device description these devices are precision timing circuits for generation of accurate time delays or oscillation. advanced circuit design means that these devices can operate from a single battery cell with the minimum of quiescent current. in monostable mode time delays are controlled by a single resistor and capacitor network. in astable mode the frequency and duty cycle can be accurately and independently controlled with two external resistors and one capacitor. the threshold and trigger levels are normally set as a proportion of v cc by internal resistors. these levels can be programmed by the use of the control input pin. when the trigger input reduces to a value below the trigger level, the flip-flop is set and the output goes high. with the trigger input above the trigger level and the threshold input above the threshold level, the flip-flop is reset and the output goes low. the reset pin has priority over all the other inputs and is used to start new timing cycles. a low on the reset input causes the flip-flop to reset forcing the output low. whenever the output is forced low then the internal discharge transistor is turned on. features 0.9v supply operating voltage guaranteed pin connections comparable with 555 series timers very low quiescent current 74 m a so8 and dil8 packages operating temperature range compatible with battery technologies applications portable and battery powered equipment low voltage and low power systems precision single cell timer issue 2 - may 1998 zsct1555 7 discharge 6 thresh 2 trigger 5 control 8 vcc 4 reset 3 output 1 gnd schematic diagram 4-311
absolute maximum ratings supply voltage 9v input voltages 9v (cont, reset, thres, trig) output current 100ma operating temperature -20 to 100c storage temperature -55 to 150c power dissipation (t amb =25c) dil8 625mw so8 625mw recommended operating conditions supply voltage 0.9v(min) 6v(max) input voltages 6v(max) (cont, reset, thres, trig) output current sink 100ma(max) source 150 m a(max) electrical characteristics test conditions (unless otherwise stated):t amb = 25c,v cc = 1.5v symbol parameter conditions limits units min. typ. max. v cc supply voltage 0.9 6 v i cc supply current no load v cc = 5v, no load 74 150 120 200 ma v th threshold voltage v cc = 5v 1.195 3.9 1.22 4 1.245 4.1 v i th threshold current (note 1) 0 20 100 na v tr trigger voltage v cc = 5v 0.2 0.57 0.25 0.62 0.3 0.67 v i tr trigger current 0 -35 -100 na t pd trigger propagation delay delay from trigger to output 2 m s v rs reset voltage 0.1 0.2 0.4 v i rs reset current reset @ 0v 0 -5 -10 m a i ds discharge switch off-state current 0 10 100 na v ds discharge switch on-state voltage i ds = 0.2ma v cc = 5v, i ds = 0.3ma 0 0 180 240 225 350 mv v ct control voltage (open circuit) v cc = 5v 1.195 3.9 1.22 4 1.245 4.1 v v ol output voltage (low) i ol =10ma i ol =50ma v cc =5v, i ol =10ma v cc =5v, i ol =100ma 0 0 0 0 0.15 0.45 0.13 0.65 0.3 0.65 0.3 1 v v oh output voltage (high) i oh = 100 m a v cc = 5v, i oh = 150 m a 1 4.5 1.1 4.6 1.5 5 v zsct1555 4-312
symbol parameter conditions limits units min. typ. max. t r output pulse rise time c l = 10pf v cc =5v, c l =10pf 1.6 1.2 m s t f output pulse fall time c l = 10pf v cc =5v, c l =10pf 240 24 ns d t ia (m) d t v (m) d t t (m) timing error, monostable initial accuracy (note 2) drift with supply voltage drift with temperature ra= 10 to 50 k w rb= 10 to 50 k w c t = 68nf 1.6 0.262 100 % %/v ppm/c d t ia (a) d t v (a) d t t (a) timing error, astable initial accuracy (note 2) drift with supply voltage drift with temperature ra= 10 to 50 k w rb= 10 to 50 k w c t = 68nf 4.8 0.662 150 % %/v ppm/c f a astable maximum frequency ra=20 k w rb= 10 k w c t =47pf 330 khz note 1: this will influence the maximum values of ra and rb (ra max =10m w ,rb max =1.5m w ) note 2: is defined as the difference between the measured value and the average value of a random sample taken on a batch basis zsct1555 electrical characteristics (continued) test conditions (unless otherwise stated):t amb =25c,v cc =1.5v 4-313
zsct1555 01234 5 0.80 0.85 0.90 0.95 1.00 1.05 pulse duration relative to vcc=5v supply voltage (v) normalized output pulse duration v supply voltage 6 -20c +25c +100c 200 160 120 80 40 0 1.0 2.0 3.0 4.0 5.0 0.0 supply current (a) supply voltage (v) supply current v supply voltage 8 6 4 2 0 00.2 propagation delay (s) lowest voltage level of trigger pulse (xvcc) output propagation delay vcc=5v 0.1 +100c +25c -20c rout/vcc=1k 5 4 3 2 1 0 00.10.2 propagation delay (s) lowest voltage level of trigger pulse (xvcc) output propagation delay vcc=1.5v +25c -20c rout/vcc=1k 5 4 3 2 1 0 00.1 +100c +25c -20c minimum pulse width (s) lowest voltage level of trigger pulse (xvcc) minimum pulse width required for triggering vcc=1.5v rout/vcc = 1k 5 4 3 2 1 0 00.2 +100c +25c -20c minimum pulse width (s) lowest voltage level of trigger pulse (xvcc) minimum pulse width required for triggering vcc=5v 0.1 rout/vcc = 1k +100c typical characteristics 4-314
zsct1555 vcc=5v -20c +25c +100c 1 0.1 0.01 0.001 sink current (ma) discharge transistor voltage v sink current 10 1 0.1 0.01 discharge transistor voltage (v) vcc=1.5v -20c +25c +100c 1 0.1 0.01 0.001 sink current (ma) discharge transistor voltage v sink current 10 1 0.1 0.001 discharge transistor voltage (v) 2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 0.01 0.1 1 10 100 low level output current (ma) output low voltage drop v output current low level output voltage (v) vcc=1.5v -20c +25c +100c 1.0 0.8 0.6 0.4 0.2 0.0 0.01 0.1 1 10 100 low level output current (ma) output low voltage drop v output current low level output voltage (v) -20c +25c +100c vcc=5v 0.5 0.4 0.3 0.2 0.1 0.0 -20c +25c +100c vcc=5v vcc - vout (v) 0.001 0.01 0.1 1.0 high level output current (ma) output high voltage drop v output current 1.0 0.8 0.6 0.4 0.2 0.0 1.0 0.1 0.01 0.001 -20c +25c +100c vcc=1.5v high-level output current (ma) output high voltage drop v output current vcc - vout (v) typical characteristics 4-315
functional diagram functional table reset trigger value threshold voltage output discharge switch low n/a n/a low on high v cc /5 >4v cc /5 low on high >v cc /5 <4v cc /5 as previously established power derating table package ta 25c power rating derating factor above ta=25c t a =70c power rating t a =85c power rating n8 625mw 6.25mw/c 330mw 250mw d8 625mw 6.25mw/c 330mw 250mw zsct1555 4-316
applications information many configurations of the zsct1555 are possible. the following gives a selection of a few of these using the most basic monostable and astable connections. the final application example in astable mode shows the device optimum use for low voltage and power economy in a single cell boost converter. monostable operation figure 1 shows connection of the timer as a one-shot whose pulse period is independent of supply voltage. initially the capacitor is held discharged. the application of a negative going trigger pulse sets an internal flip flop which allows the capacitor to start to charge up via ra and forces the output high. the voltage on the capacitor incr eases for time t, where t = 1.63rac t , at the end of this period the voltage on the capacitor is 0.8 v cc . at this point the flip flop resets, the capacitor is discharged and the output is driven low. figure 2 shows the timing diagram for this function. during the output high period further trigger pulses are locked out however the circuit can be reset by application of a negative going pulse on the reset pin. once the output is driven low it remains in this state until the application of the next trigger pulse. if the reset function is not used then it is recommended to connect to v cc to eliminate any possibility of false triggering. figure 3 gives an easy selection of ra and c t values for various time delays. this configuration of circuit can be used as a frequency divider by adjusting the timing period. figure 4 indicates a divide by three. figure 1 figure 2 figure 3 100 10 1 0.1 0.01 0.001 10us 100us 1ms 10ms 100ms 1s 10s c - capacitance (uf) time delay 100k 1m 10m r a figure 4 zsct1555 4-317
figure 5 shows the monostable mode used as a pulse width modulator. here the trigger pin is supplied with a continuous pulse train, the resulting output pulse width is modulated by a signal applied to the control pin. figure 6 shows typical waveform examples. astable operation the configuration of figure 7 produces a free running multivibrator circuit whose frequency is independent of supply voltage. the ratio of resistors ra and rb precisely sets the circuit duty cycle. the capacitor is charged and discharged between thresholds at 0.2v cc and 0.8v cc . oscillation frequency (f) and duty cycle (d) can be calculated using the following equations:- f = 0.62/(ra + 2rb)c t d = rb /(ra + 2rb) figure 8 shows the waveforms generated in this mode of operation. figure 5 figure 6 figure 8 zsct1555 figure 7 4-318
zsct1555 figure 9 gives an easy selection for ra, rb and c t values. similar to the pwm circuit of figure 5 the astable circuit can be configured with modulation of the control input as shown in figure 10. the result is a pulse position modulated, ppm, circuit where the pulse position is altered by the control input voltage. figure 11 shows the result of modulation with a triangle wave input to the control pin. figure 11 (ra+2rb) 100 10 1 0.1 0.01 0.001 0.1 1 10 100 1k 10k 100k c - capacitance (uf) free running frequency (hz) 10m 1m 100k figure 10 figure 9 4-319
figure 12 zsct1555 the circuit of figure 12 shows the device in astable mode operating as part of a single cell boost converter. this circuit generates a 5 volt supply from a single battery cell. the circuit output voltage is maintained down to 0.9 volts input and power economy is optimised for extended battery life. 4-320 ordering information part number package part mark ZSCT1555D8 dil8 zsct1555 zsct1555n8 so8 zsct1555 connection diagram
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