Data Sheet ADCMP391/ADCMP392/ADCMP393
Rev. D | Page 15 of 17
Resistor values from the calculation are nonindustry standard,
using industry standard resistor values resulted in a new R
DIV
value of 99.8 kΩ. Due to the discrepancy of the calculated resistor
value to the industry standard value, the threshold of each
comparator also changed. Calculate the new threshold values
by using a simple voltage divider formula:
V1 = V
REF
R1/R
DIV
(37)
where V1 =
k99.8
k26.7V1
= 267.54 mV.
Therefore, V2 = 463.93 mV, V3 = 607.21 mV, and V4 = 712.42 mV.
Because the threshold of each comparator has changed, the time
when each comparator changes its output has also changed.
Calculate the new delay values for each comparator by using the
following equation:
REF
MIRROR
PULLUPL
1
V
V1
RRCt 1ln
(38)
where t
1
= −1 µF(10 kΩ + 150 kΩ)ln
1
mV54.267
1
= 49.81 ms.
Therefore, t
2
= 99.78 ms, t
3
= 149.52 ms, and t
4
= 199.4 ms.
To c al cu late t
5
through t
8
, use Equation 32 to Equation 35:
REF
L
MIRROR
5
V
V4
lnCRt
where t
5
= −150 kΩ × 1 µF × ln
1
mV712.42
= 50.86 ms.
Therefore, t
6
= 74.83 ms, t
7
= 115.2 ms, and t
8
= 197.78 ms.
THRESHOLD AND TIMEOUT PROGRAMMABLE
VOLTAGE SUPERVISOR
Figure 36 shows a circuit configuration for a programmable
threshold and timeout circuit. The timeout, t
RESET
, defines the
duration that the input voltage (V
IN
) must be kept above the
threshold voltage to toggle the
RESET
signal, preventing the
device from operating when V
IN
is not stable. If V
IN
falls below
the threshold voltage, the
RESET
signal toggles quickly.
RESET
OUTB
OUTA
U2
U1
R
PULLUP
R1
R2
CC
C
T
IN
REF
12206-236
Figure 36. Programmable Threshold and Timeout Circuit
RESET
V
TH
V
IN
t
RESET
t
RESET
12206-237
Figure 37. Threshold and Timeout Programmable Voltage Supervisor
Timing Diagram
During startup, the ADCMP391/ADCMP392/ADCMP393
guarantee a low output state when V
CC
is still below the UVLO
threshold, preventing the voltage supervisor from toggling.
When V
IN
reaches the threshold set by the resistor divider (R1
and R2) and V
REF
, OUT1 changes from low to high and starts to
charge the timeout capacitor (C
T
). If V
IN
is kept above the threshold
voltage and the voltage in C
T
reaches V
REF
, OUT2 toggles. If V
IN
falls below the threshold voltage while C
T
is charging, the timeout
capacitor quickly discharges, preventing OUT2 from toggling
while V
IN
is not stable.
In the condition that V
IN
is tied to V
CC
, the circuit operates
when V
CC
is more than the minimum operating voltage.
The threshold voltage (V
TH
) is configured by changing the
resistor divider or V
REF
. Calculate the threshold voltage by
R2
R1
VV
REF
TH
1
(39)
Timeout is adjusted by changing the values of the pull-up
resistor or the timeout capacitor. To set the timeout value,
determine the allowable current flowing through R
PULLUP
, I
PULLUP
.
When I
PULLUP
is known, calculate R
PULLUP
and C
T
by the following
formulas:
R
PULLUP
= V
CC
/I
PULLUP
(40)
CC
REF
PULLUP
RESET
T
V
V
R
t
C
1ln
(41)
