Rev. A 10/18
13
Application Note
AN-72
www.power.com
Step 6 – Secondary Components
Enter: RFB_UPPER
Figure 9. Secondary Components Section of InnoSwitch3 PIXLs Spreadsheet.
Figure 10. Secondary Components Section of InnoSwitch3 PIXls Spreadsheet.
118
SECONDARY COMPONENTS
119
RFB_UPPER
100.00
k
Ω
Upper feedback resistor (connected to the first
output voltage)
120
RFB_LOWER
34.00
k
Ω
Lower feedback resistor
121
CFB_LOWER
330
pF
Lower feedback resistor decoupling capacitor
125
MULTIPLE OUTPUT PARAMETERS
126
OUTPUT 1
127
VOUT1
5.00
V
Output 1 voltage
128
IOUT1
4.00
A
Output 1 current
129
POUT1
20.00
W
Output 1 power
130
IRMS_SECONDARY1
5.95
A
Root mean squared value of the secondary
current for output 1
131
IRIPPLE_CAP_OUTPUT1
4.41
A
Current ripple on the secondary waveform for
output 1
132
AWG_SECONDARY1
19
AWG
Wire size for output 1
133
OD_SECONDARY1_INSULATED
1.217
mm
Secondary winding wire outer diameter with
insulation for output 1
134
OD_SECONDARY1_BARE
0.912
mm
Secondary winding wire outer diameter without
insulation for output 1
135
CM_SECONDARY1
1191
Cmils
Bare conductor effective area in circular mils for
output 1
136
NSECONDARY1
6
Number of turns for output 1
137
VREVERSE_RECTIFIER1
34.09
V
SRFET reverse voltage (not accounting parasitic
voltage ring) for output 1
138
SRFET1
Auto
AON6266
SRFET selection for output 1
139
VF_SRFET1
0.076
V
SRFET on-time drain voltage for output 1
140
VBREAKDOWN_SRFET1
60
V
SRFET breakdown voltage for output 1
141
RDSON_SRFET1
19.0
m
Ω
SRFET on-time drain resistance at 25degC and
VGS=4.4V for output 1
Upper Feedback Resistor, RFB_UPPER
The RFB_UPPER resistor value is calculated based on VOUT and the
nominal internal reference voltage of the IC (1.265 V).
Upper Feedback Resistor, RFB_LOWER
The RFB_LOWER resistor is calculated based on VOUT and the 1.265 V
internal reference voltage. The value will change if the specified
value is used for the RFB_UPPER resistor.
Lower Feedback Resistor Decoupling Capacitor, CFB_LOWER
A 330 pF surface mount ceramic X7R type capacitor (or better) is
recommended as this can be placed close to the pins of the FEEDBACK
and GROUND pins of the IC.
Step 7 – Multiple Output Parameters
This section allows the user to design up to three secondary outputs
(excluding bias supply) and choose a suitable MOSFET size for
synchronous rectification. The spreadsheet will provide a warning
should the total power of the multiple outputs exceed the power
described in the
POUT
cell.
For single output design, cells
VOUT1
,
IOUT1
and
POUT1
will be
the main output parameters entered in section 1.
Each output provides a selection of synchronous rectifier MOSFETs
(SRFET)
in the drop down menu, (see Table 10). Based on the SR
FET chosen the on-state forward voltage,
VF_SRFET (V)
, breakdown
voltage,
VBREAKDOWN_SRFET (V)
, and on-time drain resistance,
RDSON_SRFET (m
Ω
)
will be displayed in the spreadsheet.
The spreadsheet also calculates the critical electrical parameters for
each secondary output:
RMS Current of the Secondary Output, RMS_SECONDARY (A)
– Used to size the secondary winding wire.
Current Ripple on Secondary, IRIPPLE_CAP_OUTPUT (A)
– Used to size the output filter capacitor.
–
Number of Turns for Output, NSECONDARY
– Calculated turns for each output.
Additional information for the magnetic wire are also given,
AWG_
SECONDARY (AWG), OD_SECONDARY_INSULATED (mm) and
OD_SECONDARY_BARE (mm).