Power integrations LinkSwitch-4 LNK4*15D Series Application Note page 4

Application Note
If no-load to partial or full load transient step is required as in USB
chargers:
Enter the load step value into I_LOADSTEP [B148] if it is different
•
to the rated output current.
Enter the minimum load voltage allowed during no-load to partial
•
or full load transient testing into V_UNDERSHOOT [B149].
Check that FSW_NOLOAD value in [E154] is greater than FSW_
•
UNDERSHOOT in [E150]. If not, select a lower value for VCS_MIN
[B135], if already at the lowest setting or a LNK40x2S device is
being used, enter a lower value for R_PRELOAD [B152] untill the
condition is met.
Check that the no-load power specification is met, P_NOLOAD_TO-
•
TAL [E174], if not select a higher value of VCS_MIN [B135] (not
LNK40X2S) and recheck that the FSW_
NOLOAD>FSWUNDERSHOOT and no-load power requirements are
met. If using a LNK40X2S, R_PRELOAD [B152] can be increased,
but no more than 2x.
If no transient step requirement:
Select a value of VCS_MIN [B135] and R_PRELOAD [B153] that
•
gives a FSW_NOLOAD of between 1 kHz and 2 kHz and still meets
the no-load specification.
Enter the maximum allowed start-up time into STARTUP_TIME
•
[B156] if it is not to be 1 second. Or enter a preferred value into
R_STARTUP [B157], a new value of the resultant startup time is
given in STARTUP_TIME_FINAL [E158].
Supplementary Base Drive
Resistor R is used on SO-8 packaged devices to provide extra base
SBD
drive in higher power applications (7.5 W to 18 W). It should have a
value of between 390 W and 220 W for standard designs, or 120 W for
applications using the EasyStart feature. Refer to the 'Design
Testing' section to check that correct value has been selected.
4
Rev. B 10/17
Component values for the design are found in:
C + C , CIN [E13]
IN1 IN2
Selected device – [E20]
Q1 BJT – [E24]
T1 Core - [E35]
T1 Bobbin – [C37]
T1 Primary turns – [E51]
T1 Primary layers – [E98]
T1 Primary wire diameter – [E101, E102]
T1 secondary turns – [E50]
T1 Secondary layers – [E116]
T1 Secondary filars – [E117]
T1 Secondary wire diameter – [E120, E121]
T1 Bias turns – [E106]
T1 Core gap – [E93]
C , Bias capacitor value – [E138]
VCC
Total output capacitance C , [E145]
OUT
Output capacitance ripple – [E81]
R Dummy load – [E152]
OUT
R Start-up resistor – [E157]
HT
R Upper feedback resistor – [E161]
FB1
R Lower feedback resistor – [E162]
FB2
R Current sense resistor – [E74]
CS
R V setting resistor – [E136]
CS2 CSMIN
Bias diode V – [E129] usually 1N4148
RRM
D V – [E128]
OUT RRM
D Peak current – [E79]
OUT
D RMS current – [E780]
OUT
Explore the spreadsheet for more informative data.
AN-69
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