TI CAT37 Cmos white led driver boost converter Datasheet

CAT37
CMOS White LED Driver Boost Converter
FEATURES
DESCRIPTION
„ Low quiescent ground current (0.5mA typical)
The CAT37 is a DC/DC step up converter that delivers
a regulated output current. Operation at a constant
switching frequency of 1.2MHz allows the device to be
used with very small value external inductor and
ceramic capacitors.
„ Power efficiency over 80%
„ Compatible pinout with LT1932
„ Adjustable output current (up to 40mA)
„ High frequency 1.2MHz operation
The CAT37 is targeted to drive multiple white lightemitting diodes (LEDs) connected in series and
provides the necessary regulated current to control
the brightness and the color purity. An external
resistor R1 controls the output current level. LED
currents of up to 40mA can be supported over a wide
range of input supply voltages from 2.5V to 7V,
making the device ideal for battery-powered
applications.
„ Input voltage operation down to 2.5V
„ Low resistance (0.5Ω) power switch
„ Drives up to 4 White LEDs in series
„ Shutdown current less than 1µA
„ Load fault protection against open-circuits
„ Low value external components
„ Low profile (1mm) TSOT-23 5-lead package
A high voltage output stage allows up to 4 White LEDs
to be driven in series. Series drive provides inherent
current matching.
APPLICATION
„ Color LCD and keypad backlighting
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 “near zero”
quiescent current.
„ Cellular phones
„ Handheld terminals
„ Digital cameras
„ PDAs/Games
In addition to overcurrent limiting protection, the
device also includes detection circuitry to ensure
protection against open-circuit load fault conditions.
„ Portable MP3 players
For Ordering Information details, see page 11.
The device is available in a low profile (1mm max
height) 5-lead TSOT-23 package.
TYPICAL APPLICATION CIRCUIT
L1
6.8µH
D1
VIN
3V to 5V
C1
1µF
5
VIN
C2
1µF
1
SW
CAT37
ON OFF
4
FB
SHDN
GND
2
3
15mA
R1
6.34kΩ
C1: Taiyo Yuden JMK212BJ475
C2: Taiyo Yuden EMK212BJ105
D1: Zetez ZHCS400
L1: Panasonic ELJEA6R8 or equivalent
Figure 1. Driver for Four High-Brightness White LEDs
© Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
1
Doc. No. MD-5005 Rev. T
CAT37
ORDERING INFORMATION
Part Number
CAT37TDI-T3
CAT37TDI-GT3
Package
TSOT-23 5-lead (1)
TSOT-23 5-lead (2)
Quantity per Reel
3,000
3,000
Package Marking
LM
UL
PIN CONFIGURATION
TSOT-23 5-Lead
Top View
SW
1
GND
2
FB
3
5
VIN
4
SHDN
1mm maximum height
θJA = 250ºC/W [free air]
PIN DESCRIPTION
Pin Number
Name
1
SW
2
GND
3
FB
4
¯¯¯¯¯
SHDN
5
VIN
Function
Switch pin. This is the drain of the internal power switch. For minimum EMI,
minimize the trace area connected to this pin.
Ground pin. Connect pin 2 to ground.
LED (cathode) connection pin.
Shutdown pin.
Input supply pin. This pin should be bypassed with a capacitor to ground. A 1µF
capacitor mounted close to the pin is recommended.
Notes:
(1) Matte-Tin Plated Finish (RoHS-compliant).
(2) NiPdAu Plated Finish (RoHS-compliant).
Doc. No. MD-5005 Rev. T
2
© Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
CAT37
ABSOLUTE MAXIMUM RATINGS
Parameter
VIN, FB, ¯¯¯¯¯
SHDN voltage
SW voltage
Storage Temperature Range
Junction Temperature
Lead Soldering Temperature (10 secs)
ESD Rating – Human Body Model
(1)
Rating
8
20
-65 to +160
125
300
2000
Unit
V
V
ºC
ºC
ºC
V
RECOMMENDED OPERATING CONDITIONS
Parameter
VIN
Ambient Temperature Range
Inductor L1
Input Capacitor C1
Output Capacitor C2
ILED with 1 to 4 LEDs in series
Range
2.5 to 7
-40 to +85
6.8 ± 20% typical
1.0 ± 20% typical
1.0 ± 20% typical
0 to 20
Unit
V
°C
µH
µF
µF
mA
Typical application circuit with external components is shown on page 1.
ELECTRICAL OPERATING CHARACTERISTICS
Over recommended operating conditions unless otherwise specified. TA = 25ºC, VIN = 3V and V¯¯¯¯¯
SHDN = 3V.
Symbol
Parameter
Conditions
Input Voltage Range
Min
Typ
2.5
Max
Units
7
V
IQ
Quiescent Current
VFB = 0.2 V
0.5
0.7
mA
ISD
Shutdown Current
VSHDN = 0 V
0.05
1
µA
VFB
FB Pin Voltage
4 LEDs at 15 mA
95
105
mV
IFB
FB Pin Leakage Current
1
2
µA
Shutdown High Threshold
85
0.85
V
Shutdown Low Threshold
ISHDN
Shutdown Pin Current
0.25
V
1
nA
1.6
MHz
fSW
Boost Converter Frequency
0.8
1.2
DC
Maximum Switch Duty Cycle
90
95
ISWL
Switch Current Limit
400
550
780
mA
%
Switch Saturation Voltage
ISW = 300 mA
150
200
mV
Switch Leakage Current
Switch Off, VSW = 5 V
0.01
5
µA
Efficiency
Figure 1 with specified components
83
%
Notes:
(1) These are stress ratings only and functional operation is not implied. Exposure to absolute maximum ratings for prolonged time periods
may affect device reliability. All voltages are with respect to ground.
© Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
3
Doc. No. MD-5005 Rev. T
CAT37
TYPICAL CHARACTERISTICS
VIN = 3.6V, TAMB = 25ºC, CIN = 4.7µF, COUT = 1µF, L = 6.8µH, unless otherwise specified.
LED Current vs. Temperature
LED Current vs. Input Voltage
30
16.0
LEDs
3 3LEDs
LED CURRENT [mA]
LED CURRENT [mA]
20mA
20mA
20
10mA
10mA
10
15.5
15.0
4 4LEDs
LEDs
14.5
14.0
0
2
3
4
5
6
-50
-25
0
25
50
75
100
TEMPERATURE [ºC]
INPUT VOLTAGE [V]
FB Pin Voltage vs. LED Current
FB Pin Voltage vs. Temperature
100
110
FB PIN VOLTAGE [mV]
FB PIN VOLTAGE [mV]
105
3 LEDs
3 LEDs
100
95
90
85
95
90
85
4 LEDs at
at 15mA
15mA
4LEDs
VIN
=
3.6V
VIN = 3.6V
80
80
0
5
10
LED CURRENT [mA]
15
-50
20
25
50
75
100
Switching Frequency vs. Temperature
1.3
1.3
SWITCHING FREQUENCY [MHz]
SWITCH FREQUENCY [MHz]
0
TEMPERATURE [ºC]
Switching Frequency vs. Input Voltage
1.2
1.1
1.0
0.9
4 LEDs
4 LEDs
0.8
-25
1.2
1.1
LOAD
= 20mA
LOAD
=20
mA
1.0
LOAD
LOAD==33LEDs
LEDsVIN
=VIN
3.6V
= 3.6V
0.9
0.8
1
2
3
4
5
6
-50
INPUT VOLTAGE [V]
Doc. No. MD-5005 Rev. T
4
-25
0
25
50
TEMPERATURE [ºC]
75
100
© Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
CAT37
TYPICAL CHARACTERISTICS
VIN = 3.6V, TAMB = 25ºC , CIN = 4.7µF, COUT = 1µF, L = 6.8µH, unless otherwise specified.
Efficiency vs. Input Voltage
Efficiency vs. Temperature
90
86
85
84
80
82
EFFICIENCY [%]
EFFICIENCY [%]
LOAD = 20 mA
33
LEDS
LEDsatat15mA
15mA
VOUT
==
10V
VOUT
10V
75
70
65
LOAD = 15 mA
LOAD = 10 mA
80
78
LOAD = 3 LEDs
= VIN
3.6V= 3.6V
76
60
74
2
3
4
5
6
-50
INPUT VOLTAGE [V]
VSW, IL, & VOUT Waveforms
-25
0
25
50
TEMPERATURE [ºC]
75
100
PWM on SHDN
¯¯¯¯¯ pin at 1kHz
Enable Power-Up Waveforms
© Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
5
Doc. No. MD-5005 Rev. T
CAT37
OPERATION
The CAT37 device is a high efficiency, constant frequency, current regulating boost driver for white LEDs.
While maintaining LED current regulation, the CAT37
boost converter automatically adjusts the FB pin
voltage to be as low as possible. A low FB pin voltage
ensures high efficiency.
The device includes a switch and an internally
compensated loop for the regulation of the current in
the LEDs.
Current through the internal power switch is
continuously monitored cycle-by-cycle. If the current
limit is exceeded, the switch is immediately turned off,
protecting the device, for the remainder of the cycle.
Operation can be best understood by examining the
block diagram. The FB pin is regulated at 95mV and
the current through the external resistor will set the
regulated current in the LEDs at:
ILED =
PWM dimming operation can be achieved by
switching the ¯¯¯¯¯
SHDN pin or by pulling the FB pin
higher than 95mV.
0.095
R1
BLOCK DIAGRAM
D1
L1
VIN
5
C1
1
VIN
4
C2
SW
SHDN
1.2MHz
Oscillator
Over Voltage
Protection
(22V)
90kΩ
6kΩ
PWM
& Logic
ILED
FB
3
Error
Amp
R1
0.095V
REF
Current
Sense
Amp
CAT37
GND
2
Figure 2. CAT37 Block Diagram
Doc. No. MD-5005 Rev. T
6
© Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
CAT37
APPLICATION INFORMATION
CAPACITOR SELECTION
Table 2: Schottky Diode Suppliers
Low ESR (equivalent series resistance) capacitors
should be used at the output to minimize the output
ripple voltage. The low ESR and small package
options available with multilayer ceramic capacitors
make them excellent choices. The X5R and X7R
capacitor types are preferred because they retain their
capacitance over wider voltage and temperature
ranges than the Y5V or Z5U types. A 1.0µF output
capacitor is recommended for most applications.
Part
MBR0520
MBR0530
MBR0540
ZHCS400
Table 4: R1 Resistor Values
www.t-yuden.com
Murata
www.murata.com
Kemet
www.kemet.com
AVX
www.avxcorp.com
For other LED current values, use the following
equation to choose R1.
R1 =
DIODE SELECTION
Characteristics subject to change without notice
0.095
ILED
Most white LEDs are driven at maximum currents of
15mA to 20mA. Some higher power designs will use
two parallel strings of LEDs for greater light output,
resulting in 30mA to 40mA (two strings of 15mA to
20mA) flowing through the R1 resistor.
Schottky diodes, with their low forward voltage drop
and fast switching speed, are the ideal choice for high
efficiency applications. Table 2 shows several
different Schottky diodes that work well with the
CAT37. Make sure that the diode has a voltage rating
greater than the output voltage. The diode conducts
current only when the power switch is turned off
(typically less than one-third the time), so a 0.4A or
0.5A diode will be sufficient for most designs.
© Catalyst Semiconductor, Inc.
R1 (Ω)
2.37
3.16
4.75
6.34
7.87
9.53
19.1
ILED (mA)
40
30
25
20
15
10
5
Table 1: Ceramic Capacitor Manufacturers
Taiyo Yuden
Zetex
The LED current is programmed with a single resistor
connected to the FB pin. The FB pin is internally
regulated to 95 mV, which sets the current flowing
through R1 and the LEDs as equal to 0.095/R1. For
the best accuracy, a 1% or better resistor is
recommended. Table 3 shows several typical 1% R1
values.
Low profile ceramic capacitors with a 1mm maximum
height/thickness are available for designs height
requirements. Ceramic capacitors also make a good
choice for the input capacitor, which should be
mounted as close as possible to the CAT37. A 1µF or
4.7µF input capacitor is recommended. Table 1 shows
a list of several ceramic capacitor manufacturers.
Consult the manufacturers for detailed information as
new products and package options are introduced
regularly.
Web
ON Semiconductor
www.onsemi.com
800.282.9855
LED CURRENT PROGRAMMING
The voltage rating of the output capacitor C2 depends
on the number of LEDs driven in the series. A 16V
ceramic capacitor is recommended when driving 3 or
4 LEDs.
Supplier
Supplier
7
Doc. No. MD-5005 Rev. T
CAT37
LED DIMMING WITH DC SIGNAL
LED DIMMING WITH A LOGIC SIGNAL
Dimming the LEDs can be done by applying a variable
DC voltage as shown on Figure 3. As the VDC increase
the voltage across R1 decreases and therefore lower
the LED current. The resistors R2 and R3 must be
large enough so that their current (tens of µA) is much
smaller than the LED current but much larger than the
FB leakage current (IFB). When adjusting VDC between
0V and 2V, the resistors shown on Figure 3 will set
the LED current between 0mA and 15mA.
For applications that need to adjust the LED
brightness in discrete steps, a logic signal can be
used as shown in Figure 5. R1 sets the minimum LED
current value (when the NMOS switch is OFF):
R1 =
RINCR determines how much LED current increases
when the external NMOS switch is turned ON.
LED DIMMING WITH PWM SIGNAL
PWM brightness control provides the widest dimming
range (greater than 20:1). By turning the LEDs ON
and OFF using the control signal, the LEDs operate at
either zero or full current, but their average current
changes with the PWM signal duty cycle. Typically, a
5kHz to 40kHz PWM signal is used.
RINCR =
The SW pin, schottky diode and capacitor C2 signal
path should be kept as short as possible. The ground
connection for the R1 resistor should be tied directly to
the GND pin and not be shared with other components.
CAT37
CAT37
FB
FB
FB
R2
1kΩ
VDC
PWM
R1
6.3Ω
Figure 3. Dimming with a
DC Voltage
Doc. No. MD-5005 Rev. T
10kΩ
ILED(INCREASE )
The CAT37 is a high-frequency switching regulator
where proper PCB board layout and component
placement can minimize noise and radiation and
increase efficiency. To maximize efficiency, the
CAT37 design has fast switch rise and fall times. To
prevent radiation and high frequency resonance
problems minimize the length and area of all traces
connected to the SW pin and use a ground plane
under the switching regulator.
In addition to providing the widest dimming range,
PWM brightness control also ensures the “purest”
white LED color over the entire dimming range. The
true color of a white LED changes with operating
current, and is the “purest” white at a specific forward
current, usually 15mA or 20mA. If the LED current is
less than or more than this value, the emitted light
becomes more blue. Applications involving color
LCDs can find the blue tint objectionable.
R3
18kΩ
0.095 V
PCB LAYOUT GUIDELINES
A filtered PWM signal is used to dim the LEDs, as
shown in Figure 4.
CAT37
0.095 V
ILED(MIN)
R3
18kΩ
R2
1kΩ
0.1µF
Figure 4. Dimming with a
Filtered PWM Signal
8
RINCR
R1
6.3Ω
Logic
Signal
2N7002
R1
6.3Ω
Figure 5. Dimming with a
Logic Signal
© Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
CAT37
TYPICAL APPLICATION CIRCUITS
Efficiency – Two LEDs
Two LEDs with DC Level Dimming Control
L1
6.8µH
D1
VIN
3V to 4.2V
90
VDC
Dimming
5
VIN
1
SW
18k
15mA
CAT37
4
C2
1µF
EFFICIENCY [%]
C1
1µF
FB
SHDN
1k
3
VIN==3.6V
3.6V
VIN
85
VIN == 3.0V
3.0V
VIN
80
75
70
65
60
GND
2
0
R1
6.34kΩ
10
15
20
25
30
LED CURRENT [mA]
Efficiency –- Three LEDs
Three LEDs with DC Level Dimming Control
L1
6.8µH
5
D1
VIN
3V to 4.2V
90
5
VIN
1
SW
18k
15mA
CAT37
4
C2
1µF
FB
SHDN
3
1k
VIN
= 3.6V
VIN=3.6V
85
EFFICIENCY [%]
VDC
Dimming
C1
1µF
80
VIN =VIN=3.0V
3.0V
75
70
65
60
GND
2
R1
6.34kΩ
0
D1
0.1µF
18k
CAT37
4
FB
SHDN
GND
2
© Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
C2
1µF
15mA
3
EFFICIENCY [%]
85
10k
1
SW
20
25
30
90
PWM
5
VIN
15
Efficiency – Four LEDs
VIN
3V to 4.2V
C1
1µF
10
LED CURRENT [mA]
Four LEDs with PWM Dimming Control
L1
6.8µH
5
VIN
= 3.6V
VIN=3.6V
80
VIN=3.0V
VIN
= 3.0V
75
70
65
60
1k
0
R1
6.34kΩ
9
5
10
15
20
LED CURRENT [mA]
25
30
Doc. No. MD-5005 Rev. T
CAT37
PACKAGE OUTLINE DRAWING
TSOT-23 5-Lead (TD) (1)(2)
SYMBOL
D
MIN
NOM
MAX
A1
0.01
0.05
0.10
A2
0.80
0.87
0.90
b
0.30
c
0.12
A
e
E1
E
1.00
0.45
0.15
D
2.90 BSC
E
2.80 BSC
E1
1.60 BSC
e
0.95 TYP
L
0.30
0.40
L1
0.60 REF
L2
0.25 BSC
θ
0º
0.20
0.50
8º
TOP VIEW
A2 A
b
θ
L
A1
c
L1
SIDE VIEW
L2
END VIEW
For current Tape and Reel information, download the PDF file from:
http://www.catsemi.com/documents/TapeandReel.pdf
Notes:
(1) All dimensions are in millimeters. Angles in degrees.
(2) Complies with JEDEC standard MO-193.
Doc. No. MD-5005 Rev. T
10
© Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
CAT37
EXAMPLE OF ORDERING INFORMATION 1
Prefix
Device #
CAT
37
Suffix
TD
Product Number
37
Optional
Company ID
I
–G
Industrial Temperature
I: Range -40ºC to + 85ºC
Package
TD: TSOT-23
T3
Tape & Reel
T: Tape & Reel
3: 3,000/Reel
Lead Finish
Blank: Matte-Tin
G: NiPdAu
Notes:
(1) All packages are RoHS-compliant (Lead-free, Halogen-free).
(2) The standard lead finish is NiPdAu.
(3) The device used in the above example is a CAT37TDI-GT3 (TSOT-23, NiPdAu, Tape & Reel, 3,000/Reel).
(4) For additional package and temperature options, please contact your nearest Catalyst Semiconductor Sales office.
© 2005 Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
11
Doc. No. 5014 Rev. A
CAT37
REVISION HISTORY
Date
Rev.
25-Sept-03
H
25-Sept-03
I
Reason
Updated Ordering Information - part numers
Changed L1 for each figure from 22µH to 6.8µH
Changed VIN for Typical Application from 2.7V to 4.2V to 3V to 5V
Changed C1 for each typical application circuit from 4.7µF to 1µF
Changed C2 for each typical application circuit from 2.2µF to 1µF
Changed VIN for each for each typical application circuit from 1.8V to 3V to 3V to 4.2V
Updated Ordering Information - part numbers
Updated Features
Changed R1 for Typical Application figure and Typical Application Circuit figures from
6.34Ω to 6.8Ω
Updated Description (2V to 2.5V input supply voltage)
Updated Ordering Information (added package marking code)
Updated Electrical Specifications
Updated Table 4 (R1 Resistor Value) with new values
Updated LED dimming with logic signal (0.095V to 0.105V)
Updated Typical Application figures
Updated Electrical Specifications
Updated Operation text
Updated LED current programming text
Updated Table 4 (R1 Resistor Value) with new values
Updated LED dimming equations
Updated Typical Application Circuit figures
6-Nov-03
J
8-Dec-03
K
10-Dec-03
L
18-Dec-03
M
22-Dec-03
N
9-June-04
O
Updated FB Pin Leakage Current in Electrical Specifications
Added Typical Characteristics graphs (pages 4-6)
Added Efficiency graphs to Typical Application Circuits
Changed package drawing for 5-lead SOT-23
Updated Absolute Maximum Ratings
Deleted temp range from Electrical Specifications
Added Recommended Operating Conditions
Updated Block Diagram
Updated Electrical Specifications (changed VRSET to VFB in IQ)
15-June-04
P
Reoved Preliminary data sheet designation
22-Sept-04
Q
Added Green Packages in all areas
1-Nov-04
R
Eliminated TDFN (3 x 4.9mm) package Updated Ordering Information
07-July-05
S
19-May-08
T
Doc. No. MD-5005 Rev. T
Update Features
Update Description
Update Ordering Information
Update Pin Configuration Update Pin Description
Update Block Diagram
Update Package Outlines
Add TSOT-23 in NiPdAu plated finish
Add Example of Ordering Information
Update Package Outline Drawing
Add MD- to document number
12
© Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
Copyrights, Trademarks and Patents
© Catalyst Semiconductor, Inc.
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PRODUCTS FOR ANY PARTICULAR PURPOSE, NOR THAT THE USE OF ITS PRODUCTS WILL NOT INFRINGE ITS INTELLECTUAL PROPERTY RIGHTS OR THE
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OUT OF ANY SUCH USE OR APPLICATION, INCLUDING BUT NOT LIMITED TO, CONSEQUENTIAL OR INCIDENTAL DAMAGES.
Catalyst Semiconductor products are not designed, intended, or authorized for use as components in systems intended for surgical implant into the body, or other
applications intended to support or sustain life, or for any other application in which the failure of the Catalyst Semiconductor product could create a situation where
personal injury or death may occur.
Catalyst Semiconductor reserves the right to make changes to or discontinue any product or service described herein without notice. Products with data sheets labeled
"Advance Information" or "Preliminary" and other products described herein may not be in production or offered for sale.
Catalyst Semiconductor advises customers to obtain the current version of the relevant product information before placing orders. Circuit diagrams illustrate typical
semiconductor applications and may not be complete.
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Corporate Headquarters
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Santa Clara, CA 95054
Phone: 408.542.1000
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0Hwww.catsemi.com
Document No: MD-5005
Revision:
T
Issue date:
05/19/2008
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