Manual

UG:301 vicorpower.com Applications Engineering: 800 927.9474 Page 3
2. Default Pin Strap Configuration
a. Ensure the pin straps are in the following default locations before proceeding:
nENABLE = Not Used (enabled)
nTRIM_UP = Not Used
nTRIM_DN = Not Used
nOPT1 = Not Used
nOPT2 = 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:
R
low
=
(
–V
)
•
R
INT
(
–Vout
nom
)
+ V
desired
desired
R
high
= ( –RSS ) •
(
–Vout
nom
)
• V
ERO
+ V • V
ref
V
ref
[
( –Vout
nom
) + V
]
desired
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 so start configuration where C7 = C
REF
C
REF
=
T
ssdesired
– 230 • 10
−6
23000
ENABLE
TRIM/SS
SGND
RSS
Rhigh
Rlow
VERO
Vref
PI31xx
10k
•
•
•
Figure 4.
PI31xx Trimming Equivalent
Circuit
Figure 2.
PI31xx Trim Equation
Figure 3.
PI31xx Soft Start Equation