The 74HC; 74HCT are dual retriggerable monostable multivibrators with output pulse width control by three methods: 1. Alternatively an output delay can be terminated at any time by a LOW-going edge on input nRD, which also inhibits the triggering. Schmitt-trigger action in the nA and nB inputs, makes the circuit highly tolerant to slower input rise and fall times. Features and benefits? Direct reset terminates output pulse?
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Direct reset terminates output pulse? Schmitt-trigger action on all inputs except for the reset input? The external resistor and capacitor are normally connected as shown in Fig. Alternatively an output delay can be terminated at any time by a LOW-going edge on input nRD, which also inhibits the triggering.
An internal connection from nRD to the input gates makes it possible to trigger the circuit by a positive-going signal at input nRD as shown in the function table. Figures 7 and 8 illustrate pulse control by retriggering and early reset. Schmitt-trigger action in the nA and nB inputs, makes the circuit highly tolerant to slower input rise and fall times.
CPD is used to determine the dynamic power dissipation PD in? If the monostable was triggered before this condition was established, the pulse will continue as programmed. CEXT external timing capacitor no limits pF 2. ICC for a unit load of 1 is given in the family specifications. To determine? ICC per input, multiply this value by the unit load coefficient shown in the table below.
The output pulse width will only be extended when the time between the active-going edges of the trigger input pulses meets the minimum retrigger time. Product speci? Power-down considerations A large capacitor CX may cause problems when powering-down the monostable due to the energy stored in this capacitor. When a system containing this device is powered-down or a rapid decrease of VCC to zero occurs, the monostable may substain damage, due to the capacitor discharging through the input protection diodes.
To avoid this possibility, use a damping diode DX preferably a germanium or Schottky type diode able to withstand large current surges and connect as shown in Fig. A1 min. A2 max. Plastic or metal protrusions of 0. Plastic interlead protrusions of 0. Wave soldering is often preferred when through-hole and surface mounted components are mixed on one printed-circuit board. However, wave soldering is not always suitable for surface mounted ICs, or for printed-circuits with high population densities.
In these situations reflow soldering is often used. This text gives a very brief insight to a complex technology. The total contact time of successive solder waves must not exceed 5 seconds. The device may be mounted up to the seating plane, but the temperature of the plastic body must not exceed the specified maximum storage temperature Tstg max.
If the printed-circuit board has been pre-heated, forced cooling may be necessary immediately after soldering to keep the temperature within the permissible limit. Reflow soldering requires solder paste a suspension of fine solder particles, flux and binding agent to be applied to the printed-circuit board by screen printing, stencilling or pressure-syringe dispensing before package placement.
Several techniques exist for reflowing; for example, thermal conduction by heated belt. Dwell times vary between 50 and seconds depending on heating method. Preheating is necessary to dry the paste and evaporate the binding agent. Wave soldering is not recommended for SSOP and TSSOP packages, because of the likelihood of solder bridging due to closely-spaced leads and the possibility of incomplete solder penetration in multi-lead devices.
A double-wave a turbulent wave with high upward pressure followed by a smooth laminar wave soldering technique should be used. The longitudinal axis of the package footprint must be parallel to the solder flow and must incorporate solder thieves at the downstream end. Even with these conditions:? Only consider wave soldering SSOP packages that have a body width of 4. During placement and before soldering, the package must be fixed with a droplet of adhesive. The adhesive can be applied by screen printing, pin transfer or syringe dispensing.
The package can be soldered after the adhesive is cured. A mildly-activated flux will eliminate the need for removal of corrosive residues in most applications. Use only a low voltage soldering iron less than 24 V applied to the flat part of the lead. This data sheet contains preliminary data; supplementary data may be published later. This data sheet contains? Stress above one or more of the limiting values may cause permanent damage to the device.
These are stress ratings only and operation of the device at these or at any other conditions above those given in the Characteristics sections of the speci?
Exposure to limiting values for extended periods may affect device reliability. Application information Where application information is given, it is advisory and does not form part of the speci? Philips customers using or selling these products for use in such applications do so at their own risk and agree to fully indemnify Philips for any damages resulting from such improper use or sale.
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