Delta Electronics NC15 Series Features Descriptions Con, Input Under-Voltage Lockout, RsΩ =, Vout

FEATURES DESCRIPTIONS (CON.)

Input Under-Voltage Lockout

The input under-voltage lockout prevents the converter from being damaged while operating when the input voltage is too low. The lockout occurs between 7.0V to 8.0V.

Over-Current and Short-Circuit Protection

The NC series modules have non-latching over-current and short-circuit protection circuitry. When over current condition occurs, the module goes into the non-latching hiccup mode. When the over-current condition is removed, the module will resume normal operation.

An over current condition is detected by measuring the voltage drop across the high-side MOSFET. The voltage drop across the MOSFET is also a function of the MOSFET’s Rds(on). Rds(on) is affected by temperature, therefore ambient temperature will affect the current limit inception point. Please see the electrical characteristics for details of the OCP function.

The detection of the Rds(on) of the high side MOSFET also acts as an over temperature protection since high

The NC06/NC15/NC20 module has a trim range of 0.9V to 5.0V. The trim resistor equation for the NC6A/NC15A/ NC20A is :

Rs(Ω) = 1170

Vout − 0.9

Vout is the output voltage setpoint

Rs is the resistance between Trim and Ground Rs values should not be less than 280Ω

Output Voltage	Rs (Ω)
+0.9 V	OPEN
+1.2 V	3.92K
+1.5 V	1.96K
+1.8 V	1.3K
+2.5 V	732
+3.3 V	487
+5.0 V	287

Figure 28: Typical trim resistor values

NC6A/15A/20A

Vout

Vin

1.3K

temperature will cause the Rds(on) of the MOSFET to increase, eventually triggering over-current protection.

Enable

Trim

Rt Vt

Rs

Output Voltage Programming

The output voltage of the NC series is trimmable by connecting an external resistor between the trim pin and output ground as shown Figure 27 and the typical trim resistor values are shown in Figure 28. The output can also be set by an external voltage connected to trim pin as shown in Figure 29.

NC6A/15A/20A

Ground Ground

Figure 29: Output voltage trim with voltage source

To use voltage trim, the trim equation for the NC6A/NC15A/ NC20A is (please refer to Fig. 29) :

Rt(kΩ) =	Rs(1.3Vt − 1.17)
	1.17 − Rs(Vout − 0.9)

Vin

Vout

Vout is the desired output voltage Vt is the external trim voltage

Enable

Trim

Rs

Rs is the resistance between Trim and Ground (in KΩ)

Rt is the resistor to be defined with the trim voltage (in KΩ)

Ground Ground

Figure 27: Trimming Output Voltage

NC12S15A_01102008

Below is an example about using this voltage trim equation :

Example：

If Vt = 1.25V, desired Vout = 2.5V and Rs = 0.715KΩ

Rt(KΩ) =	Rs(1.3Vt − 1.17)	= 12.51KΩ
	1.17 − Rs(Vout − 0.9)

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