SP7618 [SIPEX]
Constant Current LED Driver; 恒流LED驱动器
| 型号： | SP7618 |
| 厂家： | 
SIPEX CORPORATION |
| 描述： | Constant Current LED Driver |
| 文件： | 总10页 (文件大小：409K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
Solved by
SP7618
TM
Constant Current LED Driver
FEATURES
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Very low dropout voltage (ꢀ00mV @ ꢀA)
Accurate current regulation down to dropout
voltage
No external components
Built-in current DAC
Output current adjustable with 33.3 mA/steps
Power-saving shutdown mode of ꢀµA
Fast turn-on (<50µs)
Timeout function to protect the LED
Thermal Shutdown protection
ꢀA current capability
8
7
6
5
LED
LED
1
2
3
4
GNDP
GNDP
GND
SP7618
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■
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■
■
■
■
■
■
V
CC
8 Pin DFN
EN
CTRL
APPLICATIONS
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Next Generation Mobile Phones
PDA, DSC, MP3 Players
Handheld Computers
LCD Display Modules
Keyboard Backlight
RoHS compliant, Lead Free packaging:
Space saving 2mmx3mm 8pin DFN
GENERAL DESCRIPTION
The SP76ꢀ8 is a linear, low-side constant-current driver designed to drive high power LEDs
from an input voltage rail. The driver acts as a current source, ensuring constant LED current
for a range of input voltages. The SP76ꢀ8 allows implementing the lowest cost LED driver
for a variety of applications. Internal circuitry maintains the preset constant current output
for a wide voltage range at the LED input. The LED current can be adjusted up to ꢀ033mA
with an external clock applied to the CTRL pin. The built-in thermal protection automatically
stops LED current to prevent overheating. A timeout function serves as a failsafe, shutting
down the output for currents greater than 266mA after 4 seconds of continuous operation if
the enable input is not cycled. The part can be shut down by using the EN pin, or sent into
Sleep Mode holding the CTRL pin low for more than ꢀ00µS.
TYPICAL APPLICATION CIRCUIT
Date: Dec 5-06 Rev E
Constant Current LED Driver
© 2006 Sipex Corporation
ꢀ
ABSOLUTE MAXIMUM RATINGS
Supply Voltage (Vcc) .………………………..6.0V
Input Voltage at any input .….-0.6V to Vcc +0.5V
8-pin DFN Package
These are stress ratings only and
functional operation of the device at
these ratings or any other above those
indicated in the operation sections of
the specifications below is not implied.
Exposure to absolute maximum rating
conditions for extended periods of time
may affect reliability.
0
Thermal Resistance................................ 59 C/W
0
0
*
Junction Temperature .......... -40 C to +ꢀ70 C
Storage Temperature ..………...-65°C to +ꢀ50°C
Soldering Temperature ...………………+240°C**
*) Internally limited
**) Duration ꢀ0s maximum
ELECTRICAL CHARACTERISTICS
Ambient temperature Ta = 25°C, 3.0V < Vcc < 5.5V, ꢀ.0V < VLED < 3.0V, ꢀ00mA < ILED <ꢀ033A. Bold denotes
specifications which apply over the full operating temperature range, -40°C to +85°C.
PARAMETER
MIN
2.5
TYP
MAX UNITS CONDITIONS
ꢀ
Vcc Voltage Operating Range
Quiescent Current
5.5
420
ꢀ
V
350
µA
Iled = 35mA
Shutdown Mode
Sleep Mode
EN = GND, CTRL = DC
EN = Vcc, CTRL = GND
EN = Vcc, CTRL = DC
Vled = ꢀ.0V, Vcc = 5.5V
Supply
Current
350
350
µA
nA
2
After Time Duration
3
LED
0 pulses on CTRL
ꢀ25
35
Output
Current
after
4
ꢀ pulse on CTRL
4
3 pulses on CTRL
ꢀ02
ꢀ033
mA
3ꢀ pulses on CTRL
5
LED Current Accuracy
-8
8
%
35mA < Iled < ꢀ033 mA
6
LED Current Line Regulation
0.ꢀ
ꢀ.5
0.5
%/V
3.0 < Vcc < 5.5V,Vled =ꢀV
ꢀ < Vled < 2.5V, Vcc =
5.5V
7
LED Current Load Regulation
6
%
LED Current Thermal Regulation
0.0ꢀ
50
%/°C
Iled = ꢀ00 mA
ꢀ00
ꢀ85
2ꢀ0
Iled = ꢀ00mA @ 25°C
Iled = 700mA @ 25°C
Iled = ꢀ033mA @ 25°C
8
VLED Dropout Voltage
90
mV
ꢀ00
Thermal Shutdown Die Tempera-
ture
ꢀ60
°C
Iled = 35mA
Thermal Shutdown Hysteresis
25
°C
µs
9
Setup Time after last count
50
CTRL input Data Rate
4
MHz
EN = LOW to HIGH,
CTRL = DC
EN = HIGH to LOW,
CTRL = DC
EN = HIGH, CTRL =
HIGH to LOW
Iled > 266 mA, EN =
HIGH, CTRL = HIGH
Driver in Shutdown Mode
Wake-up Time from Shutdown
50
30
µs
µs
µs
Turn-off Time into Shutdown
Turn-off Time into Sleep Mode
Time Duration before Sleep Mode
ꢀ25
450
2
4
7
s
LOW
HIGH
0.4
V
EN and CTRL pin
Logic Voltage
10
1.4
Vcc
20
2.5V ≤ Vcc ≤ 5.5V
ꢀꢀ
Power-on-Reset
ms
See notes on next page
Date: Dec 5-06 Rev E
Constant Current LED Driver
© 2006 Sipex Corporation
2
Notes (Continued from previous page)
ꢀ. Vcc must be always higher than LED pin voltage (Vled)
2. After 4s at current higher than 266 mA
3. Power MOSFET leakage current
4. Three initial Iled current steps are higher than other 28
5. Iled Variations from specified Iled value
6. Iled Variations per volt Vcc change
7. Iled Variations at Vled change from ꢀ to 2.5V
8. 5% change of ILED compared with ILED value at Vled = ꢀV
9. Iled = ꢀ00 mA settles 50µs later after 3rd pulse
ꢀ0. Logic HIGH level should never exceed Vcc voltage
ꢀꢀ. Delay between applying Vcc voltage and operating condition
PIN ASSIGNMENTS
Pin
#
Pin
Name
Pin Function
ꢀ - 2
LED LED Current Sink. Connect LED cathode to this pin. Voltage at this pin
should be above ꢀ00 mV to maintain regulation.
3
4
Vcc
EN
Power Supply Input. Place ꢀµF decoupling capacitor next to this pin.
Enable/Shutdown pin used to enable/disable driver and reset DAC: Logic
High – enable, Logic Low – disable/reset.
5
CTRL DAC Serial Input pin is used to control LED current. Positive pulse edges
sequentially increase LED current with 33.33mA steps up to ꢀ033 mA (3ꢀ
steps). When this pin is held LOW for longer than ꢀ00µs the part enters
Sleep Mode.
6
GND Ground pin for control and bias blocks.
7 - 8 GNDP Ground pin. LED current flows through this pin to ground.
BLOCK DIAGRAM
Date: Dec 5-06 Rev E
Constant Current LED Driver
© 2006 Sipex Corporation
3
APPLICATION INFORMATION
ꢀ200
ꢀ000
800
600
400
200
0
0
0.5
ꢀ
ꢀ.5
Vled, V
2
2.5
3
3.5
3 pulses
7 pulses
ꢀ5 pulses
3ꢀ pulses
Load regulation at Vcc = 5.5V @ 25°C
ꢀ200
ꢀ000
800
600
400
200
0
0
0.2
0.4
0.6
0.8
ꢀ
Vled, V
3 pulses
7 pulses
ꢀ5 pulses
3ꢀ pulses
Load regulation at Vcc = 5.5V @ 25°C
ꢀꢀ00
ꢀ050
ꢀ000
950
900
850
800
750
700
0
ꢀ00
200
300
25C
400
85C
500
600
700
Load regulation vs. temperature at Iled = ꢀA and Vcc = 5.5V
Date: Dec 5-06 Rev E
Constant Current LED Driver
© 2006 Sipex Corporation
4
APPLICATION INFORMATION
ꢀ200
ꢀ000
800
600
400
200
0
0
5
ꢀ0
ꢀ5
20
25
30
35
Number of pulses
DAC linearity at Vled = 500mV
0.3
0.2
0.ꢀ
0
2.5
3
3.5
4
4.5
5
5.5
6
-0.ꢀ
-0.2
-0.3
-0.4
-0.5
Vcc, V
Line regulation at Vled = ꢀ00mA
Setup Time at Iled = ꢀ033A
Date: Dec 5-06 Rev E
Constant Current LED Driver
© 2006 Sipex Corporation
5
THEORY OF OPERATION
Introduction
The SP76ꢀ8 is a linear low-side, constant-
current driver designed to drive high power
LEDs from an input voltage rail. The design
consists of a regulator reference voltage
source, DAC, voltage-to-current converter,
thermal shutdown, timeout shutdown, and
outputdriver.Theprecisionreferencevoltage
ensuresgoodperformanceovervoltageand
temperature. The built-in thermal protection
automatically stops LED current to prevent
overheating. A timeout function serves as
a failsafe, shutting down the output for cur-
rents greater than 266mA after 4 seconds
of continuous operation if the enable input
is not cycled.
If the pulse number exceeds 3ꢀ, all other
pulses are ignored and ꢀ033 mA current
is set.
The SP76ꢀ8 can be placed into Sleep Mode
by applying a logic LOW on the CTRLpin for
longerthanꢀ00µsafteranypulsesequence.
IntheSleepMode, thedriverisdisabledand
Iled current is zero, but blocks associated
with the DAC remain active, and Icc Sleep
Mode Current is always higher than Icc
current in Shutdown Mode. This function is
used to output the Iled current for a speci-
fied duration.
IftheIledcurrentexceeds266mA(8pulses)
the maximum Time Duration is 4s. After
that, the device is automatically sent into
Sleep Mode. This function is intended to
protect the LED if, for example, the device
was left on in a high current condition for a
long period of time.
Current Setting DAC
The LED output current is defined by a cur-
rentcontrolDAC.TheinputtotheDACisthe
CTRL pin. The DAC outputs a unit current
of 33.33mA with each applied pulse at the
CTRL pin. The DAC has 5 bits, so the total
numberofstepsthatcanbeachievedis25 or
32. The initial step of the DAC corresponds
tozero, sothemaximumcurrentoutputis3ꢀ
times the unit current. Any multiple of the
33.33mA output current can be achieved
from ꢀ to 3ꢀ sequentially.
AppylinganewpulsesequencetotheCTRL
pinatSleepModewillwakeupthedevicebut
increasetheIledcurrentat33.3mAmultiplied
bythenumberofpulses.Toreturnthedevice
to the previous or lower Iled current value,
use Shutdown (EN =HIGH to LOW/LOW to
HIGH) and apply a new pulse sequence to
the CTRL pin.
The DAC CTRL input is positive-edge trig-
gered and may be either at high or low logic
state when the part is powered up. The EN-
ABLE pin logic HIGH level may be applied
with Vcc voltage.
ThecurrentcontrolDACacceptsclockrates
up to 4MHz. The code for the DAC loads
whiletheoutputdrivertakes50µstorespond.
This implies that the LED output current will
reachitsfinalvalue50µsafterthefinalpulse
is applied to the CTRL pin.
The CTRL input allows an increase in LED
current only. If a lower Iled current value
is required, the device should be sent into
shutdown mode (EN =HIGH to LOW/LOW
to HIGH) and a new pulse sequence should
be applied to the CTRL pin.
Date: Dec 5-06 Rev E
Constant Current LED Driver
© 2006 Sipex Corporation
6
THEORY OF OPERATION
Output Driver
theinternaltemperaturedropsby25°C. Ifthe
part remains in a high ambient temperature
environment or if a high power dissipation
condition exists, the output stage will cycle
on and off to maintain a preset internal
junction temperature to avoid catastrophic
damage. In that case,the LED will appear to
be blinking. Lower the LED voltage to avoid
excess power dissipation in the IC.
The SP76ꢀ8 features a low-side regulated
outputcurrentdriver. AlargeMOSFETdevice
is connected between the LED and GNDP
pins. The MOSFET drain is connected to
the LED pins and the MOSFET source is
connected to the GNDP pins. There are
two pins on each terminal of the MOSFET
inordertominimizepowerdissipationinside
thepackage.EventhoughtherearetwoLED
and GNDP pins, there is actually only one
output intended to drive one LED.
Shutdown
The light emitting diode connects from VCC
to the LED pins. The Iled current regulation
is guaranteed at dropout at the LED pins to
be less than ꢀ00mV. The output current is
regulated to within five percent of nominal
value even if the voltage between the LED
and GNDP pins varies over a wide range.
Thenominaloutputisguaranteedwithin±8%
of the defined current.
The SP76ꢀ8 has a low current shutdown
function. In shutdown mode, the part draws
less than 0.ꢀµAcurrent maximum. The part
can be placed into shutdown using the EN
pin.
ENABLEandCTRLpinscannotbetri-stated
or left floating. There are no predefined in-
ternalstates, soleavingthesepinsopenwill
cause the part to operate incorrectly.
Thermal Protection
Timeout
The SP76ꢀ8 has built-in thermal protection.
Aninternalp-n junctioniscomparedtothein-
ternal temperature compensated reference.
Whenthep-n junctionreachesatemperature
specific voltage, it trips a comparator which
shutsdownthedriverstageofthepartplacing
thedeviceintosleepmodewhileDACcircuit
remains active. The shutdown temperature
is defined to be 160°C.
A Time Duration Before Shutdown feature
actsasafailsafetoprotecttheLEDfromlong
ON times. The nominal timeout is defined
as 4 seconds.
Power-on-Reset
This function is used to set DAC and Time
Duration counters into their initial state after
power up. No signal applied to the CTRL
pin can be accepted during this time, even
iftheinputvoltageisappliedsimultaneously
to Vcc and ENABLE pins.
Thecomparatorcircuithasbuilt-inhysteresis
correspondingto25°C.Theoutputstagewill
resume operation and start sinking the cur-
rentthatwasdefinedpriortoshutdownwhen
Date: Dec 5-06 Rev E
Constant Current LED Driver
© 2006 Sipex Corporation
7
BOARD LAYOUT AND GROUNDING
To obtain the best performance from the
SP76ꢀ8, a printed circuit board with ground
plane is required. High quality, low series
resistance ceramic ꢀµF bypass capacitors
should be used at the Vcc pin (pin 3). These
capacitors must be located as close to pins
3 – 6 as possible. The traces connecting the
pins and the bypassing capacitors must be
kept short and should be made as wide as
possible. Pins ꢀ – 2 are connected together
internally but we recommend connecting the
LED cathode to both pins to avoid additional
power losses at high current. Pins 6, 7 and
8 should be connected to the ground plane.
BoardlayoutshouldpreventhighLEDground
current from flowing through signal ground
connected to pin 6. This pin is a separate
ground for the reference and logic sections
oftheSP76ꢀ8.Thequiescentcurrentforthe
partflowsintotheVCCpinandoutoftheGND
pin. This current is proportional to the Iled
current divided by approximately ꢀ500.
TIMING DIAGRAM
Date: Dec 5-06 Rev E
Constant Current LED Driver
© 2006 Sipex Corporation
8
PACKAGE: 8 PIN DFN
Date: Dec 5-06 Rev E
Constant Current LED Driver
© 2006 Sipex Corporation
9
ORDERING INFORMATION
Package Type
Part Number
Operating Temperature Range
SP76ꢀ8ER-L...................................-40°C to +85°C ............................Lead Free 8 Pin DFN
(2mm x 3mm)
SP76ꢀ8ER-L/TR ...... ......................-40°C to +85°C ............................Lead Free 8Pin DFN
(2mm x 3mm)
/TR = Tape and Reel
Pack quantity is 3,000 for DFN.
Solved by
Sipex Corporation
Headquarters and
Sales Office
TM
233 South Hillview Drive
Milpitas, CA 95035
TEL: (408) 934-7500
FAX: (408) 935-7600
Sipex Corporation reserves the right to make changes to any products described herein. Sipex does not assume
any liability arising out of the application or use of any product or circuit described herein; neither does it convey
any license under its patent rights nor the rights of others.
Date: Dec 5-06 Rev E
Constant Current LED Driver
© 2006 Sipex Corporation
ꢀ0
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