DEMO MANUAL SCP-LT8618-BEVALZ
Rev. 0
3
CONFIGURATION SETTINGS
Demonstration circuit SCP-LT8618-BEVALZ is a high effi-
ciency 65V, 100mA synchronous step-down regulator. The
wide input range also allows output voltage inversion by
using the SCP-LT8618-IEVALZ version of this board.
The output of the SCP-LT8618-BEVALZ is resistor-pro-
grammable from 0.8V to 48V. The board can be also con-
figured to drive VIOC-capable linear regulators.
OUTPUT VOLTAGE PROGRAMMING
Table 2.
Resistor Selection Guide for Common Output Voltages
V
OUT
(V)
R4
(
Ω
)
R5
(
Ω
)
0.8
3.24k
115k
0.9
3.83k
137k
1.0
102k
357k
1.1
42.2k
102k
1.2
102k
187k
1.25
162k
267k
1.5
205k
221k
1.8
1.00M
768k
2.0
1.15M
732k
2.5
1.47M
665k
3.0
1.02M
357k
3.3
590k
182k
3.5
357k
102k
4.0
422k
102k
4.5
511k
107k
5.0
1.02M
187k
5.5
698k
115k
6.0
1.13M
169k
6.5
787k
107k
7.0
1.50M
187k
7.5
1.27M
147k
8.0
1.30M
140k
12.0
1.47M
102k
16.0
1.50M
76.8k
20.0
1.50M
60.4k
24.0
1.50M
49.9k
30.0
1.50M
40.2k
36.0
1.50M
33.2k
42.0
1.50M
28.0k
48.0
1.50M
24.9k
EN/UV PIN CONFIGURATION
The EN/UV 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 R1 and R6, short R11 with
0
W
, and use the drive signal from connector P1. Also,
short R12 with 0
W
for output voltage monitoring.
If precision UVLO operation is desired, program enable di-
vider R1 and R6 such that:
R6 is 10k to 100k, nominal
The LT8618 has an accurate 1.05V threshold which places
the part into under voltage lockout. The hysteresis thresh-
old on the rising edge is typically 50mV and scales by the
factor:
VOLTAGE INPUT-TO-OUTPUT CONTROL (VIOC)
IMPLEMENTATION
To implement the VIOC function for this regulator, set R8
and R13
to 0
W
, respectively. Refer to the “Configuration
Settings” section in the Demo Manual for the low-dropout
(LDO) linear regulator board and use the following config-
uration for this board.
Table 3.
VIOC Cross-Reference Designators
VIOC SETTING REFERENCES
R
BOT
R
TOP
R
MAX
V
OUT
Reference Designators
R5
R4
R7
I
SINK
is the current through R
MAX
, typically 15µA, so R
BOT
should be sized such that the divider current runs a mini-
mum of 100µA to minimize the I
SINK
error term.
V
OUT
=
0 .7 7 8 V 1
+
R4
R5
⎛
⎝⎜
⎞
⎠⎟
R1
=
R6
V
IN
−
1 .0 5 V
1 .0 5 V
⎛
⎝⎜
⎞
⎠⎟
V
HYST
=
50mV
R1
+
R6
R6
V
L DOIN
−
V
L DOOUT
=
V
VIOC
=
0 .7 7 8 V
R
BOT
+
R
TOP
R
BOT
⎛
⎝⎜
⎞
⎠⎟
V
MAX
(
)
LDOIN
=
0 .7 7 8 V
R
BOT
+
R
TOP
+
R
MAX
R
BOT
⎛
⎝⎜
⎞
⎠⎟
+
I
SINK
R
MAX
