Datasheet

C
FILTER
+
ǒ
t
FLT
I
FILTER
Ǔ
ǒ
V
FILTER
1000
Ǔ
C
FILTER
+
t
FLT
ǒ
R
FILTER
SF
Ǔ
Normal operating current
Charging
Bulk
Capacitors
Fault level
Current Limit Turn On
TPS2363
SLUS680B –JANUARY 2006–REVISED JANUARY 2010 www.ti.com
Fault Timer
To avoid nuisance trips, the turn off time of the main power supplies and AUX in a normal over-current event is
controlled by a fault timer. The over current comparator’s response time, t
FLT
, is user selectable and set by
external capacitors, one for each channel. Connect the capacitor from FILTERA/B to ground. The fault timer
capacitor, C
FILTERA/B
, is calculated by the following equation:
Using the full range of V
FILTER
and I
FILTER
given in the Timing Parameters section, C
FILTER
and the associated
fault time can vary up to 60% without component tolerances. For increased accuracy of the fault timer, connect a
110-kΩ resistor from pin R
FILTERA/B
to ground. Recalculate the C
FILTERA/B
by the following equation:
Where R
FILTER
is the 110-kΩ 1% resistor and SF is the scaling factor in the Timing Parameters section. This
technique is accurate to less than 22%, apart from component tolerances.
Competitive parts based on the published datasheet calculate to 200% without the resistor and 27% with the
resistor.
Current Limit
A current limit hot plug controller protects the system against over loads and glitches to the backplane power
rails by limiting the amount of current that a module can draw. When the module has been in current limit for the
fault time then the circuit opens. If the fault goes away before the fault time expires the module goes back to the
normal running mode. The disadvantage is the voltage on the module can drop during the current limit, and can
leave the logic on the module in a unknown state or hung state. The module may have to be reset or the power
cycled to the module to reset the logic.
Figure 3 shows the module turn on using current limit, when current limiting is used the fault timer is typically set
for a longer period than circuit breaker. It takes longer to charge up the capacitors when the current is limited.
Figure 3. Hot Plug Current Limit Turn ON
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