LX1992-02W EVAL KIT MICROSEMI, LX1992-02W EVAL KIT Datasheet - Page 6

• Manufacturer Part Number: LX1992-02W EVAL KIT
• Manufacturer: MICROSEMI

Specifications of LX1992-02W EVAL KIT

• Lead Free Status / Rohs Status: Supplier Unconfirmed

Copyright © 2000
Rev. 1.1b, 2005-03-03
Therefore ,
D
An N-channel MOSFET with a relatively low threshold
voltage, low gate charge and low R
optimize overall circuit performance.
Evaluation Board uses a Fairchild FDV303. This NMOS
device was chosen because it demonstrates an R
0.33Ω and a total gate charge Q
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:
D
equals 12.8mA, L equals 47µH, C
equals 3.0V, and V
(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.
voltage characteristic must be capable of withstanding a
negative voltage transition that is greater than V
T
formula for ∆V
IODE
RANSISTOR
ESIGN
The LX1992 can source up to 100mA of gate current.
A Schottky diode is recommended for most applications
∆V
∆V
Determine the V
DROOP
OVERSHOOT
S
TM
ELECTION
∆V
E
XAMPLE
V
∆V
DROOP
RIPPLE
S
=
OVERSHOOT
ELECTION
⎛
⎜ ⎜
⎝
=
47
4
DROOP
Further, the diode’s reverse breakdown
7 .
=
= 10.2mV + 18.4mV + 10mV = 38.6mV
:
1
µH
µF
2
OUT
⎛
⎜ ⎜
⎝
×
C
RIPPLE
⎞
⎟ ⎟
⎠
⎛
⎜ ⎜
⎝
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: [phone]
is:
×
4.7
=
47
OUT
equals 13.0V:
L
(
(
3
200
1
0 .
µ
µ
2
(
(
H
13
×
F
V
−
⎞
⎟ ⎟
⎠
where I
mA
IN
⎛
⎜
⎜
⎝
⎞
⎟ ⎟
⎠
0
×
(
0 .
V
×
C
5 .
(
−
OUT
+
(
OUT
)
I
L
g
200
×
PK
0.5
0.5
of 1.64nC (typ.)
12
+
OUT
⎞
⎟
⎟
⎠
mA
×
8 .
PK
)
−
×
0.5
mA
I
3
(
OUT
equals 200mA, I
I
0 .
equals 4.7µF, V
DS(ON)
−
PK
−
A P P L I C A T I O N I N F O R M A T I O N
)
)
12
V
≅
−
)
IN
8 .
10
I
The LXE1992
OUT
mA
)
is required to
2 .
Linfinity Microelectronics Division
mV
)
)
OUT
2
2
≅
.
DS_ON
18
®
Microsemi
4 .
IN
OUT
mV
of
design tool is provided in Table 3 and the schematic is shown
in Figure 4
PCB L
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.
E
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 R
described in this section) R
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.
connections are described in Table 1.
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.
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.
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).
VALUATION
The factory installed component list for this must-have
The LX1992 produces high slew-rate voltage and current
The LXE1992 evaluation board is available from
The DC input voltage is applied to VBAT (not VCC)
The LX1992 exhibits a low quiescent current (I
AYOUT
High Efficiency LED Driver
B
P
OARD
RODUCTION
The evaluation board input and output
The designer may elect to drive the
D
SET
ATA
(i.e., R4) and diode load.
S
HEET
Q
LX1992
< 0.5µA:
CS
(as
Page 6