philips semiconductors linear products product specification NE587 led decoder/driver 530 august 31, 1994 853-1095 13721 description the NE587 is a latch/decoder/driver for 7-segment common anode led displays. the NE587 has a programmable current output up to 50ma which is essentially independent of output voltage, power supply voltage, and temperature. the data (bcd) inputs and le (latch enable) input are low-loading so that they are compatible with any data bus system. the 7-segment decoding is implemented with a rom so that alternative fonts can be made available. features ? latched bcd inputs ? low loading bus-compatible inputs ? ripple-blanking on leading- and/or trailing-edge zeros applications ? digital panel motors ? measuring instruments ? test equipment ? digital clocks ? digital bus monitoring pin configurations 1 2 3 4 5 6 7 8 9 10 11 12 18 17 16 15 14 13 1 2 3 4 5 6 7 8 9 10 11 12 13 14 20 19 18 17 16 15 d 1 d 2 le bi/rbo dig gnd rbi i p d 3 d 0 v cc f g a power gnd b e c d d 1 d 2 le bi/rbo dig gnd rbi i p d 3 d 0 v cc f g a power gnd b e nc d nc c n package d 1 package note: 1. sol and non-standard pinout. ordering information description temperature range order code dwg # 20-pin plastic small outline large (sol) package 0 to +70 c NE587d 1 0172d 18-pin plastic dual in-line package (dip) 0 to +70 c NE587n 0407a notes: 1. sol and non-standard pinout absolute maximum ratings t a =25 c unless otherwise specified. symbol parameter rating unit v cc supply voltage -0.5 to +7 v v in input voltage (d 0 -d 3 , le , rbi ) -0.5 to +15 v v out output voltage (a-g, rbo) -0.5 to +7 v p d power dissipation (25 c) 1 1000 mw t a ambient temperature range 0 to 70 c t j junction temperature 150 c t stg storage temperature range -65 to +150 c t sold soldering temperature (10sec max) 300 c notes: 1. derate power dissipation as indicated n packagee95 c/w above 55 c
philips semiconductors linear products product specification NE587 led decoder/driver august 31, 1994 531 block diagram .. .. d 1 d 2 le bi/rbo gnd rbi i p d 3 d 0 v cc f g a power gnd (10) b e d c (18) (5) (7) (1) (2) (6) (3) (8) (9) (4) (15) (14) (13) (12) (11) (17) (16) data latches bcd to 7-segment decoder segment current driver bandgap reference
philips semiconductors linear products product specification NE587 led decoder/driver august 31, 1994 532 dc electrical characteristics v cc =4.75 to 5.25v, 0 c < t a < 70 c. typical values are at v cc =5v, t a =25 c, r p =1k w ( 1%), unless otherwise specified. symbol parameter test conditions limits unit symbol parameter test conditions min typ max unit v cc operating supply voltage 4.75 5.00 5.25 v v ih input high voltage all inputs except bi 2.0 15 v bi 2.0 5.5 v il input low voltage 0.8 v v ic input clamp voltage i in =-12ma, t a =25 c -1.5 v inputs d 0 -d 3 , le , rbi m a v in =2.4v 1.0 10 i ih input high current v in =15v 15 15 input bi (pin 4) 10 100 m a rbi =h v in =v cc =5.25v v in =0.4v, inputs d 0 -d 3 -5 i il input low current le , rbi -200 m a input bi v cc =5.25v -0.7 ma rbi =h, v in =0.4v v ol output low voltage output rbo 0.2 0.5 v i out =3.0ma output rbo v oh output high voltage i out =-50 m a 3.5 4.5 v rbi =h i out output segment outputs aao through ago 20 25 30 ma aono current v out =2.0v d i out output current ratio with reference to abo segment 0.90 1.00 1.10 (all outputs on) v out =2.0v output segment outputs aao through ago i off aoffo current v out =5.0v 20 250 m a v cc =5.25v i cco supply current all outputs aono 33 55 ma v out >1v v cc =5.25v i cci supply current all outputs blanked 50 70 ma notes: NE587 programming: the NE587 output current can be programmed, provided a program resistor , r p , be connected between i p (pin 8) and ground (pin 9). the voltage at i p (pin 8) is constant ( 1.3v). thus, a current through r p is i p 1.3v/r p , as shown in figure 5. i o /i p is 20 in the 15 to 50ma output current range.
philips semiconductors linear products product specification NE587 led decoder/driver august 31, 1994 533 ac electrical characteristics v cc =5v, t a =25 c, r l =130 w , c l =30pf including probe capacity. symbol parameter test conditions limits unit symbol parameter test conditions min typ max unit t dav propagation delay (figure 2) from data to output 135 ns t dav propagation delay (figure 3) from le to output 135 ns t w latch enable pulse width (figure 4) 30 ns t s latch enable setup time (figure 4) from data to le 20 ns t h latch enable hold time (figure 4) from le to data 0 ns notes: t dav = (t hl +t lh ) truth table binary input inputs outputs display binary input le rbi d 3 d 2 d 1 d 0 a b c d e f g rbo display - h * x x x x stable ** stable 0 l l l l l l h h h h h h h l blank 0 l h l l l l l l l l l l h h 0 1 l x l l l h h l l h h h h h 1 2 l x l l h l l l h l l h l h 2 3 l x l l h h l l l l h h l h 3 4 l x l h l l h l l h h l l h 4 5 l x l h l h l h l l h l l h 5 6 l x l h h l l h l l l l l h 6 7 l x l h h h l l l h h h h h 7 8 l x h l l l l l l l l l l h 8 9 l x h l l h l l l l h l l h 9 10 l x h l h l h h h h h h l h - 11 l x h l h h l h h l l l l h e 12 l x h h l l h l l h l l l h h 13 l x h h l h h h h l l l h h l 14 l x h h h l l l h h l l l h p 15 l x h h h h h h h h h h h h blank **bi x x x x x x h h h h h h h l** blank notes: h=high voltage level, output is aoffo l=low voltage level, output is aono x=don't care * the rbi will blank the display only if a binary zero is stored in the latches. ** rbo/bi used as an input overrides all other input conditions. NE587 programming 587 output current can be programmed by using a programming resistor, rp , connected between rp (pin 8) and gnd (pin 9). the voltage at rp (pin 8) is constant ( k = 1.3v). a partial schematic of the voltage reference used in the NE587 is shown in figure 1. output current to program current ratio, i o /i p , is 20 in the 15ma to 50ma range. note that i p must be derived from a resistor (r p ), and not from a high-impedance source such as an i out dac used to control display brightness. power dissipation considerations led displays are power-hungry devices, and inevitably , somewhat inef ficient in their use of the power supply necessary to drive them. duty cycle control does afford one way of improving display efficiency , provided that the leds are not driven too far into saturation; but the improvement is marginal. operation at higher peak currents has the added advantage of giving much better matching of light output, both from segment-to-segment and digit-to-digit.
philips semiconductors linear products product specification NE587 led decoder/driver august 31, 1994 534 figure 1. i p v rp r p 1.3v r p r p i p i o v cc 1:20 pin 8 band gap reference timing diagrams figure 2. t p data to output le = l d 0 d 3 output t plh t phl figure 3. t p latch enable to output t plh t phl le d 0 d 3 output segment identification a b c d e f g an output current of 10 to 50ma was chosen so that it would be suitable for multiplexed operation of large-size led digits. when designing a display system, particular care must be taken to minimize power dissipation within the ic display driver . since the output is a constant-current source, all the remaining supply voltage, which is not dropped across the led (and the digit driver , if used), will appear across the output. thus, the power dissipation will go up sharply if the display power supply voltage rises. clearly , then, it is good design practice to keep the display supply voltage as low as possible, consistent with proper operation of the supply output current sources. inserting a resistor or diode in series with the display supply is a good way of reducing the power dissipation within the integrated circuit segment driver , although, of course, total system power remains the same. power dissipation may be calculated as follows. referring to figure 6, the two system power supplies are v cc and v s . in many cases, these will be the same voltage. necessary parameters are: v cc supply voltage to driver v s supply voltage to display i cc quiescent supply current of driver i seg led segment current v f led segment forward voltage at i seg k dc % duty cycle v f , the forward led drop, depends upon the type of led material (hence the color) and the forward current. the actual forward voltage drops should be obtained from the led display manufacturer' s literature for the peak segment current selected; however , approximate voltages at nominal rated currents are: red 1.6 to 2.0v orange 2.0 to 2.5v yellow 2.2 to 3.5v green 2.5 to 3.5v figure 4. setup and hold times le d 0 d 3 output t w t s t h
philips semiconductors linear products product specification NE587 led decoder/driver august 31, 1994 535 typical performance curves i out (ma) supply current vs supply voltage output current vs output voltage r p = 1k w normalized output current vs temperature v cc = 5.0v normalized output current vs supply voltage v o = 2v, t a = 25 c maximum power dissipation vs temperature output current vs program resistor 40.0 35.0 30.0 25.0 20.0 4.0 4.4 4.8 5.2 5.6 6.0 6.4 v cc (volts) i cc (ma) r p = 1k w v out = 2v all outputs aono (0 c) (25 c) (70 c) 40.0 30.0 20.0 10.0 i out 0 1.0 2.0 3.0 4.0 5.0 v out (volts) (70 c) (0 c) (25 c) r p = 1k w (%) i out temp ( c) 110.0 105.0 100.0 95.0 90.0 10 20 30 40 50 60 70 80 105 102 100 98 95 4.0 4.5 5.0 5.5 6.0 (%) NE587 r p = 1k w NE587 v cc (volts) 1000 800 600 400 200 0 0 25 50 75 t a ( c) (mw) p d 50.0 40.0 30.0 20.0 10.0 0.0 0 2.0 4.0 6.0 8.0 10.0 v cc = 5.0v v out = 2v t a = (25 c) r p (k w ) (ma) i out these voltages are all for single-diode displays. some early red displays had 2 series leds per segment; hence the forward voltage drop was around 3.5v. thus, a maximum power dissipation calculation when all segments are on, is: p d v cc x i cc (v s v f ) x 7 x i seg x k dc mw assuming v s = v cc = 5.25v v f = 2.0v k dc = 100% p d max = 5.25 50 + 3.25 7 30mw = 945mw however , the average power dissipation will be considerably less than this. assuming 5 segments are on (the average for all output code combinations), then p d max = 5.0 30 + 3.00 5 25mw = 525mw operating temperature range limitations can be deduced from the power dissipation graph. (see typical performance characteristics.) figure 5. driving a single digit v s v cc d 3 d 2 d 1 d 0 i p decoupling capacitor on v cc should be 0.01 m f ceramic. le rbi rbo 0.01 m f note: NE587 a b c d e f g
philips semiconductors linear products product specification NE587 led decoder/driver august 31, 1994 536 however , a major portion of this power dissipation (p d max ) is because the current source output is operating with 3.25v across it. in practice, the outputs operate satisfactorily down to 0.5v , and so the extra voltage may be dropped external to the integrated circuit. suppose the worst-case v cc /v s supply is 4.75 to 5.25v, and that the maximum v e for the led display is 2.25v. only 2.75v is required to keep the display active, and hence 2.0v may be dropped externally with a resistor from v cc to v s . the value of this resistor is calculated by: r s 2.0 7 x i seg 10 ( 1 2 w rating) assuming worst case i seg of 30ma. hence now p d max = v cc i cc + (v s - v v - r x 7 i seg ) 7 i seg k dc = 5.25 50 + 1.25 7 30mw = 525mw and p d av = 5.0 30 + 1.25 5 25 = 306 mw. if a diode (or 2) is used to reduce voltage to the display , then the voltage appearing across the display driver will be independent of the number of aono segments and will be equal to v s - v f - nv d , v d 0.8v where n is the number of diodes used, power dissipation can be calculated in a similar manner. in a multiplexed display system, the voltage drop across the digit driver must also be considered in computing device power dissipation. it may even be an advantage to use a digit driver which drops an appreciable voltage, rather than the saturating pnp transistors shown in figure 9. for example a darlington pnp or npn emitter-follower may be preferable. figure 8 shows the ne591 as the digit driver in a multiplexed display system. the ne591 output drops about 1.8v which means that the power dissipation is evenly distributed between the two integrated circuits. where v s and v cc are two different supplies, the v s supply may be optimized for minimum system power dissipation and/or cost. clearly , good regulation in the v s supply is totally unnecessary, and so this supply can be made much cheaper than the regulated 5v supply used in the rest of the system. in fact, a simple unsmoothed full-wave rectified sine wave works extremely well if a slight loss in brightness can be tolerated. a transformer voltage of about 3-4.5v rms works well in most led display systems. waveforms are shown below: v s i seg the duty cycle for this system depends upon v s , v f and the output characteristics of the display driver. with v s = 4.9v peak v f = 2.0v the duty cycle is approximately 60%.
philips semiconductors linear products product specification NE587 led decoder/driver august 31, 1994 537 figure 6. 4-digit display with brightness control and leading-edge ripple blanking v s v cc d 3 d 2 d 1 d 0 a 0 a 1 le brightness control NE587 digit decode NE587 NE587 NE587 figure 7. interfacing 8-digit led display with m p bus NE587 v cc d 0 ne591 address decode data bus address bus a b c d e f g d 1 d 2 d 3 d 4 d 5 d 6 d 7 r p .01 m f
philips semiconductors linear products product specification NE587 led decoder/driver august 31, 1994 538 figure 8. interfacing 4-digit multiplexed led display v s digit 1 digit 2 digit 3 digit 4 NE587 v cc r p d 3 d 2 d 1 d 0 le
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