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August 2012
Rev. 1.1.0
Exar Corporation www.exar.com
48720 Kato Road, Fremont CA 94538, USA Tel. +1 510 668-7000 – Fax. +1 510 668-7001
GENERAL DESCRIPTION
The XRP7618 is an 8-channel, high voltage,
constant-current sink LED driver capable of
driving up to 100mA current per channel. With
outputs rated at 30V, the XRP7618 can control
strings of multiple LEDs with better than
±1.5% channel to channel current matching.
LED channel current is programmed via an
external resistor within a 10mA to 100mA
range. Dimming control is supported through a
standard PWM scheme up to 25kHz or through
an analog signal.
Featuring Exar’s Smart TalkTM technology,
when combined with a boost converter, the
XRP7618 maximizes the overall system
efficiency by dynamically reporting the
minimum LED voltage necessary to maintain
current regulation mode. Multiple channels can
be combined to increase current driving
capability per channel and multiple XRP7618s
can be placed in parallel to drive over 8 strings
of LEDs.
An under voltage lock out, open LED and over
temperature protections insure safe operations
under abnormal operating conditions.
The XRP7618 is available in RoHS compliant,
“green”/halogen free space saving 20-pin
TSSOP (EP) package.
APPLICATIONS
LCD Backlighting
Desktop, Notebook and TV Displays
Industrial and Medical Displays
Signage Backlighting
FEATURES
8 Constant-Current Channels
Adjustable up to 100mA per Channel
Channel Paralleling for higher Current
±1.5% Current Matching Accuracy
Up to 30V LED Channel Voltage Range
5V Biasing Voltage and Control
Smart TalkTM Power Optimization
Parallel Operations Support
PWM and Analog Dimming
UVLO, Open LED & Over Temperature
protection
RoHS Compliant Halogen Free,
20-pin TSSOP (EP) Package
TYPICAL APPLICATION DIAGRAM
Fig. 1: XRP7618 Typical Application Diagram
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© 2012 Exar Corporation 2/10 Rev. 1.1.0
ABSOLUTE MAXIMUM RATINGS
These are stress ratings only and functional operation of
the device at these ratings or any other above those
indicated in the operation sections of the specifications
below is not implied. Exposure to absolute maximum
rating conditions for extended periods of time may affect
reliability.
VCC, ISET, EN, FB, SDB, PWM ...................... -0.3V to 6.0V
CHx .......................................................... -0.3V to 30V
Junction Temperature .......................................... 150°C
Storage Temperature .............................. -65°C to 150°C
Power Dissipation ................................ Internally Limited
Lead Temperature (Soldering, 10 sec).................... 260°C
ESD Rating (HBM - Human Body Model) .................... 6kV
ESD Rating (MM - Machine Model) ........................... 200V
OPERATING RATINGS
Input Voltage Range VCC .............................. 4.2V to 5.5V
PWM Dimming Frequency .......................0.1KHz to 25KHz
Current per Channel .....................................................
VCHx≥0.5V ........................................... 10mA to 25mA
VCHx≥1V .............................................. 10mA to 65mA
VCHx≥1.5V ..........................................10mA to 110mA
Operating Temperature Range ................... -40°C to 85°C
Thermal Resistance θJA (TSSOP-20) ..................... 35°C/W
ELECTRICAL SPECIFICATIONS
Specifications with standard type are for an Operating Junction Temperature of TJ = 25°C only. Minimum and Maximum
limits are guaranteed through test, design, or statistical correlation. Typical values represent the most likely parametric
norm at TJ = 25°C, and are provided for reference purposes only. Unless otherwise indicated, VCC = 5V, RISET = 8.2kΩ, TA=
25°C.
Parameter
Min.
Typ.
Max.
Units
Conditions
Operating Input Voltage Range VCC
4.2
5.0
5.5
V
Shutdown Supply Current
0.1
1
µA
VEN=0V
Quiescent Supply Current
0.5
1
mA
No load
Under Voltage Lockout threshold
3.6
3.8
4.0
V
Falling edge
Under Voltage Lockout Hysteresis
200
mV
ISET Reference Voltage
1.170
1.194
1.218
V
Current Multiplication Ratio
370
400
430
ICHX/ISET
Maximum Output Current per Channel
23
45
mA
VCHX=0.5V
65
70
VCHX=1.0V
110
120
VCHX=1.5V
LED Current Matching
-1.5
1.5
%
Any 2 channels
VCHX=1.0V, ICHX=60mA
Current Sink Saturation Voltage
0.45
V
ICHX=20mA
0.8
ICHX=60mA
1.2
ICHX=100mA
Output Current Line Regulation
2
%/V
VCC=4.2V to 5.5V
Output Current Load Regulation
4
%
VCHX=0.5V to 2.8V
Enable Logic LOW
0.8
V
XRP7618 is disabled
Enable Logic HIGH
1.8
V
XRP7618 is active
PWM Pin Logic LOW
0.8
V
XRP7618 is disabled
PWM Pin Logic HIGH
1.8
V
XRP7618 is active
SDB Pin Logic LOW
0.4
V
SDB Pin Logic HIGH
2.4
V
Feedback Output Current
5
15
µA
Thermal Shutdown Die Temperature
160
°C
Thermal Shutdown Hysteresis
20
°C
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© 2012 Exar Corporation 3/10 Rev. 1.1.0
BLOCK DIAGRAM
Fig. 2: XRP7618 Block Diagram
PIN ASSIGNMENT
Fig. 3: XRP7618 Pin Assignment
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© 2012 Exar Corporation 4/10 Rev. 1.1.0
PIN DESCRIPTION
Name
Pin Number
Description
CHx
1, 2, 3, 4,
7, 8, 9, 10
CH1 to CH8 pins
Connect an LED between each pin and LED supply rail voltage (VLED). Current value is
controlled by RSET. Connect unused channel(s) to GND.
NC
12
Not Connected
PWM
11
PWM pin
This must be held HIGH to enable the output drivers. It can be used for PWM dimming
up to 25kHz. If not used, connect to VCC.
FBX
13
FBX input pin
Used in parallel configuration as an interface terminal by connecting it to FB pin of the
next XRP7618. If not used, leave it unconnected.
ISET
14
ISET pin
Connect resistor RSET from this pin to ground to set LED channel current as per
ICHANNEL=1.194x400/RSET
FB
15
FB pin
Samples the LED cathode voltage on each channel and outputs the lowest voltage to the
step-up converter.
SDB
16
SDB output pin
SDB signal is synchronous with the PWM signal during PWM Dimming. It outputs low
logic to the step-up converter under conditions such as shutdown or when all channels
are inactive.
SDBX
17
SDBX input pin
Used in parallel configuration as an interface terminal by connecting it to SDB pin of the
next XRP7618. If not used, connect it to GND.
AGND
18
Ground pin
VCC
19
Input Voltage pin
Must be closely decoupled to GND pin with a 0.1μF ceramic capacitor.
EN
20
Enable pin
This pin must be held HIGH to enable the XRP7618.
PGND
5, 6
Ground pin
EP
Exposed Pad
Exposed Pad
Connect to ground
ORDERING INFORMATION
Part Number
Temperature
Range
Marking
Package
Packing Quantity
Note 1
Note 2
XRP7618IGB-F
-40°C≤TA≤+85°C
EXAR
XRP7618IGB
YYWWF
XXXX
TSSOP-20
Bulk
Halogen Free
RoHS Compliant
Exposed Pad
XRP7618IGBTR-F
1.5K/Tape & Reel
XRP7618EVB
XRP7618 Evaluation Board
“YY” = Year – “WW” = Work Week – “X” = Lot Number, when applicable.
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© 2012 Exar Corporation 5/10 Rev. 1.1.0
TYPICAL PERFORMANCE CHARACTERISTICS
All data taken at VCC = 5V, RISET = 8kΩ, TA = 25°C, unless otherwise specified - Schematic and BOM from Application
Information section of this datasheet.
Fig. 4: Current per Channel vs Temperature
Fig. 5: PWM Dimming: Current per Channel vs Duty Cycle
Fig. 6: Current per Channel vs Input Voltage
Fig. 7: Current per Channel vs Voltage per Channel
Fig. 8: Maximum Output Current vs Voltage per Channel
Fig. 9: Current per Channel vs RSET resistor
0
2
4
6
8
10
12
14
16
18
20
0 20 40 60 80 100
Current per Channel (mA)
Duty cycle (%)
1kHz
100Hz
25kHz
56
57
58
59
4 4.2 4.4 4.6 4.8 5 5.2 5.4 5.6
Current per Channel (mA)
Input Voltage (V)
56
57
58
59
0.5 1.0 1.5 2.0 2.5 3.0
Current per Channel (mA)
Voltage per channel (V)
10
20
30
40
50
60
70
80
90
100
0 10 20 30 40
Current per Channel (mA)
Rset (kΩ)
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© 2012 Exar Corporation 6/10 Rev. 1.1.0
THEORY OF OPERATION
The XRP7618 is an eight channel
programmable constant current LED driver
capable of up to 100mA per channel. A single
external resistor adjusts the current for each
channel over a 10mA to 100mA range with
tight matching between channels.
Dimming is supported through a standard
PWM scheme or through an analog signal.
Furthermore, the XRP7618 maximizes the
overall system efficiency by dynamically
reporting the minimum LED voltage necessary
to remain in current regulation mode when
used with a boost converter.
Multiple XRP7618s can be placed in parallel to
drive over 8 strings of LEDs; however, unused
channels should be tied to ground.
Built-in under voltage lock out, open LED and
over temperature protections insure safe
operations under abnormal operating
conditions.
LED CHANNELS CURRENT SETTING
The maximum LED current can be set up to
100mA per channel through the ISET pin. To
set the reference current ISET, connect a
resistor RSET between this pin and ground. The
value of RSET can be calculated by the following
formula:
This reference current is multiplied internally
with a gain (K) of 400 then mirrored on all
enabled channels. This sets the maximum LED
current, referred to as 100% current (ILEDMAX).
The value can be calculated by the following
formula:
or,
The LED current can be reduced from 100%
by PWM dimming control.
PWM DIMMING CONTROL
The LED current can be adjusted by applying a
PWM signal to the PWM pin. In this mode, all
enabled channels are adjusted at the same
time and brightness is adjusted from 1% to
100% of ILEDMAX.
The supported external PWM signal frequency
is 100Hz to 25kHz.
ANALOG DIMMING CONTROL
Besides PWM dimming control, the LED
current can be controlled continuously (from
highest to lowest LED current) by raising the
voltage at the bottom of RSET from 0V
normally to 1V max, respectively. RSET value
may be determined as
where, 1.194V is a typical ISET pin voltage,
VMOD is an adjustment voltage applied to the
bottom side of RSET, 400 is the typical current
multiplication ratio, and ILEDMAX is the required
LED current per channel.
Fig. 10: XRP7618 Analog Dimming Control
If adjustment voltage VMOD isn’t used, RSET
resistor should be connected to ground.
SYSTEM POWER OPTIMIZATION
The Smart Talk feature enables XRP7618 to
maximize the overall system power efficiency,
when used with a step-up converter, by
dynamically reporting the minimum LED
channel voltage needed to maintain current
regulation mode. The XRP7618 samples the
voltage on each channel input and reports the
lowest voltage of all strings via the FB signal
to the associated step up converter.
If placed in shutdown through the EN pin or if
all channels are inactive, the XRP7618 outputs
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© 2012 Exar Corporation 7/10 Rev. 1.1.0
a logic low to the converter via the SDB signal.
Furthermore, the SDB signal is synchronous to
the PWM signal when PWM dimming is used.
OPEN LED PROTECTION
The XRP7618 provides a built-in protection for
open LED channel. Upon detection of an open
LED channel event, the FB signal is driven low
to allow the step-up converter to operate open
loop which in turn raises the voltage on the
remaining CHx pins. Upon reaching an
internally pre-set threshold of 3V, the
XRP7618 identifies the faulty channel and
removes it from the control and reporting
loop. At this point the FB signal resumes its
normal function of reporting the lowest LED
channel voltage and hence restores the proper
operations of the converter. Note that the
open LED channel is not disabled; however, its
CHx voltage is no longer reported. Upon
reconnection of the open LED channel, current
will be driven at the programmed level.
PARALLEL MODE OF OPERATION
Multiple XRP7618s can be placed in parallel to
drive over 8 strings of LEDs; however, unused
channels should be tied to ground.
While the initial XRP7618 is connected to the
step-up converter via its FB and SDB pins, the
daisy chained XRP7618s are connected to each
other through the respective FBX and SDBX
pins. In this configuration, the initial XRP7618
reports the lowest LED voltage and SDB signal
of all the XRP7618s in parallel. Refer to figure
12.
TYPICAL APPLICATION SCHEMATICS
Fig. 11: Single XRP7618 Application
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© 2012 Exar Corporation 8/10 Rev. 1.1.0
Fig. 12: Parallel Operations with the XRP7618
Fig. 13: Single Supply Operations with the XRP7618
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© 2012 Exar Corporation 9/10 Rev. 1.1.0
PACKAGE SPECIFICATION
20-PIN TSSOP (EXPOSED PAD)
Unit: mm (inch)
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© 2012 Exar Corporation 10/10 Rev. 1.1.0
REVISION HISTORY
Revision
Date
Description
1.0.0
07/26/2011
Initial Release of datasheet
1.1.0
08/24/2012
Corrected package drawings
FOR FURTHER ASSISTANCE
Email: customersupport@exar.com
Exar Technical Documentation: http://www.exar.com/TechDoc/default.aspx?
EXAR CORPORATION
HEADQUARTERS AND SALES OFFICES
48720 Kato Road
Fremont, CA 94538 – USA
Tel.: +1 (510) 668-7000
Fax: +1 (510) 668-7030
www.exar.com
NOTICE
EXAR Corporation reserves the right to make changes to the products contained in this publication in order to improve
design, performance or reliability. EXAR Corporation assumes no responsibility for the use of any circuits described herein,
conveys no license under any patent or other right, and makes no representation that the circuits are free of patent
infringement. Charts and schedules contained here in are only for illustration purposes and may vary depending upon a
user’s specific application. While the information in this publication has been carefully checked; no responsibility, however,
is assumed for inaccuracies.
EXAR Corporation does not recommend the use of any of its products in life support applications where the failure or
malfunction of the product can reasonably be expected to cause failure of the life support system or to significantly affect its
safety or effectiveness. Products are not authorized for use in such applications unless EXAR Corporation receives, in
writing, assurances to its satisfaction that: (a) the risk of injury or damage has been minimized; (b) the user assumes all
such risks; (c) potential liability of EXAR Corporation is adequately protected under the circumstances.
Reproduction, in part or whole, without the prior written consent of EXAR Corporation is prohibited.
