STM1404 Tamper detection
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4 Tamper detection
4.1 Physical
There are four (4) high-impedance physical tamper detect input pins, 2 normally set to high
(NH) and 2 normally set to low (NL). Each input is designed with a glitch immunity (see
Table 7 on page 29). These inputs can be connected externally to several types of actuator
devices (e.g., switches, wire mesh). A tamper on any one of the four inputs that causes its
state to change will trigger the security alarm (SAL
) and drive it to active-low. Once the
tamper condition no longer exists, the SAL
will return to its normal high state.
TP
1
and TP
3
are set normally to high (NH). They are connected externally through a closed
switch or a high-impedance resistor to V
OUT
(in the case of STM1404A or STM1404A) or
V
TPU
(in the case of STM1404B/C), A tamper condition will be detected when the input pin
is pulled low (see Figure 5 and Figure 6 on page 10). If not used, tie the pin to V
OUT
or V
TPU
.
TP
2
and TP
4
are set normally to low (NL). They are connected externally through a high-
impedance resistor or a closed switch to V
SS
. A tamper condition will be detected when the
input pin is pulled high (see Figure 7 and Figure 8 on page 10). If not used, tie the pin to
V
SS
.
4.2 Supply voltage
The internally switched supply voltage, V
INT
(either V
CC
input or V
BAT
input) is continuously
monitored. If V
INT
should exceed the over voltage trip point, V
HV
(set at 4.2V, typical), or
should go below the under voltage trip point, V
LV
(set at 2.0v, typical). SAL will be driven
active-low. Once the tamper condition no longer exists, the SAL
pin will return to its normal
high state.
4.3 Temperature
The STM1404 has a built-in, bandgap-based sensor to monitor the temperature. If a preset
(customer-selectable, factory-programmed) over-temperature trip point (T
H
) or under-
temperature trip point (T
L
) is exceeded, the SAL is asserted low.
When no tamper condition exists, SAL
is normally high (see Section 2: Pin descriptions on
page 11).
When a tamper is detected, the SAL
is activated (driven low), independent of the part type.
V
OUT
can be driven to one of three states, depending on which variant of STM1404 is being
used (see Table 1 on page 1):
● ON
● High-Z or
● Ground (V
SS
)
Note: The STM1404 must be initially powered above V
RST
to enable the tamper detection alarms.
For example, if the battery is on while V
CC
= 0 V, no alarm condition can be detected until
V
CC
rises above V
RST
(and t
rec
expires). From this point on, alarms can be detected either
on battery or V
CC
. This is done to avoid false alarms when the device goes from no power to
its operational state.
