Microsemi
Integrated Products Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 1
Copyright 2000
Rev. 1.1, 2002-11-21
WWW.Microsemi .COM
LX1741
High Efficiency High Voltage Boost Controller
PRODUCTIO N D
A
TA SHEET
INTEGRATED PRODUCTS
DESCRIPTION
The LX1741 is a compact high
efficiency step-up boost controller.
Featuring a pseudo-hysteretic pulse
frequency modulation topology, the
LX1741 was designed for maximum
efficiency, reduced board size, and
minimal cost.
Utilizing an external N-Channel
MOSFET, the LX1741 offers
designers maximum flexibility with
respect to efficiency and cost. The
LX1741 provides several design
enhancements that improve overall
performance under very light load
currents by implementing control
circuitry that is optimized for portable
systems - thus providing a quiescent
supply current of only 80µA (typ) and
a shutdown current of less than 1µA.
The input voltage ranges from 1.6V
to 6.0V, allowing for a wide selection
of system battery voltages. Start-up
operation is guaranteed at 1.6V input
The output voltage is programmed
easily using two external resistors in
conjunction with the feedback pin.
Depending on the MOSFET selected,
the LX1741 is capable of achieving
output voltages much higher than 40V.
The LX1741 has an additional feature
for simple dynamic adjustment of the
output voltage (i.e., up to ±15% of the
nominal output voltage). Voltage
adjustment is achieved via an analog
reference signal or a direct PWM input
signal applied to the ADJ pin. Any
PWM amplitude is easily accom-
modated with a single external resistor.
The LX1741 is available in both the 8-
Pin MSOP, and the miniature 8-Pin MLP
requiring minimal PCB area.
IMPORTANT: For the most current data, consult MICROSEMI’s website: http://www.microsemi.com
KEY FEATURES
> 85% Maximum Efficiency
80µA Typical Quiescent Supply
Current
Externally Programmable Peak
Inductor Current Limit For
Maximum Efficiency
Logic Controlled Shutdown
< 0.5 µA Shutdown Current (typ)
Dynamic Output Voltage
Adjustment Via Analog Reference
Or Direct PWM Input
8-Pin MSOP Package or 8-Pin
MLP
APPLICATIONS/BENEFITS
Pagers
Wireless Phones
PDAs
Handheld Computers
General LCD Bias Applications
LED Driver
PRODUCT HIGHLIGHT
C1
4.7µF
RCS
1kΩ
L1
47µH
1206 Case Size
VBAT = 1.6V to 6.0V
ON OFF
VLCD = 18V ± 15%
LX1741
GND
SHDN
IN
ADJ
FB
CS
NDRV
SRC
PACKAGE ORDER INFO
TA (°C) LM Plastic MLP
8-Pin DU Plastic MSOP
8-Pin
0 to 70 LX1741CLM LX1741CDU
Note: Available in Tape & Reel.
Append the letter “T” to the part number. (i.e. LX1741CDUT)
L
LX
X1
17
74
41
1
Microsemi
Integrated Products Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 2
Copyright 2000
Rev. 1.1, 2002-11-21
WWW.Microsemi .COM
LX1741
High Efficiency High Voltage Boost Controller
PRODUCTIO N D
A
TA SHEET
INTEGRATED PRODUCTS
ABSOLUTE MAXIMUM RATINGS
Supply Voltage (VCC)..................................................................................... -0.3V to 7.0V
Feedback Input Voltage (VFB).............................................................. -0.3V to VIN + 0.3V
Shutdown Input Voltage (VSHDN)........................................................ -0.3V to VIN + 0.3V
PWM Input Amplitude......................................................................... -0.3V to VIN + 0.3V
Analog Adjust Input Voltage (VADJ) ................................................................ -0.3V to VIN
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
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 8-Pin
THERMAL RESISTANCE-JUNCTION TO AMBIENT, θJA 206°C/W
THERMAL RESISTANCE-JUNCTION TO CASE, θJC 39°C/W
LM Plastic MLP 8-Pin
THERMAL RESISTANCE-JUNCTION TO AMBIENT, θJA 41°C/W
THERMAL RESISTANCE-JUNCTION TO CASE, θJC 5.2°C/W
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.
PACKAGE PIN OUT
1
2
4
3
5
6
8
7
SRC
CS
GND IN
NDRV
FB
ADJ SHDN
DU PACKAGE
(Top View)
4
3
2
1
5
6
7
8SRC
CS
GND
SHDN
NDRV
FB
IN
ADJ
LM PACKAGE
(Top View)
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 – Connect to a resistive divider network between the output and GND to set the voltage at VFB
(see Output Voltage Programming: Application Information).
SHDN Active-Low Shutdown Input – A logic low shuts down the device and reduces the supply current to 0.1µA.
Connect SHDN to VCC for normal operation.
NDRV MOSFET Gate Driver – Connects to an external N-Channel MOSFET.
CS Current-Sense Amplifier Input – Connecting a resistor between CS and GND sets the peak inductor current limit.
GND Common terminal for ground reference.
ADJ
An applied PWM Signal Input becomes the internal reference, via an internal filter and gain resistor, thus allowing
for a dynamic output voltage adjustment of ±15% (i.e., corresponding to the duty cycle variance). Connecting this
pin to ground causes the device to revert to the internal voltage reference (note: refer to figure 8).
SRC MOSFET Current Sense Input - Connects to the External N-Channel MOSFET Source.
P
PA
AC
CK
KA
AG
GE
E
D
DA
AT
TA
A
Microsemi
Integrated Products Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 3
Copyright 2000
Rev. 1.1, 2002-11-21
WWW.Microsemi .COM
LX1741
High Efficiency High Voltage Boost Controller
PRODUCTIO N D
A
TA SHEET
INTEGRATED PRODUCTS
ELECTRICAL CHARACTERISTICS
Unless otherwise specified, the following specifications apply over the operating ambient temperature 0°C≤ TA ≤ 70°C except where
otherwise noted and the following test conditions: VIN = 3V, VOUT = 18.5V, VADJ = 0V, RLOAD = 9.25kΩ, SHDN = VIN
LX1741
Parameter Symbol Test Conditions Min Typ Max
Units
Operating Voltage VIN 1.6 6.0 V
Minimum Start-up Voltage VSU TA = +25°C 1.6 V
Start-up Voltage Temperature
Coefficient kVST -2
mV/°C
VFB = 1.5V 80 100 µA
Quiescent Current IQ VSHDN < 0.4V 0.2 0.5
µA
FB Threshold Voltage VFB V
ADJ = GND 1.264 1.290 1.316 V
FB Input Bias Current IFB V
FB = 1.4V -200 200 nA
ADJ Input Voltage Range 1 VADJ 0
VIN –
100mV V
ADJ Input Bias Current IADJ V
ADJ = VFB = 1.29V 0.3 1.0
µA
SRC Input Current ISRC 0.8 ARMS
Shutdown Input Bias Current ISHDN SHDN = GND -50 50 nA
Shutdown High Input Voltage VSHDN VIN = 2V 1.6 V
Shutdown Low Input Voltage VSHDN VIN = 2V 0.4 V
Current Sense Bias Current ICS 3.0 5.0 7.0
µA
Minimum Peak Current IMIN GBNT 2 145 mA
Comparator A Delay tD GBNT 2 620 ns
NDRV Sink Current ISNK V
IN = 5V 50 mA
NDRV Source Current ISRC V
IN = 5V 100 mA
Minimum Off-Time tOFF VFB = 1V 100 500 ns
Notes:
1. When using a DC source to adjust VOUT, the recommended VADJ (range) is from 0.9V to 1.50V: see figure 3 and 8.
2. Guaranteed typical value (not tested) @ TA = 25oC (see section “Inductor Selection and Current Limit Programming”)
SIMPLIFIED BLOCK DIAGRAM
Logic
Controller
Reference
Logic
ADJ
FB
Shutdown
Logic SHDN
CS
Driver
GND
NDRV
IN
4µA
SRC
2.5MΩ
50pF
A
B
1.29V
Reference
E
EL
LE
EC
CT
TR
RI
IC
CA
AL
LS
S
Microsemi
Integrated Products Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 4
Copyright 2000
Rev. 1.1, 2002-11-21
WWW.Microsemi .COM
LX1741
High Efficiency High Voltage Boost Controller
PRODUCTIO N D
A
TA SHEET
INTEGRATED PRODUCTS
APPLICATION CIRCUITS
Typical LCD Bias Applications
VBAT = (1.6V to 6.0V)
+=
2
1
REFOUT R
R
1VV
R1
R2
C1
4.7µF
C2
*
1nF
RCS
1kΩ
L1
* Optional Component
used to reduce output
voltage ripple.
47µH
LX1741
NDRV
SHDN
IN
SRC
GND
FB
CS
ADJ
Figure 1 – Fixed Output Voltage Operation
VBAT = (1.6V to 6.0V)
+=
2
1
ADJOUT R
R
1VV
R1
R2
C1
4.7µF
C2
*
1nF
RCS
1kΩ
L1
* Optional Component
used to reduce output
voltage ripple.
47µH
RPWM
100kHz
VPWM = 3.0V 625kΩ
LX1741
NDRV
SHDN
IN
SRC
GND
FB
CS
ADJ
Figure 2 – Dynamic Output Voltage Operation Via PWM Input
Note: An in-series RPWM will attenuate the PWM amplitude to the proper signal level at the ADJ pin. With the RPWM value
shown, a PWM signal having a duty of 30% to 50% will generate 0.9V to 1.5V at the ADJ pin.
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Microsemi
Integrated Products Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page
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Copyright 2000
Rev. 1.1, 2002-11-21
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LX1741
High Efficiency High Voltage Boost Controller
PRODUCTIO N D
A
TA SHEET
INTEGRATED PRODUCTS
APPLICATION CIRCUITS (CONTINUED)
Typical LCD Bias Applications (Cont)
VBAT = (1.6V to 6.0V)
+=
2
1
ADJOUT R
R
1VV
R1
R2
C1
4.7µF
C2
*
1nF
RCS
1kΩ
L1
* Optional Component
used to reduce output
voltage ripple.
47µH
VADJ = 0.9V to 1.5V +
-
LX1741
NDRV
SHDN
IN
SRC
GND
FB
CS
ADJ
Figure 3 – Dynamic Output Voltage Operation Via Analog Voltage Input
LED Driver Application
C1
4.7µF
RCS
1kΩ
L1
47µH
1206 Case Size
R3
63.4Ω
VBAT = 1.6V to 6.0V
ON OFF R1
1ΜΩ
R2
59kΩ
VF = 3.6V typ.
ILED = 20mA to 0.25mA
()
+
−
=21
2
FADJ
3
LED RR
R
V4V
R
1
I
LX1741
NDRV
SHDN
IN
SRC
GND
FB
CS
ADJ
Figure 4 – LED Driver with Full-Range Dimming Via PWM 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.
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Microsemi
Integrated Products Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 6
Copyright 2000
Rev. 1.1, 2002-11-21
WWW.Microsemi .COM
LX1741
High Efficiency High Voltage Boost Controller
PRODUCTIO N D
A
TA SHEET
INTEGRATED PRODUCTS
APPLICATION CIRCUITS (CONTINUED)
Rcs
20K
R2
30.9K
R1
1M
L1
47µH
D1
B150/B
50V
C2
1nF
50V
C1
4.7uF
50V
Q1
3 x BSS138
Vbat = 3.2V Vout = 40V
7
5
4
2
3
6
8
1
LX1741
Figure 5 – Application of Fixed Output, 40V @ 20mA
VBAT +VOUT
R8
4.02K
R2
49.9K
R1
787K
L1
47µH
-VOUT
D1
UPS5819
C1
1uF
25V
C3
1uF
25V
D2
UPS5819
D3
UPS5819
D4
UPS5819
C1
1000pF
50V
C5
1uF
25V
C6
1uF
25V
C4
4.7uF
25V
Q1
FDV303N
7
5
4
2
3
6
8
1
LX1741
Figure 6 – Application of Dual Output, ± 20V @ 2mA
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Microsemi
Integrated Products Division
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Page 7
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Rev. 1.1, 2002-11-21
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LX1741
High Efficiency High Voltage Boost Controller
PRODUCTIO N D
A
TA SHEET
INTEGRATED PRODUCTS
APPLICATION INFORMATION
FUNCTIONAL DESCRIPTION
The LX1741 is a Pulse Frequency Modulated (PFM)
boost converter that is optimized for large step up voltage
applications like LCD biasing. It operates in a pseudo-
hysteretic mode with a fixed switch “off time” of 300ns.
Converter switching is enabled when the feedback voltage,
VFB, falls below the 1.29V reference or VADJ (see Block
Diagram). When this occurs, comparator A activates the
off-time controller. The off-time controller and the current
limiter circuit activate comparator B which toggles the
NDRV output circuit. The NDRV 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.
The 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.
This causes the output voltage to continue to rise at the
input to the feedback circuit (i.e., comparator A). If the
voltage at the FB input is still less than 1.29V at the end of
the off-time period, the NDRV output switches the external
FET “on” and the inductor charging cycle repeats until VFB
is greater than the internal reference. This switching
behavior is shown in Figure 9 and 11.
The application of an external voltage source at the ADJ
pin allows for output voltage adjustment over a typical
range of approximately ±15%. The designer can select one
of two possible methods. One option is to vary the
reference voltage directly at the ADJ pin by applying a DC
voltage from 0.9 to 1.5V. The second option is to connect a
PWM logic signal to the ADJ pin (e.g., see Figure 2). The
LX1741 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 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. If the DC voltage at the ADJ pin drops below
0.6V, the device will revert to the internal reference voltage
level of 1.29V. A typical adjustment curve is shown in
Figure 8 (see section titled: Characteristic Curves).
Disabling the LX1741 is achieved by driving the SHDN pin
with a low-level logic signal thus reducing the device power
consumption to less than 1µA.
OUTPUT VOLTAGE PROGRAMMING
Selecting the appropriate values for R1 and R2 in the
voltage divider connected to the feedback pin programs the
output voltage. Using a value of 49.9K for R2 works well
in most applications. R1 can be determined by the
following equation (where VREF = 1.29V nominal):
(
)
V
V-V
R2R1
REF
REFOUT
×=
DESIGN EXAMPLE:
Let R2 equals 49.9K and the required VOUT equal to
18V.
(
)
Ω=×Ω= K4.646 49.9KR1 1.29V
1.29V- 18V
INDUCTOR SELECTION AND CURRENT LIMIT
PROGRAMMING
Setting the level of peak inductor current to, at least, 1.5x
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:
CS
SCALE
D
IN
MINPEAK RIt
L
V
II
++=
The maximum IPEAK value is limited by the ISRC value
(max. = 0.8ARMS). The minimum IPEAK value is defined
when RCS is zero. A typical value for the minimum peak
current (IMIN) at 25oC is 145mA. The parameter tD is related
to internal operation of comparator A. A typical value at
25oC is 620ns. A typical value of ISCALE at 25oC is 31mA
per KΩ. 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.
4.02KΩ
kΩ
31mA
620ns
H47
3.0V
145mAIPEAK ×+×+=
µ
The result of this example yields a nominal IPEAK equal to
145mA + 39.6mA + 124.6ma = 309.2mA.
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Microsemi
Integrated Products Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page
8
Copyright 2000
Rev. 1.1, 2002-11-21
WWW.Microsemi .COM
LX1741
High Efficiency High Voltage Boost Controller
PRODUCTIO N D
A
TA SHEET
INTEGRATED PRODUCTS
APPLICATION INFORMATION (CONTINUED)
OUTPUT RIPPLE 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
0.5v value in the denominator is an estimate of the voltage
drop across the inductor and the FET’s RDS_ON:
()
()
0.5V
II
C
L
∆V
IN
OUTPK
OUT
DROOP −
××
=
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:
()
()
INOUT
2
OUTPK
OUT
2
1
OVERSHOOT V0.5V
II
C
L
∆V−+
−×
×
=
DESIGN EXAMPLE:
Determine the VRIPPLE where IPK equals 200mA, IOUT
equals 35mA, L equals 47µH, COUT equals 4.7µF, VIN
equals 3.0V, and VOUT equals 18.0V:
()
()
mV82
0.53.0
35mA200mA
F4.7
H47
∆VDROOP =
−
××
µ
µ
=
()
()
mV4.9
0.30.50.81
mA53mA200
F4.7
H47
∆V
2
2
1
OVERSHOOT =
−+
−×
µ
µ
×
=
Therefore, for COUT equals 4.7µF:
VRIPPLE = 28mV + 9.4mV + 10mV = 47.4mV
Increasing the output capacitor value results in the
reduction of the output voltage ripple voltage. Low ESR
capacitors are recommended to reduce ripple caused by the
switching current. Multi-layer ceramic capacitors with
X5R or X7R dielectric are a superior choice featuring small
size, very low ESR, and a temperature stable dielectric.
Low ESR electrolytic capacitors such as solid tantalum or
OS-CON types are also acceptable. Moreover, adding a
capacitor from the output to the feedback pin (C2) allows
the internal feedback circuitry to respond faster which
further minimizes output voltage ripple and reduces noise
coupling into the high impedance feedback input.
DIODE SELECTION
A Schottky diode is recommended for most applications
(e.g. Microsemi UPS5819). 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.
TRANSISTOR SELECTION
The LX1741 can drive up to 100mA of gate drive
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
LXE1741 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.).
PCB LAYOUT
The LX1741 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
circuit.
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Microsemi
Integrated Products Division
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Page
9
Copyright 2000
Rev. 1.1, 2002-11-21
WWW.Microsemi .COM
LX1741
High Efficiency High Voltage Boost Controller
PRODUCTIO N D
A
TA SHEET
INTEGRATED PRODUCTS
EVALUATION BOARD
OVERVIEW
The LXE1741 evaluation board is available from
Microsemi for assessing overall circuit performance. The
evaluation board, shown in Figure 5, is 3 by 3 inches (i.e.,
7.6 X 7.6cm) square and factory calibrated to provide a
nominal 18V output from a 1.6V to 6.0V input. Circuit
designers can easily modify output voltage and current to
suit their particular application by replacing the R1 and RCS
values respectively. Moreover, inductor, FET, and diodes
are easily swapped out to promote design verification of a
circuit that maximizes efficiency and minimizes cost for any
particular application. The input and output connections are
described in Table 1.
ELECTRICAL CONNECTIONS
Apply the DC input voltage to VBAT (not VCC)
however, the LX1741 IC may be driven from a separate DC
source via the VCC input (if desired). Connect the test load
to VOUT. Primary output voltage adjustment is
accomplished by selecting the appropriate value for R1.
Optional fine adjustment of the output voltage is achieved
by applying either a DC voltage or a PWM-type signal to
the VADJ input. Both low frequency (f < 100KHz) and high
frequency (f > 100KHz) PWM signals are accommodated
by choosing the appropriate jumper connection. Further, the
VADJ circuit can be bypassed by selecting the appropriate
jumper position (see Table 2).
The LX1741 exhibits a low quiescent current (IQ < 1µA:
typ) during shutdown mode. The SHDN pin can be used to
examine shutdown performance on the evaluation board.
This pin is pulled-up to VCC via a 10KΩ resistor.
Grounding the SHDN pin shuts down the IC however, the
load is still capable of drawing current through the inductor
& diode circuit path. Hence, VOUT during shutdown will be
approximately VBAT minus the inductor and diode forward
voltage drop.
The LX1741 can achieve output voltages in excess of
25V. In certain applications, it is necessary to protect the
load from excessive voltage excursions. The evaluation
board provides a VLIM jumper position for this purpose.
Engaging this jumper position ensures that the output
voltage does not exceed 25V.
The LXE1741 evaluation board provides an easy and cost
effective solution for evaluation on the LX1741. The
factory installed component list for the evaluation board is
provided in Table 3 and the schematic is shown in Figure 6.
Figure 7 – LX1741 Circuit Evaluation Board
Table 1: Input and Output Pin Assign ments
Pin
Name Allowable
Range Description
VBAT 0 to 6V Main power supply for output. (Set external current limit to 0.5A)
VCC 1.6V to 6V LX1741 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..
SHDN 0 to VCC Pulled up to VCC on board (10KΩ), Ground to inhibit the LX1741.
VOUT VCC to 25V Programmed for 18V output, adjustable up to 25V.
VADJ IN 0 to VCC Apply a DC input or PWM input to adjust the output voltage.
Note: All pins are referenced to ground.
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Microsemi
Integrated Products Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 10
Copyright 2000
Rev. 1.1, 2002-11-21
WWW.Microsemi .COM
LX1741
High Efficiency High Voltage Boost Controller
PRODUCTIO N D
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TA SHEET
INTEGRATED PRODUCTS
EVALUATION BOARD (CONTINUED)
Table 2: Jumper Pin Position Assignments
Jumper / Position Function
VCC/ VBAT 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).
REF/ EXT Use this position when using an external source to adjust the output voltage.
REF/ INT Use this position when using the fixed output voltage mode. In this mode the output voltage can be
varied by changing the value of R1 as described in the data sheet.
ADJ/ HF Use this position when adjusting the output with an external PWM that has a repetition rate in excess of
100KHz.
ADJ/ LF Use this position when adjusting the output with an external PWM that has a repetition rate less than
100KHz. Or when using a DC adjustment voltage.
VLIM/ IN Use this position when adjusting the output voltage to prevent the output voltage from accidentally
exceeding 25V.
VLIM/ OUT This position disables the output voltage adjustment clamp. This position may be desired if maximizing
efficiency when operating near 25V output level.
Note: Always put jumpers in one of the two possible positions
Table 3: Factory Installed Component List for the L X 1741Evaluation Board
Ref Description Supplier Part Number
C1 CAPACITOR, COG, 1000pF, 0402, 50V MURATA GRM36X7R102M050
C2 CAPACITOR, X7R, 0.1uF, 0805, 50V MURATA GRM40X7R104M050
C3 CAPACITOR, Y5V, 2.2uF, 0805, 16V AVX 0805YG225ZAT
C4,5 CAPACITOR, X5R, 4.7uF, 1210, 25V TAIYO YUDEN CETMK325BJ475MN
CR1 RECTIFIER, SCHOTTKY, 1A, 40V,
POWERMITE MICROSEMI UPS5819
L1 INDUCTOR, 47UH, 480mA, SMT TOKO A920CY-470M
JP1-7 3 TERM HEADER, 0.1 IN CTR 3M 929647-09-36-I
SB1-4 JUMPER 3M 929955-06
Q1 MOSFET, N-CHAN, 25V, SOT-23 FAIRCHILD FDV303N
Q2 TRANSISTOR, NPN, 40V, SOT-23 ON MMBT3904LT1
R1 RESISTOR, 698K, 1/16W, 0603 PANASONIC ERJ3EKF6983
R2 RESISTOR, 49.9K, 1/16W, 0603 PANASONIC ERJ3EKF4992
R3 RESISTOR, 619K, 1/16W, 0603 PANASONIC ERJ3EKF6193
R4 RESISTOR, 100K, 1/16W, 0603 PANASONIC ERJ3EKF1003
R5,R6 RESISTOR, 1.00K, 1/16W, 0603 PANASONIC ERJ3EKF1001
R7 RESISTOR, 10.0K, 1/16W, 0603 PANASONIC ERJ3EKF1002
R8 RESISTOR, 4.02K, 1/16W, 0603 PANASONIC ERJ3EKF4021
U1 IC, BOOST CONTROLLER MICROSEMI LX1741
VR1 ZENER, 24V,225mW, SOT-23 ON BZX84C24LT1
Note: The minimum part set for a working power supply consists of: C1, C2, C5, CR1, L1, Q1, R1, R2, R8, U1
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Microsemi
Integrated Products Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 11
Copyright 2000
Rev. 1.1, 2002-11-21
WWW.Microsemi .COM
LX1741
High Efficiency High Voltage Boost Controller
PRODUCTIO N D
A
TA SHEET
INTEGRATED PRODUCTS
EVALUATION BOARD (CONTINUED)
VBAT
GND
VCC
SHDN
VADJ
VOUT
GND
C5
4.7µF
25V
C1
1000pF
50V
C4
4.7µF
25V
C2
0.1µF
50V
C3
2.2µF
16V
R7
10K
R8
4.02K
R3
619K
R4
100K
R2
49.9K
R1
698K
R5
1K
R6
1K
JB1
VCC
JB2
REF
ADJ
JB4
VLIM
Q2
MMBT3904LT1
CR1
UPS5819
LX1741
Q1
FDV303N
VR1
24V
225mW
BZX84C24LT1
L1
47µH
X
X
Figure 8 – LX1741 Boost Evaluation Board Schematic
CHARACTERISTIC CURVES
Channel 1
Channel 2
Figure 9 – VOUT and Inductor Current Waveforms
Channel 1: VOUT (AC coupled; 100mV/div)
Channel 2: Inductor Current (100mA/div.)
Configuration: VIN = 1.6V, VOUT = 5.0V, IOUT = 20.0mA
0
5
10
15
20
25
30
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6 1.7
Adjustment Voltage
Output Voltage
Figure 10 – Typical VOUT versus VADJ
• 0 ~ 0.6V : LX1741 uses internal 1.29V reference.
• 0.7V ~ 0.8V : transition from internal to external reference.
• 0.9 to 1.6V : LX1741 defaults to external voltage reference.
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Microsemi
Integrated Products Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 12
Copyright 2000
Rev. 1.1, 2002-11-21
WWW.Microsemi .COM
LX1741
High Efficiency High Voltage Boost Controller
PRODUCTIO N D
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TA SHEET
INTEGRATED PRODUCTS
CHARACTERISTIC CURVES
Channel 1
Channel 2
Figure 11 – VOUT and Inductor Current Waveforms (mA)
Channel 1: VOUT (AC coupled; 100mV/div)
Channel 2: Inductor Current (100mA/div.)
Configuration: VIN = 3.0V, VOUT = 17.9V, IOUT = 11.0mA
50%
60%
70%
80%
90%
100%
1 2 3 4 5 6 7 8 9 101112131415 1617181920
Output Current
Efficiency (%)
Figure 12 – Efficiency vs. Output Current (mA)
Configuration: VIN = 3.0V, VOUT = 17.9V, L1 = 47.0µH
50%
60%
70%
80%
90%
100%
1 2 3 4 5 6 7 8 9 10 111213141516 17181920
Output Current
Efficiency (%)
Figure 13 – Efficiency vs. Output Current (mA)
Configuration: VIN = 5.2V, VOUT = 17.9V, L1 = 94.0µH
50%
60%
70%
80%
90%
100%
1 2 3 4 5 6 7 8 9 101112131415 1617181920
Output Current
Efficiency (%)
Figure 14 – Efficiency vs. Output Current (mA)
Configuration: VIN = 3.0V, VOUT = 10.0V, L1 = 47.0µH
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Microsemi
Integrated Products Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 1
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Copyright 2000
Rev. 1.1, 2002-11-21
WWW.Microsemi .COM
LX1741
High Efficiency High Voltage Boost Controller
PRODUCTIO N D
A
TA SHEET
INTEGRATED PRODUCTS
CHARACTERISTIC CURVES
50%
60%
70%
80%
90%
100%
1 2 3 4 5 6 7 8 9 10 111213141516 17181920
Output Current
Efficiency (%)
Figure 15 – Efficiency vs. Output Current (mA)
Configuration: VIN = 1.6V, VOUT = 5.0V, L1 = 47.0µH
50%
60%
70%
80%
90%
100%
1 2 3 4 5 6 7 8 9 10 11121314151617181920
Output Current
Efficiency (%)
Figure 16 – Efficiency vs. Output Current (mA)
Configuration: VIN = 3.0V, VOUT = 5.0V, L1 = 47.0µH
50%
60%
70%
80%
90%
100%
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 2 0
Output Current
Efficiency (%)
Figure 17 – Efficiency vs. Output Current (mA)
Configuration: VIN = 3.0V, VOUT = 5.0V, L1 = 47.0µH
0
1
2
3
4
5
6
0 20 40 60 80 100 120
Drive Current (mA)
Gate Drive Voltage (V)
Figure 18 – Gate Drive Voltage vs. Drive Current (mA)
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Microsemi
Integrated Products Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 14
Copyright 2000
Rev. 1.1, 2002-11-21
WWW.Microsemi .COM
LX1741
High Efficiency High Voltage Boost Controller
PRODUCTIO N D
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TA SHEET
INTEGRATED PRODUCTS
PACKAGE DIMENSIONS
DU 8-Pin Miniature Shrink Outline Package (MSOP)
NL
P
K
M
B
D
G
H
C
A
MILLIMETERS INCHES
Dim MIN MAX MIN MAX
A 2.85 3.05 .112 .120
B 2.90 3.10 .114 .122
C – 1.10 – 0.043
D 0.25 0.40 0.009 0.160
G 0.65 BSC 0.025 BSC
H 0.38 0.64 0.015 0.025
J 0.13 0.18 0.005 0.007
K 0.95 BSC 0.037 BSC
L 0.40 0.70 0.016 0.027
M 3° 3°
N 0.05 0.15 0.002 0.006
P 4.75 5.05 0.187 0.198
LM 8-Pin Plastic MLP-Micro Exposed Pa d
e
D
E
b
A3
Internally Connected
together, but isolated
from all other terminals
L2
L2
D2
E2
L
A2 A
A1
K
Θ
MILLIMETERS INCHES
Dim MIN MAX MIN MAX
A 0.80 1.00 0.031 0.039
A1 0.00 0.05 0.000 0.002
A2 0.65 0.75 0.025 0.029
A3 0.15 0.25 0.005 0.009
b 0.28 0.38 0.011 0.015
D 2.90 3.10 0.114 0.122
E 2.90 3.10 0.114 0.122
e 0.65 BSC 0.025 BSC
D2 1.52 2.08 0.060 0.082
E2 1.02 1.31 0.040 0.052
K 0.20 * 0.008 *
L 0.20 0.60 0.008 0.023
L2 0 0.13 0 0.005
Θ 0° 12° 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.
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Microsemi
Integrated Products Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 1
5
Copyright 2000
Rev. 1.1, 2002-11-21
WWW.Microsemi .COM
LX1741
High Efficiency High Voltage Boost Controller
PRODUCTIO N D
A
TA SHEET
INTEGRATED PRODUCTS
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.
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