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NPH15S SERIES

Isolated 15W Single Output DC/DC Converters

APPLICATION NOTES

OUTPUT VOLTAGE ADJUSTMENT

3.4

5.1

12.1

15.1

S

22.2973

20.59761

28.79096

39.95902

T

10.1351

9.36255

15.42373

20.77869

R

17.9994

24.49487

94.9661

147.7314

L

-1.6241

-2.48374

-5.942857

-7.990244

TRIM UP

TRIM DOWN

When the output voltage is trimmed up, output current must be derated so that the maximum output power is not exceeded.

Example to decrease output voltage of NPH15S4805EiC by 0.1V:

SET VOLTAGE

The output voltage of all units is set to 100mV above nominal, to offset resistive losses and thus assist with worst case error calculations. For the EiC versions, this

allowance can be altered with a single fixed resistor, connected from the trimming pin to one of the output pins.

SHUTDOWN

FREQUENCY CONTROL

When the shutdown pin is shorted to the negative input, the converter will

stop. Its current consumption will then be less than 1mA at nominal supply

voltage. The voltage must be less than 1.5V to ensure that the unit stops, and

must be able to sink at least 1mA.

The unit will restart if the control pin is left open circuit or raised to a value

close to its normal open circuit voltage. This is typically 10V. Note however,

that the unit will not meet specification while a significant current drain from

this pin remains.

If the shutdown pin is to be connected to a long wire, it is recommended that a

capacitor decouples the pin to the supply common in order to avoid the risk of

injecting noise into the converter circuit. A series resistor may also be helpful.

Values of 10nF and 1kΩ may be used.

Many NPH series converters may be switched together simply by linking the

primary control pins. The primary common pins must also be linked.

If the primary side dc control voltage is pulled away from its open circuit

voltage, the converter frequency will be changed, approximately in proportion

to the voltage. With +8.5VDC voltage to SS pin, the typical switching frequency

will be 300kHz. If this is raised to 15VDC, the switching frequency will typically

be 510kHz. The frequency may thus be moved away from a sensitive value or

into a safe area. Deviation of at least –10% to +30% is achievable, though the

efficiency will decline with significant changes. Also note that if the frequency

is lowered, the switching frequency component of output ripple will increase.

Since the design uses no large electrolytic capacitors, any use of a lower

frequency must allow for the effects of increased ripple. Additional external

filtering may be required.

TRIM

NPH15S

The trim resistor equations are:

Rup = (R/Vup) - S kΩ

Rdown = (L x T ) - T - S kΩ

TRIM

NPH15S

(

)

-0.1