Configuration Settings - Analog Devices Linear ADI Power SCP-LT8609S-BEVALZ Demo Manual

CONFIGURATION SETTINGS

Demonstration circuit SCP-LT8609S-BEVALZ is a 42V,
2A/3A peak micropower synchronous step-down regula-
tor featuring the LT8609S. The demo board is designed for
5V output from a 5.5V to 42V input.
The output of the SCP-LT8609S-BEVALZ is resistor-pro-
grammable from 0.8V to 24V. The board can be also con-
figured to drive VIOC-capable LDO regulators.
OUTPUT VOLTAGE PROGRAMMING
⎛ ⎞
R
4
= 0 .7 7 4 V 1 +
V
⎝ ⎜ ⎠ ⎟
FB
OUT
R
5
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
8.5
9.0
9.5
10.0
12.0
16.0
20.0
24.0
DEMO MANUAL SCP-LT8609S-BEVALZ
R4 (Ω) R5 (Ω)
3.57k 107k
17.4k 107k
102k 348k
29.4k 69.8k
73.2k 133k
115k 187k
187k 200k
215k 162k
187k 118k
255k 115k
348k 121k
332k 102k
357k 102k
442k 102k
511k 107k
549k 100k
698k 115k
931k 137k
787k 107k
909k 113k
887k 102k
953k 102k
1.00M 100k
1.00M 93.1k
1.00M 88.7k
1.00M 84.5k
1.00M 68.1k
1.00M 51.1k
1.00M 20.2k
1.00M 33.2k
EN/UVLO PIN CONFIGURATION
The EN/UVLO pin is tied to the optional SCP Run/Se-
quence 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 for either pull-up
or pull-down resistors R1 and R6, short R7 with 0W, and
use the drive signal from connector P1.
If precision UVLO operation is desired, program enable di-
vider R5 and R6 such that:
R6 is 10k to 100k, nominal
⎛ − 1 .0 5 V ⎞
V
IN TH
R5 = R6
⎝ ⎜ ⎠ ⎟
1 .0 5 V
TH
The LT8330 has an accurate 1.60V threshold which
places the part into under voltage lockout. The hysteresis
threshold on the rising edge is typically 80mV and scales
by the factor:
R5 + R6
V = 50mV
HYST
R6
VOLTAGE INPUT-TO-OUTPUT CONTROL (VIOC)
IMPLEMENTATION
To implement the VIOC function for this regulator, set R13
and R14 to 0W, respectively. Refer to the "Configuration
Settings" section in the Demo Manual for the LDO board
and use the following configuration for this board.
Table 3. VIOC Cross-Reference Designators
VIOC SETTING REFERENCES
V Reference Designators
OUT
V − V = V = 0 .7 7 4 V
L DOIN L DOOUT VIOC
⎛
R
BOT
V = 0 .7 7 4 V
( )
⎝ ⎜
FB
MAX LDOIN
I is the current through R
SINK
should be sized such that the divider current runs a mini-
mum of 100µA to minimize the I
R R R
BOT TOP MAX
R4 R5 R13
⎛ ⎞
R + R
BOT TOP
⎝ ⎜ ⎠ ⎟
FB
R
BOT
⎞
+ R + R
TOP MAX
+ I R
⎠ ⎟
SINK MAX
R
BOT
, typically 15µA, so R
MAX
error term.
SINK
BOT
Rev. 1
3