVOUT + 0.3
V
Pin Voltage - FLASH, CTRL, ISET, C1-, C2Pin Voltage - C1+, C2+
Thermal Resistance, Junction to Ambient
(JESD51 Standard Method)(1)
qJA
49
°C/W
VOUT Short Circuit Duration
SC
Indefinite
s
Operating Ambient Temperature Range
TA
-40 to +85
°C
Junction Temperature Range
TJ
-40 to +150
°C
Storage Temperature Range
TSTG
-60 to +150
°C
Peak IR Flow Temperature
TLEAD
260
°C
ESD Protection Level(2)
VESD
2
kV
(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 = 25°C for TYP, -40°C to +60°C for MIN and MAX;
CBUCKET = COUT = 1.0μF (ESR < 0.1Ω); CIN = 10.0μF; VVIN = 3.0V to 5.25V; VVOUT = 2.8V to 4.25V; RSET = 0.5Ω (0.1%).
Parameter
Output Current
ISET Reference Voltage
Quiescent Current
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Symbol
IOUT
VISET
IQ
Conditions
Min
Typ
Max
FLASH high, RISET = 1.25W
3.3V < VVIN < 4.2V
2.8V < VVOUT = 4.25V
184
200
216
FLASH low, CTRL high, RISET = 1.25W
3.0V < VVIN < 4.5V
2.8V < VVOUT < 4.5V
68
80
92
FLASH high, RISET = 1.25W
3.3V < VVIN < 4.2V
2.8V < VVOUT < 4.25V
230
250
270
FLASH low, CTRL high, RISET = 1.25W
3.0V < VVIN < 4.5V
2.8V < VVOUT < 4.5V
85
Units
mA
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
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POWER MANAGEMENT
Electrical Characteristics (Cont.)
Parameter
Symbol
Conditions
Flash Mode Start-up Time(1)
tF-SU
t = 0 when FLASH goes high to IOUT = 90%
of final value
Flash Mode Pulse Duration
tFLASH
3.3V < VVIN < 4.2V
IOUT = 200mA, VVOUT > 2.8V
Spotlight Mode Start-up Time(1)
tS-SU
t = 0 when CTRL goes high to IOUT = 90%
of final value
Oscillator Frequency
fOSC
Device enabled
Oscillator Frequency Accuracy
Short-circuit Output Current
Limit
Min
VOUT shorted to GND
Input Current Limit
ILIMIT
3.3V < VVIN < 4.2V
Over-temperature Protection(1)
TOT
Logic Input High Threshold
Units
1
ms
s
1
250
1.0
10
VIH
FLASH, CTRL
1.5
Logic Input Low Threshold
VIL
FLASH, CTRL
Logic Input High Current
IIH
Logic Input High Current
IIL
ms
kHz
15
%
465
mA
2.1
A
150
Hysteresis
VISET(P-P)
Max
indefinite
-15
DfOSC
ISC
ISET Ripple Voltage(1)
Typ
°C
V
0.4
FLASH
1
20
35
CTRL
2
40
70
FLASH, CTRL
0.1
2.0
Spotlight mode - IOUT = 80mA
25
FLASH mode - IOUT = 200mA
100
V
µA
µA
mV
Notes:
(1) Guaranteed by design - not tested in production.
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SC635
POWER MANAGEMENT
Pin Configuration
Ordering Information
DEVICE
PACKAGE
SC635MLTRT(1)(2)
MLPD-10 3x3
SC635EVB
Evaluation Board
(2)(1)
VIN
1
10
C2+
C2-
2
9
VOUT
GND
3
8
C1+
C1-
4
7
CTRL
FLASH
5
6
ISET
TOPVIEW
T
(1)
Notes:
(1) Available in tape and reel only. A reel contains 3,000 devices.
(2) Available in lead-free package only. Device is WEEE and
RoHS compliant.
MLP10:3X310LEAD
Pin Descriptions
Pin#
Pin Name
Pin Function
1
VIN
Input voltage.
2
C2-
Negative terminal of bucket capacitor 2.
3
GND
4
C1-
5
FLASH
Flash mode enable pin - puts the device in active Flash mode when high and also overrides
CTRL.
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+
9
VOUT
10
C2+
T
Thermal
Pad
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Ground - connect to ground plane using multiple vias.
Negative terminal of bucket capacitor 1.
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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SC635
POWER MANAGEMENT
Pin
Configuration
Applications
Information
the output current being set too low.
General Operation
The SC635 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. Protection Circuitry
The SC635 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
(OT) Protection, Over-Current Protection (OCP), and ShortCircuit Current Protection (SCCP).
In Flash mode the SC635 output can drive 200mA at
4.25V into an LED for an unlimited duration under all
temperature and input conditions. The FLASH pin is used
to trigger this mode (active high). In Spotlight mode the
SC635 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.
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 current is regulated by attaching the ISET pin to
the cathode(s) of the LED package and a low resistance
sense resistor (typically 1.25Ω). 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. Output Over-Voltage Protection
Output over-voltage protection is included to prevent the
SC635 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
Flash Mode
Flash mode is enabled whenever the FLASH pin is pulled decreases to a level within the acceptable range. This
high and remains active until the FLASH pin is released. circuit allows the device to drive LEDs with high forward
This mode has higher priority than Spotlight mode, so the voltages at a reduced level without exceeding the output
state of the CTRL pin is overridden whenever the FLASH voltage limits specified for the device. Note, however, that
pin is activated. While in Flash mode the reference volt- this effect is a consequence of the OVP circuit and is not
its intended purpose.
age on the ISET pin is set to 250mV. Over-Temperature Protection
The over-temperature circuit helps prevent 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. As with the UVLO
and OVP circuits, hysteresis is included to prevent toggling
between modes.
Output currents other than the rated maximum of 200mA
can be set by changing the RISET value. In Flash mode,
IOUT = 250mV/RISET. Spotlight Mode
Spotlight mode is enabled by setting the CTRL pin high
and keeping the FLASH pin low. When in Spotlight mode,
the SC635 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 80mA when a 1.25Ω resistor is used. Spotlight current
is always 40% of flash current for any given value of RISET. In spotlight mode, IOUT = 100mV/RISET. The resistor value should not exceed 2Ω, however, to ensure the SC635
does not become unstable while in Spotlight mode due to
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Over-Current Protection
When the SC635 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.
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SC635
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Applications Information (Cont.)
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.
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 SC635. 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 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 resistance. It is recommended that the resistor be
selected to match the desired LED current for Flash mode. This allows the designer to set the SC635’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 1.25Ω resistor to set
a flash mode current of 200mA and spotlight mode current of 80mA. A high precision resistor should be used to
ensure the specified accuracy for LED current. Capacitor Selection
The SC635 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 SC635 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 SC635
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. It is critical
to maintain adequate ground plane around the device to
maximize heat transfer and avoid over-temperature shutdown.
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
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SC635
POWER MANAGEMENT
Typical Characteristics
200mA Flash Duration, RISET = 1.25W,
VOUT = 3.30V(start) to 3.25V(LED heated 500ms)
Flash Current at 500ms, RISET = 1.25W, VOUT = 3.25V
203.0
203.0
201.0
LED Current [mA]
205.0
LED Current [mA]
205.0
201.0
VIN = 4.2V
VIN = 3.7V
199.0
199.0
VIN = 3.3V
197.0
197.0
195.0
195.0
0
100
200
300
Pulse Duration [ms]
400
3.3
500
Flash Current at 100ms, RISET = 1.25W, VOUT = 3.28V
3.45
3.6
3.75
VIN [V]
3.9
4.05
4.2
Flash Current at 10ms, RISET = 1.25W, VOUT = 3.30V
205.0
203.0
203.0
LED Current [mA]
LED Current [mA]
205.0
201.0
201.0
199.0
199.0
197.0
197.0
195.0
195.0
3.3
3.45
3.6
3.75
3.9
VIN [V]
4.05
4.2
3.3
3.45
3.6
3.75
VIN [V]
3.9
4.05
4.2
80mA Spotlight Current, RISET = 1.25W, VOUT = 2.96V
85.0
LED Current [mA]
83.0
81.0
79.0
77.0
75.0
3
3.45
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3.9
VIN [V]
4.35
4.8
5.25
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SC635
POWER MANAGEMENT
Typical Characteristics (Cont.)
Flash Mode Ripple, RISET = 1.25W
Spotlight Mode Ripple, RISET = 1.25W
Ch1 50mV/div
Ch2 200mV/div
Ch3 200mV/div
4us/div
Ch1 50mV/div
Ch2 100mV/div
Ch3 100mV/div
4us/div
Startup Flash Mode 200mA
Ch1 100mV/div
Ch2 2V/div
Ch3 2V/div
Ch4 2V/div
40us/div
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SC635
POWER MANAGEMENT
Suggested Layout
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 200mA pulsed
for one half clock cycle. C3 is the output decoupling capacitor placed near the SC635 VOUT pin. C4 is the input decoupling capacitor placed near the SC635 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
Top Copper
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SC635
POWER MANAGEMENT
Block Diagram
VIN
1
LDO
250kHz
8
C+
4
C-
10 C2+
CTRL
7
FLASH
5
LogicControl
CHARGE
PUMP
Reference
Voltage
Generator
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10
2
C2-
9
VOUT
3
GND
6
ISET
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SC635
POWER MANAGEMENT
Outline Drawing - MLPD-10
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
A2
.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
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
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 Information
Top Mark
635
yyww
xxxx
yyww = Datecode (Example = 0552)
xxxx = Semtech Lot Number
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SC635
POWER MANAGEMENT
Land Pattern - MLPD-10
K
(C)
H
DIM
G
Y
X
P
Z
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
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
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