LX1994 [MICROSEMI]

High Efficiency LED Driver; 高效率LED驱动器
LX1994
型号: LX1994
厂家: Microsemi    Microsemi
描述:

High Efficiency LED Driver
高效率LED驱动器

驱动器
文件: 总13页 (文件大小:302K)
中文:  中文翻译
下载:  下载PDF数据表文档文件
LX1994  
®
TM  
High Efficiency LED Driver  
PRODUCTION DATA SHEET  
KEY FEATURES  
ƒ Efficiency > 92%  
ƒ Dual PFM Architecture To  
Extend Battery Life  
ƒ VIN Range 2.0V To 5.5V. Start  
Up Warranty @ 2.0V  
ƒ Logic Control Shutdown  
ƒ 100µA Typical Quiescent  
Current  
ƒ Shutdown IQ Current <1µA  
ƒ OVP For Open String Output  
Voltage  
ƒ Low Voltage And Offset  
Current Sense  
ƒ Light Sensor (LX1970)  
interface  
ƒ Dual Dimming Options (PWM  
or DC Voltage)  
ƒ No External Zener Clamp  
Diode  
DESCRIPTION  
Microsemi’s LX1994 is a compact,  
The use of external N-channel  
high efficiency, step-up boost MOSFET allows design to optimize  
controller which is designed to drive a system efficiency.  
string of white or colored LED’s in a  
The OVP protection comparator  
backlight or front light system. The eliminates the need of an external Zener  
LX1994 design is based on a dual diode clamp. The OVP function can be  
mode PFM architecture and provides scaled for any output voltage.  
maximum typical efficiency greater Maximum output current is achievable  
than 92%.  
by selection of the current sense  
These features make the  
The LX1994 has many unique resistor.  
design features and advantages over controller ideal for PDA or digital  
competitor solutions. The features camera applications  
included:  
low quiescent current  
To enhance system battery life, the  
(100µA typical), low shut down LX1994 provides 2 dimming options  
current (<1µA), dedicate ambient light and a dedicated ambient light sensor  
sensor interface (LX1970), dual (LX1970) interface.  
dimming modes, low voltage and low  
offset current sense, and integrated of system battery voltage inputs which  
OVP protection. ranges from 2.0 to 5.5V. The LX1994  
The LX1994 supports a wide range  
ƒ 10-Pin MLP or MSOP  
The converter achieves high is guaranteed to start up at 2.0V input.  
efficiency, low cost, and flexible The LX1994 is available in miniature  
design by selection of an external N- 10-pin MLP or MSOP packages.  
Channel MOSFET, current sense  
APPLICATIONS  
ƒ Pagers  
ƒ PDA  
ƒ Cell Phone  
ƒ Portable Display  
ƒ Digital Cameras  
resistors,  
and  
integrated  
OVP  
protection.  
IMPORTANT: For the most current data, consult MICROSEMI’s website: http://www.microsemi.com  
PRODUCT HIGHLIGHT  
33µH  
UPS5819  
VIN = 2.0V to 5.5V  
LX1994  
FDV303  
VIN  
DRV  
SRC  
OVP  
FB  
Auto Adjust for  
Ambient Light  
S/P  
BRT  
LS  
3V  
VDD  
VSS  
SNK  
SRC  
LX1970  
CMP  
GND  
PACKAGE ORDER INFO  
Plastic MLP  
10-Pin  
Plastic MSOP  
10-Pin  
TA (°C)  
-40 to 85  
LD  
DU  
LX1994CLD  
LX1994CDU  
Note: Available in Tape & Reel. Append the letters “TR” to the part number. (i.e.  
LX1994CDU-TR)  
Copyright © 2003  
Rev. 1.0a, 2004-08-10  
Microsemi  
Page 1  
Integrated Products Division  
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570  
LX1994  
®
TM  
High Efficiency LED Driver  
PRODUCTION DATA SHEET  
ABSOLUTE MAXIMUM RATINGS  
PACKAGE PIN OUT  
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  
1
2
10  
9
VIN  
S/P  
DRV  
SRC  
OVP  
FB  
3
4
5
8
7
6
BRT  
LS  
GND  
CMP  
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.  
1
2
3
4
5
10  
DRV  
VIN  
S/P  
THERMAL DATA  
9
SRC  
Plastic MSOP 10-Pin  
8
DU  
OVP  
BRT  
LS  
THERMAL RESISTANCE-JUNCTION TO AMBIENT, θJA  
113°C/W  
49°C/W  
Connect Bottom to  
Power GND  
7
FB  
6
GND  
CMP  
Plastic MLP 10-Pin  
LD  
LD PACKAGE  
(Top View)  
THERMAL RESISTANCE-JUNCTION TO AMBIENT, θJA  
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.  
FUNCTIONAL PIN DESCRIPTION  
Name  
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.  
IN  
Common terminal for ground reference.  
GND  
BRT  
FB  
LED Current Adjustment - Accepts a DC analog input.  
LED Current Sense – Connect to current sense resistor.  
MOSFET Current Sense Input - Connects to the external N-Channel MOSFET source.  
MOSFET Gate Driver – Connects to an external N-Channel MOSFET gate.  
SRC  
DRV  
Over Voltage Programming Pin – Connects to a resistor divider between the output load and GND to set the  
maximum output voltage.  
OVP  
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.  
LS  
CMP  
S/P  
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. 1.0a, 2004-08-10  
Microsemi  
Page 2  
Integrated Products Division  
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570  
LX1994  
®
TM  
High Efficiency LED Driver  
PRODUCTION DATA SHEET  
ELECTRICAL CHARACTERISTICS  
Unless otherwise specified, the following specifications apply over the operating ambient temperature -40°C TA 85°C except where  
otherwise noted and the following test conditions: VIN = 3.6V, ILOAD = 20mA  
LX1994  
Typ Max  
Parameter  
Symbol  
Test Conditions  
Units  
Min  
`
Operating Voltage  
VIN  
2.0  
5.5  
2.0  
V
V
Minimum Start-up Voltage  
TA = +25°C  
Start-up Voltage Temperature  
Coefficient  
For Reference Only  
-2  
mV/°C  
SHDN = VIN, No external FET  
SHDN = GND  
100  
0.35  
10.5  
110  
200  
1
µA  
µA  
µA  
µA  
V
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  
IBRT  
IBRT  
VS/P  
S/P = VIN, VBRT = GND, ILS = 0A  
S/P = VIN, VBRT = GND, ILS = 100µA  
7.5  
13.5  
0.6  
VS/P  
1.4  
-1  
V
S/P = VIN  
0.05  
1
µA  
KHz  
ns  
10  
1000  
S/P Pulse Width  
50  
BRT PWM Voltage  
VBRT  
VBRT  
VOS  
IPK  
VS/P = VIN (DCS/P = 100%)  
DCS/P = 50%, FPWM = 100KHZ  
VFB – VBRT, VBRT = 0mV  
270  
300  
150  
4
330  
300  
mV  
mV  
mV  
mA  
%
BRT PWM Voltage  
Feedback Comparator Offset  
SCR peak current  
180  
240  
92  
HYST mode; TA = +25°C  
Efficiency  
VOUT = 18V, ILOAD = 20mA, VIN = 5.0V  
η
DRV Sink/Source Current  
Maximum Switch On-Time  
Minimum Switch Off-Time  
OVP Threshold Voltage  
OVP Input Bias Current  
140  
10  
200  
15  
mA  
µs  
tON  
tOFF  
VOVP  
IOVP  
20  
460  
1.34  
50  
240  
1.10  
-50  
350  
1.22  
ns  
V
VOVP = 1V  
nA  
Copyright © 2003  
Rev. 1.0a, 2004-08-10  
Microsemi  
Page 3  
Integrated Products Division  
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570  
LX1994  
®
TM  
High Efficiency LED Driver  
PRODUCTION DATA SHEET  
SIMPLIFIED BLOCK DIAGRAM  
1.2V  
OVP  
CSM  
HYST  
200mV  
BURST  
I PEAK  
DRIVE  
DRV  
CSM  
SWITCH  
LOGIC  
I PEAK  
100mV  
SRC  
x10  
0.2  
K
J
GND  
J/K  
LATCH  
CLEAR  
OUT  
Q
CSM  
16 BIT SHIFT  
REGISTER  
I PEAK  
CLOCK  
0.6V  
100K  
FB  
CMP  
10uA  
3mV  
LS  
S/P  
BRT  
30k  
PWM &  
SHUTDOWN  
DETECTION  
SLEEP  
MODE  
CONTROL  
REF  
VIN  
Figure 1 – Simplified Block Diagram  
Copyright © 2003  
Rev. 1.0a, 2004-08-10  
Microsemi  
Page 4  
Integrated Products Division  
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570  
LX1994  
®
TM  
High Efficiency LED Driver  
PRODUCTION DATA SHEET  
THEORY OF OPERATION  
Basic PFM operation  
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.  
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.  
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 15. The LED  
current equals:  
300mV  
= 20mA  
15  
Copyright © 2003  
Rev. 1.0a, 2004-08-10  
Microsemi  
Page 5  
Integrated Products Division  
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570  
LX1994  
®
TM  
High Efficiency LED Driver  
PRODUCTION DATA SHEET  
THEORY OF OPERATION (CONTINUED)  
Dimming Modes  
Protection and IC Shutdown  
Microsemi’s LX1994 provides two dimming options:  
PWM or DC voltage input.  
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.  
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  
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.  
Copyright © 2003  
Rev. 1.0a, 2004-08-10  
Microsemi  
Page 6  
Integrated Products Division  
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570  
LX1994  
®
TM  
High Efficiency LED Driver  
PRODUCTION DATA SHEET  
6 LED EFFICIENCY (3.7V INPUT)  
14 LED EFFICIENCY (3.7V INPUT)  
100  
100  
90  
80  
70  
60  
50  
90  
80  
70  
60  
50  
0
5
10  
15  
20  
25  
0
5
10  
15  
20  
25  
LED CURRENT  
LED CURRENT  
HYSTERETIC MODE WAVEFORMS  
CONTINUOUS MODE WAVEFORMS  
blue = sense voltage  
Green = inductor current  
blue = sense voltage  
Green = inductor current  
Copyright © 2003  
Rev. 1.0a, 2004-08-10  
Microsemi  
Page 7  
Integrated Products Division  
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570  
LX1994  
®
TM  
High Efficiency LED Driver  
PRODUCTION DATA SHEET  
APPLICATION CIRCUITS  
33uH  
UPS5819  
FDV303  
VIN = 2.0 to 5.5V  
LX1994  
VIN  
S/P  
BRT  
DRV  
R6  
1M  
SRC  
OVP  
PWM  
FB  
R4  
2.94k  
LS  
C2  
1uF  
R1  
CMP  
GND  
28.7k  
R7  
AUTO  
R5  
15  
30k  
R2  
0.1uF  
226k  
VDD  
VSS  
SNK  
SRC  
R3  
23.2k  
AUTO MODE RESPONSE  
LX1970  
C1  
22uF  
100% DUTY  
MAX  
LED  
80% DUTY  
60% DUTY  
40% DUTY  
20% DUTY  
0% DUTY  
CURRENT  
AMBIENT LIGHT  
Figure 2 –PWM Dimming applied to S/P Input and Light Sensor (Dimming option 1)  
Vcc  
1M  
BSS123  
33uH  
UPS5819  
FDV303  
-
VIN = 2.0 to 5.5V  
110k  
+
LX1994  
VIN  
S/P  
BRT  
DRV  
R6  
1M  
SRC  
OVP  
PWM  
FB  
R4  
2.94k  
LS  
C2  
1uF  
R1  
CMP  
GND  
28.7k  
R7  
AUTO  
R5  
15  
30k  
R2  
0.1uF  
226k  
VDD  
VSS  
SNK  
SRC  
R3  
4.99k  
AUTO MODE RESPONSE  
LX1970  
C1  
100uF  
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. 1.0a, 2004-08-10  
Microsemi  
Integrated Products Division  
Page 8  
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570  
LX1994  
®
TM  
High Efficiency LED Driver  
PRODUCTION DATA SHEET  
APPLICATION CIRCUITS  
33uH  
UPS5819  
VIN = 2.0V to 5.5V  
LX1994  
FDV303  
1M  
VIN  
S/P  
BRT  
DRV  
PWM dimming  
SRC  
OVP  
CMP  
FB  
0.1uF  
LS  
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  
FDV303  
1M  
VIN  
S/P  
BRT  
DRV  
ON  
SRC  
OVP  
OFF  
DIMMING  
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.  
Copyright © 2003  
Rev. 1.0a, 2004-08-10  
Microsemi  
Page 9  
Integrated Products Division  
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570  
LX1994  
®
TM  
High Efficiency LED Driver  
PRODUCTION DATA SHEET  
APPLICATION INFORMATION  
LIGHT SENSOR INTERFACE  
OVP PROGRAMMING  
Resistors R6 and R7 of Figure 2 program the over voltage  
clamp level. The value of R6 can be as high (like 1M.) 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.  
For the circuit of Figure 2, the describing equations are:  
VOVP  
R7=R6×  
Rp×30k  
Rp+30k  
1
VOUT -VOVP  
R4=  
or G4=Gp-  
30k  
DESIGN EXAMPLE:  
Auto Mode:  
Let R6 equal 1M and the required clamp voltage is 25V.  
1.2  
I
+10µA × R1×R2×Rp  
(
) (  
)
SRC  
R7 = 1M×R  
= 50.4  
R1×R2 + R1×Rp + R2×Rp  
(
) (  
) (  
)
DutyCycle  
25-1.2  
ILED  
=
×
R5  
VCC× R1×Rp  
(
)
INDUCTOR AND CAPACITOR SELECTION  
+
R1×R2 + R1×Rp + R2×Rp  
(
) (  
) (  
)
)
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.  
VCC -VCOMPLIANCE -VBRT(MAX)  
ISRC(MAX)  
=
R3  
Manual Mode:  
10µA× R1×R2×Rp  
(
)
R1×R2 + R1×Rp + R2×Rp  
(
) (  
) (  
)
DutyCycle  
R5  
ILED  
=
×
TRANSISTOR AND DIODE SELECTION  
VCC× R2×Rp  
(
)
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.  
+
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.  
LAYOUT GUIDELINES  
With R5 = 15 ohms; ILED = 20mA max, VBRT(MAX) =  
300mV.  
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.  
With ISRC clamp at 100µA, Vcompliance (LX1970) =  
0.68V, VCC = 3.3V, so  
3.3-0.68-0.3  
(
)
=23.2k  
1
2
10  
9
VIN  
S/P  
DRV  
SRC  
OVP  
FB  
R3=  
100µA  
3
4
5
8
7
6
BRT  
LS  
GND  
CMP  
0.1uF  
Copyright © 2003  
Rev. 1.0a, 2004-08-10  
Microsemi  
Page 10  
Integrated Products Division  
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570  
LX1994  
®
TM  
High Efficiency LED Driver  
PRODUCTION DATA SHEET  
APPLICATION INFORMATION  
R3 = 23.2k  
The equations above can be solved for G1, G2 and Gp:  
G1=34.8×10-6  
G2=4.45×10-6  
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:  
Gp=376×10-6  
ISRC× R1×R2×Rp  
(
)
Knowing Gp we can find  
1
80%×ILED(MAX)×R5=  
R1×R2 + R1×Rp + R2×Rp  
(
)
) (  
) (  
)
G4=Gp-  
=343×10-6  
30k  
This implies:  
The resistance values are the reciprocal of the  
conductance’s so:  
R1×R2×Rp  
(
0.8×.02×15  
=
=2.4k  
R1×R2 + R1×Rp + R2×Rp  
100µA  
(
) (  
) (  
)
R1 = 28.7k  
R2 = 225k  
R4 = 2.91k  
Since the left side is the three resistors in parallel, this can  
be restated as:  
The value of C1 is selected to give a time constant of ½  
second and works into R3 (which is 23.2k).  
1
1
1
416×10-6 =  
+
+
=G1+G2+Gp  
R1 R2 Rp  
0.5  
C1=  
C1 = 21.5µF  
The manual mode equation can be reduced to this assuming  
100% duty and 20mA LED current (that is 0.3V sense  
resistor voltage):  
23.2k  
The value of C2 works into Rp and the pole should be set  
at 1/100 of the PWM frequency.  
R2×Rp  
0.3×R1  
0.3×R1  
=
=
1
C2=  
R2+Rp (10µA×R1)+VCC -0.3 (10µA×R1)+3.0  
10kHz  
6.28×  
×2.66k  
This can be restated as:  
100  
1
1
10  
=33×10-6 +  
or G2+Gp=33×10-6 + 10×G1  
For a 10KHz PWM, C2 = 599nF, and a value of 1µf  
works well.  
+
(
)
R2 Rp  
R1  
Circuit of Figure 3:  
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):  
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.  
R1×Rp  
R1+Rp  
0.3×R2  
=
(I  
+10µA)×R2 +VCC -0.3  
(
)
SRC  
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.  
0.3×R2  
0.3×R2  
=
=
(100µ+10µA)×R2 +VCC -0.3  
110µA×R2 +3.0  
(
)
(
)
This can be restated as:  
1
1
10  
+
=367×10-6 +  
or G1+Gp=367×10-6 + 10×G2  
(
)
R1 Rp  
R2  
Copyright © 2003  
Rev. 1.0a, 2004-08-10  
Microsemi  
Page 11  
Integrated Products Division  
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570  
LX1994  
®
TM  
High Efficiency LED Driver  
PRODUCTION DATA SHEET  
PACKAGE DIMENSIONS  
10-Pin Miniature Shrink Outline Package (MSOP)  
DU  
D
MILLIMETERS  
INCHES  
Dim  
MIN  
0.05  
0.15  
0.13  
2.90  
MAX  
1.10  
0.15  
0.30  
0.23  
3.10  
MIN  
0.002  
0.006  
0.005  
0.114  
MAX  
A
A1  
b
c
D
e
0.043  
0.006  
0.012  
0.009  
0.122  
E1  
0.50 BSC  
0.020 BSC  
E
E1  
L
4.75  
2.90  
0.41  
5.05  
3.10  
0.70  
0.187  
0.114  
0.016  
0.198  
0.122  
0.028  
S
e
E
L1  
S
Θ
0.95 BSC  
0.50 BSC  
0° 6°  
0.037 BSC  
0.020  
Θ
A
c
0°  
6°  
L1  
b
A1  
L
10-Pin Plastic Micro Lead frame Package (MLP)  
LD  
D
e
Pin1  
L
ID  
MILLIMETERS  
MIN MAX  
INCHES  
1
2
3
4
5
Dim  
MIN  
MAX  
A
A1  
A3  
b
0.80 1.00 0.0315 0.0394  
0.05 0.0019  
0.20 REF 0.0079 REF  
0.18 0.30 0.0071 0.0118  
3.00 BSC 0.1181 BSC  
E
E2  
0
0
10  
9
8
7
6
Top View  
Bottom  
View  
D
b
D2 2.23 2.48 0.0878 0.0976  
D2  
e
0.50 BSC  
0.0197 BSC  
E
3.00 BSC  
0.1181 BSC  
E2  
L
1.49 1.74 0.0587 0.0685  
0.30 0.50 0.0071 0.0197  
A
A3  
A1  
Note: Dimensions do not include mold flash or protrusions; these shall not exceed 0.155mm(.006”) on any side.  
Copyright © 2003  
Rev. 1.0a, 2004-08-10  
Microsemi  
Integrated Products Division  
Page 12  
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570  
LX1994  
®
TM  
High Efficiency LED Driver  
PRODUCTION DATA SHEET  
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. 1.0a, 2004-08-10  
Microsemi  
Integrated Products Division  
Page 13  
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570  

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