ON CAT32 Cmos white led driver Datasheet

CAT32
CMOS White LED Driver
Description
The CAT32 is a DC/DC step up converter that delivers a regulated
output current. Operation at a constant switching frequency of
1.2 MHz allows the device to be used with very small value external
inductor and ceramic capacitors.
The CAT32 is targeted to drive multiple white light−emitting diodes
(LEDs) connected in series and provides the necessary regulated current
to control the brightness and the color purity. An external resistor RSET
controls the output current level. LED currents of up to 40 mA can be
supported over a wide range of input supply voltages from 2 V to 7 V,
making the device ideal for battery−powered applications.
A high voltage output stage allows up to 4 White LEDs to be driven
in series. Series drive provides inherent current matching.
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.
In addition to overcurrent limiting protection, the device also
includes detection circuitry to ensure protection against open−circuit
load fault conditions.
The device is available in a low profile (1 mm max height) 6−lead
TSOT−23 package.
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1
TSOT−23
TD SUFFIX
CASE 419AF
PIN CONNECTIONS
1
GND
SHDN
LED
RSET
TSOT−23
1 mm Maximum Height
qJA = 250°C/W (free air)
(Top View)
Features
•
•
•
•
•
•
•
•
•
•
•
•
•
VIN
SW
Low Quiescent Ground Current (0.5 mA Typical)
Power Efficiency Over 80%
Compatible Pinout with LT1932
Adjustable Output Current (up to 40 mA)
High Frequency 1.2 MHz Operation
Input Voltage Operation down to 2.0 V
Low Resistance (0.5 W) High Voltage Power Switch
Drives up to 4 White LEDs in Series
Shutdown Current Less than 1 mA
Load Fault Protection Against Open−circuits
Low Value External Components
Low Profile (1 mm) TSOT−23 6−lead Package
These Devices are Pb−Free, Halogen Free/BFR Free and are RoHS
Compliant
MARKING DIAGRAMS
VFYM
VF = CAT32TDI−GT3
Y = Production Year (Last Digit)
M = Production Month (1−9, A, B, C)
ORDERING INFORMATION
Device
CAT32TDI−GT3
Package
Shipping
TSOT−23
(Pb−Free)
3,000/
Tape & Reel
Applications
•
•
•
•
•
•
Color LCD and Keypad Backlighting
Cellular Phones
Handheld Terminals
Digital Cameras
PDAs/Games
Portable MP3 Players
© Semiconductor Components Industries, LLC, 2014
April, 2014 − Rev. 5
1
Publication Order Number:
CAT32/D
CAT32
Typical Application Circuit
D1
L1 6.8 mH
VIN
2.7 V
to
4.2 V
C1
4.7 mF
C1: Taiyo Yuden JMK212BJ475
C2: Taiyo Yuden EMK212BJ105
D1: Zetez ZHCS400
L1: Sumida CLQ4D106R8
(Panasonic ELJEA6R8)
1
SW
6
VIN
CAT32
PWM
DIMMING
CONTROL
5
LED
SHDN
RSET
4
RSET
1.50 kW
GND
2
3
C2
1 mF
15 mA
TSOT−23 Pin Numbers
Figure 1. Li−Ion Driver for Four High−Brightness White LEDs
Table 1. PIN DESCRIPTION
Pin Number
SOT23
Pin Number
TDFN
Name
Function
1
8
SW
Switch pin. This is the drain of the internal power switch. For minimum EMI, minimize the trace area connected to this pin.
2
5
GND
Ground pin. Connect pin 2 to ground.
3
6
LED
LED (cathode) connection pin.
4
4
RSET
5
3
SHDN
6
2
VIN
−
1
Power
Ground
RESET pin. A resistor connected from pin 4 to ground sets the LED current. This
pin is also used to dim the LEDs.
Shutdown pin.
Input supply pin. This pin should be bypassed with a capacitor to ground. A
4.7 mF capacitor mounted close to the pin is recommended.
Power Ground
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CAT32
Table 2. ABSOLUTE MAXIMUM RATINGS
Parameter
Rating
Unit
VIN, LED, SHDN voltage
8
V
SW voltage
20
V
RSET voltage
1
V
−65 to +150
°C
Junction Temperature
125
°C
Lead Soldering Temperature (10 secs)
300
°C
ESD Rating – Human Body Model
2000
V
Storage Temperature Range
Stresses exceeding those listed in the Maximum Ratings table may damage the device. If any of these limits are exceeded, device functionality
should not be assumed, damage may occur and reliability may be affected.
Table 3. RECOMMENDED OPERATING CONDITIONS
Parameter
Range
Unit
2 to 7
V
−40 to +85
°C
Inductor L1
6.8 ±20% typical
mH
Input Capacitor C1
4.7 ±20% typical
mF
Output Capacitor C2
1.0 ±20% typical
mF
0 to 20
mA
VIN
Ambient Temperature Range
ILED with 1 to 4 LEDs in series
Functional operation above the stresses listed in the Recommended Operating Ranges is not implied. Extended exposure to stresses beyond
the Recommended Operating Ranges limits may affect device reliability.
NOTE: Typical application circuit with external components is shown on page 2.
Table 4. ELECTRICAL OPERATING CHARACTERISTICS
(Over recommended operating conditions unless otherwise specified. TA = 25°C, VIN = 2 V and VSHDN = 1.2 V.)
Parameter
Symbol
IQ
IGND
Ground Current in Shutdown
LED Pin Voltage
ILED
LED Current Adjust Range
ILED
Programmed LED Current
VRSET
Typ
Max
Unit
VRSET = 0.2 V
0.5
0.7
mA
VSHDN = 0 V
0.05
1
mA
VIN < VOUT, ILED = 15 mA
120
180
mV
40
mA
mA
Quiescent Current
VLED
ILED
Conditions
Min
5
RSET = 562 W
33
38
45
RSET = 750 W
25
30
36
RSET = 1.5 kW
12.5
15
17.5
RSET = 4.53 kW
5
LED Pin Current Temperature Coefficient
ILED = 15 mA
−0.01
mA/°C
RSET Pin Voltage
RSET = 1.5 kW
100
mV
Shutdown Pin Logic High Level
0.85
V
Shutdown Pin Logic Low Level
fSW
Boost Converter Frequency
ISWL
Switch Current Limit
RSW
Switch Resistance
Switch Leakage Current
Efficiency
0.25
V
0.8
1.2
1.6
MHz
400
550
780
mA
VIN = 2 V, ISW = 100 mA
0.7
1.2
W
VIN = 3 V, ISW = 100 mA
0.5
0.9
Switch Off, VSW = 5 V
0.01
5
Components shown on Figure 1
83
mA
%
Product parametric performance is indicated in the Electrical Characteristics for the listed test conditions, unless otherwise noted. Product
performance may not be indicated by the Electrical Characteristics if operated under different conditions.
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CAT32
TYPICAL CHARACTERISTICS
(VIN = 3.6 V, TAMB = 25°C, CIN = 4.7 mF, COUT = 1 mF, L = 6.8 mH, unless otherwise specified.)
600
QUIESCENT CURRENT (mA)
QUIESCENT CURRENT (mA)
600
500
400
300
3
4
5
6
7
300
−25
0
25
50
75
100
125
INPUT VOLTAGE (V)
TEMPERATURE (°C)
Figure 2. Quiescent Current vs. Input Voltage
Figure 3. Quiescent Current vs. Temperature
2.0
SWITCH FREQUENCY (MHz)
2.0
SWITCH FREQUENCY (MHz)
VIN = 2 V
400
200
−50
200
2
VIN = 7 V
500
1.6
1.2
0.8
0.4
3
4
5
6
1.2
0.8
0.4
0
−50
0
2
1.6
7
−25
0
25
50
75
100
INPUT VOLTAGE (V)
TEMPERATURE (°C)
Figure 4. Switching Frequency vs. Input
Voltage
Figure 5. Switching Frequency vs.
Temperature
125
20
35
RSET = 750 W
LED CURRENT (mA)
LED CURRENT (mA)
30
25
RSET = 1.13 kW
20
RSET = 1.50 kW
15
RSET = 2.26 kW
10
15
10
5
5
0
−50
0
2
3
4
5
6
7
−25
0
25
50
75
100
INPUT VOLTAGE (V)
TEMPERATURE (°C)
Figure 6. LED Current vs. Input Voltage
Figure 7. LED Current vs. Temperature
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125
CAT32
TYPICAL CHARACTERISTICS
(VIN = 3.6 V, TAMB = 25°C, CIN = 4.7 mF, COUT = 1 mF, L = 6.8 mH, unless otherwise specified.)
1.0
SWITCH RESISTANCE (W)
SWITCH RESISTANCE (W)
1.0
0.8
0.6
0.4
0.2
3
4
5
0.6
VIN = 3 V
0.4
0.2
0
−50
0
2
0.8
6
−25
0
25
50
75
100
125
INPUT VOLTAGE (V)
TEMPERATURE (°C)
Figure 8. Switch Resistance vs. Input Voltage
Figure 9. Switch Resistance vs. Temperature
LED PIN VOLTAGE (mV)
300
250
200
150
100
50
0
0
8
16
24
32
40
LED CURRENT (mA)
Figure 10. LED Pin Voltage vs. LED Current
Figure 11. VSW, IL, & VOUT Signal Waveforms
85
EFFICIENCY (%)
80
75
4 LEDs at 15 mA
VOUT = 13 V
70
65
60
2
3
4
5
6
INPUT VOLTAGE (V)
Figure 12. Efficiency vs. Input Voltage
Figure 13. PWM on SHDN Pin Waveform
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CAT32
Operation
The CAT32 device is a high efficiency, constant
frequency, current regulating boost converter.
The device includes a switch and an internally
compensated loop for the regulation of the LED current.
Operation can be best understood by examining the block
diagram. The RSET pin is regulated at 100 mV and the
current through the external resistor will set the regulated
current in the LEDs (from 5 mA to 40 mA) with a
multiplication factor of 225.
While maintaining LED current regulation, the CAT32
automatically adjusts the LED pin voltage to be as low as
possible. A low LED pin voltage ensures high efficiency.
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.
PWM dimming operation can be achieved by switching
the SHDN pin or by pulling the RSET pin higher than 0.1 V.
Block Diagram
L1
VIN
D1
C2
1
C1
SW
Over Voltage
Protection
(22 V)
1.2 MHz
Oscillator
LED
−
PWM
& Logic
+
Current
Sense
−
Amp
6
VIN
5
SHDN
3
+
100 mV
Current
Control
225x
IS
CAT32
GND
RSET
2
4
RSET
Figure 14. CAT32 Block Diagram
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ILED = 225 x IS
ILED
CAT32
Application Information
Inductor Selection and Efficiency
Inductor vendors are shown below. Contact the manufacturer for detailed technical data and new product information.
Table 5. INDUCTOR MANUFACTURERS
L (mH)
Maximum DCR (mW)
Maximum
Height (mm)
ELJEA4R7
4.7
180
2.2
ELJEA6R8
6.8
250
2.2
4.7
260
2.2
Inductor
Vendor
Web
Panasonic
714.373.7334
www.panasonic.com
Murata
770.436.1300
www.murata.com
Taiyo Yuden
408.573.4150
www.t−yuden.com
Sumida
847.956.0666
www.sumida.com
LQH3C4R7M24,
LQH32CN4R7M11
LQH3C100K24,
10
300
2.2
LB2016B4R7
4.7
250
2.0
LB2016B100
3.8
350
2.0
CMD4D06−4R7
4.7
216
0.8
CMD4D06−6R8
6.8
296
0.8
CLQ4D10−4R7
4.7
162
1.2
CLQ4D10−6R8
6.8
195
1.2
LQH32CN100K11
Capacitor Selection
Diode Selection
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 1.0 mF or
2.2 mF output capacitor is recommended for most
applications.
The voltage rating of the output capacitor C2 depends on
the number of LEDs driven in series. A 10 V ceramic
capacitor is recommended when driving two LEDs. A 16 V
ceramic capacitor is recommended when driving 3 or 4
LEDs.
Schottky diodes, with their low forward voltage drop and
fast switching speed, are the ideal choice for high efficiency
applications. Table 7 shows several different Schottky
diodes that work well with the CAT32. 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 0.4 A
or 0.5 A diode will be sufficient for most designs.
Table 7. SCHOTTKY DIODE SUPPLIERS
Part
MBR0520
MBR0540
ON Semiconductor
www.onsemi.com
800.282.9855
ZHCS400
Zetex
MBR0530 s
Table 6. CERAMIC CAPACITOR MANUFACTURERS
Supplier
Supplier
Phone
Web
Taiyo Yuden
408.573.4150
www.t−yuden.com
LED Current Programming
Murata
814.237.1431
www.murata.com
Kemet
408.986.0424
www.kemet.com
The LED current is programmed with a single resistor
connected to the RSET pin. The RSET pin is internally
regulated to 100 mV, which sets the current flowing out of
this pin, ISET, equal to 100 mV/RSET. The CAT32 regulates
the current into the LED pin, ILED, to 225 times the value of
ISET. For the best accuracy, a 1% or better resistor is
recommended. Table 8 shows several typical 1% RSET
values.
Low profile ceramic capacitors with a 1 mm 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 CAT32. A 2.2 mF or 4.7 mF input capacitor is
recommended. Table 6 shows a list of several ceramic
capacitor manufacturers. Consult the manufacturers for
detailed information as new products and package options
are introduced regularly.
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CAT32
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 15 mA or
20 mA. 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.
When a PWM control signal is used to drive the SHDN pin
of the CAT32, the LEDs are turned off and on at the PWM
frequency. The current through them alternates between full
current and zero current, so the average current changes with
duty cycle. This ensures that when the LEDs are on, they can
be driven at the appropriate current to give the purest white
light. LED brightness varies linearly with the PWM duty
cycle.
Table 8. RSET RESISTOR VALUES
ILED (mA)
RSET
40
562 W
30
750 W
25
909 W
20
1.13 kW
15
1.50 kW
10
2.26 kW
5
4.53 kW
For other LED current values, use the following equation
to choose RSET.
0.1 V
I LED
R SET + 255
Most white LEDs are driven at maximum currents of
15 mA to 20 mA. Some higher power designs will use two
parallel strings of LEDs for greater light output, resulting in
30 mA to 40 mA (two strings of 15 mA to 20 mA) flowing
into the LED pin.
LED Dimming with a Logic Signal
For applications that need to adjust the LED brightness in
discrete steps, a logic signal can be used. RMIN sets the
minimum LED current value (when the NMOS is OFF):
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 5 kHz to 40 kHz PWM signal
is used. PWM dimming with the CAT32 can be
accomplished two different ways.
The SHDN pin can be driven directly or a resistor can be
added to drive the RSET pin. If the SHDN pin is used,
increasing the duty cycle will increase the LED brightness.
Using this method, the LEDs can be dimmed and turned off
completely using the same control signal. A 0% duty cycle
signal will turn off the CAT32, reducing the total quiescent
current to near zero.
If the RSET pin is used, increasing the duty cycle will
decrease the brightness. Using this method, the LEDs are
dimmed using RSET and turned off completely using
SHDN. If the RSET pin is used to provide PWM dimming,
the approximate value of RPWM should be calculated (where
VMAX is the “HIGH” value of the PWM signal):
R PWM + R SET
ǒ
RINCR determines how much LED current increases when
the external NMOS switch is turned ON.
R INCR + 255
R ADJ + 225
CAT32
SHDN
5
RSET
4
RSET
4
RPWM
RSET
CAT32
CAT32
RSET
4
RSET
4
PWM
PWM
RPWM
RADJ
10 kW
RSET
V MAX * 0.1 V
I LED(MAX) * I LEAD(MIN)
PCB Layout Guidelines
The CAT32 is a high−frequency switching regulator and
therefore proper PCB board layout and component
placement can minimize noise and radiation and increase
efficiency. To maximize efficiency, the CAT32 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.
The switch, schottky output diode and output capacitor
signal path should be kept as short as possible. The ground
connection for the RSET resistor should be tied directly to the
GND pin and not be shared with other components.
Ǔ
CAT32
0.1 V
I LED(Increase)
LED Dimming with a DC Voltage
V MAX
*1
0.15 V
CAT32
PWM
0.1 V
I LED(MIN)
R MIN + 255
LED Dimming with PWM Signal
0.1 mF
RSET
Figure 15. LED Dimming Circuits
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VDC
RMIN
RINCR
Logic
Signal
CAT32
TYPICAL APPLICATION CIRCUITS
(The application diagrams below are shown for the TSOT−23 packages.)
L1
VIN
6.8 mH
6
D1
1
SW
VIN
CAT32
C1
4.7 mF
5
2.5 V DC
DIMMING
CONTROL
SHDN
LED
RSET
4
60.40 kW
GND
2
C2
2.2 mF
3
15 mA
RSET
1.50 kW
Figure 16. Two LEDs with DC Level Dimming Control
D1
L1 6.8 mH
VIN
85
6
VIN
VIN = 4.2 V
1
SW
5
2.5 V DC 60.40 kW
DIMMING
CONTROL
SHDN
LED
RSET
4
GND
2
C2
3
1 mF
15 mA
EFFICIENCY (%)
CAT32
C1
4.7 mF
VIN = 3.0 V
80
75
70
65
RSET
1.50 kW
60
0
5
10
15
20
LED CURRENT (mA)
Figure 17. Three LEDs with DC Level Dimming Control
D1
L1 6.8 mH
VIN
Figure 18. Efficiency − Three LEDs
85
VIN = 4.2 V
80
6
1
EFFICIENCY (%)
C1
4.7 mF
SW
VIN
CAT32
PWM
DIMMING
CONTROL
5
SHDN
RSET
4
RSET
1.50 kW
LED
GND
2
C2
3
1 mF
15 mA
VIN = 3.0 V
75
70
65
60
0
5
10
15
LED CURRENT (mA)
Figure 19. Four LEDs with PWM Dimming Control
Figure 20. Efficiency − Four LEDs
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20
CAT32
PACKAGE DIMENSIONS
TSOT−23, 6 LEAD
CASE 419AF−01
ISSUE O
SYMBOL
D
MIN
NOM
A
e
E1
MAX
1.00
A1
0.01
0.05
0.10
A2
0.80
0.87
0.90
b
0.30
c
0.12
E
0.45
0.15
D
2.90 BSC
E
2.80 BSC
E1
1.60 BSC
e
0.95 TYP
L
0.30
L1
0.40
0.20
0.50
0.60 REF
L2
0.25 BSC
0º
θ
8º
TOP VIEW
A2 A
b
q
L
A1
c
L1
SIDE VIEW
END VIEW
Notes:
(1) All dimensions are in millimeters. Angles in degrees.
(2) Complies with JEDEC MO-193.
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L2
CAT32
1.
2.
3.
4.
5.
All packages are RoHS−compliant (Lead−free, Halogen−free).
The standard lead finish is NiPdAu.
The device used in the above example is a CAT32TDI−GT3 (TSOT−23, Industrial Temperature Range, NiPdAu, Tape & Reel, 3,000 / Reel).
For additional package and temperature options, please contact your nearest ON Semiconductor Sales office.
For information on tape and reel specifications, including part orientation and tape sizes, please refer to our Tape and Reel Packaging
Specifications Brochure, BRD8011/D.
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CAT32/D