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LX1990
INTEGRATED PRODUCTS
Dual Programmable LED Current Sink
DESCRIPTION
KEY FEATURES
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The LX1990 is a dual output current sink optimized for driving light emitting diodes. This low cost bipolar IC enables precise current regulation in LED display lighting applications, yet requires far fewer parts than discrete solutions. The LX1990 is supplied in a micro-miniature 6 lead MLP package featuring a 3 x 3 mm footprint, a profile of less than 1mm, and much improved thermal performance. Its two output sink currents are accurately matched and require only one resistor to program. Program current is only 1% of the output currents, and quiescent current is low, providing a very high efficiency driver for battery-powered displays. The LX1990 is based on a currentmirror architecture that transfers a reference current produced at the ISET pin to each of two open-collector current sinking outputs. The output stages multiply this reference current by 100 to sink independently regulated currents up to 30 mA.
Light output from LED's is proportional to average current through them; they can easily produce a brightness range of 500:1. However, color of emitted light is shifted by current amplitude. Color shift at low light levels can be reduced by driving the LED's with a constant peak current while dimming with duty cycle control. This is achieved by driving the ISET resistor with a PWM signal. A 500:1 brightness range can be achieved by choosing 270 Hz as the PWM frequency (to avoid optical beating with 50/60 Hz room lights) and pulse width from 3.7 milliseconds to 7.4 microseconds. The LX1990 features a shutdown mode via the Enable pin. In this mode the LX1990 consumes less than 1A and holds the two open collector output stages off. This pin may also be used to pulse width modulate output current. See applications section for dimming details.
* Programmable Sink Current 0.1 to 30mA x 2 Channels * Replaces Discrete Transistor Circuitry With A Single Package * 300mV Maximum Current Sink Dropout Voltage at 20mA * 2.7 to 5.5V Power Supply Input * IOUT Compliance Voltage from 0.1 to 10VDC * Enable Input With <1A Sleep Current * Amplitude and PWM Dimming * Current rise and fall time may be controlled to reduce EMI
APPLICATIONS * Cell Phone Display Illumination * PDA White LED Display Lighting * Automotive Display Illumination * Digital Still Camera * Camcorders * Consumer Electronics Front Panels
IMPORTANT: For the most current data, consult MICROSEMI's website: http://www.microsemi.com
PRODUCT HIGHLIGHT
5V VDD ON/OFF ENA I O UT B I O UT A GND R SE T LX1990 ISET
V LO AD
LX1990 LX1990
PACKAGE ORDER INFO Plastic MLP TA (C) LM 6-Pin -40 to 85 LX1990ILM
Note: Available in Tape & Reel. Append the letter "T" to the part number. (i.e. LX1990ILM-T)
Copyright 2001 Rev. 1.0c, 2002-05-29
Microsemi
Integrated Products 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 1
LX1990
INTEGRATED PRODUCTS
Dual Programmable LED Current Sink
ABSOLUTE MAXIMUM RATINGS
PACKAGE PIN OUT
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Supply Voltage (VDD)........................................................................................ 6V ENA Voltage ..................................................................................................... 6V ISET Maximum Current ..............................................................Internally Limited ISET Maximum Voltage...................................................................................VDD IOUT Maximum Compliance Voltage ............................................................... 12V Current Source Outputs .............................................................................. 100mA Operating Temperature Range......................................................... -40C to 85C Maximum Junction Temperature..................................................................125C Storage Temperature ..................................................................... -65C to 150C Lead Temperature (Soldering, 10sec)........................................................... 300C
Note: Exceeding these ratings could cause damage to the device. All voltages are with respect to Ground. Currents are positive into, negative out of specified terminal.
ISET VDD ENA
1
6
I OUTA G ND I OUTB
2
5
3
4
LM PACKAGE
(Top View)
1990 xxxx LMI
LM PACKAGE MARKINGS
xxxx - Denotes Date Code / Lot Identification
THERMAL DATA
LM Plastic MLP 6-Pin
THERMAL RESISTANCE-JUNCTION TO AMBIENT, JA
41C/W
Junction Temperature Calculation: TJ = TA + (PD x JA). The JA numbers are guidelines for the thermal performance of the device/pc-board system. All of the above assume no ambient airflow. FUNCTIONAL PIN DESCRIPTION NAME VDD Input Supply DESCRIPTION
GND
Common ground reference Chip Enable Input. If logic high, current source outputs are enabled. If logic low, internal power is disconnected from the VDD pin, disabling all functions. Logic threshold is 1.2 V. Output Current Source. Two separate constant current outputs. Outputs may be loaded in any combination without affecting regulation of the loaded output. If only one output is needed IOUTA & IOUTB must be shorted together. In this case the value of ISET resistor must be doubled. Compliance voltage range is 0.1V to 10V.
ENA IOUTA & IOUTB ISET
PACKAGE DATA PACKAGE DATA
Output current programming pin.
Copyright 2001 Rev. 1.0c, 2002-05-29
Microsemi
Integrated Products 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 2
LX1990
INTEGRATED PRODUCTS
Dual Programmable LED Current Sink
RECOMMENDED OPERATING CONDITIONS Parameter
Supply Voltage (VDD) ENA (ENABLE) Input Voltage ISET Voltage ISET Current IOUTA / IOUTB Compliance Voltage Range IOUTA / IOUTB Output Current Range
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Min
2.7 0 0 0 0.1 0.1
LX1990 Typ
Max
5.5 VDD 1.25 300 10 30
Units
V V V A V mA
ELECTRICAL CHARACTERISTICS Unless otherwise specified, the following specifications apply over the operating ambient temperature -40C TA 85C and the following test conditions: VDD = 2.7 to 5.5 VDC, ISET = 200A, VOUT 5.5V, VLOAD 10V. Typical values are at TA= 25C Parameter
Power Characteristics Quiescent Current Quiescent Current Sleep Current1 Enable Input Enable Logic Threshold Enable Input Current ISET to Out Pulse Response ISET to Out Pulse Response ISET Input ISET Current Range ISET Voltage Output Characteristics Output Current Amplitude OUTA to OUTB Current Matching ISET to IOUT Current Ratio ISET to IOUT Current Ratio Output Current ISET = 0A Dropout Voltage Dropout Voltage
2 2
Symbol
Test Conditions
Min
LX1990 Typ
1.4 3.0 0.08
Max
2 4 1
Units
I_QUI I_QUI I_SLEEP
VDD = 2.7V; ISET = 0uA VDD = 5.5V; ISET = 300uA VDD = 5.5V, ENA
mA mA A
0.4V
VTH_EN IIN_EN TD(ON) TD(OFF) ENA = VDD = 5.5V
0.8
1.55 4 1.2 1.4
2.4 10 2 2
V A S S
IISET VISET
RSET terminated to GND ISET = 200uA
0 1.225 1.25
300 1.275
A VDC
IOUT IOUT_MATCH IOUT_RATIO IOUT_RATIO IOUT_ZERO VDROPOUT VDROPOUT
0.5 < VOUT < 5.5V, ISET = 200A IOUT = 20mA ; (IOUTA - IOUTB ) / IOUTA * 100 IOUT/ISET; ISET = 200A ; VDD = 5.5V IOUT/ISET; ISET = 200A ; VDD = 2.7V 0.5 < VOUT < VLOAD, ISET = 0A IOUT = 20mA IOUT = 30mA
18.5
20 0.4 102 99 10 150 200
21.5 5
mADC %
E ELECTRICALS
100 300 400
ADC mV mV mADC ADC
Maximum Output Current, ISET VISET = Zero Volts; VDD=5V 100 ISC Shorted To Gnd. Each Output 20 Output Off State Current IOUTOFF ENA 0.4V 1 At enable voltages greater than 0.4V but less than 0.8V the outputs will remain off but the sleep current may be greater than 1A. 2 Dropout is defined as the OUTA/B to GND voltage at which the output current sink drops 10% from the nominal value.
Copyright 2001 Rev. 1.0c, 2002-05-29
Microsemi
Integrated Products 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 3
LX1990
INTEGRATED PRODUCTS
Dual Programmable LED Current Sink
SIMPLIFIED BLOCK DIAGRAM
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I OUTA
I OUTB
VDD
1:1 Current Mirror
1.25V REF
100X
100X
+ -
ENABLE
Bias
ISET
Figure 1 - Simplified Block Diagram
GND
BLOCK DIAGRAM BLOCK DIAGRAM
Copyright 2001 Rev. 1.0c, 2002-05-29
Microsemi
Integrated Products 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 4
LX1990
INTEGRATED PRODUCTS
Dual Programmable LED Current Sink
APPLICATIONS
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FUNCTIONAL DESCRIPTION The LX1990 is designed to drive LED's used in display illumination and signaling applications such as cellular telephones and PDA's. With a 5V supply, the two independently regulated constant current outputs can drive 2 white LED's (VF < 4.5V) in parallel, or 4 green or amber LED's (VF < 2.25V each) arranged as 2 parallel x 2 in series. With Dropout voltage of only 300 mV at 20 mA, the LX1990 provides regulated current for 2 green / amber LED's in a cell phone all the way down to the minimum NiCd cutoff of 2.7 volts for three cells. The LX1990 features resistor settable output current. Connecting a resistor between ISET and a voltage of zero to 1.25 volts generates a current that is mirrored into each of the output with a gain of about 100. Output current can be varied in an analog fashion by varying ISET resistance or termination voltage (see application schematics). Duty cycle dimming with a fixed current amplitude is accomplished by switching the ISET current on and off with an open collector or open drain pulse width modulated logic signal. Switching frequency can exceed 20 KHz, making it practical to use a PWM output channel from popular micro controllers. The upper limit on frequency is minimum switching response from ISET to output. As frequency increases, these fixed delays will cause an error in expected output current duty cycle. All inputs and outputs are ESD and short circuit protected making the LX1990 an exceptionally robust component. However it is not recommended to indefinitely short the ISET input to ground while shorting the outputs to 10V as the power dissipation under these conditions is the greatest. APPLICATION NOTES Each output has an independent current sink, however both must be held above about 0.5 volts to maintain specified current regulation accuracy. If only one output is needed, the two outputs should be connected together and the programming resistor value doubled so each output supplies 1/2 the desired current. In this case, more than 60 mA total current can be delivered from the combined output. Package power dissipation can be calculated from the following equation:
n IOUT VLOAD VLED PD
= = = = =
Number of outputs used Current from each output Output Supply Voltage Minimum LED forward voltage Power Dissipated in mW
When the ENA input is at zero volts, less than 20A current flows into or out of the outputs. If the disable function is used , ENA must be driven below 0.4 volts to insure minimum current from VDD. The ISET pin may be driven with a digital open collector or open drain logic PWM signal to dim the LED's. Recommended PWM frequency for dimming is between 100 Hz and 20 KHz. Below 100 Hz flicker may be observed. Above 20 KHz duty cycle accuracy is reduced due to switching delays from ISET to outputs. Totem pole output drive may also be used as long as the maximum driver voltage never exceeds the VDD supply. Since the totem pole drive will exceed the 1.25V ISET voltage it can introduce delays that may limit the useful frequency and maximum dim range. If PWM dimming is used, use separate power and ground lines directly from the power source point to prevent noise generated from the LED current transients from entering video or audio subsystems on the same supply rails. Additional power supply filtering may be needed in PWM dimming applications. Care should be exercised in the PCB layout to prevent coupling from the outputs to the ISET pin, as this may cause the part to oscillate. Current out of the ISET pin may be varied for current amplitude dimming. There are two ways to do this: If a mechanical input is needed, a rheostat in series with a resistor connected from GND to ISET can be used. The second method is to connect a fixed resistor from ISET to the output of a voltage DAC or other low impedance voltage source. Varying the voltage between zero and 1.25 volts will cause a corresponding output current change from IOUT max to zero:
APPLICATIONS APPLICATIONS
I OUT = Current Ratio x ISET
The ENA pin may be used to duty cycle dim the output in applications where only one control line is available for dimming and shutdown. A narrow current spike that may be as high as 100 mA is produced when the ENA signal has very fast rise times. This is not harmful to the LED, but will cause dimming linearity errors when operating at very low duty cycles.
PD = (n I OUT ) (VLOAD - VL ED )
Copyright 2001 Rev. 1.0c, 2002-05-29
Microsemi
Integrated Products 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 5
LX1990
INTEGRATED PRODUCTS
Dual Programmable LED Current Sink
TYPICAL CHARACTERISTICS VDD = 5V, ENA = 5V, ISET = 200A, TA = 25C. Unless otherwise noted. IOUT Vs. Temperature @ ISET = 200A
20.8 20.6
IOUTA @ 5V
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Output Off Leakage Current vs.VOUT ENA=0.4V
1 4 1 2
5.5V
IOUT Leakage (A)
IOUT Current (mA)
20.4 20.2 20 1 9.8
IOUTB @ 5V
1 0 8 6 4
2.7V 5V
IOUT A @ 2.7V
IOUTB @ 2.7V
2 0
1 9.6 -45 -20 5 30 55 80 1 05 1 30
0
2
4
6
8
1 0
1 2
Tem p (C)
V OUT (V)
IOUT vs ISET
45 40 35
2.7V 5V 5.5V
VDROPOUT vs. Current
35 30
30mA
30
25
IOUT (mA)
IOUT (mA)
25mA
25 20 1 5 1 0 5 0 0 50 1 00 1 50 200 250 300 350 400
20
20mA
1 5
15mA
1 0
10mA
5
5mA
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
ISET (A)
Dropout (V)
Output Current vs. VDD
20.7 20.6
Enable to Output Response
Output Current (mA)
20.5
AOUT
ENA 2V / DIV
20.4
CHARTS CHARTS
20.3
BOUT
20.2 20.1 20 1 9.9 2.7 3.7 4.7 5.7
10s / DIV IOUT 10mA / DIV
VDD (V)
Copyright 2001 Rev. 1.0c, 2002-05-29
Microsemi
Integrated Products 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 6
LX1990
INTEGRATED PRODUCTS
Dual Programmable LED Current Sink
APPLICATIONS
3.3V V LO AD
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VDD I O UTB
Figure 2 - Auto Dashboard or Instrument Front Panel LED Array
ON/OFF
ENA I O UTA ISET GND
4K
.1F
Open Collector or Open Drain Drive
+5V
.1F
G RN W HT
VDD IO UTB
GRN
ON/OFF
ENA I OUTA ISET G ND 1.25V
4K
D0 D1 OUT D2 D3
+5V
Up to 10 Volts
Figure 3 - Color LCD Display & Keypad Illumination
VDD I OUTB
LOAD
APPLICATIONS
O N/OFF
ENA I OUTA ISET GND
100K
4K
Figure 4 - Variable Current Driver
Copyright 2001 Rev. 1.0c, 2002-05-29
Microsemi
Integrated Products 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 7
LX1990
INTEGRATED PRODUCTS
Dual Programmable LED Current Sink
DIMMING METHODS
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VDD IOUTB
VDD IOUTB
3V
VDD IOUTB ENA IOUTA ISET GND
PWM
ENA IOUTA ISET GND
ON / OFF
ENA IOUTA ISET GND
RMIN
RSET
RSTEP RMIN
RMAX
Figure 5 - PWM on Enabled (Lowest IQ)
Figure 6 - Precision 2 Steps
Figure 7 - Manual Control
VDD IOUTB
ON / OFF
VDD IOUTB ENA IOUTA
6.3K
ON / OFF
VDD I OUTB ENA I OUTA ISET GND
R SET
8.2nF CSLOPE 1K
ENA IOUTA ISET GND
ISET GND
5K
PWM
10K 100K
2N2222A
PWM
10K 100K
2N2222
PW M
1V / DIV
1V / DIV
1V / DIV
10mA / DIV
10A / DIV
10mA / DIV
APPLICATIONS
10s / DIV
20s / DIV
20s / DIV
Figure 8 - PWM Dimming Totem Pole Output
Figure 9 - PWM - Low EMI Wide Range
Figure 10 - PWM - Wide Range 500:1 +
Copyright 2001 Rev. 1.0c, 2002-05-29
Microsemi
Integrated Products 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 8
LX1990
INTEGRATED PRODUCTS
Dual Programmable LED Current Sink
APPLICATION
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48V
Optional circuit for higher efficiency LX432SC
.47F
10 W hite LEDs each output
2.2K
BC846B x2
3.3V
ON/OFF
VDD I O UTB
20K
ENA I O UTA ISET G ND
R SET
20K
PW M
10K 100K
Figure 11 - Using the LX1990 With High Voltage Supplies
A APPLICATIONS
Copyright 2001 Rev. 1.0c, 2002-05-29
Microsemi
Integrated Products 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 9
LX1990
INTEGRATED PRODUCTS
Dual Programmable LED Current Sink
PACKAGE DIMENSIONS
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LM
6-Pin Plastic MLP-Micro Exposed Pad
A K J B E H I G F
Dim A B C D E F G H I J K
Note:
MILLIMETERS MIN MAX 2.90 3.10 2.90 3.10 0.65 0.75 0.15 0.25 1.841 BSC 0.27 0.43 0.95 BSC 1.22 BSC 0 0.10 0.21 0.37 0 0.10
INCHES MIN MAX 0.114 0.122 0.114 0.122 0.025 0.029 0.005 0.009 0.075 BSC 0.010 0.016 0.037 BSC 0.048 BSC 0 0.003 0.008 0.014 0 0.003
C D
Internally Connected together, but isolated from all other terminals
1. Dimensions do not include mold flash or protrusions; these shall not exceed 0.155mm(.006") on any side. Lead dimension shall not include solder coverage.
MECHANICALS MECHANICALS
Copyright 2001 Rev. 1.0c, 2002-05-29
Microsemi
Integrated Products 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 10
LX1990
INTEGRATED PRODUCTS
Dual Programmable LED Current Sink
NOTES
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NOTES NOTES
PRODUCTION DATA - Information contained in this document is proprietary to Microsemi and is current as of publication date. This document may not be modified in any way without the express written consent of Microsemi. Product processing does not necessarily include testing of all parameters. Microsemi reserves the right to change the configuration and performance of the product and to discontinue product at any time.
Copyright 2001 Rev. 1.0c, 2002-05-29
Microsemi
Integrated Products 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
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