LX1994
®
TM
High Efficiency LED Driver
P RODUCTION D ATA S HEET
KEY FEATURES
DESCRIPTION
The use of external N-channel
MOSFET allows design to optimize
system efficiency.
The OVP protection comparator
eliminates the need of an external Zener
diode clamp. The OVP function can be
scaled for any output voltage.
Maximum output current is achievable
by selection of the current sense
resistor.
These features make the
controller ideal for PDA or digital
camera applications
To enhance system battery life, the
LX1994 provides 2 dimming options
and a dedicated ambient light sensor
(LX1970) interface.
The LX1994 supports a wide range
of system battery voltage inputs which
ranges from 2.0 to 5.5V. The LX1994
is guaranteed to start up at 2.0V input.
The LX1994 is available in miniature
10-pin MLP or MSOP packages.
IMPORTANT: For the most current data, consult MICROSEMI’s website: http://www.microsemi.com
Efficiency > 92%
Dual PFM Architecture To
Extend Battery Life
VIN Range 2.0V To 5.5V. Start
Up Warranty @ 2.0V
Logic Control Shutdown
100µA Typical Quiescent
Current
Shutdown IQ Current <1µA
OVP For Open String Output
Voltage
Low Voltage And Offset
Current Sense
Light Sensor (LX1970)
interface
Dual Dimming Options (PWM
or DC Voltage)
No External Zener Clamp
Diode
10-Pin MLP or MSOP
WWW . Microsemi .C OM
Microsemi’s LX1994 is a compact,
high efficiency, step-up boost
controller which is designed to drive a
string of white or colored LED’s in a
backlight or front light system. The
LX1994 design is based on a dual
mode PFM architecture and provides
maximum typical efficiency greater
than 92%.
The LX1994 has many unique
design features and advantages over
competitor solutions. The features
included:
low quiescent current
(100µA typical), low shut down
current (<1µA), dedicate ambient light
sensor interface (LX1970), dual
dimming modes, low voltage and low
offset current sense, and integrated
OVP protection.
The converter achieves high
efficiency, low cost, and flexible
design by selection of an external NChannel MOSFET, current sense
resistors,
and
integrated
OVP
protection.
APPLICATIONS
Pagers
PDA
Cell Phone
Portable Display
Digital Cameras
Patent Pending
PRODUCT HIGHLIGHT
33µH
UPS5819
VIN = 2.0V to 5.5V
LX1994
Auto Adjust for
Ambient Light
FDV303
VIN
DRV
S/P
SRC
BRT
OVP
3V
VDD
VSS
SNK
SRC
LS
LX1970
GND
FB
CMP
LX1994
PACKAGE ORDER INFO
TA (°C)
-40 to 85
LD
Plastic MLP
10-Pin
DU
Plastic MSOP
10-Pin
RoHS Compliant / Pb-free
RoHS Compliant / Pb-free
LX1994CLD
LX1994CDU
Note: Available in Tape & Reel. Append the letters “TR” to the part number. (i.e. LX1994CDU-TR)
Copyright © 2003
Rev. 1.0d, 2006-02-09
Microsemi
Integrated Products Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 1
LX1994
®
TM
High Efficiency LED Driver
P RODUCTION D ATA S HEET
ABSOLUTE MAXIMUM RATINGS
PACKAGE PIN OUT
VIN
1
10
DRV
S/P
2
9
SRC
BRT
3
8
OVP
LS
4
7
FB
GND
5
6
CMP
Peak Package Solder Reflow Temp (40 seconds max. exposure) ................. 260°C (+0, -5)
DU PACKAGE
(Top View)
Note: Exceeding these ratings could cause damage to the device. All voltages are with respect to
Ground. Currents are positive into, negative out of specified terminal.
THERMAL DATA
DU
Plastic MSOP 10-Pin
THERMAL RESISTANCE-JUNCTION TO AMBIENT, θJA
LD
113°C/W
VIN
1
10
DRV
S/P
2
9
SRC
BRT
3
8
OVP
LS
4
7
FB
GND
5
6
CMP
Plastic MLP 10-Pin
Connect Bottom to
Power GND
WWW . Microsemi .C OM
Supply Input Voltage (IN) ...................................................................-0.3V to 7V
All Input Pins ......................................................................................-0.3V to VIN
SRC Input Current ......................................................................................600mA
Operating Temperature Range .........................................................-40°C to 85°C
Maximum Operating Junction Temperature ................................................ 150°C
Storage Temperature Range...........................................................-65°C to 150°C
Lead Temperature (Soldering 10 seconds) .................................................. 235°C
LD PACKAGE
THERMAL RESISTANCE-JUNCTION TO AMBIENT, θJA
(Top View)
49°C/W
Junction Temperature Calculation: TJ = TA + (PD x θJA).
The θJA numbers are guidelines for the thermal performance of the device/pc-board system. All of the
above assume no ambient airflow.
RoHS / Pb-free 100% Matte Tin Lead Finish
FUNCTIONAL PIN DESCRIPTION
Name
IN
Description
Unregulated IC Supply Voltage Input – Input range from 2.0V to 5.5V. Bypass with a 1μF or greater capacitor for
operation below 2.0V.
GND
Common terminal for ground reference.
BRT
LED Current Adjustment - Accepts a DC analog input.
FB
LED Current Sense – Connect to current sense resistor.
MOSFET Current Sense Input - Connects to the external N-Channel MOSFET source.
DRV
MOSFET Gate Driver – Connects to an external N-Channel MOSFET gate.
OVP
Over Voltage Programming Pin – Connects to a resistor divider between the output load and GND to set the
maximum output voltage.
LS
CMP
S/P
Light Sensor Input – Allows light sensor current input to be modulated by the PWM control causing LED
brightness to be a product of the PWM duty cycle and ambient light level.
Compensation Pin – Apply a 0.1µF capacitor for loop compensation.
Shutdown/PWM Pin – A logic low longer than 100μs causes the IC to enter Shutdown mode. Applying a PWM
signal to this pin and a filter capacitor to the BRT pin allows amplitude independent PWM control.
Copyright © 2003
Rev. 1.0d, 2006-02-09
Microsemi
Integrated Products Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 2
PACKAGE DATA
SRC
LX1994
®
TM
High Efficiency LED Driver
P RODUCTION D ATA S HEET
ELECTRICAL CHARACTERISTICS
Parameter
Symbol
Test Conditions
Min
≤
85°C except where
LX1994
Typ Max
Units
`
Operating Voltage
Minimum Start-up Voltage
Start-up Voltage Temperature
Coefficient
VIN
Quiescent Current
IQ
BRT Full scale bias current
BRT Light sensor current
S/P Logic Low Voltage
S/P Logic High Voltage
S/P Input DC Bias Current
S/P PWM frequency
S/P Pulse Width
BRT PWM Voltage
BRT PWM Voltage
Feedback Comparator Offset
SCR peak current
Efficiency
DRV Sink/Source Current
Maximum Switch On-Time
Minimum Switch Off-Time
OVP Threshold Voltage
OVP Input Bias Current
2.0
5.5
2.0
TA = +25°C
For Reference Only
IBRT
IBRT
VS/P
VS/P
η
tON
tOFF
VOVP
IOVP
mV/°C
SHDN = VIN, No external FET
100
200
μA
SHDN = GND
S/P = VIN, VBRT = GND, ILS = 0A
0.35
10.5
110
1
13.5
μA
μA
μA
V
V
7.5
S/P = VIN, VBRT = GND, ILS = 100μA
0.6
S/P = VIN
VBRT
VBRT
VOS
IPK
-2
V
V
VS/P = VIN (DCS/P = 100%)
DCS/P = 50%, FPWM = 100KHZ
VFB – VBRT, VBRT = 0mV
HYST mode; TA = +25°C
VOUT = 18V, ILOAD = 20mA, VIN = 5.0V
VOVP = 1V
1.4
-1
10
50
270
180
140
10
240
1.10
-50
0.05
1
1000
300
150
4
240
92
200
15
350
1.22
330
300
20
460
1.34
50
WWW . Microsemi .C OM
Unless otherwise specified, the following specifications apply over the operating ambient temperature -40°C ≤ TA
otherwise noted and the following test conditions: VIN = 3.6V, ILOAD = 20mA
μA
KHz
ns
mV
mV
mV
mA
%
mA
μs
ns
V
nA
ELECTRICALS
Copyright © 2003
Rev. 1.0d, 2006-02-09
Microsemi
Integrated Products Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 3
LX1994
®
TM
High Efficiency LED Driver
P RODUCTION D ATA S HEET
SIMPLIFIED BLOCK DIAGRAM
WWW . Microsemi .C OM
1.2V
O VP
CSM
200m V
HYST
B U RS T
CSM
I PEAK
DRV
D R IV E
S W ITCH
LO G IC
I PEAK
100m V
SRC
x10
0.2
K
GND
J/K
LA TC H
C LE A R
J
OUT
Q
CSM
16 B IT S H IFT
RE G IS TE R
CLO C K
I PEAK
0.6V
FB
100K
CMP
10uA
3m V
LS
S /P
BR T
30k
S LEE P
MODE
CO N TR O L
ELECTRICALS
PWM &
S H UTD O W N
D ETEC TIO N
RE F
V IN
Figure 1 – Simplified Block Diagram
Copyright © 2003
Rev. 1.0d, 2006-02-09
Microsemi
Integrated Products Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 4
LX1994
TM
®
High Efficiency LED Driver
P RODUCTION D ATA S HEET
THEORY OF OPERATION
Losses
There are two types of losses in PFM regulator design: the
switching loss, and conduction loss; that contribute to
system inefficiency.
Switching loss: Energy switching losses are associated
with a NFET’s switch changing state (from on to off or
vice versa) as a simultaneous high level of voltage and
current are at the NFET’s switch during the transition.
This switching loss is proportional to the switching
frequency.
Conduction loss: the loss due to current flow in the series
resistance of the switch, inductor, and current sense
resistor. Conduction loss is proportional to the square of
the switch current.
Output Current Selection
The LED output current is regulated by adjusting of the
FB pin voltage. If the FB pin voltage equals the BRT pin
voltage, the LED current is the result of the FB pin
voltage divided by the selected current sense resistor.
For example: in a 100% duty cycle design, FB pin voltage
is 300mV, the current sense resistor is 15Ω. The LED
current equals:
300mV
= 20mA
15Ω
Microsemi
Integrated Products Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
APPLICATIONS
Copyright © 2003
Rev. 1.0d, 2006-02-09
The LX1994 is a highly efficient PFM boost converter; its
design is based on dual mode PFM for driving a series of
white or color LEDs. The advantage of PFM switching is
to minimize system efficiency losses in both heavy and
light load operations. The LX1994 does not require an
external oscillator due to PFM dual modes switching.
In light load operation, the converter minimizes switching
losses by delivering more energy than necessary during
switching burst period than the inactivity coast period.
In heavy load condition, the converter uses the
Continuous Switching Current Mode (CSM) regulation
scheme. This minimized peak switching current and
thereby minimizes the conduction losses.
WWW . Microsemi .C OM
Basic PFM operation
The LX1994 dual mode PFM modulator is implemented in
two switching modes: the hysteretic and Continuous
Switching Mode (CSM).
In hysteretic switching mode, the basic PFM modulator
logic/timing block uses a Fixed Peak Current/ Fixed Off
Time where the switch turns on and allows the inductor
current to ramp to a finite peak level then shuts off for a
fixed duration of time. The basic modulation cycle repeats
as long as the converter output voltage is less than the
maximum regulation level. When the maximum regulation
level is reached, the switch remains off until the output
voltage capacitor discharges to a level less than the
minimum regulation level. The input signals to the switch
logic block are the burst on/off control signal and the peak
current detection signals. For low and negligible switch
conduction losses the designer may set the peak current
comparator at 20mV corresponding to 200mA of output
current.
In Continuous Switching Mode (CSM), the level to the
peak current comparator is variable. This current level is
developed by integrating the output of the feedback
comparator which functions as a high gain bandwidth
limited error amplifier. This current is clamped to the peak
switch current limit of 600mA. The integrated capacitor is
attached at the CMP pin when the burst on/off control line
is forced to the “ON” state.
The conversion from hysteretic to CSM mode is performed
when the burst length exceeds more than 16 switching
cycles counting by an internal 16 bits shift register. The
internal register is clocked by the switch transitions during
each burst period. When the switching cycles exceed 16
cycles, the converter automatically switches over to CSM
mode. CSM mode switching is latched by a J/K flip-flop.
The conversion from CSM mode to hysteretic mode is
performed when the error amplifier output falls below
10mV (corresponding to 100mA peak current) as
determined by a comparator. This resets the J/K flip-flop
and converts back to hysteric mode.
Page 5
LX1994
®
TM
High Efficiency LED Driver
P RODUCTION D ATA S HEET
THEORY OF OPERATION (CONTINUED)
PWM dimming
A PWM signal applied to S/P pin (see figure 4). This
PWM signal is scaled to the reference such that a N% duty
cycle PWM signal will produce an LED current of
{N% • (10μA+ILS) • RBRT}
RFB
Protection and IC Shutdown
OVP: The LX1994 provides OVP protections.
If the
voltage at the OVP pin exceeds the internal reference
voltage (1.2V), the converter will suspend switching. The
converter will attempt to regulate the OVP pin to its
nominal 1.2V.
IC Shutdown: To force the IC into shutdown mode, the
S/P pin must pull low for a duration longer 100µs. In
shutdown mode, the switch is off and the LED string
current typically reduces to a few nano amps of leakage
current.
WWW . Microsemi .C OM
Dimming Modes
Microsemi’s LX1994 provides two dimming options:
PWM or DC voltage input.
If a light sensor (such as Microsemi’s LX1970) is used, the
light sensor current is applied to the LS pin and adds to the
10µA internal current source; in this case the internal
current source determines the adjustment range in a pitch
black ambient. The PWM signal will scale the light sensor
signal allowing the dimming range to increase as the
ambient light increases.
DC dimming mode
In “DC dimming mode” (see figure 5) the BRT pin input
voltage can be applied directly to BRT pin with the S/P pin
pulled high or developed indirectly by applying a PWM
signal to the S/P pin and using a scaling resistor and filter
capacitor at the BRT pin. The internal current source
produces a 10µA reference current that is scaled by the
resistance applied to the BRT pin.
APPLICATIONS
Copyright © 2003
Rev. 1.0d, 2006-02-09
Microsemi
Integrated Products Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 6
LX1994
®
TM
High Efficiency LED Driver
P RODUCTION D ATA S HEET
14 LED EFFICIENCY (3.7V INPUT)
100
90
90
EFFICIENCY
100
80
70
60
WWW . Microsemi .C OM
EFFICIENCY
6 LED EFFICIENCY (3.7V INPUT)
80
70
60
50
0
5
10
15
20
25
LED CURRENT
50
0
5
10
15
20
25
LED CURRENT
HYSTERETIC MODE WAVEFORMS
CONTINUOUS MODE WAVEFORMS
blue = sense voltage
Green = inductor current
blue = sense voltage
Green = inductor current
CHARTS
Copyright © 2003
Rev. 1.0d, 2006-02-09
Microsemi
Integrated Products Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 7
LX1994
®
TM
High Efficiency LED Driver
P RODUCTION D ATA S HEET
APPLICATION CIRCUITS
WWW . Microsemi .C OM
33uH
UPS5819
VIN = 2.0 to 5.5V
LX1994
R6
1M
SRC
S/P
PWM
FDV303
DRV
VIN
OVP
BRT
R4
2.94k
R1
28.7k
FB
LS
C2
1uF
CMP
GND
R7
30k
AUTO
R2
R5
15
0.1uF
226k
VDD
SNK
VSS
SRC
R3
23.2k
LX1970
AUTO MODE RESPONSE
C1
22uF
100% DUTY
MAX
80% DUTY
LED
CURRENT
60% DUTY
40% DUTY
20% DUTY
0% DUTY
AMBIENT LIGHT
Figure 2 –PWM Dimming applied to S/P Input and Light Sensor (Dimming option 1)
Vcc
1M
BSS123
33uH
110k
UPS5819
VIN = 2.0 to 5.5V
+
LX1994
VIN
S/P
PWM
FDV303
DRV
R6
1M
SRC
OVP
BRT
R1
28.7k
R4
2.94k
FB
LS
C2
1uF
GND
CMP
R7
30k
AUTO
R2
0.1uF
R5
15
226k
VDD
SNK
VSS
SRC
R3
4.99k
C1
100uF
AUTO MODE RESPONSE
APPLICATIONS
LX1970
100% DUTY
80% DUTY
60% DUTY
MAX
LED
CURRENT
40% DUTY
20% DUTY
0% DUTY
AMBIENT LIGHT
Figure 3 –PWM Dimming applied to S/P Input and Light Sensor (Dimming option 2)
Copyright © 2003
Rev. 1.0d, 2006-02-09
Microsemi
Integrated Products Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 8
LX1994
®
TM
High Efficiency LED Driver
P RODUCTION D ATA S HEET
APPLICATION CIRCUITS
WWW . Microsemi .C OM
33uH
UPS5819
VIN = 2.0V to 5.5V
LX1994
FDV303
DRV
VIN
1M
PWM dimming
SRC
S/P
OVP
BRT
CMP
LS
0.1uF
FB
GND
0.1uF
51k
15
Figure 4 – LED Driver with PWM Dimming applied to S/P Input
33uH
UPS5819
VIN = 2.0V to 5.5V
LX1994
VIN
FDV303
DRV
1M
ON
S/P
OFF
DIMMING
SRC
OVP
BRT
FB
LS
CMP
GND
51k
15
0.1uF
Figure 5 – LED Driver with DC Dimming applied to BRT Input
Note:
The component values shown are only examples for a working system. Actual values will vary greatly depending
on desired parameters, efficiency, and layout constraints.
APPLICATIONS
Copyright © 2003
Rev. 1.0d, 2006-02-09
Microsemi
Integrated Products Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 9
LX1994
®
TM
High Efficiency LED Driver
P RODUCTION D ATA S HEET
APPLICATION INFORMATION
LIGHT SENSOR INTERFACE
Resistors R6 and R7 of Figure 2 program the over voltage
clamp level. The value of R6 can be as high (like 1MΩ.) to
minimize the quiescent current. The value of R7 can be
determined using the following equation where VOVP is
found in the ELECTRICAL CHARACTERISTICS TABLE:
The LX1994 has a LS input pin to simplify the interface to
an LX1970 light sensor. Two different circuits are
described which provide slightly different response curves.
The equations for calculating the component values are
also given.
R7=R6×
For the circuit of Figure 2, the describing equations are:
⎛ VOVP ⎞
⎜
⎟
⎝ VOUT -VOVP ⎠
R4=
Let R6 equal 1M and the required clamp voltage is 25V.
⎛ 1.2 ⎞
⎜
⎟
⎝ 25-1.2 ⎠
or G4=Gp-
Auto Mode:
⎡ ( ISRC +10μA ) × ( R1×R2×Rp ) ⎤
⎢
⎥
DutyCycle ⎢ ( R1×R2 ) + ( R1×Rp ) + ( R2×Rp ) ⎥
I LED =
×
⎢
⎥
R5
VCC × ( R1×Rp )
⎢+
⎥
⎣⎢ ( R1×R2 ) + ( R1×Rp ) + ( R2×Rp ) ⎦⎥
= 50.4Ω
INDUCTOR AND CAPACITOR SELECTION
The output filter inductor should be a 1µF capacitor with
sufficient voltage rating for the OVP setting. Inductors in
the range of 10µH to 47µH work best. For the best
efficiency a larger value of inductor such as 47µH is
recommended; larger value inductors will reduce ripple
current which reduces peak currents and improves
efficiency. Smaller value inductors may be use less board
space, so a design trade off is in order.
ISRC(MAX) =
LAYOUT GUIDELINES
VIN
1
10
DRV
S/P
2
9
SRC
BRT
3
8
OVP
LS
4
7
FB
GND
5
6
CMP
R3
⎡
⎤
10μA× ( R1×R2×Rp )
⎢
⎥
DutyCycle ⎢ ( R1×R2 ) + ( R1×Rp ) + ( R2×Rp ) ⎥
I LED =
×
⎢
⎥
R5
VCC × ( R2×Rp )
⎢+
⎥
⎢⎣ ( R1×R2 ) + ( R1×Rp ) + ( R2×Rp ) ⎥⎦
Example:
Select R5 = 15 ohms; ILED = 20mA max; ISRC clamp at
100µA; VCC = 3.3; ILED in full darkness and 100% duty
cycle = 4mA.
With R5 = 15 ohms; ILED = 20mA max, VBRT(MAX) =
300mV.
With ISRC clamp at 100µA, Vcompliance (LX1970) =
0.68V, VCC = 3.3V, so
R3=
(3.3-0.68-0.3) =23.2k
100μA
0.1uF
Copyright © 2003
Rev. 1.0d, 2006-02-09
Microsemi
Integrated Products Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 10
APPLICATIONS
The LX1994 requires a tight layout of the CMP pin
capacitance. For best results, the 0.1µF CMP capacitor
should be located directly adjacent to the LX1994 package
with etch lengths as short as possible.
VCC -VCOMPLIANCE -VBRT(MAX)
Manual Mode:
TRANSISTOR AND DIODE SELECTION
A Schottky diode should be used with a 1 Amp current
rating and voltage rating equivalent to the OVP setting. The
transistor should be a N-channel MOSFET with a logic
level gate voltage: good candidates are the FDV303N and
the FDN337. For higher voltages, several BSS138 can be
wired in parallel.
1
30k
Rp+30k
DESIGN EXAMPLE:
R7 = 1M ×R
Rp×30k
WWW . Microsemi .C OM
OVP PROGRAMMING
LX1994
®
TM
High Efficiency LED Driver
P RODUCTION D ATA S HEET
APPLICATION INFORMATION
The level at 100% duty cycle in full darkness is 4mA,
which is 20% of the maximum level of 20mA; this implies
80% is attributable to ISCR. Combining this information with
the describing equation for AUTO mode gives:
80%×I LED(MAX) ×R5=
(
ISRC × R1×R2×Rp
)
( R1×R2) + ( R1×Rp ) + ( R2×Rp )
G1=34.8×10
G2=4.45×10
Gp=376×10
G4=Gp-
-6
416×10 =
1
R1
+
1
+
R2
1
=G1+G2+Gp
-6
=33×10 +
Rp
R1+Rp
=
the
reciprocal
of
the
C1 = 21.5µF
23.2k
The value of C2 works into Rp and the pole should be set
at 1/100 of the PWM frequency.
1
6.28×
10kHz
×2.66k
100
10
R1
=
0.5
C2=
(10μA×R1)+3.0
or G2+Gp=33×10 + (10×G1)
-6
The auto mode equation can be reduced to this assuming
100% duty , 100µA ISRC current and 20mA LED current
(that is 0.3V sense resistor voltage):
R1×Rp
are
0.3×R1
=
(10μA×R1)+VCC -0.3
C1=
This can be restated as:
R2
-6
R1 = 28.7k
R2 = 225k
R4 = 2.91k
Rp
0.3×R1
=
1
=343×10
The value of C1 is selected to give a time constant of ½
second and works into R3 (which is 23.2k).
The manual mode equation can be reduced to this assuming
100% duty and 20mA LED current (that is 0.3V sense
resistor voltage):
+
1
The resistance values
conductance’s so:
Since the left side is the three resistors in parallel, this can
be restated as:
1
-6
30k
( R1×R2×Rp )
0.8×.02×15
=
=2.4k
( R1×R2 ) + ( R1×Rp ) + ( R2×Rp ) 100μA
R2+Rp
-6
Knowing Gp we can find
This implies:
R2×Rp
-6
0.3×R2
( (ISRC +10μA)×R2 ) +VCC -0.3
0.3×R2
=
0.3×R2
For a 10KHz PWM, C2 = 599nF, and a value of 1µf
works well.
Circuit of Figure 3:
The second light sensor interface is very similar to the first;
the choice is a matter of user preference. In the second
circuit, an active 325mV clamp is used to clamp the
maximum LED current in auto mode.
In this circuit, resistor R3 is reduced to extend the
operating ambient light range of the light sensor and filter
capacitor C1 must therefore be increased.
APPLICATIONS
( (100μ+10μA)×R2) +VCC -0.3 (110μA×R2 ) +3.0
This can be restated as:
1
R1
+
1
-6
=367×10 +
Rp
Copyright © 2003
Rev. 1.0d, 2006-02-09
WWW . Microsemi .C OM
The equations above can be solved for G1, G2 and Gp:
R3 = 23.2k
10
R2
or G1+Gp=367×10 + (10×G2 )
-6
Microsemi
Integrated Products Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 11
LX1994
®
TM
High Efficiency LED Driver
P RODUCTION D ATA S HEET
PACKAGE DIMENSIONS
10-Pin Miniature Shrink Outline Package (MSOP)
D
E1
S
e
E
c Θ
A
b
A1
LD
WWW . Microsemi .C OM
DU
Θ
L1
L
Dim
A
A1
b
c
D
e
E
E1
L
L1
S
MILLIMETERS
MIN
MAX
–
1.10
0.05
0.15
0.15
0.30
0.13
0.23
2.90
3.10
0.50 BSC
4.75
5.05
2.90
3.10
0.41
0.70
0.95 BSC
0.50 BSC
0°
6°
INCHES
MIN
MAX
–
0.043
0.002
0.006
0.006
0.012
0.005
0.009
0.114
0.122
0.020 BSC
0.187
0.198
0.114
0.122
0.016
0.028
0.037 BSC
0.020
0°
6°
10-Pin Plastic Micro Lead frame Package (MLP)
D
e
Pin1
ID
E
L
1
2
3
4
5
E2
10
Top View
9
8
7
6
Bottom
View
b
D2
A3
MILLIMETERS
MIN MAX
0.80 1.00
0
0.05
0.20 REF
0.18 0.30
3.00 BSC
2.23 2.48
0.50 BSC
3.00 BSC
1.49 1.74
0.30 0.50
INCHES
MIN
MAX
0.0315 0.0394
0
0.0019
0.0079 REF
0.0071 0.0118
0.1181 BSC
0.0878 0.0976
0.0197 BSC
0.1181 BSC
0.0587 0.0685
0.0071 0.0197
MECHANICALS
A
Dim
A
A1
A3
b
D
D2
e
E
E2
L
A1
Note:
Dimensions do not include mold flash or protrusions; these shall not exceed 0.155mm(.006”) on any side.
Copyright © 2003
Rev. 1.0d, 2006-02-09
Microsemi
Integrated Products Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 12
LX1994
TM
®
High Efficiency LED Driver
P RODUCTION D ATA S HEET
NOTES
WWW . Microsemi .C OM
NOTES
PRODUCTION DATA – Information contained in this document is proprietary to
Microsemi and is current as of publication date. This document may not be modified in
any way without the express written consent of Microsemi. Product processing does not
necessarily include testing of all parameters. Microsemi reserves the right to change the
configuration and performance of the product and to discontinue product at any time.
Copyright © 2003
Rev. 1.0d, 2006-02-09
Microsemi
Integrated Products Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 13