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19-3808; Rev 0; 7/05
16-Port, 36V Constant-Current LED Driver
General Description
The MAX6971 serial-interfaced LED driver provides 16 open-drain, constant-current-sinking LED driver outputs rated at 36V. The MAX6971 operates from a 3V to 5.5V supply. The MAX6971 supply and the LEDs' supply or supplies can power up in any order. The constant-current outputs are programmed together to up to 55mA using a single external resistor. The MAX6971 operates with a 25Mb, industry-standard, 4-wire serial interface. The MAX6971 uses the industry-standard, shift-registerplus-latch-type serial interface. The driver accepts data shifted into a 16-bit shift register using data input DIN and clock input CLK. Input data appears at the DOUT output 16 clock cycles later to allow cascading of multiple MAX6971s. The latch-enable input, LE, loads the 16 bits of shift register data into a 16-bit output latch to set which LEDs are on and which are off. The outputenable, OE, gates all 16 outputs on and off, and is fast enough to be used as a PWM input for LED intensity control. For applications requiring LED fault detection, refer to the MAX6983*, which automatically detects open-circuit LEDs. For safety-related applications requiring a watchdog timer, refer to the MAX6983, which includes a fail-safe feature that blanks the display if the serial interface becomes inactive for more than 1s. The MAX6971 is one of a family of 12 shift-register-pluslatch-type LED drivers. The family includes 8-port and 16-port types, with 5.5V- or 36V-rated LED outputs, with and without open-circuit LED detection and watchdog. All versions operate from a 3V to 5.5V supply, and are specified over the -40C to +125C temperature range. 3V to 5.5V Logic Supply 16 Constant-Current LED Outputs Rated at 36V Up to 55mA Continuous Current per Output Output Current Programmed by Single Resistor 3% Current Matching Between Outputs 6% Current Matching Between ICs High-Dissipation, 24-Pin Packages -40C to +125C Temperature Range
Features
25Mb, Industry-Standard, 4-Wire Serial Interface
MAX6971
Ordering Information
PART MAX6971AUG MAX6971ANG TEMP RANGE -40C to +125C -40C to +125C PIN-PACKAGE 24 TSSOP 24 Narrow PDIP
Typical Application Circuit and Selector Guide appear at end of data sheet.
Pin Configuration
TOP VIEW
GND 1 DIN 2 24 V+ 23 SET 22 DOUT 21 OE
Applications
Variable Message Signs Marquee Displays Point-of-Order Signs Traffic Signs Gaming Features Architectural Lighting
*Future product--contact factory for availability.
CLK 3 LE 4 OUT0 5 OUT1 6 OUT2 7 OUT3 8 OUT4 9 OUT5 10 OUT6 11 OUT7 12
MAX6971AUG MAX6971ANG
20 OUT15 19 OUT14 18 OUT13 17 OUT12 16 OUT11 15 OUT10 14 OUT9 13 OUT8
TSSOP/PDIP
________________________________________________________________ Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at 1-888-629-4642, or visit Maxim's website at www.maxim-ic.com.
16-Port, 36V Constant-Current LED Driver MAX6971
ABSOLUTE MAXIMUM RATINGS
Voltage with respect to GND. V+ ............................................................................-0.3V to +6V OUT_ .....................................................................-0.3V to +40V DIN, CLK, LE, OE, SET ................................-0.3V to (V+ + 0.3V) DOUT Current ..................................................................10mA OUT_ Sink Current .............................................................60mA Total GND Current ...........................................................960mA Continuous Power Dissipation (TA = +70C) 24-Pin TSSOP (derate 12.2mW/C over +70C) ..........975mW 24-Pin PDIP (derate 13.3mW/C over +70C)............1067mW Operating Temperature Range .........................-40C to +125C Junction Temperature ......................................................+150C Storage Temperature Range .............................-65C to +150C Lead Temperature (soldering, 10s) .................................+300C
Stresses beyond those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(Typical Operating Circuit, V+ = 3V to 5.5V, TA = TMIN to TMAX, unless otherwise noted. Typical values are at V+ = 5V, TA = +25C.) (Note 1)
PARAMETER Operating Supply Voltage Output Voltage Standby Current (Interface Idle, All Output Ports High Impedance, RSET = 360) Standby Current (Interface Running, All Output Ports High Impedance, RSET = 360) Supply Current (Interface Idle, All Output Ports Active Low, RSET = 360) Input High Voltage DIN, CLK, LE, OE Input Low Voltage DIN, CLK, LE, OE Hysteresis Voltage DIN, CLK, LE, OE Input Leakage Current DIN, CLK, LE, OE Output High-Voltage DOUT Output Low Voltage Output Current OUT_ Output Leakage Current OUT_ SYMBOL V+ VOUT I+ All logic inputs at V+ or GND, DOUT unloaded 5.7 CONDITIONS MIN 3.0 TYP MAX 5.5 36 8 UNITS V V mA
I+
fCLK = 5MHz, OE = V+, DIN and LE = V+ or GND, DOUT unloaded
6
8.5
mA
I+
All logic inputs at V+ or GND, DOUT unloaded 0.7 x V+
18
25
mA
VIH VIL VI IIH, IIL VOH VOL IOUT ILEAK ISOURCE = 4mA ISINK = 4mA V+ = 3V to 5.5V, VOUT = 0.8V to 2.5V, RSET = 360 OE = V+
V 0.3 x V+ 0.8 V V +1 A V 0.5 V mA A
-1 V+ - 0.5V
37
50
61 1
Note 1: All parameters tested at TA = +25C. Specifications over temperature are guaranteed by design.
2
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16-Port, 36V Constant-Current LED Driver
5V TIMING CHARACTERISTICS
(Typical Operating Circuit, V+ = 4.5V to 5.5V, TA = TMIN to TMAX, unless otherwise noted.) (Notes 1, 2, 3)
PARAMETER CLK Clock Period CLK Pulse-Width High CLK Pulse-Width Low DIN Setup Time DIN Hold Time DOUT Propagation Delay DOUT Rise and Fall Time LE Pulse-Width High LE Setup Time LE Rising to OUT_ Rising Delay LE Rising to OUT_ Falling Delay CLK Rising to OUT_ Rising Delay CLK Rising to OUT_ Falling Delay OE Rising to OUT_ Rising Delay OE Falling to OUT_ Falling Delay LED Output OUT_ Turn-On Fall Time LED Output OUT_ Turn-Off Rise Time SYMBOL tCP tCH tCL tDS tDH tDO tDR, tDF tLW tLS tLRR tLRF tCRR tCRF tOEH tOEL tf tr (Note 3) (Note 3) (Note 3) (Note 3) (Note 3) (Note 3) 80% to 20%, pullup resistor = 65 20% to 80%, pullup resistor = 65 CDOUT = 10pF, 20% to 80% 20 10 100 300 100 310 100 320 120 120 CONDITIONS MIN 40 19 19 4 8 12 32 10 TYP MAX UNITS ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns
MAX6971
Note 1: All parameters tested at TA = +25C. Specifications over temperature are guaranteed by design. Note 2: See Figure 3. Note 3: A 65 pullup resistor connected from OUT_ to 5.5V.
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3
16-Port, 36V Constant-Current LED Driver MAX6971
3.3V TIMING CHARACTERISTICS
(Typical Operating Circuit, V+ = 3V to 5.5V, TA = TMIN to TMAX, unless otherwise noted.) (Notes 1, 2)
PARAMETER CLK Clock Period CLK Pulse-Width High CLK Pulse-Width Low DIN Setup Time DIN Hold Time DOUT Propagation Delay DOUT Rise and Fall Time LE Pulse-Width High LE Setup Time LE Rising to OUT_ Rising Delay LE Rising to OUT_ Falling Delay CLK Rising to OUT_ Rising Delay CLK Rising to OUT_ Falling Delay OE Rising to OUT_ Rising Delay OE Falling to OUT_ Falling Delay LED Output OUT_ Turn-On Fall Time LED Output OUT_ Turn-Off Rise Time SYMBOL tCP tCH tCL tDS tDH tDO tDR, tDF tLW tLS tLRR tLRF tCRR tCRF tOEH tOEL tf tr (Note 3) (Note 3) (Note 3) (Note 3) (Note 3) (Note 3) 80% to 20% (Note 3) 20% to 80% (Note 3) CDOUT = 10pF, 20% to 80% 20 15 120 310 120 330 120 330 120 120 CONDITIONS MIN 52 24 24 4 8 12 50 12 TYP MAX UNITS ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns
Note 1: All parameters tested at TA = +25C. Specifications over temperature are guaranteed by design. Note 2: See Figure 3. Note 3: A 65 pullup resistor connected from OUT_ to 5.5V.
Typical Operating Characteristics
(TA = +25C, unless otherwise noted.)
SUPPLY CURRENT vs. SUPPLY VOLTAGE (INTERFACE IDLE, ALL OUTPUTS OFF, RSET = 720)
MAX6971 toc01
MAX6971 toc02
TA = +85C TA = +125C
TA = +125C SUPPLY CURRENT (mA) 1.95
TA = +85C
35 SUPPLY CURRENT (mA) 30 25 20
SUPPLY CURRENT (mA)
3.65 TA = +125C 3.60 TA = +85C
1.90 TA = -40C 1.85 TA = +25C
TA = +25C TA = -40C
3.55 TA = -40C
TA = +25C
15 10
1.80 3.0 3.5 4.0 4.5 5.0 5.5 SUPPLY VOLTAGE (V)
3.50 3.0 3.5 4.0 4.5 5.0 5.5 SUPPLY VOLTAGE (V)
3.0
3.5
4.0
4.5
5.0
5.5
SUPPLY VOLTAGE (V)
4
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MAX6971 toc03
2.00
3.70
SUPPLY CURRENT vs. SUPPLY VOLTAGE (INTERFACE IDLE, ALL OUTPUTS OFF, RSET = 360)
SUPPLY CURRENT vs. SUPPLY VOLTAGE (INTERFACE IDLE, ALL OUTPUTS ON, RSET = 720)
40
16-Port, 36V Constant-Current LED Driver MAX6971
Typical Operating Characteristics (continued)
(TA = +25C, unless otherwise noted.)
SUPPLY CURRENT vs. SUPPLY VOLTAGE (INTERFACE IDLE, ALL OUTPUTS ON, RSET = 360)
MAX6971 toc04
PORT OUTPUT CURRENT vs. PORT OUTPUT VOLTAGE (RSET = 720, V+ = 3.3V)
MAX6971 toc05
PORT OUTPUT CURRENT vs. PORT OUTPUT VOLTAGE (RSET = 360, V+ = 3.3V)
TA = -40C
MAX6971 toc06
45 40 SUPPLY CURRENT (mA) TA = +125C 35 30 25 20 15 3.0 3.5 4.0 4.5 5.0 TA = +25C TA = +85C
30 25 20 15 10 5 0 TA = -40C
60 50 40 30 TA = +125C 20 10 0
PORT OUTPUT CURRENT (mA)
PORT OUTPUT CURRENT (mA)
TA = +25C TA = +85C TA = +125C
TA = +25C TA = +85C
TA = -40C 5.5
0
0.5
1.0
1.5
2.0
2.5
3.0
0
0.5
1.0
1.5
2.0
2.5
3.0
SUPPLY VOLTAGE (V)
PORT OUTPUT VOLTAGE (V)
PORT OUTPUT VOLTAGE (V)
PORT OUTPUT CURRENT vs. PORT OUTPUT VOLTAGE (RSET = 720, V+ = 5.0V)
MAX6971 toc07
PORT OUTPUT CURRENT vs. PORT OUTPUT VOLTAGE (RSET = 360, V+ = 5.0V)
MAX6971 toc08
PORT OUTPUT CURRENT vs. SUPPLY VOLTAGE (RSET = 720, VOUT = 2V)
MAX6971 toc09
30 TA = -40C PORT OUTPUT CURRENT (mA) 25 20 15 10 5 0 0 0.5 1.0 1.5 2.0 2.5 TA = +25C TA = +85C TA = +125C
60 TA = -40C PORT OUTPUT CURRENT (mA) 50 40 TA = +25C 30 20 10 0 TA = +85C TA = +125C
25.0
PORT OUTPUT CURRENT (mA)
24.5 TA = +125C 24.0
TA = +85C
TA = +25C 23.5 TA = -40C
23.0 0 0.5 1.0 1.5 2.0 2.5 3.0 3.0 3.5 4.0 4.5 5.0 5.5 PORT OUTPUT VOLTAGE (V) SUPPLY VOLTAGE (V)
3.0
PORT OUTPUT VOLTAGE (V)
PORT OUTPUT CURRENT vs. SUPPLY VOLTAGE (RSET = 360, VOUT = 2V)
MAX6971 toc10
PORT OUTPUT CURRENT vs. RSET RESISTANCE (V+ = 5.0V)
MAX6971 toc11
49
50
PORT OUTPUT CURRENT (mA)
PORT OUTPUT CURRENT (mA)
40
48 TA = -40C
TA = +25C
30
20
47 TA = +125C
TA = +85C
10
46 3.0 3.5 4.0 4.5 5.0 5.5 SUPPLY VOLTAGE (V)
0 0 1 2 3 4 5 RSET RESISTANCE (k)
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5
16-Port, 36V Constant-Current LED Driver MAX6971
Pin Description
PIN 1 2 3 4 5-20 21 22 23 24 NAME GND DIN CLK LE OUT0-OUT15 OE DOUT SET V+ Ground Serial-Data Input. Data is loaded into the internal 16-bit shift register on CLK's rising edge. Serial-Clock Input. Data is loaded into the internal 16-bit shift register on CLK's rising edge. Load-Enable Input. Data is loaded transparently from the internal shift register(s) to the output latch(es) while LE is high. Data is latched into the output latch(es) on LE's falling edge, and retained while LE is low. LED Driver Outputs. OUT0 to OUT15 are open-drain, constant-current-sinking outputs rated to 28V. Output-Enable Input. High forces outputs OUT0 to OUT15 high impedance, without altering the contents of the output latches. Low enables outputs OUT0 to OUT15 to follow the state of the output latches. Serial-Data Output. Data is clocked out of the 16-bit internal shift register to DOUT on CLK's rising edge. LED Current Setting. Connect SET to GND through a resistor (RSET) to set the maximum LED current. Positive Supply Voltage. Bypass V+ to GND with a 0.1F ceramic capacitor. FUNCTION
CLK MAX6971
DIN
D0
SERIAL-TO-PARALLEL SHIFT REGISTER
D15
DOUT
LE
D0
LATCHES
D15
POWER-ON RESET
V+
OE
V+
D0
CONSTANT-CURRENT SINKS
D15
CURRENT REFERENCE
RSET OUT0 OUT1 OUT2 OUT3 OUT4 OUT15 GND GND
Figure 1. Block Diagram
6
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16-Port, 36V Constant-Current LED Driver
Detailed Description
The MAX6971 LED driver comprises a 4-wire serial interface driving 16 constant-current-sinking, opendrain output ports. The outputs drive LEDs in either static or multiplex applications (Figure 1). The constantcurrent outputs are guaranteed for current accuracy not only with chip-supply voltage variations (5V 10% and 3V to 5.5V), but also over a realistic range of driver output voltage drop (0.8V to 2.5V). The drivers use current-sensing feedback circuitry (not simple current mirrors) to ensure very small current variations over the full allowed range of output voltage (see the Typical Operating Characteristics). The 4-wire serial interface comprises a 16-bit shift register and a 16-bit transparent latch. The shift register is written through a clock input, CLK, and a data input, DIN, and the data propagates to a data output, DOUT. The data output allows multiple drivers to be cascaded and operated together. The contents of the 16-bit shift register are loaded into the transparent latch through a latch-enable input, LE. The latch is transparent to the shift register outputs when high, and latches the current state on the falling edge of LE. Each driver output is an open-drain, constant-current sink that should be connected to the cathode of either a single LED or a series string of multiple LEDs. The LED anode can be connected to a supply voltage of up to 36V, independent of the MAX6971 supply, V+. The constant-current capability is up to 55mA per output, set for all eight outputs by an external resistor, RSET.
MAX6971
4-Wire Serial Interface
The serial interface on the MAX6971 is a 4-wire serial interface using four inputs (DIN, CLK, LE, OE) and a data output (DOUT). This interface is used to write display data to the MAX6971. The serial-interface data word length is 16 bits, D0-D15. See Figure 2. The functions of the five interface pins are as follows. DIN is the serial-data input, and must be stable when it is sampled on the rising edge of CLK. Data is shifted in, MSB first. This means that data bit D15 is clocked in first, followed by 15 more data bits finishing with the LSB, D0.
LE tCL tCH tCP CLK tDH tDS DIN D15 D14 D1 tDO DOUT D0 tLS
tLW tLF
D7
OE tOEL
tOEW
tOEH 80% . tr 20% tf
OUT_
Figure 2. 4-Wire Serial-Interface Timing Diagram
_______________________________________________________________________________________
7
16-Port, 36V Constant-Current LED Driver MAX6971
CLK is the serial-clock input, which shifts data at DIN into the MAX6971 16-bit shift register on its rising edge.
LE tLRF OUT_
LE tLRR OUT_
CLK tCRF OUT_
CLK tCRR OUT_
LE is the latch load input of the MAX6971 that transfers data from the MAX6971 16-bit shift register to its 16-bit latch when LE is high (transparent latch), and latches the data on the falling edge of LE (Figure 2). The fourth input provides output-enable control of the output drivers. OE is high to force outputs OUT0-OUT15 high impedance, without altering the contents of the output latches, and low to enable outputs OUT0-OUT15 to follow the state of the output latches. OE is independent of the operation of the serial interface. Data can be shifted into the serial-interface shift register and latched, regardless of the state of OE. DOUT is the serial-data output, which shifts data out from the MAX6971's 16-bit shift register on the rising edge of CLK. Data at DIN is propagated through the shift register and appears at DOUT 16 clock cycles later.
Figure 3. LE and CLK to OUT_ Timing
Table 1. 4-Wire Serial-Interface Truth Table
SERIAL CLOCK DATA INPUT INPUT CLK D0 DIN H L X -- -- -- -- -- -- H L R0 X P1 -- SHIFT-REGISTER CONTENTS D1 R1 R1 R1 X P2 -- D2 R2 R2 R2 X P3 -- LOAD INPUT LE ... Dn-1 Dn ... Rn-2 Rn-1 ... Rn-2 Rn-1 ... Rn-1 Rn ... X X ... Pn-1 Pn ------ -- -- -- H L -- LATCH CONTENTS D0 -- -- -- R0 P0 X D1 -- -- -- R1 P1 X D2 -- -- -- R2 P2 X OUTPUT CONTENTS BLANKING INPUT OE ... Dn-1 Dn D0 D1 D2 ... Dn-1 Dn -- -- -- -- -- -- -- -- -- -- L H -- -- -- -- P0 -- -- -- -- P1 -- -- -- -- P2 -- -- -- -- -- -- -- -- -- -- -- --
-- -- --
-- Rn-1 Rn ... Pn-1 Pn ... X X
... Pn-1 Pn Hi-Z Hi-Z Hi-Z ... Hi-Z Hi-Z
L = Low-logic level. H = High-logic level. X = Don't care. P = Present state. R = Previous state. Hi-Z = High impedance.
8
_______________________________________________________________________________________
16-Port, 36V Constant-Current LED Driver
Applications Information
Selecting External Component RSET to Set LED Output Current
The MAX6971 uses an external resistor, RSET, to set the LED current for outputs OUT0-OUT15. The minimum allowed value of RSET is 327.3, which sets the output currents to 55mA. The maximum allowed value of RSET is 5k. The reference value, 360, sets the output currents to 50mA. To set a different output current, use the formula: RSET = 18,000 / IOUT where IOUT is the desired output current in mA.
Overtemperature Cutoff
The MAX6971 contains an internal temperature sensor that turns off all outputs when the die temperature exceeds approximately +165C. The outputs are enabled again when the die temperature drops below approximately +140C. Register contents are not affected, so when a driver is overdissipating, the external symptom is the load LEDs cycling between on and off as the driver repeatedly overheats and cools, alternately turning the LEDs off and then back on again.
MAX6971
Power-Supply Considerations
The MAX6971 operates with a chip supply V+, and one or more LED supplies. Bypass each supply to GND with a 0.1F capacitor as close to the MAX6971 as possible. This is normally adequate for static LED driving. For multiplex or PWM applications, it is necessary to add an additional bulk electrolytic capacitor of 4.7F or more to each supply for every 4 to 16 MAX6971s. The necessary capacitance depends on the LED load current, PWM switching frequency, and serial-interface speed. Inadequate V+ decoupling can cause timing problems, and very noisy LED supplies can affect LED current regulation.
Computing Power Dissipation
The upper limit for power dissipation (P D ) for the MAX6971 is determined by the following equation: PD = (V+ x I+) + (VOUT x DUTY x IOUT x N) where: V+ = supply voltage I+ = operating supply current when sinking IOUT LED drive current into N outputs DUTY = PWM duty cycle applied to OE N = number of MAX6971 outputs driving LEDs at the same time (maximum is 16) VOUT = MAX6971 port output voltage when driving load LED(s) IOUT = LED drive current programmed by RSET PD = power dissipation, in mW if currents are in mA Dissipation example: IOUT = 20mA, N = 16, DUTY = 1, VOUT = 2V, V+ = 5.25V PD = (5.25V x 25mA) + (2V x 1 x 20mA x 16) = 0.77W Thus, for a 24-pin TSSOP package (TJA = 1 / 0.0122 = +82C/W from the Absolute Maximum Ratings), the maximum allowed ambient temperature TA is given by: TJ(MAX) = TA + (PD x TJA) = +150C = TA + (0.77 x 82C/W) so TA = +86C.
Chip Information
PROCESS: BiCMOS
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9
16-Port, 36V Constant-Current LED Driver MAX6971
Selector Guide
PART MAX6968 MAX6977 MAX6978 MAX6970* MAX6981* MAX6980* MAX6969 MAX6979 MAX6971 MAX6983 16 16 5.5 36 8 36 55 8 5.5 NUMBER OF OUTPUTS MAX OUTPUT VOLTAGE (V) MAX OUTPUT CURRENT (mA) LED FAULT DETECTION -- Yes Yes -- Yes Yes -- Yes -- Yes WATCHDOG -- -- Yes -- -- Yes -- Yes -- Yes
*Future product--contact factory for availability.
Typical Application Circuit
+28V
+5V
C SCLK MOSI MISO LOAD ENABLE 360
V+ CLK DIN DOUT LATCH OE SET GND
MAX6971
OUT0 OUT1 OUT2 OUT3 OUT4 OUT5 OUT6 OUT7 OUT8 OUT9 OUT10 OUT11 OUT12 OUT13 OUT14 OUT15
0V
0V
10
______________________________________________________________________________________
16-Port, 36V Constant-Current LED Driver
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information go to www.maxim-ic.com/packages.)
MAX6971
PACKAGE OUTLINE, TSSOP 4.40mm BODY
21-0066
G
1
1
______________________________________________________________________________________
TSSOP4.40mm.EPS
11
16-Port, 36V Constant-Current LED Driver MAX6971
Package Information (continued)
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information go to www.maxim-ic.com/packages.)
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
12 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 2005 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products, Inc.
Heaney
PDIPN.EPS

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