LX1991 Datasheet PDF - Microsemi Corporation
| Part Number | LX1991 | |
| Description | Six Output Programmable LED Current Sink | |
| Manufacturers | Microsemi Corporation | |
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LX1991
TM ® Six Output Programmable LED Current Sink
PRODUCTION DATA SHEET
DESCRIPTION
LED Display Driver: This six channel 1000:1 Dimming Range: The DIG_DIM
current sink driver is ideal for controlling input accepts a TTL or CMOS logic signal
brightness and hue of high quality that controls duty cycle of the output
dimmable LED displays. High accuracy, currents.
dual mode dimming, and controlled current Independent Channels: The six channels
switching time provides consistent color feature independent regulation with respect
hue, at brightness ratios of up to 1000:1, to output voltage, so one does not affect the
and keeps electro magnetic emissions in others. Any one or more outputs can be left
check.
unloaded without affecting current
Its wide compliance voltage range regulation of the other channels. Multiple
combined with 43 volt breakdown cap- channels can also be connected together to
ability make the LX1991 ideal for sink more current in a single load.
automotive in-dash displays.
Precision current control: Precision
current mirror circuitry sets all channels to
EMI Control: Rise and fall time of sink
currents are precisely controlled by placing
a capacitor on the SLOPE_C pin. Special
the same current with a single programming control circuitry maintains symmetrical rise
input. Sinking current value can be pro- and fall times, preserving the LX1991’s
grammed up to 30 mA per channel with a ability to provide accurate output current
single resistor or potentiometer from ISET+ to
ISET-. Channel to channel matching is ty-
pically within ±1 percent of channel mean
at the rated output current.
response to very narrow input pulses on the
DIG_DIM pin.
Power Handling: The LX1991 is
supplied in a 4x4 MLPQ package capable
Dual Mode Dimming: Display dimming of 1.5 watts dissipation. Logic Enable: A
can be achieved by controlling either separate input puts the LX1991 to sleep at
current amplitude or duty cycle, and both less than 1 uA IDD.
methods can be employed at the same time.
IMPORTANT: For the most current data, consult MICROSEMI’s website: http://www.microsemi.com
KEY FEATURES
Six precision independent
current sink channels
Simultaneous Analog and
Digital Dimming Modes
Precision programming of
current rise & fall times
1% band gap reference
40 volt rated output stages
3V / 5V logic input compatible
1.5 watt power dissipation
On-chip thermal shutdown
16 Pin 4 x 4 MLPQ Package
BENEFITS
Consistent LED color hue
results from high current
accuracy
1000:1 dimming ratio with
digital dimming
Lowered emissions with
current slope programming
Reduced component count
for compact designs
Drive up to 108 colored
LED’s per IC (6 x 18 @ 2.1
volts)
Drive up to 60 white or blue
LED’s per IC (6 x 10 @ 3.8
volts)
PRODUCT HIGHLIGHT
5V
PWM
SIGNAL
SLEW CONTROL
ON
OFF
1.5K
LX1991
VDD
SINK1
CSLOPE
SINK2
DIG_DIM SINK3
LX1991
ENA
SINK4
ISET+
ISET-
SINK5
SINK6
GND
+36V
54 White LED’s
VF ~3.7V
@20mA
Bill of Materials
1 LX1991
1 Cap
1 Resistor
54 White LEDs
57 Total Count
Copyright © 2001
Rev. 1.0, 5/18/2005
DataSheet4 U .com
PACKAGE ORDER INFO
TJ (°C)
MIN VDD
MAX VDD
Plastic 4x4 MLPQ
LQ 16-PIN
RoHS Compliant / Pb-free Transition DC: 0436
-40 to 85
4.5
5.5V
LX1991ILQ
Note: Available in Tape & Reel. Append the letters “TR” to the part number. (i.e. LX1991ILQ-TR)
Microsemi
Integrated Products
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 1
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www.DataSheet4U.com
TM
LX1991
® Six Output Programmable LED Current Sink
PRODUCTION DATA SHEET
THEORY OF OPERATION / APPLICATION NOTE
FUNCTIONAL DESCRIPTION
The LX1991 is designed to drive LED’s used in display
illumination and signaling applications such as cellular
telephones, PDA’s automotive dashboard lighting, panel
illumination etc. With a single 5V supply, the six independently
regulated constant current outputs can drive 6 white LED’s (VF <
4.0V), or 12 green or amber LED’s (VF < 2.0V each) arranged as
6 parallel x 2 in series. With a separate high voltage LED supply
(up to 40V) a large matrix of LED’s (>100) can be driven.
The LX1991 features resistor settable output current.
Connecting a resistor between ISET+ and ISET- pins generates a
current that is mirrored into each of the outputs with a gain ratio
of about 24. This ratio remains linear for output currents from 3 to
30mA, at output current less than 3mA the ratio increases
somewhat. Output current can be varied in an analog fashion by
varying RSET resistor, typically this resistor shall be chosen in the
range of 1K to 40K.
Duty cycle dimming with a fixed current amplitude is
accomplished by driving the DIG_DIM input. The switching
frequency can exceed 100 KHz, making it practical to use a PWM
output channel from popular micro controllers. The upper limit on
frequency correlates to the minimum DIG_DIM sink pulse width
which is typically about 5µS.
To use the LX1991 at the maximum usable frequency, or
minimum pulse width the CSLOPE pin must be open. The
CSLOPE pin allows precise control of the sink current rise and
fall time. As the value of the CSLOPE capacitor is increased the
slope of the rise and fall time will change correspondingly along
with some delay to output. Special control circuitry maintains
symmetrical rise and fall times, preserving the LX1991’s ability to
provide accurate output current response to very narrow input
pulses on the DIG_DIM pin.
The ENABLE input is TTL compatible with a turn on threshold
of about 1.6V with about 150mV of hysteresis. Below 0.8V the
chip is disabled and the sink outputs are off. However ENABLE
must be driven below 0.4 volts to insure the minimum sleep
current from VDD and output off current.
All inputs and outputs are ESD and short circuit protected
making the LX1991 an exceptionally robust component. The
device also includes thermal shutdown however it is not
recommended to short the ISET+ and ISET- inputs together while
shorting the outputs to 40V as the power dissipation under these
conditions is the greatest.
APPLICATION NOTES
POWER CONSIDERATIONS
Each output has an independent current sink, however each must be
held above about 600-800mV (typically) to perform properly and
maintain the specified current regulation accuracy. The device is
designed however to allow one or more of the outputs to be unused
(open) without affecting the other channels Or conversely if more
than 30mA is needed the outputs can be combined for higher total
currents.
Package power dissipation can be calculated from the following
equation:
( ) ( )PD = n×IOUT × VLOAD -VLED
n = Number of outputs used
IOUT
VLOAD
VLED
PD
= Current from each output
= Output Supply Voltage
= Minimum LED forward voltage
= Power Dissipated in mW
Care should be exercised not to exceed the power dissipation of the
package or the maximum junction temperature of the die. Proper
mounting of the package with thermal vias (see PCB Land Guidelines
and Thermal Pad Design section) enhances power dissipation
capability. As an example to drive 24 white LED’s, 4 per channel
from a 18V VLED supply @ 25mA per LED string, we will assume
the minimum LED forward voltage to be 3.5V with an maximum
operating ambient of 50°C.
PD = (6×25mA)×(18V-(4×3.5V)) = 15×4V = 0.6W
This represents a 21.6°C temperature rise (36°C/W *0.6W) for a
die temperature of about 72°C, ignoring device drain current power
dissipation that only represents about a 3°C rise worst case. This is
well under the die junction temperature maximum rating of 150°C,
and within the 85°C electrical specifications.
DIMMING
Dimming can be accomplished both with current amplitude control
(changing the RSET resistor value) with a PWM signal (toggling the
DIG_DIM input) or both. Current between the ISET+ and ISET- pins
may be varied for current amplitude dimming. If a mechanical input
is needed, a rheostat in series with a resistor connected from ISET+ to
ISET- can be used.:
IOUT =Current Ratio×ISET
Copyright © 2001
Rev. 1.0, 5/18/2005
DataSheet4 U .com
Microsemi
Integrated Products
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 5
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Part DetailsOn this page, you can learn information such as the schematic, equivalent, pinout, replacement, circuit, and manual for LX1991 electronic component. |
| Information | Total 9 Pages | |
| Link URL | [ Copy URL to Clipboard ] | |
| Download | [ LX1991.PDF Datasheet ] | |
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