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| PRECISION SINGLE CELL TIMER ISSUE 2 - MAY 1998 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 du t y cy c l e c a n be a c c u r a t e l y an d independently controlled with two external resistors and one capacitor. The threshold and trigger levels are normally set as a proportion of VCC 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 ZSCT1555 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 A SO8 and DIL8 packages Operating temperature range compatible with battery technologies APPLICATIONS Portable and battery powered equipment Low voltage and low power systems SCHEMATIC DIAGRAM 8 VCC CONTROL 5 6 THRESH 2 TRIGGER 7 DISCHARGE 3 OUTPUT 4 RESET 1 GND 4-311 ZSCT1555 ABSOLUTE MAXIMUM RATINGS Supply Voltage Input Voltages (Cont, Reset, Thres, Trig) Output Current Operating Temperature Storage Temperature 9V 9V 100mA -20 to 100C -55 to 150C Power Dissipation (Tamb=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 150A(max) ELECTRICAL CHARACTERISTICS TEST CONDITIONS (Unless otherwise stated):Tamb= 25C,VCC= 1.5V SYMBOL PARAMETER CONDITIONS MIN. VCC ICC VTH ITH VTR ITR tPD VRS IRS IDS VDS VCT VOL Supply Voltage Supply Current Threshold Voltage VCC= 5V Threshold Current (Note 1) Trigger Voltage VCC= 5V Trigger Current Trigger Propagation delay Reset Voltage Reset Current Discharge switch Off-state current Discharge switch On-state voltage Control Voltage (Open Circuit) VCC= 5V Output Voltage (Low) IOL=10mA IOL=50mA VCC=5V, IOL=10mA VCC=5V, IOL=100mA Reset @ 0V Delay from trigger to output 0.1 0 0 0 IDS= 0.2mA VCC= 5V, IDS= 0.3mA 0 no load VCC= 5V, no load 0.9 74 150 1.195 1.22 3.9 4 0 0.2 0.57 0 20 0.25 0.62 -35 2 0.2 -5 10 180 240 0.4 -10 100 225 350 LIMITS TYP. MAX. 6 120 200 V mA UNITS 1.245 V 4.1 100 0.3 0.67 -100 nA V nA s V A nA mV 1.195 1.22 3.9 4 0 0 0 0 0.15 0.45 0.13 0.65 1.1 4.6 1.245 V 4.1 0.3 0.65 0.3 1 1.5 5 V VOH Output Voltage (High) 1 IOH= 100A VCC= 5V, IOH= 150A 4.5 V 4-312 ZSCT1555 ELECTRICAL CHARACTERISTICS (Continued) TEST CONDITIONS (Unless otherwise stated):Tamb=25C,VCC=1.5V SYMBOL PARAMETER CONDITIONS MIN. tR tF Output pulse rise time Output pulse fall time Timing error, Monostable Initial accuracy (Note 2) Drift with supply voltage Drift with temperature Timing error, Astable Initial accuracy (Note 2) Drift with supply voltage Drift with temperature Astable maximum frequency CL= 10pF VCC=5V, CL=10pF CL= 10pF VCC=5V, CL=10pF RA= 10 to 50 k RB= 10 to 50 k CT = 68nF RA= 10 to 50 k RB= 10 to 50 k CT = 68nF RA=20 k RB= 10 k CT =47pF LIMITS TYP. 1.6 1.2 240 24 1.6 0.262 100 4.8 0.662 150 330 MAX. s ns UNITS tIA(m) tV(m) tT(m) tIA(a) tV(a) tT(a) fA % %/V ppm/C % %/V ppm/C kHz Note 1: This will influence the maximum values of RA and RB (RAMAX=10M,RBMAX=1.5M) Note 2: Is defined as the difference between the measured value and the average value of a random sample taken on a batch basis 4-313 ZSCT1555 TYPICAL CHARACTERISTICS Minimum Pulse Width (s) Vcc=1.5v Rout/Vcc = 1K Minimum Pulse Width (s) 5 4 3 2 1 0 0 0.1 +100C +25C -20C 5 Vcc=5v Rout/Vcc = 1K 4 3 2 1 0 0 0.1 0.2 +100C +25C -20C Lowest Voltage Level of Trigger Pulse (xVcc) Lowest Voltage Level of Trigger Pulse (xVcc) Minimum Pulse Width Required for Triggering 5 Vcc=1.5v Rout/Vcc=1K +100C Minimum Pulse Width Required for Triggering 8 Vcc=5v Rout/Vcc=1K Propagation Delay (s) 4 3 +25C -20C Propagation Delay (s) 6 4 +100C +25C -20C 2 1 0 0 2 0 0 0.1 0.2 0.1 0.2 Lowest Voltage Level of Trigger Pulse (xVcc) Lowest Voltage Level of Trigger Pulse (xVcc) Output Propagation Delay 200 1.05 Output Propagation Delay Supply Current (A) Pulse Duration relative to Vcc=5v 160 120 80 40 0 0.0 1.0 2.0 3.0 4.0 5.0 -20C +25C +100C 1.00 0.95 0.90 0.85 0.80 0 1 2 3 4 5 6 Supply Voltage (V) Supply Voltage (V) Supply Current v Supply Voltage Normalized Output Pulse Duration v Supply Voltage 4-314 ZSCT1555 TYPICAL CHARACTERISTICS 1.0 0.8 Vcc=1.5v 0.5 0.4 Vcc=5v Vcc - Vout (V) Vcc - Vout (V) 0.6 0.4 0.2 0.0 0.001 -20C +25C +100C 0.3 0.2 0.1 0.0 0.001 -20C +25C +100C 0.01 0.1 1.0 0.01 0.1 1.0 High-Level Output Current (mA) High Level Output Current (mA) Output High Voltage Drop v Output Current Low Level Output Voltage (V) Low Level Output 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 Vcc=1.5v Output High Voltage Drop v Output Current 1.0 0.8 0.6 0.4 0.2 0.0 0.01 Vcc=5v -20C +25C +100C -20C +25C +100C 0.1 1 10 100 0.1 1 10 100 Low Level Output Current (mA) Low Level Output Current (mA) Output Low Voltage Drop v Output Current Discharge Transistor Voltage (V) Discharge Transistor Voltage (V) 10 Vcc=1.5v Output Low Voltage Drop v Output Current 10 Vcc=5v 1 -20C +25C +100C 1 -20C +25C +100C 0.1 0.1 0.001 0.001 0.01 0.1 1 0.01 0.001 0.01 0.1 1 Sink Current (mA) Sink Current (mA) Discharge Transistor Voltage v Sink Current Discharge Transistor Voltage v Sink Current 4-315 ZSCT1555 FUNCTIONAL DIAGRAM FUNCTIONAL TABLE RESET Low High High High TRIGGER VALUE THRESHOLD VOLTAGE N/A As Previously established POWER DERATING TABLE Package TA25C Power Rating N8 D8 625mW 625mW Derating Factor Above TA=25C 6.25mW/C 6.25mW/C TA=70C Power Rating 330mW 330mW TA=85C Power Rating 250mW 250mW 4-316 ZSCT1555 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 increases for time t, where t = 1.63RACT, at the end of this period the voltage on the capacitor is 0.8 VCC. At this point the flip flop resets, the capacitor is discharged and the output is driven low. Figure 2 Figure 3 gives an easy selection of RA and CT values for various time delays. 100 100k RA C - Capacitance (uF) 10 1M 1 10M 0.1 0.01 0.001 10us 100us 1ms 10ms 100ms 1s 10s Figure 3 Time Delay 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 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 VCC to eliminate any possibility of false triggering. 4-317 Figure 4 ZSCT1555 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. 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 0.2VCC and 0.8VCC. Oscillation frequency (f) and duty cycle (d) can be calculated using the following equations:f = 0.62/(RA + 2RB)CT d = RB /(RA + 2RB) Figure 5 Figure 6 shows typical waveform examples. Figure 7 Figure 8 shows the waveforms generated in this mode of operation. Figure 6 Figure 8 4-318 ZSCT1555 Figure 9 gives an easy selection for RA, RB and CT values. 100 Figure 11 shows the result of modulation with a triangle wave input to the control pin. C - Capacitance (uF) 100k 10 1M 1 10M 0.1 0.01 0.001 0.1 (RA+2RB) 1 10 100 1k 10k 100k Free Running Frequency (Hz) Figure 9 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 Figure 10 4-319 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. CONNECTION DIAGRAM ORDERING INFORMATION Part Number ZSCT1555D8 ZSCT1555N8 Package DIL8 SO8 Part Mark ZSCT1555 ZSCT1555 Figure 12 4-320 |
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