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PDF CAT4237 Data sheet ( Hoja de datos )
| Número de pieza | CAT4237 | |
| Descripción | High Voltage CMOS Boost White LED Driver | |
| Fabricantes | Catalyst Semiconductor | |
| Logotipo |  |
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CAT4237
High Voltage CMOS Boost White LED Driver
Features
• Drives 6 to 8 White LEDs in series from 3V
• Up to 87% Efficiency
• Low Quiescent Ground Current 0.6mA
• Adjustable Output Current (up to 40mA)
• High Frequency 1MHz Operation
• High Voltage Power Switch
• Shutdown current less than 1µA
• Open LED low power mode
• Automatic Shutdown at 1.9V (UVLO)
• Thermal shutdown protection
• Thin SOT23 5-Lead (1mm max height)
Applications
• Color LCD and keypad Backlighting
• Cellular Phones
• Handheld Devices
• Digital Cameras
• PDAs
• Portable Game Machine
Ordering Information
Part Package
Number
CAT4237TS TSOT23-5
CAT4237TD TSOT23-5
Lead Free1
Note 1: NiPdAu Lead Plating
Quantity
per Reel
3000
3000
Package
Marking
LS
LT
Product Description
The CAT4237 is a DC/DC step-up converter that
delivers an accurate constant current ideal for
driving LEDs. Operation at a constant 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 from 2.8V to 5.5V, making the device
ideal for battery-powered applications. The
CAT4237 high-voltage output stage is perfect for
driving six, seven or eight white LEDs in series
with inherent current matching in LCD backlight
applications.
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.
Pin Configuration
Typical Application Circuit
Top View
5-Lead Thin SOT23
1mm max height
L: Sumida CDRH3D16-330
D: Central CMDSH05-4 (rated 40V)
C2: Taiyo Yuden UMK212BJ224 (rated 50V)
© 2005 Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
1 of 13
Doc. No. 5013, Rev. A
1 page  
CAT4237
Typical Characteristics
VIN = 3.6V, CIN = 4.7uF, COUT = 0.22µF, L = 33µH with 8 LEDs at 20mA, TAMB=25ºC, unless otherwise specified.
Quiescent Current vs. VIN (Not Switching)
140
120
100
80
60
40 VFB =0.4V
20 (not switching)
0
2.7 3.0 3.3 3.6 3.9 4.2 4.5 4.8
INPUT VOLTAGE [V]
Quiescent Current vs. VIN (Switching)
2.0
1.5
1.0
0.5
0.0
2.5
3.0 3.5 4.0 4.5
INPUT VOLTAGE [V]
5.0
FB Pin Voltage vs. Supply Voltage
315
8LEDs at 20mA
310 VOUT= 26V
305
300
295
290
285
2.7 3.0 3.3 3.6 3.9 4.2 4.5 4.8
INPUT VOLTAGE [V]
FB Pin Voltage vs. Output Current
315
310
8 LEDs
305
300
295
290
285
0
5 10 15 20 25 30
OUTPUT CURRENT [mA]
Switching Frequency vs. Supply Voltage
1040
Switching Waveforms
1020
1000
980
960
2.7 3.0 3.3 3.6 3.9 4.2 4.5 4.8
INPUT VOLTAGE [V]
© 2005 Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
5 of 13
Doc. No. 5013, Rev. A
5 Page 
BOARD LAYOUT
The CAT4237 is a high-frequency switching
regulator. The traces that carry the high-
frequency switching current have to be
carefully layout 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 CAT4237 internal
switch is closed. On Figure 4 is shown the
current loop, when the CAT4237 switch is
Figure 3. Closed-switch current loop
CAT4237
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 CAT4237 allows for direct connection of
the capacitors to ground. The resistor R1
must be connected directly to the GND pin of
the CAT4237 and not shared with the
switching current loops and any other
components.
Figure 4. Open-switch current loop
closed
open
© 2005 Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
11 of 13
Doc. No. 5013, Rev. A
11 Page | ||
| Páginas | Total 13 Páginas | |
| PDF Descargar | [ Datasheet CAT4237.PDF ] | |
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