NCP300, NCP301
www.onsemi.com
16
So, V
DET+_max
can be easily figured out just using a single
variable V
DET−_typ
.
For example, for NCP300LSN18T1G V
DET−_typ
= 1.8 V;
then
V
DET+_max
+ 1.8 1.09 + 1.962 V
(eq. 8)
The NCP30X detection voltage option must be chosen such
that:
V
CC_min
t V
DET+_max
t V
in_min
(eq. 9)
The significance of V
CC_min
< V
DET+_max
is that it makes
sure the the reset from NCP30X remains asserted (in RESET
hold state) till after the power supply exceeds the V
CC_min
requirement; this prevents incorrect device (uP) initiation.
Having V
DET+_max
< V
in_min
makes sure that the
NCP30X is able to start up when V
in
is at the V
in_min
.
The theoretical ideal V
DET−_typ
voltage option to be
selected by the user, V
DET−_typ_ideal
, can be given by the
following formula:
V
DET−_typ_ideal
+
ǒ
V
in_min
) V
CC_min
Ǔ
(
2 1.09
)
(eq. 10)
The following example shows how to select the device
voltage option in a real world application.
1. Power supply output specification: 3.3 V $3%
2. Microprocessor core voltage specification: 3.3 V
$5%
So, we have:
V
in_min
+ 3.3 V * 3% + 3.201 V
(eq. 11)
V
CC_min
+ 3.3 V * 5% + 3.135 V
(eq. 12)
Then the ideal voltage option = (3.201 + 3.135) / (2 * 1.09)
= 2.9064 V
Therefore, a device voltage option of 2.9 V will be the right
choice.
PROPAGATION DELAY VARIATION
On the other hand (see above paragraph), a minimum
overdrive value from V
threshold
to V
CC
must be respected.
That means V
in
(minimum value of V
CC
) must be higher
enough than V
DET+
(V
DET−
+ hysteresis) at the risk of
significantly increasing propagation delay. (Figure 25) This
propagation delay is temperature sensitive.
To avoid acceptable time response, a minimum 100 mV
difference between V
in
and V
DET+
must be selected.
Figure 25. t
pLH
and t
pHL
vs. Input Voltage
for the NCP301SNT1
t
pLH
t
pHL
5.0
4.54.03.5
5
DET
TIME DELAY (ms)
100
0
300
200
500
400
600
3.0
3.168
V
in
, PULSE HIGH INPUT VOLTAGE (V)
