Addressing Contact Bounce Issue
Dealing with the persistent problem of contact bounce in various pushbutton switches and keypads connected to digital components has been a long-standing challenge. Strategies employed to handle the repeated closing of contacts upon initial activation involve the use of RC networks, flip-flop circuits, and software routines. However, a recent development introduces a single IC designed to seamlessly manage this task, providing clean digital pulses to the subsequent circuitry.
Introducing MAX 6816, MAX 6817, and MAX 6818 ICs
The MAX 6816, MAX 6817, and MAX 6818 ICs serve as robust pushbutton switch debouncers, offering one, two, and eight inputs, respectively. The wiring for these ICs is straightforward, as illustrated in Figure 1, and they do not require external components. The connected switches simply need to make contact with the ground, as internal pull-up resistors are already integrated. These ICs operate effectively within a supply voltage range of 2.7 V to 5.5 V, with a low current consumption of under 20 µA. Furthermore, the inputs can withstand (fault) voltages up to ±25 V and electrostatic discharges of up to ±15 kV.
Debouncing Mechanism and Functionality
Each MAX 681x IC utilizes an internal oscillator to clock a counter. The counter is consistently reset whenever the input level undergoes a change within 40 ms. The counter will only increment to its final count and enable the output signal once the input level remains stable for more than 40 ms. This debouncing mechanism is applied to both the closure and opening of the switch.
MAX 6818 Features and Compatibility
The MAX 6818 offers additional features, including an enable input (/EN) that switches the outputs to a high-impedance (tri-state) condition when a High level is applied. It also features a Change output (/CH), signifying a change of state in one of the pressed keys. The /CH output can be directly connected to the interrupt input of a microprocessor system. Notably, the pinout of the MAX 6818 aligns with that of the well-known 74xx573 latch, allowing for a straightforward substitution of the latter IC. The MAX 6816 is available in a compact SOT-143-SMD package, while the MAX 6817 comes in a 6-pin SOT23 SMD package, and the MAX 6818 is housed in an SSOP20 package. You can access datasheets for these debouncer ICs via the Internet at www.maxim-ic.com.