ICM7249_01 Datasheet, PDF (8/9 Pages) Intersil Corporation – 5 1/2 Digit LCD, Micro-Power Event/Hour Meter

ICM7249
debounce filtering. Referring to Figure 4, only the pulses with
a frequency of less than 40Hz are valid and will be counted.
Input pulses with a frequency of 50Hz to 120kHz are not
counted individually, but each burst of input pulses will be
counted as one pulse if it lasts at least 12.5ms. Driving S/S
with a frequency between 40Hz to 50Hz has an indetermi-
nate result and should be avoided.
In counter modes 5, 7, 9 and 11 the S/S input is not
subjected to any debouncing action and input pulses will be
counted up to a frequency of 120kHz.
Wink Segment
The wink segment is provided as a annunciator to indicate the
ICM7249 is working. It can be connected to any kind of annun-
ciator on an LCD, like the flashing colons in a clock type LCD.
In the timer modes, the wink segment flashes while timing is
taking place. The wink segment waveform is shown on
Figure 3 for timer modes. On the positive transition of S/S,
the wink output turns off. It remains off for 16 BP cycles and
turns back on for another 16 cycles. If timing is still active,
this will be repeated, giving a wink flash rate of 1Hz; other-
wise, the wink segment remains on while timing is not active.
In the counter modes, the wink segment stays on until a
pulse occurs on S/S input, then it winks off indicating a pulse
is counted. This will happen regardless of whether the
display is incremented. Figure 5 shows the wink waveform
for counter modes. When a count occurs, the wink segment
turns off at the end of the 16th BP cycle and turns back on at
the end of the 32nd BP cycle, giving a half-second wink. If
the counting occurs more frequently than once a second, the
wink output will continue to flash at the constant rate of 1Hz.
A typical use of the ICM7249 is seen in Figure 8, the Motor
Hour Meter. In this application the ICM7249 is configured as
an hours-in-use meter and shows how many whole hours of
line voltage have been applied. The resistor network and
high-pass filtering allow AC line activation of the S/S input.
This configuration, which is powered by a 3V lithium cell, will
operate continuously for 2¹/₂ years. Without the display,
which only needs to be connected when a reading is
required, the span of operation is extended to 10 years.
When the ICM7249 is configured as an attendance counter,
as shown in Figure 9, the display shows each increment. By
using mode 2, external debouncing of the gate switch is
unnecessary, provided the switch bounce is less than 10ms.
The 3V lithium battery can be replaced without disturbing
operation if a suitable capacitor is connected in parallel with
it. The display should be disconnected, if possible, during
the procedure to minimize current drain. The capacitor
should be large enough to store charge for the amount of
time needed to physically replace the battery (∆t = ∆VC/I). A
100µF capacitor initially charged to 3V will supply a current
of 1.0µA for 50 seconds before its voltage drops to 2.5V,
which is the minimum operating voltage for the ICM7249.
Before the battery is removed, the capacitor should be
placed in parallel, across the V_DD and GND terminals. After
the battery is replaced, the capacitor can be removed and
the display reconnected.
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FIGURE 7. DIGITS SEGMENT ASSIGNMENT
Display Test and Reset
The display may be tested at any time without disturbing
operation by pulsing DT high, as seen in Figure 6. On the
next positive transition of BP, all the segments turn on and
remain on until the end of the 16th BP cycle. This takes a
half-second or less. All the segments then turn off for an
additional 48 BP cycles (the end of the 64th cycle), after
which valid data returns to the display. As long as DT is held
high, the segments will remain on.
Additional display testing is provided by using mode 12. In this
mode each displayed decade is incremented on each positive
transition of S/S. Modes 13 and 14 are manufacturer testing only.
Mode 15 resets all the decades and internal counters to zero,
essentially bringing everything back to power-up status.
Applications
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