AD5100
Rev. A | Page 13 of 36
MONITORING INPUTS
V
1MON
V
1MON
is a high voltage monitoring input that controls the
SHDN
and
RESET
functions of the external devices. In addition,
it provides a shutdown warning to the system. V
1MON
monitors
inputs from 6 V to 30 V.
The V
1MON
pin is monitored by two comparators, one for overvol-
tage and one for undervoltage detection. Both are designed with
1.5% hysteresis.
When the V
1MON
input goes above the programmed overvoltage
(OV) threshold, the comparator becomes active immediately,
indicating that an OV condition has occurred. Due to hysteresis,
the V
1MON
input must be brought below the programmed OV
threshold by 1.5% before the comparator becomes inactive,
indicating that the OV condition has gone away (see Figure 6).
5692-007
V
1MON
V
1MON_UV
OV
COMPARATOR
ACTIVE
OV
COMPARATOR
INACTIVE
UV
COMPARATOR
ACTIVE
UV
COMPARATOR
INACTIVE
1MON_OV
HYSTERESIS
HYSTERESIS
Figure 6. V
1MON
Hysteresis
When the V
1MON
input drops below the programmed under-
voltage (UV) threshold, the comparator becomes active
immediately, indicating that a UV condition has occurred.
Similarly, due to hysteresis, the V
1MON
input must be brought
above the programmed UV threshold by 1.5% before the
comparator becomes inactive, indicating that the UV condition
has gone away.
Both V
1MON
comparators are used (in conjunction with hold and
delay timers) to control the
SHDN
and
RESET
pins.
V
1MON
has a 16-level programmable OV threshold (Register 0x01)
and UV threshold (Register 0x02) with an 8-step 0.07 ms to
200 ms shutdown hold time (t
1SD_HOLD
) and 0.07 ms to 1200 ms
shutdown delay (t
1SD_DELAY
). The shutdown hold time means that
the
SHDN
signal is held low for t
1SD_HOLD
after V
1MON
returns
within its UV and OV thresholds. The shutdown delay means
that the
SHDN
signal activation is delayed until the programmed
t
1SD_DELAY
has elapsed.
SHDN
activates once the voltage on V
1MON
is outside the OV or UV threshold for a time longer than t
GLITCH
.
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
) is set relative to the
SHDNWARN
propagation
delay (t
FD_DELAY
). This feature attempts to allow the system to
finish any critical housekeeping tasks before shutting down the
external device.
The V
1MON
, shutdown, and shutdown warning timing diagrams
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
1MON
exhibits typical input resistance of 55 kΩ that users
should take into account for loading effect.
The voltage at V
1MON
provides the power for the AD5100, but
a valid signal on V
2MON
must be present before the internal
power rail, V
REG
, starts operation. Details are explained in the
Power Requirements section.
