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Preliminary DS_NE12S20A_07272007
6
DESIGN CONSIDERATIONS
The NE12S0A0V(H)20 uses a single phase and voltage
mode controlled buck topology. The output can be
trimmed in the range of 0.59Vdc to 5.1Vdc by a resisto
r
from Trim pin to Ground.
The converter can be turned ON/OFF by remote control
with positive on/off (ENABLE pin) logic. The converte
r
DC output is disabled when the signal is driven lo
w
(below 0.3V). This pin is also used as the input turn on
threshold judgment. Its voltage is percent of Inpu
t
voltage during floating due to internal connection. So we
do not suggest using an active high signal (higher than
0.8V) to turn on the module because this high level
voltage will disable UVLO function. The module will turn
on when this pin is floating and the input voltage is
higher than the threshold.
The converter can protect itself by entering hiccup mode
against over current and short circuit condition. Also, the
converter will shut down when an over voltage protection
is detected.
Safety Considerations
It is recommended that the user to provide a very
fast-acting type fuse in the input line for safety. The
output voltage set-point and the output current in the
application could define the amperage rating of the fuse.
FEATURES DESCRIPTIONS
Enable (On/Off)
The ENABLE (on/off) input allows external circuitry to
put the NE converter into a low power dissipation (sleep)
mode. Positive ENABLE is available as standard. With
the active high function, the output is guaranteed to turn
on if the ENABLE pin is driven above 0.8V. The outpu
t
will turn off if the ENABLE pin voltage is pulled below
0.3V
The ENABLE pin is also used as input UVLO function.
Leaving the Enable floating, the module will turn on if the
input voltage is higher than turn on threshold and turn of
f
if the input voltage is lower than turn off threshold. The
default Turn-on voltage is 4.3V with 1V Hysteresis.
The Turn-on voltage may be adjusted with a resisto
r
placed between the “Enable” pin and “Ground” pin.
The formula for calculating the value of this resistor is:
5.1
2.18
)2.18(50
_
+
×
+
×
=
R
R
V
RTHEN
1
__
−
=
RTHENFTHEN
VV
NE20A
R
Enable
Fig. 18. Enable POR circuit.
FTHEN
V
_
is the falling threshold
RTHEN
V
_
is the rising threshold that you want.
R (Kohm) is the outen resistor that you connect from
Enable pin to the GND
Also, you will see an active high voltage will disable the
input UVLO function