Datasheet

LOAD _ TOL T _ TOL ON
CT
(1 C C ) t
(1 0.2 0.1) 0.012
C 0.39 F
40000 40000
+ + ´
+ + ´
= = = m
RFLT,max
185.58
R 0.99 47.97k
3.7 0.13
= ´ = W
+
TPS2590
CT
OUT
IN
FLT
ILIM
RTRY
IFLT
GND
38.3kΩ
C
LOAD
Optional:
To System
Monitor
12V Bus
16
EN
6 7 8 9
15
0.39µF
47.5kΩ
TPS2590
SLUS960G –JULY 2009–REVISED JANUARY 2014 www.ti.com
Figure 18. Design Example Schematic
1. Calculate maximum R
RFLT
to ensure that minimum I
FAULT
is above maximum operating load current using
Equation 16 as shown below in Equation 21.
(21)
● Choose a standard 1% value below R
RFLT,max
for R
RFLT
= 47.5 kΩ
● I
FAULT,min
= 3.738 A using Equation 13 and meets the maximum operating current requirement of 3.7 A
without starting the fault timer during maximum steady state operation for R
RFLT
= 47.5 kΩ, 1%.
● I
FAULT,max
= 4.674 A using Equation 14 for R
RFLT
= 47.5 kΩ, 1%.
2. Based on maximum I
FAULT
= 4.674 A, choose minimum I
LIM
= 4.7 A.
● Calculate R
RLIM,max
= 38.9 kΩ using Equation 20 and 1% tolerance.
● Choose a standard 1% value below R
RLIM,max
for R
RLIM
= 38.3 kΩ.
● I
LIM,min
= 4.779 A and I
LIM,max
= 5.705 A using Equation 17 and Equation 18 for R
RLIM
= 38.3 kΩ, 1%.
3. Minimum R
LOAD
at start-up using Equation 11 is 12 Ω. Because R
LOAD
= 13 Ω is present during circuit
start-up, use t
ON
= 12 ms from Table 2 for C
LOAD
= 100 µF and R
LOAD
= 13 Ω.
● Calculate C
CT
= 0.39 µF including C
LOAD
and C
CT
tolerances (C
LOAD_TOL
= 20% and C
CT_TOL
= 10%)
using Equation 22.
(22)
Transient Protection
The need for transient protection in conjunction with hot-swap controllers should always be considered. When
the TPS2590 device interrupts current flow, input inductance generates a positive voltage spike on the input and
output inductance generates a negative voltage spike on the output. Such transients can easily exceed twice the
supply voltage if steps are not taken to address the issue. Typical methods for addressing transients include;
• Minimizing lead length/inductance into and out of the device.
• Transient Voltage Suppressors (TVS) on the input to absorb inductive spikes.
• Schottky diode across the output to absorb negative spikes.
• A combination of ceramic and electrolytic capacitors on the input and output to absorb energy.
The following equation estimates the magnitude of these voltage spikes:
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