Microsemi
Integrated Products
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 1
Copyright © 2001
Rev. 1.0d, 2005-03-14
WWW.Microsemi .COM
LX1990
Dual Pro
g
rammable
LED Current Sink
TM ®
DESCRIPTION
The LX1990 is a dual output current
sink optimized for driving light emitting
diodes. This low cost bipolar IC en able s
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 current-
mirror architecture that transfers a
reference current produced at the I
SET
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 ligh
t
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 I
SET
resistor with a PWM signal. A 500:1
b
rightness range can be achieved by
choosing 270 Hz as the PW M frequency (to
avoid optical beating with 50/60 Hz roo
m
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 1µA 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.
IMPORTANT: For the most current data, consult MICROSEMI’s website: http://www.microsemi.com
KEY FEATURES
• 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
• I
OUT
Compliance Voltage from
0.1 to 10V
DC
• Enable Input With <1µA 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
PRODUCT HIGHLIGHT
5V
LX1990
VDD I
OUTB
GND I
OUTA
ISET
R
SET
ENA
V
LOAD
ON/OFF
PACKAGE ORDER INFO
LM
Plastic MLP
6-Pin
T
A
(°C)
RoHS Compliant / Pb-free Transition DC: 0452
-40 to 85 LX1990ILM
Note: Available in Tape & Reel. Append the letters “TR” to the part number. (i.e. LX1990ILM-TR)
L
LX
X1
19
99
90
0
Microsemi
Integrated Products
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 2
Copyright © 2001
Rev. 1.0d, 2005-03-14
WWW.Microsemi .COM
LX1990
Dual Pro
g
rammable
LED Current Sink
TM ®
ABSOLUTE MAXIMUM RATINGS
Supply Voltage (V
DD
)....................................................................................... 6V
ENA Voltage..................................................................................................... 6V
I
SET
Maximum Current.............................................................. Internally Limited
I
SET
Maximum Voltage..................................................................................
V
DD
I
OUT
Maximum Compliance Voltage ...............................................................12V
Current Source Outputs.............................................................................. 100mA
Operating Temperature Range.........................................................-40°C to 85°C
Maximum Junction Temperature.................................................................125°C
Storage Temperature......................................................................-65°C to 150°C
Peak Package Solder Reflow Temperature
(40 seconds maximum exposure).................................................... 260°C (+0, -5)
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
.
THERMAL DATA
LM
Plastic MLP 6-Pin
THERMAL RESISTANCE
-
JUNCTION TO
A
MBIENT
,
θ
JA
41°C/W
Junction Temperature Calculation: T
J
= T
A
+ (P
D
x θ
JA
).
The θ
JA
numbers are guidelines for the thermal performance of the device/pc-board
system. All of the above assume no ambient airflow.
PACKAGE PIN OUT
VDD
ENA
GND
I
OUTB
I
OUTA
ISET
1
2
34
5
6
LM
P
ACKAGE
(Top View)
1990
xxxx
LMI
LM
P
ACKAGE
M
ARKINGS
xxxx – Denotes Date Code / Lot Identification
RoHS / Pb-free 100% Matte Tin Lead Finish
FUNCTIONAL PIN DESCRIPTION
N
AME
D
ESCRIPTION
V
DD
Input Supply
GND Common ground reference
ENA Chip Enable Input. If logic high, current sour ce outputs are ena bled. If logic low, internal power is disconnected
from the VDD pin, disabling all functions. Logic threshold is 1.2 V.
I
OUTA
&
I
OUTB
Output Current Source. T wo separate constant current outp uts. O utputs ma y be lo aded in any combination
without affecting regulation of the loaded output. If only one output is needed I
OUTA
& I
OUTB
must be shorted
together. In this case the value of ISET resistor must be doubled. Compliance voltage range is 0.1V to 10V.
I
SET
Output current programming pin.
P
PA
AC
CK
KA
AG
GE
E
D
DA
AT
TA
A
Microsemi
Integrated Products
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
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Copyright © 2001
Rev. 1.0d, 2005-03-14
WWW.Microsemi .COM
LX1990
Dual Pro
g
rammable
LED Current Sink
TM ®
RECOMMENDED OPERATING CONDITIONS
LX1990
Parameter Min Typ Max
Units
Supply Voltage (V
DD
) 2.7 5.5 V
ENA (ENABLE) Input Voltage 0 V
DD
V
I
SET
Voltage 0 1.25 V
I
SET
Current 0 300 µA
I
OUTA
/ I
OUTB
Compliance Voltage Range 0.1 10 V
I
OUTA
/ I
OUTB
Output Current Range 0.1 30 mA
ELECTRICAL CHARACTERISTICS
Unless otherwise specified, the following specifications apply over the operating ambient temperature -40°C
≤
T
A
≤
85°C and the
following test conditions: V
DD
= 2.7 to 5.5 V
DC
, I
SET
= 200µA
, V
OUT
≤
5.5V, VLOAD
≤
10V. Typical values are at T
A
= 25°C
LX1990
Parameter Symbol Test Conditions Min Typ Max
Units
Power Characteristics
Quiescent Current I
_QUI
VDD = 2.7V; ISET = 0uA 1.4 2 mA
Quiescent Current I
_QUI
VDD = 5.5V; ISET = 300uA 3.0 4 mA
Sleep Current
1
I
_SLEEP
VDD = 5. 5V, ENA
≤
0.4V 0.08 1 µA
Enable Input
Enable Logic Threshold V
TH_EN
0.8 1.55 2.4 V
Enable Input Current I
IN_EN
ENA = V
DD
= 5.5V 4 10 µA
I
SET
to Out Pulse Response T
D(ON)
1.2 2 µS
I
SET
to Out Pulse Response T
D(OFF)
1.4 2 µS
ISET Input
I
SET
Current Range I
ISET
R
SET
terminated to GND 0 300 µA
I
SET
Voltage V
ISET
I
SET
= 200uA 1.225 1.25 1.275 V
DC
Output Characteristics
Output Current Amplitude I
OUT
0.5 < V
OUT
< 5.5V, I
SET
= 200µA 18.5 20 21.5 mA
DC
OUTA to OUTB Current Matching I
OUT_MATCH
I
OUT
= 20mA ; (I
OUTA
– I
OUTB
) / I
OUTA
* 100 0.4 5 %
ISET to IOUT Current Ratio I
OUT_RATIO
I
OUT
/I
SET
; I
SET
= 200µA ; V
DD
= 5.5V 102
ISET to IOUT Current Ratio I
OUT_RATIO
I
OUT
/I
SET
; I
SET
= 200µA ; V
DD
= 2.7V 99
Output Current I
SET
= 0µA I
OUT_ZERO
0.5 < V
OUT
< V
LOAD
, I
SET
= 0µA 10 100 µA
DC
Dropout Voltage
2
V
DROPOUT
I
OUT
= 20mA 150 300 mV
Dropout Voltage
2
V
DROPOUT
I
OUT
= 30mA 200 400 mV
Maximum Output Current, I
SET
Shorte d To Gn d. Each Output I
SC
V
ISET
= Zero Volts; VDD=5V 100 mA
DC
Output Off State Current I
OUTOFF
ENA
≤
0.4V 20 µA
DC
1
At enable voltages greater than 0.4V but less than 0.8V the outputs will remain off but the sleep c ur rent may be greater than 1µA.
2
Dropout is defined as the OUTA/B to GND voltage at which the output current sink drop s 10% from the nominal value.
E
EL
LE
EC
CT
TR
RI
IC
CA
AL
LS
S
Microsemi
Integrated Products
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 4
Copyright © 2001
Rev. 1.0d, 2005-03-14
WWW.Microsemi .COM
LX1990
Dual Pro
g
rammable
LED Current Sink
TM ®
SIMPLIFIED BLOCK DIAGRAM
VDD
ENABLE
+
-
ISET
1 :1 Cu rre n t M irro r
100X 100X
GND
I
OUTA
I
OUTB
1.25V
REF
Bias
Figure 1 – Simplified Block Diagram
B
BL
LO
OC
CK
K
D
DI
IA
AG
GR
RA
AM
M
Microsemi
Integrated Products
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 5
Copyright © 2001
Rev. 1.0d, 2005-03-14
WWW.Microsemi .COM
LX1990
Dual Pro
g
rammable
LED Current Sink
TM ®
APPLICATIONS
F
UNCTIONAL
D
ESCRIPTION
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 (V
F
< 4.5V) in parallel, or 4 green or
amber LED’s (V
F
< 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 I
SET
and a voltage of zero to
1.25 volts generates a current that is mirrored in to each of
the output with a gain of about 100. Output current can be
varied in an analog fashion by varying I
SET
resistance or
termination voltage (see application schematics).
Duty cycle dimming with a fixed current amplitude is
accomplished by switching the I
SET
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 I
SET
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 I
SET
input to ground while shorting
the outputs to 10V as the power dissipation under these
conditions is the greatest.
A
PPLICATION
N
OTES
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 ½ 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 :
()( )
EDLOAD LOUTD
VVInP −⋅⋅=
n = Number of outputs used
I
OUT
= Current from each output
V
LOAD
= Output Supply Voltag e
V
LED
= Minimum LED forward voltage
P
D
= Power Dissipated in mW
When the ENA input is at zero volts, less than 20µA
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 V
DD
.
The I
SET
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 I
SET
to outputs. Totem pole output
drive may also be used as long as the maximum driver
voltage never exceeds the V
DD
supply. Since the totem po le
drive will exceed the 1.25V I
SET
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 I
SET
pin,
as this may cause the part to oscillate.
Current out of the I
SET
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 I
SET
can be used. The
second method is to connect a fixed resistor from I
SET
to the
output of a voltage DAC or other low impedance voltage
source. Varying the voltag e between zero and 1.25 volts will
cause a corresponding output current change from I
OUT
max
to zero:
SETOUT
IRatioCurrent I ×=
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 h armful to the LED, but will
cause dimming linearity errors when operating at very low
duty cycles.
A
AP
PP
PL
LI
IC
CA
AT
TI
IO
ON
NS
S
Microsemi
Integrated Products
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
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Copyright © 2001
Rev. 1.0d, 2005-03-14
WWW.Microsemi .COM
LX1990
Dual Pro
g
rammable
LED Current Sink
TM ®
TYPICAL CHARACTERISTICS
VDD = 5V, ENA = 5V, I
SET
= 200µA, T
A
= 25°C. Unless otherwise noted.
I
OUT
Vs. Temperature @ I
SET
= 200µA
19 .6
19 .8
20
20.2
20.4
20.6
20.8
-45-205305580105130
Temp (°C)
I
OUT
Current (mA)
IOUT A @ 2.7V
IOUTB @ 2.7V
IOUTA @ 5V
IOUTB @ 5V
Output Off Leakage Current vs.V
OUT
ENA=0.4V
0
2
4
6
8
10
12
14
024681012
V
OUT
(V)
I
OUT
Leakage (µA)
2.7V
5V
5.5V
I
OUT
vs I
SET
0
5
10
15
20
25
30
35
40
45
0 50 100 150 200 250 300 350 400
I
SET
(µA)
I
OUT
(mA)
2.7V
5.5V
5V
V
DROPOUT
vs. Current
0
5
10
15
20
25
30
35
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
Dropout (V)
I
OUT
(mA)
5mA
10mA
15mA
20mA
25mA
30mA
Output Current vs. VDD
19 .9
20
20.1
20.2
20.3
20.4
20.5
20.6
20.7
2.73.74.75.7
VDD (V)
Output Current (mA)
BOUT
AOUT
Enable to Output Response
ENA
2V /
DIV
IOUT
1
0mA /
DIV
10
µ
s / DIV
C
CH
HA
AR
RT
TS
S
Microsemi
Integrated Products
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
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Copyright © 2001
Rev. 1.0d, 2005-03-14
WWW.Microsemi .COM
LX1990
Dual Pro
g
rammable
LED Current Sink
TM ®
APPLICATIONS
4K
3.3V V
LOAD
VDD
ENA
ISET GND
I
OUTA
I
OUTB
ON/OFF
Open C ollector or
Open D rain D rive
.1µF
100K
+5V
VDD
ENA
ISET GND
I
OUTA
I
OUTB
ON/OFF
4K
LOAD
U p to 1 0 V o lts
4K
WHT
GRN
GRN
+5V
VDD
ENA
ISET GND
IOUTA
IOUTB
D0
D1
D2
D3 OUT
1.25V
ON/OFF
.1µF
Figure 2 – Auto Dashboard
or Instrument Front Panel
LED Array
Figure 3 – Color LCD Display &
Keypad Illumination
Figure 4 – Variable Current Driver
A
AP
PP
PL
LI
IC
CA
AT
TI
IO
ON
NS
S
Microsemi
Integrated Products
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
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Copyright © 2001
Rev. 1.0d, 2005-03-14
WWW.Microsemi .COM
LX1990
Dual Pro
g
rammable
LED Current Sink
TM ®
DIMMING METHODS
VDD
ENA
ISET GND
IOUTA
IOUTB
PWM
R
SET
VDD
ENA
ISET GND
I
OUTA
I
OUTB
ON / OFF
R
MIN
R
STEP
VDD
ENA
ISET GND
I
OUTA
I
OUTB
3V
R
MIN
R
MAX
Figure 5 – PWM on Enabled
(Lowest IQ) Figure 6 – Precision 2 Steps Figure 7 – Manual Control
VDD
ENA
ISET GND
I
OUTA
I
OUTB
ON / OFF
R
SET
PWM
VDD
ENA
ISET GND
I
OUTA
I
OUTB
1K
C
SLOPE
5K
10K
100K
PWM
2N2222A
8.2nF
VDD
ENA
ISET GND
I
OUTA
I
OUTB
6.3K
2N2222
10K
100K
PWM
ON / OFF
1V /
DIV
10
µ
s / DIV
10mA /
DIV
1V /
DIV
20µs / DIV
10µA /
DIV
1V /
DIV
20µs / DIV
10mA /
DIV
Figure 8 – PWM Dimming Totem Pole
Output Figure 9 – PWM – Low EMI
Wide Range
Figure 10 – PWM – Wide Range 500:1 +
A
AP
PP
PL
LI
IC
CA
AT
TI
IO
ON
NS
S
Microsemi
Integrated Products
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
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Copyright © 2001
Rev. 1.0d, 2005-03-14
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LX1990
Dual Pro
g
rammable
LED Current Sink
TM ®
APPLICATION
VDD
ENA
ISET GND
I
OUTA
I
OUTB
R
SET
100K
10K
PWM
20K
BC 846B x2
20K
.47µF
3.3V
10 White
LED s each
output
48V
ON/OFF
2.2K
LX432SC
Optional circuit for
higher efficiency
Figure 11 – Using the LX 1990 With High Voltage Supp lies
A
AP
PP
PL
LI
IC
CA
AT
TI
IO
ON
NS
S
Microsemi
Integrated Products
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
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Copyright © 2001
Rev. 1.0d, 2005-03-14
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LX1990
Dual Pro
g
rammable
LED Current Sink
TM ®
PACKAGE DIMENSIONS
LM
6-Pin Plastic MLP-Micro Exposed Pad
G
A
B
F
H
E
D
CInternally Connected
together, but
isolated fr om all
other term inals
K
J
I
Note:
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.
M
ILLIMETERS INCHES
Dim MIN MAX MIN MAX
A 2.90 3.10 0.114 0.122
B 2.90 3.10 0.114 0.122
C 0.65 0.75 0.025 0.029
D 0.15 0.25 0.005 0.009
E 1.841 BSC 0.075 BSC
F 0.27 0.43 0.010 0.016
G 0.95 BSC 0.037 BSC
H 1.22 BSC 0.048 BSC
I 0 0.10 0 0.003
J 0.21 0.37 0.008 0.014
K 0 0.10 0 0.003
M
ME
EC
CH
HA
AN
NI
IC
CA
AL
LS
S
Microsemi
Integrated Products
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
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Copyright © 2001
Rev. 1.0d, 2005-03-14
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LX1990
Dual Pro
g
rammable
LED Current Sink
TM ®
NOTES
PRODUCTION DATA – Information contained in this document is proprietary to Microsemi
and is current as of publication date. This do cument 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.
N
NO
OT
TE
ES
S
