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DESIGN CONSIDERATIONS
The NC30 is designed using two-phase synchronous
buck topology. Block diagram of the converter is shown in
Figure 25. The output can be trimmed in the range of
0.9Vdc to 5.0Vdc by a resistor from trim pin to ground. A
remote sense function is provided and it is able to
compensate for a drop from the output of converter to
point of load.
The converter can be turned ON/OFF by remote control.
Positive on/off (ENABLE pin) logic implies that the
converter DC output is enabled when this signal is driven
high (greater than 2.4V) or floating and disabled when the
signal is driven low (below 0.8V). Negative on/off logic is
optional and could also be ordered.
The converter provides an open collector signal called
Power Good. The power good signal is pulled low when
output is not within ±10% of Vout or Enable is OFF.
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.
The converter has an over temperature protection which
can protect itself by shutting down for an over
temperature event. There is a thermal hysteresis of
typically 30℃
Figure 25: Block Diagram
Safety Considerations
It is recommended that the user to provide two 12A very
fast-acting type fuses (Little fuse R451 012) in parallel in
the input line for safety.
DS_NC12S30A_05222008
FEATURES DESCRIPTIONS
ENABLE (On/Off)
The ENABLE (on/off) input allows external circuitry to put
the NC converter into a low power dissipation (sleep) mode.
Positive (active-high) ENABLE is available as standard.
Positive ENABLE (active-high) units of the NC series are
turned on if the ENABLE pin is high or floating. Pulling the
pin low will turn off the unit. With the active high function,
the output is guaranteed to turn on if the ENABLE pin is
driven above 2.4V. The output will turn off if the ENABLE
pin voltage is pulled below .8V.
The ENABLE input can be driven in a variety of ways as
shown in Figures 26, 27 and 28. If the ENABLE signal
comes from the primary side of the circuit, the ENABLE can
be driven through either a bipolar signal transistor (Figure
26) or a logic gate (Figure 27). If the enable signal comes
from the secondary side, then an opto-coupler or other
isolation devices must be used to bring the signal across
the voltage isolation (please see Figure 28).
NC30/NC40
Vin
Enable
Ground
Figure 26: Enable Input drive circuit for NC series
5V
Figure 27: Enable input drive circuit using logic gate.
Figure 28: Enable input drive circuit example with isolation.
Vout
Trim
Ground
NC30/NC40
Vout
Vin
Enable
Trim
Ground
Ground
NC30/NC40
Vout
Vin
Enable
Trim
Ground
Ground
7
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