74HC4538

HD74HC4538 Dual Precision Retriggerable/Resettable Monostable Multivibrators Description Each multivibrator features both a negative, A, and a positive, B, transition triggered input, either of which can be used as an inhibit input. Also included is a clear input that when taken low resets the one short. The HD74HC4538 is retriggerable. That is, it may be triggered repeatedly while their outputs are generating a pulse and the pulse will be extended. Pulse width stability over a wide range of temperature. The output pulse equation is simply: tw = 0.7 (R) (C). Features • • • • • High Speed Operation: tpd (A or B to Y) = 22 ns typ (CL = 50 pF) High Output Current: Fanout of 10 LSTTL Loads Wide Operating Voltage: VCC = 2 to 6 V Low Input Current: 1 µA max Low Quiescent Supply Current Function Table Inputs CD L H H H H X: Irrelevant H L A X L H Not triggered Not triggered B X Outputs Q L Q H HD74HC4538 Pin Arrangement T1A T2A CDA AA BA QA QA GND 1 2 3 4 5 6 7 8 (Top view) T1 T2 T1 16 VCC 15 T1B 14 T2B 13 CDB 12 AB 11 BB 10 QB 9 QB CD T2 A CD B A Q B Q Q Q 2 HD74HC4538 Block Diagram CX RX VCC T1A T2A QA AA BA QA CDA CX RX VCC T1B T2B QB AB BB QB CDB RX and CX are external components 3 HD74HC4538 Absolute Maximum Ratings Item Supply voltage range Input voltage Output voltage DC input diode current DC input diode current pin 2, 14 DC output diode current DC current drain per pin DC current drain per VCC, GND Power dissipation per package Storage temperature Symbol VCC Vin Vout I IK I IK I OK Iout I CC, I GND PT Tstg Rating –0.5 to +7.0 –0.5 to VCC + 0.5 –0.5 to VCC + 0.5 ±20 ±30 ±20 ±25 ±50 500 –65 to +150 Unit V V V mA mA mA mA mA mW °C 4 HD74HC4538 DC Characteristics Ta = 25°C Item Input voltage Symbol VIH Ta = –40 to +85°C Max — — — 0.5 1.35 1.8 — — — — — 0.1 0.1 0.1 0.33 0.33 ±1.0 220 µA µA I OL = 4 mA I OL = 5.2 mA Vin = VCC or GND Vin = VCC or GND, QA = QB = GND, Iout = 0 µA Vin = VCC or GND, QA = QB = VCC Pin 2, 14 = 0.5 VCC V I OH = –4 mA I OH = –5.2 mA Vin = VIH or VIL I OL = 20 µA V Vin = VIH or VIL I OH = –20 µA V Unit V Test Conditions VCC (V) Min Typ Max Min 2.0 4.5 6.0 1.5 — 3.15 — 4.2 — — — — — — — — — — 0.5 1.5 3.15 4.2 — VIL 2.0 4.5 6.0 1.35 — 1.8 — 1.9 4.4 5.9 4.13 5.63 — — — Output voltage VOH 2.0 4.5 6.0 4.5 6.0 1.9 2.0 — 4.4 4.5 — 5.9 6.0 — 4.18 — 5.68 — — — — — — — — — — VOL 2.0 4.5 6.0 4.5 6.0 0.0 0.1 0.0 0.1 0.0 0.1 — — — — 0.26 — 0.26 — ±0.1 — 130 — Input current Quiescent supply current (standby state) Current drain (active state) Iin I CC 6.0 6.0 I CC 6.0 — — 130 — 220 µA 5 HD74HC4538 AC Characteristics (CL = 50 pF, Input tr = tf = 6 ns) Ta = 25°C Item Symbol Ta = –40 to +85°C Max 295 59 50 325 65 55 295 59 50 295 59 50 — — — — — — — — — — — — % RX = 10 kΩ, CX = 1000 pF µs RX = 10 kΩ, CX = 10000 pF µs RX = 10 kΩ, CX = 1000 pF µs RX = 10 kΩ, CX = 100 pF ns RX = 1 kΩ, CX = 12 pF ns A, B, C D ns CD to Q ns CD to Q ns A or B to Q Unit ns Test Conditions A or B to Q VCC (V) Min Typ Max Min 2.0 4.5 6.0 — — — — — — — — — — — — 80 16 14 — — — — — — — — — — 22 — — 23 — — 17 — — — — — — — 235 — 47 40 — — Propagation delay t PLH time t PHL 2.0 4.5 6.0 260 — 52 44 — — t PHL 2.0 4.5 6.0 235 — 47 40 — — t PLH 2.0 4.5 6.0 235 — 47 40 — — — — — 100 20 17 — — — — — — — — — Pulse width tw 2.0 4.5 6.0 Output pulse width t WQ 3.0 5.0 3.0 5.0 3.0 5.0 3.0 5.0 150 — 100 — — — 1.3 — — 9 — 70 — — — — Pulse width match ∆tWQ between circuits in the same package 5.0 ±0.1 — Caution in use: In order to prevent any malfunctions due to noise, connect a high frequency performance capacitor between V CC and GND, and keep the wiring between the External components and Cext, Rext/Cext pins as short as possible. 6 HD74HC4538 Circuit Operation Fig. 3 shows the HC4538 configured in the retriggerable mode. Briefly, the device operates as follows (refer to Fig. 1): In the quiescent state, the external timing capacitor, CX, is charged to V CC. When a trigger occurs, the Q output goes high and CX discharges quickly to the lower references voltage (Vref Lower 1/3 V CC). CX then charges, through RX, back up to the upper reference voltage (Vref Upper 2/3 V CC), at which point the one-shot has timed out and the Q output goes low. The following, more detailed description of the circuit operation refers to both the function diagram (Fig. 1) and the timing diagram (Fig. 2) Quiescent State In the quiescent state, before an input trigger appears; the output latch is high and the reset latch is high (1 in Fig. 2). Thus the Q output (pin 6 or 10) of the monostable multivibrator is low (2 Fig. 2). The output of the trigger-control circuit is low (3), and transistors M1, M2, and M3 are turned off. The external timing capacitor, CX, is charged to VCC (4), and the upper reference circuit has a low output (5). Transistor M4 is turned on and analog switch S1 is turned off. Thus the lower reference circuit has V CC at the noninverting input and a resulting low output (6). In addition, the output of the trigger-control reset circuit is low. Trigger Operation The HC4538 is triggered by either a rising-edge signal as input A (7) or a falling-edge signal at input B (8), with the unused trigger input and the Reset input held at the voltage levels shown in the Function Table. Either trigger signal will cause the output of the trigger-control circuit to go high (9). The trigger-control circuit going high simultaneously initiates three events. First, the output latch goes low, thus taking the Q output of the HC4538 to a high state (10). Second, transistor M3 is turned on, which allows the external timing capacitor, CX, to rapidly discharge toward ground (11). (Note that the voltage across CX appears at the input of the upper reference circuit comparator). Third, transistor M4 is turned off and analog switch S1 is turned on, thus allowing the voltage across C X to also appear at the input of the lower reference circuit comparator. When CX discharges to the reference voltage of the lower reference circuit (12), the outputs of both reference circuits will be high (13). The trigger-control circuit flip-flop to a low state (14). This turns transistor M3 off again, allowing CX to begin to charge back up toward VCC, with a time constant t = RXCX (15). In addition, transistor M4 is turned on and analog switch S1 is turned off. Thus a high voltage level is applied to the input of the lower reference circuit comparator, causing its output to go low (16). The monostable multivibrator may be retriggered at any time after the trigger-control circuit goes low. When CX charges up to the reference voltage of the upper reference circuit (17), the output of the upper reference circuit goes low (18). This causes the output latch to toggle, taking the Q output of the HC4538 to a low state (19), and completing the time-out cycle. 7 HD74HC4538 Reset Operation A low voltage applied to the Reset pin always forces the Q output of the HC4538 to a low state. The timing diagram illustrates the case in which reset occurs (20) while C X is charging up toward the reference voltage of the upper reference circuit (21). When a reset occurs, the output of the reset latch goes low (22), turning on transistor M1. Thus CX is allowed to quickly charge up to VCC (23) to await the next trigger signal. Retrigger Operation When used in the retriggerable mode (Fig. 3), the HC4538 may be retriggered during timing out of the output pulse at any time after the trigger-control circuit flip-flopw has been reset (24). Because the triggercontrol circuit flip-flop resets shortly after CX has discharged to the reference voltage of the lower reference circuit (25), the minimum retrigger time, trr (Switching Waveform 1) is a function of internal propagation delays and the discharge time of CX: Fig. 4 shows the device configured in the non-retriggerable mode. Power-Down Considerations Large values of CX may cause problems when powering down the HC4538 because of the amount of energy stored in the capacitor. When a system containing this device is powered down, the capacitor may discharge from VCC through the input protection diodes at pin 2 or pin 14. Current through the protection diodes must be limited to 30 mA; therefore, the turn-off time of the V CC power supply must not be faster than t = VCC•CX/(30 mA). For example, if VCC = 5 V and CX = 15 µF, the VCC supply must turn off no faster than t = (5 V)•(15 µF)/30 mA = 2.5 ms. This is usually not a problem because power supplies are heavily filtered and cannot discharge at this rate. When a more rapid decrease of VCC to zero voltage occurs, the HC4538 may sustain damage. To avoid this possibility, use an external clamping diode. 8 HD74HC4538 VCC RX T2 CX 2, 14 VCC M2 M1 2kΩ Upper Reference Circuit Output Latch M3 + – Vref Upper S1 VCC M4 Lower Reference Circuit 7, 9 6, 10 Q + – 4, 12 A B 5, 11 CQ CR Trigger-Control Reset Circuit Trigger-Control Circuit Vref Lower Q 3, 13 CD Reset Latch Fig. 1 Function Diagram 9 HD74HC4538 Quiescent State Trigger Cycle (A Input) Trigger Cycle (B Input) Reset trr 7 Retrigger Trigger Input A (Pin 4 or 12) Trigger Input B (Pin 5 or 11) 8 Reset Input CD (Pin 3 or 13) 21 9 24 14 11 15 20 23 Trigger-Control Circuit Output T2 Input (Pin 2 or 14) Upper Reference Circuit Output Lower Reference Circuit Output Reset Latch Output 3 4 12 17 Vref Lower 13 5 13 6 16 Vref Upper 25 1 22 10 Q Output (Pin 6 or 10) 2 19 tWQ tW (H) A 50% tWQ tWQ+trr tW (L) B tPLH Q 50% tPHL Q 50% tPHL tWQ 50% tPLH A trr B tf CD tTLH Q tTHL Q 90% 10% 90% 10% tPLH 50% 50% tW (L) tPHL 50% tr 90% 10% tWQ+trr 50% (Retriggered Pulse) 50% Fig. 2 Timing Diagram 10 HD74HC4538 CX RX VCC T1 T2 A Rising-Edge Trigger B Q Q CD CX RX VCC T1 T2 A B Rising-Edge Trigger CD Q Q Fig. 3 Retriggerable Monostable Circuitry 11 HD74HC4538 CX RX VCC T1 T2 A Falling-Edge Trigger B Q Q CD CX RX VCC T1 T2 A B Falling-Edge Trigger CD Q Q Fig. 4 Nonritriggerable Monostable Circuitry 12 19.20 20.00 Max 16 9 7.40 Max 6.30 Unit: mm 1 1.3 1.11 Max 8 0.51 Min 2.54 Min 5.06 Max 7.62 2.54 ± 0.25 0.48 ± 0.10 0.25 – 0.05 0° – 15° Hitachi Code JEDEC EIAJ Weight (reference value) + 0.13 DP-16 Conforms Conforms 1.07 g Unit: mm 10.06 10.5 Max 16 9 5.5 1 *0.22 ± 0.05 0.20 ± 0.04 8 0.80 Max 2.20 Max 0.20 7.80 + 0.30 – 1.15 0° – 8° 0.70 ± 0.20 1.27 *0.42 ± 0.08 0.40 ± 0.06 0.12 M Hitachi Code JEDEC EIAJ Weight (reference value) FP-16DA — Conforms 0.24 g *Dimension including the plating thickness Base material dimension 0.10 ± 0.10 0.15 Unit: mm 9.9 10.3 Max 16 9 3.95 1 1.27 0.635 Max 8 0.11 0.14 + 0.04 – 1.75 Max *0.22 ± 0.03 0.20 ± 0.03 0.10 6.10 + 0.30 – 1.08 0° – 8° 0.67 0.60 + 0.20 – *0.42 ± 0.08 0.40 ± 0.06 0.15 0.25 M *Dimension including the plating thickness Base material dimension Hitachi Code JEDEC EIAJ Weight (reference value) FP-16DN Conforms Conforms 0.15 g Cautions 1. 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