Design Considerations

The NC15 is a single phase and voltage mode controlled Buck topology. Block diagram of the converter is shown in Figure 23. The output can be trimmed in the range of 0.9Vdc to 5.0Vdc by a resistor from Trim pin to Ground.

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.

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 24, 25 and 26. If the ENABLE signal comes from the primary side of the circuit, the ENABLE can be driven through either a bipolar signal transistor (Figure 24) or a logic gate (Figure 25). 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 26).

NC6A/15A/20A

Vin

Vout

Figure 23: Block Diagram

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 current rating of the fuse.

Enable Trim

Ground Ground

Figure 24: Enable Input drive circuit for NC series

5V	NC6A/15A/20A
5V
	Vin	Vout
	Vin
	Enable	Trim

Ground Ground

Figure 25: Enable input drive circuit using logic gate.

NC6A/15A/20A

Vin Enable

Vout

Trim

Ground Ground

Figure 26: Enable input drive circuit example with isolation.

NC12S15A_01102008