= 50.4鈩?/div>
I
NDUCTOR AND
C
APACITOR
S
ELECTION
The output filter inductor should be a 1碌F capacitor with
sufficient voltage rating for the OVP setting. Inductors in
the range of 10碌H to 47碌H work best. For the best
efficiency a larger value of inductor such as 47碌H 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.
T
RANSISTOR AND
D
IODE
S
ELECTION
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.
L
AYOUT
G
UIDELINES
The LX1994 requires a tight layout of the CMP pin
capacitance. For best results, the 0.1碌F CMP capacitor
should be located directly adjacent to the LX1994 package
with etch lengths as short as possible.
VIN
S/P
BRT
LS
GND
1
2
3
4
5
10
9
8
7
6
鈳?/div>
(
I
SRC
+10碌A(chǔ)
)
脳
(
R1脳R2脳Rp
)
鈳?/div>
鈳?/div>
鈳?/div>
DutyCycle
鈳?/div>
(
R1脳R2
)
+
(
R1脳Rp
)
+
(
R2脳Rp
)
鈳?/div>
I
LED
=
脳
鈳?/div>
鈳?/div>
R5
V
CC
脳
(
R1脳Rp
)
鈳?/div>
+
鈳?/div>
(
R1脳R2
)
+
(
R1脳Rp
)
+
(
R2脳Rp
)
鈳?/div>
鈳?/div>
鈳?/div>
鈳?/div>
I
SRC(MAX)
=
V
CC
-V
COMPLIANCE
-V
BRT(MAX)
R3
Manual Mode:
鈳?/div>
鈳?/div>
10碌A(chǔ)脳
(
R1脳R2脳Rp
)
鈳?/div>
鈳?/div>
DutyCycle
鈳?/div>
(
R1脳R2
)
+
(
R1脳Rp
)
+
(
R2脳Rp
)
鈳?/div>
I
LED
=
脳
鈳?/div>
鈳?/div>
R5
V
CC
脳
(
R2脳Rp
)
鈳?/div>
+
鈳?/div>
(
R1脳R2
)
+
(
R1脳Rp
)
+
(
R2脳Rp
)
鈳?/div>
鈳?/div>
鈳?/div>
鈳?/div>
Example:
Select R5 = 15 ohms; ILED = 20mA max; ISRC clamp at
100碌A(chǔ); 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 100碌A(chǔ), Vcompliance (LX1970) =
0.68V, VCC = 3.3V, so
R3=
A
PPLICATIONS
A
PPLICATIONS
DRV
SRC
OVP
FB
CMP
(
3.3-0.68-0.3
)
=23.2k
100碌A(chǔ)
0.1uF
Copyright
漏
2003
Rev. 1.0a, 2004-08-10
Microsemi
Integrated Products Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 10
LX1994 PDF文件相關(guān)型號(hào)
LX1994CDU
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