Monitoring Inputs; 1Mon - Analog Devices AD5100 Manual

MONITORING INPUTS

V

1MON

V is a high voltage monitoring input that controls the
1MON
SHDN and RESET functions of the external devices. In addition,
it provides a shutdown warning to the system. V
inputs from 6 V to 30 V.
The V pin is monitored by two comparators, one for overvol-
1MON
tage and one for undervoltage detection. Both are designed with
1.5% hysteresis.
When the V input goes above the programmed overvoltage
1MON
(OV) threshold, the comparator becomes active immediately,
indicating that an OV condition has occurred. Due to hysteresis,
the V input must be brought below the programmed OV
1MON
threshold by 1.5% before the comparator becomes inactive,
indicating that the OV condition has gone away (see Figure 6).
V
1MON_OV
V
1MON
V
1MON_UV
OV
COMPARATOR COMPARATOR
ACTIVE INACTIVE
Figure 6. V
When the V input drops below the programmed under-
1MON
voltage (UV) threshold, the comparator becomes active
immediately, indicating that a UV condition has occurred.
Similarly, due to hysteresis, the V
above the programmed UV threshold by 1.5% before the
comparator becomes inactive, indicating that the UV condition
has gone away.
Both V
comparators are used (in conjunction with hold and
1MON
delay timers) to control the SHDN and RESET pins.
V has a 16-level programmable OV threshold (Register 0x01)
1MON
and UV threshold (Register 0x02) with an 8-step 0.07 ms to
200 ms shutdown hold time (t
monitors
1MON
HYSTERESIS
HYSTERESIS
OV
UV UV
COMPARATOR COMPARATOR
ACTIVE INACTIVE
Hysteresis
1MON
input must be brought
1MON
) and 0.07 ms to 1200 ms
1SD_HOLD
shutdown delay (t
the SHDN signal is held low for t
within its UV and OV thresholds. The shutdown delay means
that the SHDN signal activation is delayed until the programmed
has elapsed. SHDN activates once the voltage on V
t
1SD_DELAY
is outside the OV or UV threshold for a time longer than t
RESET follows SHDN delay and hold timings when triggered
by V .
IMON
The OV threshold chosen must be greater than the UV threshold.
When the shutdown is triggered, either because the input has
reached the OV or UV threshold, such fault conditions are
temporarily recorded in the fault detection register.
The SHDNWARN output transitions low for signaling before
the shutdown output, SHDN , activates. The timing of the SHDN
output is dependent on how long the shutdown-programmed
delay (t
1SD_DELAY
delay (t ). This feature attempts to allow the system to
FD_DELAY
finish any critical housekeeping tasks before shutting down the
external device.
The V , shutdown, and shutdown warning timing diagrams
1MON
are shown in Figure 7.
The ranges of OV and UV thresholds are shown in Table 6, and
the programming codes for the selected thresholds are found in
Table 7. The defaulted OV threshold is 18.00 V and, for UV
threshold, it is 8.43 V. Similarly, the ranges of shutdown hold
and delay times are shown in Table 8, and the programming
codes for the selected timings are shown in Table 9.
V exhibits typical input resistance of 55 kΩ that users
1MON
should take into account for loading effect.
The voltage at V
a valid signal on V
power rail, V
REG
Power Requirements section.
Rev. A | Page 13 of 36
). The shutdown hold time means that
1SD_DELAY
after V
1SD_HOLD
) is set relative to the SHDNWARN propagation
provides the power for the AD5100, but
1MON
must be present before the internal
2MON
, starts operation. Details are explained in the
AD5100
returns
1MON
1MON
.
GLITCH