MICROSEMI LX1992CDU

LX1992
®
TM
High Efficiency LED Driver
P RODUCTION D ATA S HEET
KEY FEATURES
DESCRIPTION
Programming the output current is
readily achieved by using one external
current sense resistor in series with the
LEDs.
In this configuration, LED
current provides a feedback signal to the
FB pin, maintaining constant current
regardless of varying LED forward
voltage (VF). Moreover, the LX1992 is
capable of achieving output currents in
excess of 150mA, depending on the
MOSFET selected.
The LX1992 has an additional feature
for simple dynamic adjustment of the
output current (i.e., up to 100% of the
maximum
programmed
current).
Designers can make this adjustment via
an analog reference signal or a direct
PWM generated signal applied to the
ADJ pin and any PWM amplitude is
easily accommodated with a single
external resistor.
The LX1992 is available in both the 8Pin MSOP, and the miniature 8-Pin MLP
requiring minimal PCB area.
ƒ > 90% Efficiency
ƒ 80µA Typical Quiescent Supply
Current
ƒ Externally Programmable Peak
Inductor Current Limit For
Maximum Efficiency
ƒ Logic Controlled Shutdown
ƒ < 1µA Shutdown Current
ƒ Dynamic Output Current
Adjustment Via Analog
Reference Or Direct PWM Input
ƒ 8-Pin MSOP Package or 8-Pin
MLP
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The LX1992 is a compact high
efficiency step-up boost controller for
driving white or color LEDs in
backlight or frontlight systems and
offers designers maximum flexibility
with respect to efficiency and cost.
The LX1992 features a pseudohysteretic pulse frequency modulation
topology and uses an external NChannel MOSFET.
Further, the
LX1992 features control circuitry that
is optimized for portable systems (e.g.,
quiescent supply current of 80µA
(typ) and a shutdown current of less
than
1µA).
These
design
enhancements provide for improved
performance in battery operated
systems applications.
The device input voltage range is
from 1.6V to 6.0, allowing for a wide
selection of system battery voltages
and
start-up
operation
is
guaranteed at 1.6V input.
APPLICATIONS/BENEFITS
ƒ
ƒ
ƒ
ƒ
ƒ
ƒ
ƒ
Pagers
Wireless Phones
PDAs
Handheld Computers
General LCD Bias Applications
LED Driver
Digital Camera Displays
IMPORTANT: For the most current data, consult MICROSEMI’s website: http://www.microsemi.com
PRODUCT HIGHLIGHT
L1
V BAT = 1.6V to 6.0V
47 µ H
1206 C ase Size
C1
4.7 µ F
DR V
IN
SR C
ON
O FF
SHD N
LX1992
FB
CS
ADJ
GND
R CS
4 kΩ
V F = 3.6V typ.
I LED = 20mA to 0mA
0 to 70
15Ω
LX1992
TA (°C)
R SET
PACKAGE ORDER INFO
Plastic MLP
Plastic MSOP
LM 8-Pin
DU 8-Pin
RoHS Compliant / Pb-free
Transition DC: 0452
RoHS Compliant / Pb-free
Transition DC: 0432
LX1992CLM
LX1992CDU
Note: Available in Tape & Reel. Append the letters “TR” to the part number. (i.e.
LX1992CDU-TR)
Copyright © 2000
Rev. 1.1b, 2005-03-03
Microsemi
Linfinity Microelectronics Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 1
LX1992
®
TM
High Efficiency LED Driver
P RODUCTION D ATA S HEET
PACKAGE PIN OUT
Supply Voltage (VIN) ........................................................................-0.3V to 7.0V
Feedback Input Voltage (VFB) ................................................-0.3V to VIN + 0.3V
Shutdown Input Voltage (V SHDN ) ...........................................-0.3V to VIN + 0.3V
Analog Adjust Input Voltage (VADJ).......................................-0.3V to VIN + 0.3V
Source Input Current (ISRC).................................................................... 0.80 ARMS
Operating Junction Temperature.................................................................. 150°C
Storage Temperature Range...........................................................-65°C to 150°C
Lead Temperature (Soldering 180 seconds) ................................................ 235°C
Peak Package Solder Reflow Temp. (40 second max. exposure) ... 260°C (+0, -5)
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
SRC
1
8
DRV
GND
2
7
IN
CS
3
6
FB
ADJ
4
5
SHDN
DU P ACK AGE
(Top View)
SRC
1
8
DRV
GND
2
7
IN
CS
3
6
FB
ADJ
4
5
SHDN
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ABSOLUTE MAXIMUM RATINGS
LM P ACK AGE
(Top View)
DU
Plastic MSOP 8-Pin
THERMAL RESISTANCE-JUNCTION TO AMBIENT, θJA
THERMAL RESISTANCE-JUNCTION TO CASE, θJC
206°C/W
39°C/W
RoHS / Pb-free 100% Matte Tin Lead Finish
LM Plastic MLP 8-Pin
THERMAL RESISTANCE-JUNCTION TO AMBIENT, θJA
41°C/W
5.2°C/W
THERMAL RESISTANCE-JUNCTION TO CASE, θJC
Junction Temperature Calculation: TJ = TA + (PD x θJC).
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
IN
Unregulated IC Supply Voltage Input – Input range from +1.6V to 6.0V. Bypass with a 1µF or greater capacitor
for operation below 2.0V.
FB
Feedback Input – Connects to a current sense resistor between the output load and GND to set the output
current.
SHDN
CS
MOSFET Gate Driver – Connects to an external N-Channel MOSFET.
Current-Sense Amplifier Input – Connecting a resistor between CS and GND sets the peak inductor current limit.
GND
Common terminal for ground reference.
ADJ
Adjustment Signal Input – Provides the internal reference, via an internal filter and gain resistor, allowing a
dynamic output current adjustment corresponding to a varying duty cycle. The actual ADJ pin voltage range is
from VIN to GND. In order to minimize the current sense resistor power dissipation a practical range of VADJ =
0.0V to 0.5V should be used.
SRC
MOSFET Current Sense Input - Connects to the External N-Channel MOSFET Source.
Note: ADJ pin should not be left floating.
Copyright © 2000
Rev. 1.1b, 2005-03-03
Microsemi
Linfinity Microelectronics Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 2
PACKAGE DATA
DRV
Active-Low Shutdown Input – A logic low shuts down the device and reduces the supply current to 0.2µA (Typ).
Connect SHDN to VCC for normal operation.
LX1992
®
TM
High Efficiency LED Driver
P RODUCTION D ATA S HEET
Parameter
Symbol
Test Conditions
Min
≤
70°C except where
LX1992
Typ
Max
Units
`
Operating Voltage
Minimum Start-up Voltage
Start-up Voltage Temperature
Coefficient
VIN
VSU
FB Threshold Voltage
FB Input Bias Current
ADJ Input Voltage Range
ADJ Input Bias Current
Shutdown Input Bias Current
Shutdown High Input Voltage
Shutdown Low Input Voltage
Current Sense Bias Current
Minimum Peak Current
Efficiency
NDRV Sink Current
NDRV Source Current
Off-Time
VFB
IFB
VADJ
IADJ
I SHDN
V SHDN
V SHDN
ICS
IMIN
η
ISNK
ISRC
tOFF
6.0
1.6
-2
kVST
IQ
Quiescent Current
1.6
TA = +25°C
VFB > 0.3V
V SHDN < 0.4V
275
-100
0.0
-150
-50
1.6
VFB = 0.3V
IOUT = (VADJ)/(RSET)
VADJ < 0.3V
SHDN = GND
VFB < 0.3V
RCS = 560Ω
VIN = 3.0V, ILOAD = 20mA
VIN = 5V
VIN = 5V
VFB = 0.3V; VADJ=0.5V
3.0
53
50
0.2
300
5.0
mV/°C
100
0.5
325
100
VIN
0
50
0.4
7.0
83
85
50
100
100
V
V
500
µA
µA
mV
nA
V
nA
nA
V
V
µA
mA
%
mA
mA
ns
WWW . Microsemi .C OM
ELECTRICAL CHARACTERISTICS
Unless otherwise specified, the following specifications apply over the operating ambient temperature 0°C ≤ TA
otherwise noted and the following test conditions: VIN = 3V, ILOAD = 20mA, SHDN = VIN, and VADJ = 300mV.
SIMPLIFIED BLOCK DIAGRAM
FB
A
DRV
Reference
Logic
ADJ
50pF
SRC
Control
Logic
Driver
GND
2.5M Ω
5µA
B
Microsemi
Linfinity Microelectronics Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
ELECTRICALS
Shutdown
Logic
IN
Copyright © 2000
Rev. 1.1b, 2005-03-03
CS
SHDN
Page 3
LX1992
®
TM
High Efficiency LED Driver
P RODUCTION D ATA S HEET
WWW . Microsemi .C OM
APPLICATION CIRCUITS
Typical LED Driver Applications
L1
V BAT = 1.6V to 6.0V
47 µ H
1206 Case Size
C1
4.7 µ F
DRV
IN
SR C
ON
OFF
SHDN
LX1992
FB
CS
ADJ
G ND
R CS
4 kΩ
V F = 3.6V typ.
I LED = 0mA to 20mA
R SET
15Ω
Figure 1 – LED Driver with Full-Range Dimming Via PWM Input
L1
V BAT = 1.6V to 6.0V
47 µ H
1206 Case Size
C1
4.7 µ F
DRV
IN
SR C
ON
OFF
SHDN
LX1992
FB
CS
ADJ
G ND
R CS
4 kΩ
APPLICATION
V AD J = 0.0V to 0.3V
+
-
R SET
V F = 3.6V typ.
I LED = 0mA to 20mA
15Ω
Figure 2 – LED Driver with Full-Range Dimming Via Analog Voltage 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 © 2000
Rev. 1.1b, 2005-03-03
Microsemi
Linfinity Microelectronics Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 4
LX1992
®
TM
High Efficiency LED Driver
P RODUCTION D ATA S HEET
APPLICATION INFORMATION
The LX1992 is a PFM boost converter that is
optimized for driving a string of series connected LEDs. It
operates in a pseudo-hysteretic mode with a fixed switch
“off time” of 300ns. Converter switching is enabled as
LED current decreases causing the voltage across RSET to
decrease to a value less than the voltage at the VADJ pin.
When the voltage across RSET (i.e., VFB) is less than VADJ,
comparator A activates the control logic. The control logic
activates the DRV output circuit that connects to the gate
of the external FET. The DRV output is switched “on”
(and remains “on”) until the inductor current ramps up to
the peak current level. This current level is set via the
external RCS resistor and monitored through the CS and
SRC inputs by comparator B.
The LED load is powered from energy stored in the
output capacitor during the inductor charging cycle. Once
the peak inductor current value is achieved, the NDRV
output is turned off (off-time is typically 300ns) allowing a
portion of the energy stored in the inductor to be delivered
to the load (e.g., see Figure 5, channel 2). This causes the
output voltage to continue to rise across RSET at the input to
the feedback circuit. The LX1992 continues to switch until
the voltage at the FB pin exceeds the control voltage at the
ADJ pin.
The value of RSET is established by dividing the
maximum adjust voltage by the maximum series LED
current. A minimum value of 15Ω is recommended for
RSET. The voltage at the FB pin is the product of IOUT (i.e.,
the current through the LED chain) and RSET.
R
SET
V
⎤
= ⎡⎢ ADJmax
ILEDmax⎥⎦
⎣
Setting the level of peak inductor current to approximately
2X the expected maximum DC input current will minimize
the inductor size, the input ripple current, and the output
ripple voltage. The designer is encouraged to use inductors
that will not saturate at the peak inductor current level. An
inductor value of 47µH is recommended. Choosing a lower
value emphasizes peak current overshoot while choosing a
higher value emphasizes output ripple voltage. The peak
switch current is defined using a resistor placed between the
CS terminal and ground and the IPEAK equation is:
I PEAK = I MIN + ⎛
⎜
⎝
VIN
L
⎞⎟ t + ⎛⎜ ICS
⎞⎟R
⎠ D ⎝ R ICS ⎠ CS
The maximum IPEAK value is limited by the ISRC value
(max. = 0.8ARMS). The minimum IPEAK value is defined
when RCS is zero. The value range for parameters IMIN and
ICS are provided in the ELECTRICAL CHARACTERISTICS
section of this data sheet. The parameter tD is related to
internal operation of the device. A typical value at 25oC is
800ns. RICS is the internal current sense resistor connected to
the SRC pin. A typical value at 25oC is 200mΩ. All of these
parameters have an effect on the final IPEAK value.
DESIGN EXAMPLE:
Determine IPEAK where VIN equals 3.0V and RCS equals
4.02KΩ using nominal values for all other parameters.
⎞ × 800ns+ ⎛ 5.0µA
⎞ × 4.02KΩ
IPEAK = 73mA + ⎛⎜ 3.0V
⎜
47µH⎟⎠
200mΩ⎟⎠
⎝
⎝
The result of this example yields a nominal IPEAK of
approximately 225mA.
OUTPUT RIPPLE AND CAPACITOR SELECTION
Output voltage ripple is a function of the inductor value
(L), the output capacitor value (COUT), the peak switch
current setting (IPEAK), the load current (IOUT), the input
voltage (VIN) and the output voltage (VOUT) for a this boost
converter regulation scheme. When the switch is first turned
on, the peak-to-peak voltage ripple is a function of the output
droop (as the inductor current charges to IPEAK), the feedback
transition error (i.e., typically 10mV), and the output
overshoot (when the stored energy in the inductor is
delivered to the load at the end of the charging cycle).
Therefore the total ripple voltage is
VRIPPLE = ∆VDROOP + ∆VOVERSHOOT + 10mV
The initial droop can be estimated as follows where the
0.5 value in the denominator is an estimate of the voltage
drop across the inductor and the FET’s RDS_ON: The
Microsemi
Linfinity Microelectronics Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 5
APPLICATION
The application of an external voltage source at the
ADJ pin provides for output current adjustment over the
entire dimming range and the designer can select one of
two possible methods. The first option is to connect a
PWM logic signal to the ADJ pin (e.g., see Figure 1). The
LX1992 includes an internal 50pF capacitor to ground that
works with an external resistor to create a low-pass filter
(i.e., filter out the AC component of a pulse width
modulated input of fPWM ≥ 100KHz). The second option is
to adjust the reference voltage directly at the ADJ pin by
applying a DC voltage from 0.0 to 0.3V (e.g., see Figure
2). The adjustment voltage level is selectable (with limited
accuracy) by implementing the voltage divider created
between the external series resistor and the internal 2.5MΩ
resistor. Disabling the LX1992 is achieved by driving the
SHDN pin with a low-level logic signal thus reducing the
device power consumption to less than 0.5µA (typ).
Copyright © 2000
Rev. 1.1b, 2005-03-03
INDUCTOR SELECTION AND OUTPUT CURRENT LIMIT
PROGRAMMING
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OPERATING THEORY
LX1992
®
TM
High Efficiency LED Driver
P RODUCTION D ATA S HEET
APPLICATION INFORMATION
∆VDROOP
PCB LAYOUT
⎛ L ⎞
⎜⎜
⎟⎟ × (I PK × I OUT )
C OUT ⎠
⎝
=
(VIN − 0.5)
The output overshoot can be estimated as follows where the
0.5 value in the denominator is an estimate of the voltage
drop across the diode:
1
∆VOVERSHOOT =
⎛ L ⎞
⎜
⎟ × (I PK − IOUT )2
⎟
⎝ COUT ⎠
(VOUT + 0.5 − VIN )
2×⎜
EVALUATION BOARD
DESIGN EXAMPLE:
Determine the VRIPPLE where IPK equals 200mA, IOUT
equals 12.8mA, L equals 47µH, COUT equals 4.7µF, VIN
equals 3.0V, and VOUT equals 13.0V:
∆VDROOP
⎛ 47µH ⎞
⎟ × (200mA × 12.8mA )
⎜⎜
4.7µF ⎟⎠
≅ 10.2mV
=⎝
(3.0 − 0.5)
1
∆VOVERSHOOT =
⎛ 47µH ⎞
⎟⎟ × (200mA − 12.8mA )2
⎝ 4.7µF ⎠
≅ 18.4mV
(13.0 + 0.5 − 3.0)
2×⎜
⎜
Therefore, VRIPPLE = 10.2mV + 18.4mV + 10mV = 38.6mV
DIODE SELECTION
TRANSISTOR SELECTION
The LX1992 can source up to 100mA of gate current.
An N-channel MOSFET with a relatively low threshold
voltage, low gate charge and low RDS(ON) is required to
optimize overall circuit performance. The LXE1992
Evaluation Board uses a Fairchild FDV303. This NMOS
device was chosen because it demonstrates an RDS_ON of
0.33Ω and a total gate charge Qg of 1.64nC (typ.)
The LXE1992 evaluation board is available from
Microsemi for assessing overall circuit performance. The
evaluation board, shown in Figure 3, is 3 by 3 inches (i.e.,
7.6 by 7.6cm) square and programmed to drive 4 LEDs
(provided). Designers can easily modify circuit parameters
to suit their particular application by replacing RCS (as
described in this section) RSET (i.e., R4) and diode load.
Moreover, the inductor, FET, and switching diode are easily
swapped out to promote design verification of a circuit that
maximizes efficiency and minimizes cost for a specific
application.
The evaluation board input and output
connections are described in Table 1.
The DC input voltage is applied to VBAT (not VCC)
however the LX1992 IC may be driven from a separate DC
source via the VCC input. The output current (i.e., LED
brightness) is controlled by adjusting the on-board
potentiometer.
The designer may elect to drive the
brightness adjustment circuit from VBAT or via a separate
voltage source by selecting the appropriate jumper position
(see Table 2). Optional external adjustment of the output
LED current is achieved by disengaging the potentiometer
and applying either a DC voltage or a PWM-type signal to
the VADJ input. The PWM signal frequency should be
higher than 150KHz and contain a DC component les than
350mV.
The LX1992 exhibits a low quiescent current (IQ < 0.5µA:
typ) during shutdown mode. The SHDN pin is used to
exercise the shutdown function on the evaluation board.
This pin is pulled-up to VCC via a 10KΩ resistor.
Grounding the SHDN pin shuts down the IC (not the circuit
output). The output voltage (i.e., voltage across the LED
string) is readily measured at the VOUT terminal and LED
current is derived from measuring the voltage at the VFDBK
pin and dividing this value by 15Ω (i.e., R4).
The factory installed component list for this must-have
design tool is provided in Table 3 and the schematic is shown
in Figure 4
Microsemi
Linfinity Microelectronics Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 6
APPLICATION
A Schottky diode is recommended for most applications
(e.g. Microsemi UPS5817). The low forward voltage drop
and fast recovery time associated with this device supports
the switching demands associated with this circuit
topology. The designer is encouraged to consider the
diode’s average and peak current ratings with respect to
the application’s output and peak inductor current
requirements. Further, the diode’s reverse breakdown
voltage characteristic must be capable of withstanding a
negative voltage transition that is greater than VOUT.
Copyright © 2000
Rev. 1.1b, 2005-03-03
The LX1992 produces high slew-rate voltage and current
waveforms hence; the designer should take this into
consideration when laying out the circuit. Minimizing trace
lengths from the IC to the inductor, transistor, diode, input
and output capacitors, and feedback connection (i.e., pin 6)
are typical considerations. Moreover, the designer should
maximize the DC input and output trace widths to
accommodate peak current levels associated with this
topology.
WWW . Microsemi .C OM
formula for ∆VDROOP is:
LX1992
®
TM
High Efficiency LED Driver
P RODUCTION D ATA S HEET
APPLICATION INFORMATION (CONTINUED)
WWW . Microsemi .C OM
Figure 5: LXE1992 Engineering Evaluation Board
Table 1: Input and Ouput Pin Assignments
Pin Name
Allowable Range
Description
VBAT
0 to 6V
VCC
1.6V to 6V
VPOT
1.6V to 6V
VADJ IN
0 to 350mV
/SHDN
0 to VCC
Pulled up to VCC on board (10KΩ), Ground to inhibit the LX1992.
VOUT
0 to 18V
Power supply output voltage that is applied to LED string.
VFDBK
0 to 400mv
Main power supply for output. (Set external current limit to 0.5A)
LX1992 power. May be strapped to VBAT or use a separate supply if VCC jumper is in
the SEP position. Do not power output from VCC pin on board..
Potentiometer power. May be strapped to VBAT or use a separate supply if VPOT
jumper is in the SEP position. Do not power output from VPOT pin on board.
Apply a DC voltage or a PWM voltage to this pin to adjust the LED current. PWM
inputs should be greater than 120Hz and DC portion less than 350mV.
Sense resistor voltage. Divide this voltage by 15 to determine LED current.
Table 2: Jumper Pin Position Assignments
Jumper Position
Functional Description
Use this position when powering VBAT and VCC from the same supply. Do not connect power to the VCC
input when using this jumper position.
VCC/ SEP
Use this position when using a separate VCC supply (different from VBAT).
VPOT/ VBAT
VPOT/ SEP
Use this position when powering the potentiometer reference circuit from the VBAT supply. Do not connect
power to the VCC input when using this jumper position.
Use this position when using a separate power supply (different from VBAT) to power the potentiometer
reference circuit. This will lower the VBAT current and provide a more accurate efficiency reading for the
LX1992 circuit.
ADJ/ POT
Use this position when using the potentiometer to adjust LED current.
ADJ/ EXT
Use this position when adjusting the LED current with an external PWM that has a repetition rate >120Hz. Or
when using a DC adjustment voltage.
Note: Always put jumpers in one of the two possible positions
Copyright © 2000
Rev. 1.1b, 2005-03-03
Microsemi
Linfinity Microelectronics Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 7
APPLICATION
VCC/ BAT
LX1992
®
TM
High Efficiency LED Driver
P RODUCTION D ATA S HEET
Table 3: Factory Installed Component List for the LX1992 Evaluation Board
Quantity
Part
Reference
1
Q1
1
CR1
1
L1
Description
Manufacturer
Part
Number
Fairchild
FDV303N
Mosfet, N-Channel, 25V, SOT23 Type SMT
Rectifier, Schottky, 1A, 20V, Powermite Type SMT
Microsemi
UPS5817
Toko
A920CY-470
Inductor, 47uH, 540mA, SMT
2
C1, C2
Capacitor, Ceramic X5R, 4.7uF, 25V, 1210 Type SMT
Taiyo Yuden
CETMK325BJ475MN
2
C3, C4
Capacitor, Ceramic X7R, 0.1uF, 50V, 0805 Type SMT
Murata
GRM40X7R104M050
1
R4
Resistor, 15 Ohm, 1/10W, 0805 Type SMT
Panasonic
ERJ6ENF15R0
1
R5
Resistor, 1K, 1/16W, 0603 Type SMT
Panasonic
ERJ3EKF1001
1
R2
Resistor, 4.02K, 1/16W, 0603 Type SMT
Panasonic
ERJ3EKF4021
2
R3, R6
Resistor, 100K, 1/16W, 0603 Type SMT
Panasonic
ERJ3EKF1003
Panasonic
ERJ3EKF1002
Bourns
3352E-1-503
1
R1
Resistor, 10K, 1/16W, 0603 Type SMT
1
R7
Trimpot, 50K, 1/2W, Through Hole Type
1
VR1
IC, Voltage Reference, 1.25 Volts, SOT23 Type SMT
Microsemi
LX432CSC
1
VR2
Diode, Zener, 24V, 3W Powermite Type SMT
Microsemi
1PMT5934B
4
LED1 - 4
White LED
Chicago Miniature
CMD333UWC
3
JB1 - JB3
Header, 3 Pos Vertical Type
3M
929647-09-36
Jumper
3M
929955-06
3
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APPLICATION INFORMATION (CONTINUED)
Note: The minimum set of parts needed to build a working power supply are: Q1, CR1, L1, C2, C3, R2, R4, U1.
CR1
UPS5817
L1
47µH
VBAT
VPOT
VCC
C2
4.7µF
25V
C1
4.7µF
25V
VOUT
GND
Q1
FDV303N
CMD333UW C
C3
0.1µF
50V
VCC
SR C
GN
D
R1
10k
CS
R2
4.02k
AD J
NDR V
VR2
20V
1W
1PMT4114
IN
CMD333U W C
FB
SHDN
CMD333UW C
SHDN
CMD333UW C
VFDBK
R3
100k
VADJ
R4
15 Ω
VADJ
APPLICATION
R5 1k
C4
0.1µF
25V
VPOT
R6
100k
VR1
LX432
R7
50k
Figure 4 – LXE1992 Boost Evaluation Board Schematic
Copyright © 2000
Rev. 1.1b, 2005-03-03
Microsemi
Linfinity Microelectronics Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 8
LX1992
®
TM
High Efficiency LED Driver
P RODUCTION D ATA S HEET
WWW . Microsemi .C OM
CHARACTERISTIC CURVES
Figure 6: VOUT and Inductor Current Waveforms.
Figure 5: VOUT and Inductor Current Waveforms.
Channel 1: VOUT (AC coupled; 100mV/div)
Channel 2: Inductor Current (100mA/div.)
Configuration: VIN = 3.0V, VOUT = 13.7V, IIN = 120mA
Channel 1: VOUT (AC coupled; 200mV/div)
Channel 2: Inductor Current (100mA/div.)
Configuration: VIN = 3.0V, VOUT = 13.0V, IIN = 65mA
90%
80%
4
Efficiency
Drive Voltage (V)
5
3
2
60%
1
0
50%
0
20
40
60
80
100
Driv e Current (mA)
120
140
160
0
Figure 7: Gate Drive Voltage vs. Drive Current
at T = 25oC.
100%
90%
Efficiency
70%
80%
70%
60%
0
2
4
6
8
10 12 14 16
LED Current (mA)
18
20
22
24
4
6
8
10
LED Current (mA)
12
14
16
18
Figure 8: Efficiency vs. LED Output Current.
Configuration: VIN = 3.0V, L = 47µH, RCS = 4KΩ
Note: Data taken from LXE1992 Evaluation Board
Efficiency Measurement Hint: When doing an efficiency
evaluation using the LX1992 Evaluation Board, VPOT should
be driven by a separate voltage supply to account for losses
associated with the onboard reference (i.e., the 1.25V shunt
regulator and 1KΩ resistor). This circuit will have VBAT 1.25V across it and at the higher input voltages the 1KΩ
resistor could have as much as 4mA through it. This shunt
regulator circuitry will adversely effect the overall efficiency
measurement and is not normally used in an application.
Therefore it should not be considered when measuring
efficiency.
Figure 9: Efficiency vs. LED Output Current.
Configuration: VIN = 5.0V, L = 47µH, RCS = 4KΩ
Note: Data taken from LXE1992 Evaluation Board
Copyright © 2000
Rev. 1.1b, 2005-03-03
Microsemi
Linfinity Microelectronics Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 9
CH A R T S
50%
2
LX1992
®
TM
High Efficiency LED Driver
P RODUCTION D ATA S HEET
PACKAGE DIMENSIONS
WWW . Microsemi .C OM
DU
8-Pin Miniature Shrink Outline Package (MSOP)
A
Dim
B
H
G
P
M
C
N
LM
K
L
D
A
B
C
D
G
H
J
K
L
M
N
P
MILLIMETERS
MIN
MAX
2.85
3.05
2.90
3.10
–
1.10
0.25
0.40
0.65 BSC
0.38
0.64
0.13
0.18
0.95 BSC
0.40
0.70
3°
0.05
0.15
4.75
5.05
INCHES
MIN
MAX
.112
.120
.114
.122
–
0.043
0.009
0.160
0.025 BSC
0.015
0.025
0.005
0.007
0.037 BSC
0.016
0.027
3°
0.002
0.006
0.187
0.198
8-Pin Plastic MLP-Micro Exposed Pad
Dim
D
L
L2
K
D2
E
E2
e
b
Θ
A2
A
A3
A1
Internally Connected
together, but isolated
from all other terminals
INCHES
MIN
MAX
0.031
0.039
0.000
0.002
0.025
0.029
0.005
0.009
0.011
0.015
0.114
0.122
0.114
0.122
0.025 BSC
0.060
0.082
0.040
0.052
0.008
*
0.008
0.023
0
0.005
0°
12°
Note:
1. Dimensions do not include mold flash or
protrusions;
these
shall
not
exceed
0.155mm(.006”) on any side. Lead dimension
shall not include solder coverage.
Copyright © 2000
Rev. 1.1b, 2005-03-03
Microsemi
Linfinity Microelectronics Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 10
MECHANICALS
L2
A
A1
A2
A3
b
D
E
e
D2
E2
K
L
L2
Θ
MILLIMETERS
MIN
MAX
0.80
1.00
0.00
0.05
0.65
0.75
0.15
0.25
0.28
0.38
2.90
3.10
2.90
3.10
0.65 BSC
1.52
2.08
1.02
1.31
0.20
*
0.20
0.60
0
0.13
0°
12°
LX1992
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 © 2000
Rev. 1.1b, 2005-03-03
Microsemi
Linfinity Microelectronics Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 11