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Número de pieza | CAT4240 | |
Descripción | 6 Watt Boost LED Driver | |
Fabricantes | Catalyst Semiconductor | |
Logotipo | ||
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6 Watt Boost LED Driver
CAT4240
FEATURES
Switch Current Limit 750mA
Drives High Voltage LED strings (38V)
Up to 87% Efficiency
Low Quiescent Ground Current 0.6mA
1MHz Fixed Frequency Low noise Operation
Soft start “in-rush” current limiting
Shutdown current less than 1μA
Open LED Overvoltage Protection
Automatic Shutdown at 1.9V (UVLO)
Thermal overload protection
Thin SOT23 5-Lead (1mm max height)
APPLICATIONS
GPS Navigation Systems
Portable Media Players
Handheld Devices, Digital Cameras
DESCRIPTION
The CAT4240 is a DC/DC step-up converter that delivers
an accurate constant current ideal for driving LEDs.
Operation at a fixed switching frequency of 1MHz allows
the device to be used with small value external ceramic
capacitors and inductor. LEDs connected in series are
driven with a regulated current set by the external resistor
R1. The CAT4240 high-voltage output stage is perfect for
driving mid-size and large panel displays containing up to
ten white LEDs in series.
LED dimming can be done by using a DC voltage, a logic
signal, or a pulse width modulation (PWM) signal. The
shutdown input pin allows the device to be placed in
power-down mode with “zero” quiescent current.
In addition to thermal protection and overload current
limiting, the device also enters a very low power
operating mode during “Open LED” fault conditions. The
device is housed in a low profile (1mm max height) 5-lead
thin SOT23 package for space critical applications.
ORDERING INFORMATION
Part Number
Package
Quantity Package
per Reel Marking
CAT4240TD-GT3
TSOT23-5
Green*
3000
TG
* NiPdAu Plated Finish
For Ordering Information details, see page 13.
Pin Configuration
5-Lead Thin SOT23
(1mm max height)
SW 1
GND 2
FB 3
5 VIN
4 SHDN
Typical Application Circuit
VL
8V to
16V
C1
VIN
5V C3
1µF
L1 D1
47µH
4.7µF/16V
SW
VIN
C2
1µF/50V
VOUT
CAT4240
SHDN
FB (300mV) R2
GND
1kΩ
300mA
R1
1Ω
© 2007 Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
L1: Sumida CDRH6D28-470
D1: Central CMSH1-40 (rated 40V)
1
Doc. No. MD-5026 Rev. A
1 page www.DataSheet4U.com
CAT4240
TYPICAL CHARACTERISTICS
VIN = 5V, VL = 13V, TAMB = 25ºC, typical application circuit unless otherwise specified.
Maximum Output Current
Shutdown Voltage
500
400
VOUT = 20V
1.0
-25°C
0.8
-40°C
300
VOUT = 30V
200
0.6
0.4
85°C
125°C
100
8
9 10 11 12 13 14 15 16
INDUCTOR VOLTAGE [V]
0.2
3.0
3.5 4.0 4.5
INPUT VOLTAGE [V]
5.0
Switch Current Limit
1200
1100
1000
900
800
700
2.5
VOUT = 20V
3.0 3.5 4.0 4.5 5.0 5.5
INPUT VOLTAGE [V]
© 2007 Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
5
Doc. No. MD-5026 Rev. A
5 Page www.DataSheet4U.com
CAT4240
BOARD LAYOUT
The CAT4240 is a high-frequency switching regulator.
The traces that carry the high-frequency switching
current have to be carefully laid out on the board in
order to minimize EMI, ripple and noise in general.
The thicker lines on Figure 3 show the switching
current path. All these traces have to be short and
wide enough to minimize the parasitic inductance and
resistance. The loop shown on Figure 3 corresponds
to the current path when the CAT4240 internal switch
is closed. On Figure 4 is shown the current loop, when
the CAT4240 switch is open. Both loop areas should
be as small as possible.
Capacitor C1 has to be placed as close as possible to
the VIN pin and GND. The capacitor C2 has to be
connected separately to the top LED anode. A ground
plane under the CAT4240 allows for direct connection
of the capacitors to ground. The resistor R1 must be
connected directly to the GND pin of the CAT4240
and not shared with the switching current loops and
any other components.
L
VIN
D VOUT
VIN
L
D VOUT
SW
VIN
SHDN
CAT4240
Switch
Closed
FB
C1 C2
GND
SW
VIN
SHDN
CAT4240
Switch
Open FB
R1 C1
GND
C2
R1
Figure 3. Closed-switch Current Loop
Figure 4. Open-switch Current Loop
Figure 5. Recommended PCB Layout
© 2007 Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
11
Doc. No. MD-5026 Rev. A
11 Page |
Páginas | Total 14 Páginas | |
PDF Descargar | [ Datasheet CAT4240.PDF ] |
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