ADM2914 Data Sheet
Rev. F | Page 12 of 16
UV/OV OUTPUT CHARACTERISTICS
Both the
OV
and
UV
outputs have a strong pull-down to
ground and a weak internal pull-up to V
CC
. This permits the pins
to behave as open-drain outputs. When the rise time on the pin
is not critical, the weak pull-up removes the requirement for an
external pull-up resistor. The open-drain configuration allows
for wire-OR’ing of outputs, which is particularly useful when
more than one signal needs to pull down on the output.
At V
CC
= 1 V, a maximum V
OL
= 0.15 V at
UV
is guaranteed. At
V
CC
= 1 V, the weak pull-up current on
OV
is almost turned on.
Consequently, if the state and pull-up strength of the
OV
pin are
important at very low V
CC
, an external pull-up resistor of no more
than 100 kΩ is advised. By adding an external pull-up resistor,
the pull-up strength on the
OV
pin is greater. Therefore, if it is
connected in a wire-OR’ed configuration, the pull-down strength
of any single device must account for this additional pull-up
strength.
GLITCH IMMUNITY
The ADM2914 is immune to short transients that may occur on
the monitored voltage rails. The device contains internal filtering
circuitry that provides immunity to fast transient glitches. Figure 9
illustrates glitch immunity performance by showing the maximum
transient duration without causing a reset pulse. Glitch immunity
makes the ADM2914 suitable for use in noisy environments.
UNDERVOLTAGE LOCKOUT (UVLO)
The ADM2914 has an undervoltage lockout circuit that monitors
the voltage on the V
CC
pin. When the voltage on V
CC
drops below
1.9 V (minimum), the circuit is activated. The
UV
output is
asserted and the
OV
output is cleared and not allowed to assert.
When V
CC
recovers,
UV
exhibits the same timing characteristics
as if an undervoltage condition had occurred on the inputs.
SHUNT REGULATOR
The ADM2914 is powered via the V
CC
pin. The V
CC
pin can be
directly connected to a voltage rail of up to 6 V. In this mode,
the supply current of the device does not exceed 100 µA. An
internal shunt regulator allows the ADM2914 to operate at
voltage levels greater than 6 V by simply placing a dropper
resistor in series between the supply rail and the V
CC
pin to limit
the input current to less than 10 mA.
Once the supply voltage, V
IN
, has been established, an
appropriate value for the dropper resistor can be calculated.
Begin by determining the maximum supply current required,
I
CCtotal
, by adding the current drawn from the reference and/or
the pull resistors between the outputs and the V
CC
pin to the
maximum specified supply current. The minimum and
maximum shunt regulator voltage specified in Table 1, V
SHUNT min
and V
SHUNT max
, are also required in the following calculations.
Calculate the maximum and minimum dropper resistor values
CCtotal
SHUNT
IN
MAX
I
R
max
min
A100
min
max
SHUNT
IN
MIN
R
Based on these values, choose a real-world resistor value within
this range. Then, given the specified accuracy of this resistor,
calculate the minimum and maximum real resistor value
variation, R
REALmin
and R
REALmax
, respectively.
The maximum device power is calculated as follows:
CCtotal
SHUNTmax
CCtotal
REAL
SHUNT
IN
SHUNT
DeviceMax
IV
I
R
VV
VP
min
max
max
max
To check that the calculated value of the resistor will be
acceptable, calculate the maximum device temperature rise.
DeviceMax
JARISEmax
PθTemp
Add this value to the ambient operating temperature. If the
resistor value is acceptable, the result will lie within the
specified operating temperature range of the device, −40°C to
+85°C.
