LTC4223 LINER [Linear Technology], LTC4223 Datasheet - Page 16

• Manufacturer Part Number: LTC4223
• Description: Dual Ideal Diode and Hot Swap Controller
• Manufacturer: LINER [Linear Technology]

LTC4228-1/LTC4228-2
applicaTions inForMaTion
The inrush current is set to 1A by adding capacitance,
C
Choose a practical value of 15nF for C
The average power dissipated in the MOSFET is calculated
as:
The MOSFET selected must be able to tolerate 6W for
19ms during power-up. The SOA curves of the Si7336ADP
provide for 1.5A at 30V (45W) for 100ms. This is suffi-
cient to satisfy the requirement. The increase in junction
temperature due to the power dissipated in the MOSFET
is ∆T = P
thermal impedance. Under this condition, the Si7336ADP
data sheet indicates that the junction temperature will
increase by 4.8°C using Zth
The duration and magnitude of the power pulse during an
output short is a function of the TMR capacitance, C
the LTC4228’s active current limit. The short-circuit dura-
tion is given as C
The maximum short-circuit current is calculated using the
maximum active current limit threshold ∆V
and minimum R
So, the maximum power dissipated in the MOSFET is
18.9A • 12V = 227W for 0.56ms. The Si7336ADP data
sheet indicates that the worst-case increase in junction
temperature during this short-circuit condition is 22.7°C
using Zth
0.047µF will not cause the maximum junction temperature
of the MOSFET to be exceeded. The SOA curves of the
Si7336ADP provide for 15A at 30V (450W) for 1ms. This
also satisfies the requirement.
16
HG
I
SHORT(MAX)
P
C
, at the gate of the Hot Swap MOSFET.
AVG
HG
=
=
AVG
C
JC
t
L
CHARGE
E
•I
I
= 0.1°C/W (single pulse). Choosing C
• Zth
INRUSH
CL
=
HGATE(UP)
S
T
∆V
value.
• 12[ms/µF] = 0.56ms for C
JC
=
SENSE(ACL)(MAX)
where Zth
2
1
R
•
S(MIN)
=
1600µF • 12V
1600µF • 10µA
JC
= 0.8°C/W (single pulse).
19ms
JC
1A
is the junction-to-case
(
=
HG
3.96mΩ
)
75mV
.
2
SENSE(ACL)(MAX)
= 16nF
= 6W
T
= 0.047µF .
= 18.9A
T
, and
T
=
Next, select the resistive divider at the ON1 and ON2 pins
to provide an undervoltage threshold of 9.6V for the 12V
supply. First, choose the bottom resistors, R1 and R3, to be
20k. Then, calculate the top resistor value for R2 and R4:
Choose the nearest 1% resistor value of 137k for R2 and
R4. In addition, there is a 0.1µF bypass (C1) at the INTV
pin and a 10nF filter capacitor (C
the supply glitches from turning off the Hot Swap MOSFET.
PCB Layout Considerations
For proper operation of the LTC4228’s circuit breaker, Kelvin
connection to the sense resistor is strongly recommended.
The PCB layout should be balanced and symmetrical to
minimize wiring errors. In addition, the PCB layout for the
sense resistor and the power MOSFET should include good
thermal management techniques for optimal device power
dissipation. A recommended PCB layout is illustrated in
Figure 7.
Connect the IN and OUT pin traces as close as possible to
the MOSFETs’ terminals. Keep the traces to the MOSFETs
wide and short to minimize resistive losses. The PCB traces
associated with the power path through the MOSFETs
should have low resistance. The suggested trace width for
1oz copper foil is 0.03" for each ampere of DC current to
keep PCB trace resistance, voltage drop and temperature
rise to a minimum. Note that the sheet resistance of 1oz
copper foil is approximately 0.5mΩ/square, and voltage
drops due to trace resistance add up quickly in high cur-
rent applications.
It is also important to place the bypass capacitor, C1, for
the INTV
GND. Also place C
C
suppressors, Z1 and Z2, when used, should be mounted
close to the LTC4228 using short lead lengths.
CP2
R
R
TOP
TOP
near the CPO2 and IN2 pins. The transient voltage
CC
=
=




 
pin, as close as possible between INTV
1.235V
V
V
IN(UVTH)
9.6V
ON(TH)
CP1
– 1
– 1
near the CPO1 and IN1 pins, and

 

 •R

• 20k = 135k
BOTTOM
F
) at the ON pin to prevent
CC
422812f
and
CC