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PDF CAT4238 Data sheet ( Hoja de datos )
| Número de pieza | CAT4238 | |
| Descripción | High Efficiency 10 Led Boost Converter | |
| Fabricantes | Catalyst Semiconductor | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de CAT4238 (archivo pdf) en la parte inferior de esta página. Total 14 Páginas | ||
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High Efficiency 10 LED Boost Converter
CAT4238
FEATURES
Drives High Voltage LED strings (38V)
Up to 87% Efficiency
Low Quiescent Ground Current 0.6mA
Adjustable Output Current
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
Portable Game Machines
ORDERING INFORMATION
DESCRIPTION
The CAT4238 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. LED currents up to 40mA can be supported over a
wide range of input supply voltages up to 5.5V, making
the device ideal for battery-powered applications. The
CAT4238 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.
Part Number
CAT4238TD-GT3
Package
TSOT23-5
Green*
Quantity Package
per Reel Marking
3000
MU
* 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
© 2006 Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
TYPICAL APPLICATION CIRCUIT
VIN
C1
4.7µF
OFF ON
L D VOUT
47µH
C2
0.22µF
SW
VIN
CAT4238
SHDN
FB (300mV)
GND
R1
15Ω
20mA
L: Sumida CDC5D23B-470
D: Central CMDSH05-4
C2: Taiyo Yuden UMK212BJ224 (rated 50V)
1 Doc. No. 5019 Rev. A
1 page  
www.DataSheet4U.com
CAT4238
TYPICAL CHARACTERISTICS
VIN = 3.6V, CIN = 4.7μF, COUT = 0.22µF, L = 47µH with 10 LEDs at 20mA, TAMB = 25ºC, unless otherwise specified.
Quiescent Current vs. VIN (Not Switching)
Quiescent Current vs. VIN (Switching)
150
VFB = 0.4V
125
2.0
1.5
100 1.0
75 0.5
50
3.0
3.5 4.0 4.5 5.0
INPUT VOLTAGE [V]
5.5
FB pin voltage vs. Temperature
303
302
301
300
299
298
297
-50
0 50 100
TEMPERATURE [ºC]
150
Switching Frequency vs. Supply Voltage
1.2
0.0
3.0
3.5 4.0 4.5 5.0
INPUT VOLTAGE [V]
5.5
FB Pin Voltage vs. Output Current
310
305
300
295
290
5
10 LEDs
10 15 20 25 30
OUTPUT CURRENT [mA]
Switching Waveforms
1.1
1.0
0.9
0.8
3.0
3.5 4.0 4.5 5.0
INPUT VOLTAGE [V]
5.5
© 2006 Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
5
Doc. No. 5019 Rev. A
5 Page 
www.DataSheet4U.com
CAT4238
BOARD LAYOUT
The CAT4238 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 CAT4238 internal switch
is closed. On Figure 4 is shown the current loop, when
the CAT4238 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 CAT4238 allows for direct connection
of the capacitors to ground. The resistor R1 must be
connected directly to the GND pin of the CAT4238
and not shared with the switching current loops and
any other components.
Figure 3. Closed-switch Current Loop
Figure 4. Open-switch Current Loop
Figure 5. Recommended PCB Layout
© 2006 Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
11
Doc. No. 5019 Rev. A
11 Page | ||
| Páginas | Total 14 Páginas | |
| PDF Descargar | [ Datasheet CAT4238.PDF ] | |
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