DEMO MANUAL SCP-LT3483-EVALZ
Rev. 0
3
CONFIGURATION SETTINGS
Demonstration circuit SCP-LT3483-EVALZ is an inverting
converter featuring the LT3483ES6. The converter gener-
ates –15V at 8mA to 40mA from a 2.7–12V input using a
dual coupled inductor in an inverting flyback topology.
The output of the SCP-LT3483-EVALZ is resistor-program-
mable from –1V to –39V. The board can be also configured
to drive VIOC-capable linear regulators.
OUTPUT VOLTAGE PROGRAMMING
Table 2.
Resistor selection guide for common output voltages
V
OUT
(V)
R2 (
Ω
)
–1.0V
100k
–1.5V
150k
–2.0V
200k
–2.5V
249k
–3.0V
301k
–3.5V
348k
–4.0V
402k
–4.5V
453k
–5.0V
499k
–5.5V
549k
–6.0V
604k
–7.0V
698k
–8.0V
806k
–9.0V
909k
–10.0V
1.00M
–11.0V
1.10M
–12.0V
1.21M
–13.0V
1.30M
–14.0V
1.40M
–15.0V
1.50M
–16.0V
1.62M
–17.0V
1.69M
–18.0V
1.82M
–19.0V
1.91M
–20.0V
2.00M
–25.0V
2.49M
–30.0V
3.01M
–35.0V
3.48M
–39.0V
3.92M
SHDN
PIN CONFIGURATION
The
SHDN
pin is tied to the optional SCP Run/Sequence
header P1. To create a harness for this function, use Molex
part 0510650300 with crimp pin 50212-8000.
To use an active run signal, use a 1.00M resistor for either
pull-up or pull-down resistors R5 and R6, short R4 with
0
W
, and use the drive signal from connector P1.
VOLTAGE INPUT-TO-OUTPUT CONTROL (VIOC)
IMPLEMENTATION
To implement the VIOC function for this regulator, set R7
to 0
W
. Refer to the “Configuration Settings” section in the
Demo Manual for the low-dropout (LDO) linear regulator
board and use the following configuration for this board.
Table 3.
VIOC Cross-Reference Designators
VIOC SETTING REFERENCES
R
BOT
R
TOP
R
MAX
V
OUT
Reference Designators
125k
Ω
(internal to LT3483)
R2
R3
Because the V
LDOIN
term is simply the sum of the final
output voltage after the LDO and the difference the LT3483
is adding on top, it can be helpful to take the desired final
output voltage, add 1.0V, and then look up that voltage-
resistor combination from Table 2.
R
MAX
can then be obtained by figuring out the difference
between the maximum and nominal output voltages of the
LT3483, divided by the 10µA current through the internal
feedback resistor.
V
OUT
=
R2
•
10µA
V
L DOIN
−
V
L DOOUT
=
V
VIOC
=
1 .2 5 V
REF
R
TOP
R
BOT
⎛
⎝⎜
⎞
⎠⎟
V
MAX
(
)
L DOIN
=
1 .2 5 V
REF
R
TOP
+
R
MAX
R
BOT
⎛
⎝⎜
⎞
⎠⎟
+
V
VIOC
R
MAX
4 0 k
⎛
⎝⎜
⎞
⎠⎟
