Datasheet
Detailed Description
Theory of Operation
The MAX6816/MAX6817/MAX6818 are designed to
eliminate the extraneous level changes that result from
interfacing with mechanical switches (switch bounce).
Virtually all mechanical switches bounce upon opening or
closing. These switch debouncers remove bounce when
a switch opens or closes by requiring that sequentially
clocked inputs remain in the same state for a number of
sampling periods. The output does not change until the
input is stable for a duration of 40ms.
The circuit block diagram (Figure 1) shows the func-
tional blocks consisting of an on-chip oscillator, counter,
exclusive-NOR gate, and D flip-flop. When the input does
not equal the output, the XNOR gate issues a count-
er reset. When the switch input state is stable for the
full qualification period, the counter clocks the flip-flop,
updating the output. Figure 2 shows the typical opening
and closing switch debounce operation. On the MAX6818,
the change output (CH) is updated simultaneously with
the switch outputs.
Undervoltage Lockout
The undervoltage lockout circuitry ensures that the
out-puts are at the correct state on power-up. While
the supply voltage is below the undervoltage threshold
(typically 1.9V), the debounce circuitry remains
transparent. Switch states are present at the logic outputs
with no debouce delay.
Figure 1. Block Diagram
PIN
NAME FUNCTION
MAX6816 MAX6817 MAX6818
1 2 10 GND Ground
2 — — IN Switch Input
— 1, 3 — IN1, IN2 Switch Inputs
— — 2–9 IN1–IN8 Switch Inputs
3 — — OUT CMOS Debounced Output
— 4, 6 — OUT2, OUT1 CMOS Debounced Outputs
— — 12–19 OUT8–OUT1 CMOS Debounced Outputs
4 5 20
V
CC +2.7V to +5.5V Supply Voltage
— — 1
EN
Active-Low, Three-State Enable Input for outputs. Resets CH.
Tie to GND to “always enable” outputs.
— — 11
CH
Change-of-State Output. Goes low on switch input change of
state. Resets on EN. Leave unconnected if not used.
V
CC
V
CC
V
CC
R
PU
D Q
R
QD
COUNTER
LOAD
OUT
IN
ESD
PROTECTION
UNDER-
VOLTAGE
LOCKOUT
OSC.
MAX6816
MAX6817
MAX6818
www.maximintegrated.com
Maxim Integrated
│
4
MAX6816/MAX6817/
MAX6818
±15kV ESD-Protected, Single/Dual/Octal,
CMOS Switch Debouncers
Pin Description