MIC2582_14 Datasheet, PDF (16/27 Pages) Micrel Semiconductor – Single-Channel Hot Swap Controllers

Micrel, Inc.
defined by t_POR (See Applications Information for an
example).
Power-on-Reset and Overcurrent Timer Delays
The Power-on-Reset delay, tPOR, is the time period for
the /POR pin to go HIGH once the voltage at the FB pin
exceeds the power good threshold (VFB). A capacitor
connected to CPOR sets the interval and is determined
by using Equation 6:
  t_POR

C_POR

V_TH
I_CPOR
 0.5  C_POR
F
Eq. 6
where the Power-on-Reset threshold (V_TH) and timer
current (I_CPOR) are typically 1.24V and 2.5µA,
respectively.
For the MIC2583/83R, a capacitor connected to CFILTER
is used to set the timer which activates the circuit breaker
during overcurrent conditions. When the voltage across
the sense resistor exceeds the slow trip current-limit
threshold of 50mV, the overcurrent timer begins to
charge for a time period (t_OCSLOW), determined by C_FILTER.
When no capacitor is connected to CFILTER and for the
MIC2582, t_OCSLOW defaults to 5µs. If t_OCSLOW elapses, then
the circuit breaker is activated and the GATE output is
immediately pulled to ground. For the MIC2583/83R, the
following equation is used to determine the overcurrent
timer period, t_OCSLOW.
MIC2582/MIC5283
Table 2. Selected Power-on-Reset and Start-Up Delays
CPOR
0.01µF
tSTART
1.2ms
tPOR
5ms
0.02µF
2.4ms
10ms
0.033µF
4ms
16.5ms
0.05µF
6ms
25ms
0.1µF
12ms
50ms
0.33µF
40ms
165ms
0.47µF
56ms
235ms
1µF
120ms
500ms
Table 3. Selected Overcurrent Timer Delays
CFILTER
680pF
tOCSLOW
130µs
2200pF
420µs
4700pF
900µs
8200pF
1.5ms
0.033µF
6ms
0.1µF
19ms
0.22µF
42ms
0.47µF
90ms
t_OCSLOW

C_FILTER

V_TH
I_TIMER
 0.19  C_FILTER
(F)
Eq. 7
where V_TH, the CFILTER timer threshold, is 1.24V and
I_TIMER, the overcurrent timer current, is 6.5µA. Table 2 and
Table 3 provide a quick reference for several timer
calculations using select standard value capacitors.
May 23, 2014
16
Revision 5.0