LTC4417_15 Datasheet, PDF (24/32 Pages) Linear Technology – Prioritized PowerPat Controller

LTC4417
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) =
(33)
(41.2kΩ + 806kΩ) • 247nA = 209mV
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.
FROM V2
INPUT SOURCE
FROM V1
INPUT SOURCE
TO V3 INPUT SUPPLY
S
D
G
G
D
S
S
D
G
G
D
S
TO OUTPUT
0.03" PER
AMPERE
TRANSIENT
VOLTAGE
SUPPRESSOR
R3
R6 ^R2
R5 ^R1
R9
R4
R8
R7
1 EN
2 SHDN
3 HYS
4 UV1
5 OV1
6 UV2
7 OV2
8 UV3
9 OV3
10 VALID1
11 VALID2
12 VALID3
V1 24
V2 23
V3 22
VS1 21
G1 20
VS2 19
G2 18
VS3 17
G3 16
V_OUT 15
CAS 14
GND 13
C_V1
C_V2
C_V3
TO V3 COMMON SOURCE
TO V3 COMMON GATE
GND
24
NOT TO SCALE
Figure 14. Recommended PCB Layout
GND
4417f