2. Default Pin Strap Configuration
a.ꢀ Ensure the pin straps are in the following default locations before proceeding:
nꢀENABLE = Not Used (enabled)
nꢀTRIM_UP = Not Used
nꢀTRIM_DN = Not Used
nꢀOPT1 = Not Used
nꢀOPT2 = Not Used
3. Pin Strap Functions
a.ꢀ ENABLE – adding a strap on this pin will cause the converter to shut down.
b.ꢀ TRIM_UP – Adding a strap in this location will adjust the output voltage
up by 10%.
c.ꢀ TRIM_DN – Adding a strap in this location will adjust the output voltage down
by 10%. Only one strap can be connected at a time. If both trim straps are out,
the output voltage should be set to the model’s nominal output.
4. Trimming And Soft Start
a.ꢀ For those customers who wish to trim to another voltage by changing the preset
trim resistors to another value, the trim equation shown in Figure 2 can be used:
Figure 2.
RINT
Rlow = –V
(
•
)
PI31xx Trim Equation
desired
–Vout
+ V
(
)
desired
nom
–Vout
• VERO + V
• Vref
]
(
)
nom
desired
Rhigh
=
(
–RSS
)
•
Vref
(
–Voutnom) +
V
[
desired
Where: R1 = Rlow R3 = Rhigh VERO = 4.9 and Vref can be found in the appropriate
model datasheet.
Figure 3 shows an equation for soꢀ start configuration where C7 = C
REF
Figure 3.
−6
T
ssdesired – 230 • 10
PI31xx Soft Start Equation
CREF
=
23000
Figure 4.
PI31xx Trimming Equivalent
Circuit
ENABLE
PI31xx
Rhigh
10k
•
•
RSS
TRIM/SS
VERO
Vref
Rlow
•
SGND
UG:301
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Applications Engineering: 800 927.9474
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