參數(shù)資料
型號: M41ST87YMX6
廠商: STMICROELECTRONICS
元件分類: 時鐘/數(shù)據(jù)恢復(fù)及定時提取
英文描述: 1 TIMER(S), REAL TIME CLOCK, PDSO28
封裝: 0.300 INCH, ROHS COMPLIANT, PLASTIC, SOX-28
文件頁數(shù): 20/52頁
文件大?。?/td> 689K
代理商: M41ST87YMX6
M41ST87Y, M41ST87W
Operating modes
Doc ID 9497 Rev 8
2.9
Internal tamper pull-up/down current
Depending on the capacitive and resistive loading of the tamper pin input (TPXIN), the user
may require more or less current from the internal pull-up/down used when monitoring the
normally closed switch mode. The state of the tamper current hi/tamper current low bit
(TCHI/TCLOX) determines the sizing of the internal pull-up/-down. TCHI/TCLOX = '1' uses a
1 M
Ω pull-up/-down resistor, while TCHI/TCLOX = '0' uses a 10 MΩ pull-up/-down resistor
2.10
Avoiding inadvertent tampers (normally closed
configuration)
In some applications it may be necessary to use a low pass filter to reduce electrical noise
on the tamper input pin when the TCMX bit = 0 (normally closed). This is especially true if
the tamper detect switch is located some distance (> 6”) from the tamper input pin. A low
pass filter can prevent unwanted, higher frequency noise from inadvertently being detected
as a tamper condition caused by the “antenna-effect” (produced by a longer signal wire or
mesh). This low pass filter can be constructed using a series resistor (R) in conjunction with
a capacitor (C) on the tamper input pin.
The cut-off frequency fc is determined according to the formula:
Figure 21.
Low-pass filter implementation for noise immunity
Table 6.
Calculated cut-off frequency for typical capacitance and resistance
values
R (
Ω)C (F)
fc
1/fc (s)
1000
1.00E-09
15.9 MHz
6.28 s
1000
1.00E-06
159.2 Hz
6.28 ms
5000
1.00E-09
31.8 kHz
31.4 s
5000
1.00E-06
31.8 Hz
31.4 ms
10000
1.00E-09
15.9 kHz
62.8 s
10000
1.00E-06
15.9 Hz
62.8 ms
f
c
12 Pi R C
()
=
TPIN
R
C
To Tamper Detect Switch
AI11185
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