NPH25S2415IC Datasheet, PDF (3/8 Pages) Murata Manufacturing Co., Ltd. – Isolated 25W Single Output DC/DC Converters

NPH25S Series
Isolated 25W Single Output DC/DC Converters
APPLICATION NOTES
OUTPUT VOLTAGE ADJUSTMENT
The trim resistor equations are:
Rup = (R/Vup) - S kΩ
Rdown = (L x ^T ) - T - S kΩ
Vdown
VNOM 3.4
S
22.2973
T
10.1351
R
17.9994
L
-1.6241
5.1
20.59761
9.36255
24.49487
-2.48374
12.1
28.79096
15.42373
94.9661
-5.942857
15.1
39.95902
20.77869
147.7314
-7.990244
TRIM UP
+VIN
TRIM
NPH25S
+VOUT
RUP
-VOUT
TRIM DOWN
+VIN
NPH25S
TRIM
+VOUT
RDOWN
-VOUT
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 NPH25S4805EiC by 0.1V:
RDOWN = -2.48374 x 9.36255 - 9.36255 - 20.59761 = 203.18kΩ
-0.1
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
When the shutdown pin (SS) 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.
FREQUENCY CONTROL
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.
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KDC_NPH25S.H01 Page 3 of 8