Datasheet

LTC4417
24
4417f
applicaTions inForMaTion
Because this is a single resistive string R2, R3, and
I
OV_UV(HYS)
sets the hysteresis voltage with Equation (30)
OV
HYS
= (R2 + R3) • I
OVUV(HYS)
=
(41.2kΩ + 806kΩ) • 247nA = 209mV
(33)
This results in an OV threshold of 15.0V and UV threshold
of 8.9V. With hysteresis, the OV
HYS
threshold is 14.8V
and the UV
HYS
threshold is 9.1V. For the desired OV and
UV 6% accuracy, 1% resistors used in this example are
acceptable.
Values for R4 to R6 and R7 to R9 for V2 and V3 are
similarly calculated.
Layout Considerations
Sheet resistance of 1oz copper is ~530µΩ per square.
Although small, resistances add up quickly in high current
applications. Keep high current traces short with minimum
trace widths of 0.02" per amp to ensure traces stay at a
reasonable temperatures. Using 0.03" per amp or wider
is recommended. To improve noise immunity, place OV/
UV resistive dividers as close to the LTC4417 as possible.
Transient voltage suppressors should be located as close
to the input connector as possible with short wide traces
to GND. Figure 14 shows a partial layout that addresses
these issues.
Figure 14. Recommended PCB Layout
1
2
3
4
5
6
7
8
9
10
11
12
TO V3 COMMON SOURCE
TO V3 COMMON GATE
TRANSIENT
VOLTAGE
SUPPRESSOR
GNDGND
24
23
22
21
20
19
18
17
16
15
14
13
FROM V1
INPUT SOURCE
0.03" PER
AMPERE
NOT TO SCALE
EN
SHDN
HYS
UV1
OV1
UV2
OV2
UV3
OV3
VALID1
VALID2
VALID3
V1
V2
V3
VS1
G1
VS2
G2
VS3
G3
V
OUT
CAS
GND
R3
R2
R1
R6
R5
R4
C
V1
G
C
V2
C
V3
R9
R8
R7
FROM V2
INPUT SOURCE
TO V3 INPUT SUPPLY
G
S
S
G
G
S
S
D
D
D
TO OUTPUT
D