Linear ADI Power LT8618 Demo Manual page 3

CONFIGURATION SETTINGS
Demonstration circuit SCP-LT8618-IEVALZ is a high effi-
ciency 65V, 100mA synchronous step-down regulator
configured as an inverting buck topology for positive to
negative DC voltage conversion.
The output of the SCP-LT8618-IEVALZ is resistor-pro-
grammable from –0.8V to –48V.
OUTPUT VOLTAGE PROGRAMMING
⎛
V = 0 .7 7 8 V 1 +
⎝ ⎜
OUT
Table 2. Resistor Selection Guide for Common Output Voltages
V (V)
OUT
–0.8
–0.9
–1.0
–1.1
–1.2
–1.25
–1.5
–1.8
–2.0
–2.5
–3.0
–3.3
–3.5
–4.0
–4.5
–5.0
–5.5
–6.0
–6.5
–7.0
–7.5
–8.0
–12.0
–16.0
–20.0
–24.0
–30.0
–36.0
–42.0
–48.0
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R4 ⎞
⎠ ⎟
R5
R4 (Ω) R5 (Ω)
3.24k
3.83k
102k
42.2k
102k
162k
205k
1.00M
1.15M
1.47M
1.02M
590k
357k
422k
511k
1.02M
698k
1.13M
787k
1.50M
1.27M
1.30M
1.47M
1.50M
1.50M
1.50M
1.50M
1.50M
1.50M
1.50M
DEMO MANUAL SCP-LT8618-IEVALZ
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 1.00MW resistor for ei-
ther pull-up or pull-down resistors R1 and R6, short R11
with 0W, and use the drive signal from connector P1.
If precision UVLO operation is desired, program enable di-
vider R1 and R6 such that:
R6 is 10k to 100k, nominal
V
⎛
IN
R1 = R6
⎝ ⎜
115k
137k The LT8618 has an accurate 1.05V threshold which places
357k
the part into under voltage lockout. The hysteresis thresh-
102k
old on the rising edge is typically 50mV and scales by the
187k
factor:
267k
221k
V = 50mV
HYST
768k
732k
665k
VOLTAGE INPUT-TO-OUTPUT CONTROL (VIOC)
357k
IMPLEMENTATION
182k
102k
VIOC cannot be implemented with the board in the invert-
102k
ing buck configuration. If using a VIOC-capable negative
107k
linear regulator, ensure R8 and R13 are open and inde-
187k
pendently set fixed output voltages for both the SCP-
115k
LT8618-IEVALZ board and the negative linear regulator
169k
board.
107k
187k
147k
140k
102k
76.8k
60.4k
49.9k
40.2k
33.2k
28.0k
24.9k
− 1 .0 5 V
⎞
⎠ ⎟
1 .0 5 V
R1+ R6
R6
Rev. 0
3