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SP7618
Solved by
TM
SP7618
8 Pin DFN
8
7
6
5
1
2
3
4
GNDP
GNDP
GND
CTRL
LED
EN
LED
V
CC
Constant Current LED Driver
FEATURES
Very low dropout voltage (100mV @ 1A)
■
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 1µA
■
Fast turn-on (<50µs)
■
Timeout function to protect the LED
■
Thermal Shutdown protection
■
1A current capability
■
RoHS compliant, Lead Free packaging:
■
Space saving 2mmx3mm 8pin DFN
The SP7618 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 SP7618 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 1033mA
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 100µS.
APPLICATIONS
Next Generation Mobile Phones
■
PDA, DSC, MP3 Players
■
Handheld Computers
■
LCD Display Modules
■
Keyboard Backlight
■
GENERAL DESCRIPTION
TYPICAL APPLICATION CIRCUIT
Date: Dec 5-06 Rev E Constant Current LED Driver © 2006 Sipex Corporation
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ABSOLUTE MAXIMUM RATINGS
Supply Voltage (Vcc) .………………………..6.0V
Input Voltage at any input .….-0.6V to Vcc +0.5V
8-pin DFN Package
Thermal Resistance................................ 590C/W
Junction Temperature .......... -40 0C to +170 0C
Storage Temperature ..………...-65°C to +150°C
Soldering Temperature ...………………+240°C**
*) Internally limited
**) Duration 10s maximum
Ambient temperature Ta = 25°C, 3.0V < Vcc < 5.5V, 1.0V < VLED < 3.0V, 100mA < ILED <1033A. Bold denotes
specications which apply over the full operating temperature range, -40°C to +85°C.
PARAMETER MIN TYP MAX UNITS CONDITIONS
Vcc Voltage Operating Range
Quiescent Current 350 420 µA Iled = 35mA
Supply
Current
Shutdown Mode 1
Sleep Mode 350 EN = Vcc, CTRL = GND
After Time Duration
LED
Output
Current
after
0 pulses on CTRL
1 pulse on CTRL
3 pulses on CTRL
31 pulses on CTRL 1033
LED Current Accuracy
LED Current Line Regulation
LED Current Load Regulation
LED Current Thermal Regulation 0.01 %/°C Iled = 100 mA
V
Dropout Voltage
LED
8
Thermal Shutdown Die Temperature
Thermal Shutdown Hysteresis 25 °C
Setup Time after last count
CTRL input Data Rate 4 MHz
Wake-up Time from Shutdown 50 µs
Turn-off Time into Shutdown 30 µs
Turn-off Time into Sleep Mode 125 450 µs
Time Duration before Sleep Mode 2 4 7 s
EN and CTRL pin
Logic Voltage
Power-on-Reset
See notes on next page
Date: Dec 5-06 Rev E Constant Current LED Driver © 2006 Sipex Corporation
LOW 0.4 V Driver in Shutdown Mode
HIGH 1.4 Vcc
11
1
3
4
4
5
6
7
2.5 5.5 V
2
125 nA Vled = 1.0V, Vcc = 5.5V
35
102
-8 8 % 35mA < Iled < 1033 mA
0.1 0.5 %/V 3.0 < Vcc < 5.5V,Vled =1V
1.5 6 %
50 100
90 185 Iled = 700mA @ 25°C
100 210 Iled = 1033mA @ 25°C
160 °C Iled = 35mA
9
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 specications below is not implied.
Exposure to absolute maximum rating
conditions for extended periods of time
may affect reliability.
ELECTRICAL CHARACTERISTICS
EN = GND, CTRL = DC
µA
350 EN = Vcc, CTRL = DC
mA
1 < Vled < 2.5V, Vcc =
5.5V
Iled = 100mA @ 25°C
mV
50 µs
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
10
20 ms
2.5V ≤ Vcc ≤ 5.5V
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Notes (Continued from previous page)
Vcc must be always higher than LED pin voltage (Vled)
1.
After 4s at current higher than 266 mA
2.
Power MOSFET leakage current
3.
Three initial Iled current steps are higher than other 28
4.
Iled Variations from specied Iled value
5.
Iled Variations per volt Vcc change
6.
Iled Variations at Vled change from 1 to 2.5V
7.
5% change of I
8.
Iled = 100 mA settles 50µs later after 3rd pulse
9.
Logic HIGH level should never exceed Vcc voltage
10.
Delay between applying Vcc voltage and operating condition
11.
Pin #Pin
Name
1 - 2 LED LED Current Sink. Connect LED cathode to this pin. Voltage at this pin
should be above 100 mV to maintain regulation.
3 Vcc Power Supply Input. Place 1µF decoupling capacitor next to this pin.
4 EN 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 1033 mA (31
steps). When this pin is held LOW for longer than 100µs the part enters
Sleep Mode.
6 GND Ground pin for control and bias blocks.
7 - 8 GNDP Ground pin. LED current ows through this pin to ground.
compared with ILED value at Vled = 1V
LED
Pin Function
PIN ASSIGNMENTS
BLOCK DIAGRAM
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0
200
400
600
800
1000
1200
0 0.5 1 1.5 2 2.5 3 3.5
Vled , V
Iled, mA
3 pulses 7 puls es 15 pulses 31 pulses
0
200
400
600
800
1000
1200
0 0.2 0.4 0. 6 0.8 1
Vled , V
Iled. mA
3 pulses 7 puls es 15 pulses 31 pulses
700
750
800
850
900
950
1000
1050
1100
0 100 200 300 400 500 600 700
25C 85C
APPLICATION INFORMATION
Load regulation at Vcc = 5.5V @ 25°C
Date: Dec 5-06 Rev E Constant Current LED Driver © 2006 Sipex Corporation
Load regulation vs. temperature at Iled = 1A and Vcc = 5.5V
Load regulation at Vcc = 5.5V @ 25°C
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0
200
400
600
800
1000
1200
0 5 10 15 20 25 30 35
Number of pul ses
ILED, mA
-0.5
-0.4
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
2.5 3 3.5 4 4.5 5 5.5 6
Vcc, V
Line regulation, %
APPLICATION INFORMATION
DAC linearity at Vled = 500mV
Date: Dec 5-06 Rev E Constant Current LED Driver © 2006 Sipex Corporation
Line regulation at Vled = 100mA
Setup Time at Iled = 1033A
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Introduction
THEORY OF OPERATION
The SP7618 is a linear low-side, constantcurrent 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
output driver. The precision reference voltage
ensures good performance over voltage and
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 currents greater than 266mA after 4 seconds
of continuous operation if the enable input
is not cycled.
Current Setting DAC
The LED output current is dened by a current control DAC. The input to the DAC is the
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
number of steps that can be achieved is 25 or
32. The initial step of the DAC corresponds
to zero, so the maximum current output is 31
times the unit current. Any multiple of the
33.33mA output current can be achieved
from 1 to 31 sequentially.
The DAC CTRL input is positive-edge triggered and may be either at high or low logic
state when the part is powered up. The ENABLE pin logic HIGH level may be applied
with Vcc voltage.
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.
If the pulse number exceeds 31, all other
pulses are ignored and 1033 mA current
is set.
The SP7618 can be placed into Sleep Mode
by applying a logic LOW on the CTRL pin for
longer than 100µs after any pulse sequence.
In the Sleep Mode, the driver is disabled and
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-
ed duration.
If the Iled current exceeds 266 mA (8 pulses)
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.
Appyling a new pulse sequence to the CTRL
pin at Sleep Mode will wake up the device but
increase the Iled current at 33.3mA multiplied
by the number of pulses. To return the device
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 current control DAC accepts clock rates
up to 4MHz. The code for the DAC loads
while the output driver takes 50µs to respond.
This implies that the LED output current will
reach its nal value 50µs after the nal pulse
is applied to the CTRL pin.
Date: Dec 5-06 Rev E Constant Current LED Driver © 2006 Sipex Corporation
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Output Driver
The SP7618 features a low-side regulated
output current driver. A large MOSFET device
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
in order to minimize power dissipation inside
the package. Even though there are two LED
and GNDP pins, there is actually only one
output intended to drive one LED.
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 100mV. The output current is
regulated to within ve percent of nominal
value even if the voltage between the LED
and GNDP pins varies over a wide range.
The nominal output is guaranteed within ±8%
of the dened current.
THEORY OF OPERATION
the internal temperature drops by 25°C. If the
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.
Shutdown
The SP7618 has a low current shutdown
function. In shutdown mode, the part draws
less than 0.1µA current maximum. The part
can be placed into shutdown using the EN
pin.
ENABLE and CTRL pins cannot be tri-stated
or left oating. There are no predened internal states, so leaving these pins open will
cause the part to operate incorrectly.
Thermal Protection
The SP7618 has built-in thermal protection.
An internal p-n junction is compared to the in-
ternal temperature compensated reference.
When the p-n junction reaches a temperature
specic voltage, it trips a comparator which
shuts down the driver stage of the part placing
the device into sleep mode while DAC circuit
remains active. The shutdown temperature
is dened to be 160°C.
Timeout
A Time Duration Before Shutdown feature
acts as a failsafe to protect the LED from long
ON times. The nominal timeout is dened
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
The comparator circuit has built-in hysteresis
corresponding to 25°C. The output stage will
resume operation and start sinking the cur-
pin can be accepted during this time, even
if the input voltage is applied simultaneously
to Vcc and ENABLE pins.
rent that was dened prior to shutdown when
Date: Dec 5-06 Rev E Constant Current LED Driver © 2006 Sipex Corporation
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BOARD LAYOUT AND GROUNDING
To obtain the best performance from the
SP7618, a printed circuit board with ground
plane is required. High quality, low series
resistance ceramic 1µF 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 1 – 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.
Board layout should prevent high LED ground
current from owing through signal ground
connected to pin 6. This pin is a separate
ground for the reference and logic sections
of the SP7618. The quiescent current for the
part ows into the VCC pin and out of the GND
pin. This current is proportional to the Iled
current divided by approximately 1500.
TIMING DIAGRAM
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PACKAGE: 8 PIN DFN
Date: Dec 5-06 Rev E Constant Current LED Driver © 2006 Sipex Corporation
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ORDERING INFORMATION
Solved by
TM
Part Number Operating Temperature Range Package Type
SP7618ER-L...................................-40°C to +85°C ............................Lead Free 8 Pin DFN
(2mm x 3mm)
SP7618ER-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.
Sipex Corporation
Headquarters and
Sales Ofce
233 South Hillview Drive
Milpitas, CA 95035
TEL: (408) 934-7500
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
FAX: (408) 935-7600
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