MIC2593_08 Datasheet, PDF (13/26 Pages) Micrel Semiconductor – Dual-Slot PCI Hot Plug Controller

Micrel, Inc.
trip the circuit breaker, but only when the MAIN outputs
are enabled (to signal a supply input brown-out condition).
The VAUX[A/B] outputs have their own separate circuit
breaker functions. VAUX[A/B] do not incorporate a fast-
trip threshold, but instead regulate the output current into
a fault to avoid exceeding their operating current limit. The
circuit breaker will trip due to overcurrents on VAUX[A/B]
when the overcurrent fault timer (t_FLT) expires. This use of
the overcurrent timer prevents the circuit breaker from
tripping prematurely due to brief current transients.
Following a fault condition, the outputs can be turned on
again via the ON inputs (if the fault occurred on one of the
MAIN outputs), via the AUXEN inputs (if the fault occurred
on the AUX outputs), or by cycling both ON and AUXEN
(if faults occurred on both the MAIN and AUX outputs). A
fault condition can alternatively be cleared under SMI
control of the ENABLE bits in the CNTRL[A/B] registers
(See Register Bits D[1:0]). When the circuit breaker trips,
/FAULT[A/B] will be asserted if the outputs were enabled
through the Hot Plug Interface inputs. At the same time,
/INT will be asserted (unless interrupts are masked). Note
that /INT is de-asserted by writing a Logic 1 back into the
respective fault bit position(s) in the STAT[A/B] register or
the Common Status Register. The response time (t_FLT) of
the MIC2593’s primary overcurrent detector is set by
external capacitors at the CFILTER[A/B] pins to GND. For
Slot A, CFILTER[A] is located at Pin 2; for Slot B,
CFILTER[B] is located at Pin 35. For a given response
time, the value for CFILTER[A/B] is given by.
CFILTER[A/B](μF) = ^{tFLT[A/B] (ms) × IFILTER (μA)}
V_FILTER (V) × 10³
3VAUX_UV[A/B]⁽¹⁾
MIC2593
where t_FLT[A/B] is the selected overcurrent response time
and I_FILTER and V_FILTER are specified in the “Electrical
Characteristics” table.
Thermal Shutdown
The internal +12V, –12V, and V_AUX MOSFETs are
protected against damage not only by current limiting, but
by dual-mode overtemperature protection as well. Each
slot controller on the MIC2593 is thermally isolated from
the other. Should an overcurrent condition raise the
junction temperature of one slot’s controller and internal
pass elements to 140°C, all of the outputs for that slot
(including V_AUX) will be shut off, and the slot’s /FAULT
output will be asserted. The other slot’s operation will
remain unaffected. However, should the MIC2593’s
overall die temperature exceed 160°C, both slots (all
outputs, including V_AUXA and V_AUXB) will be shut off,
whether or not a current limit condition exists. A 160°C
overtemperature condition additionally sets the
overtemperature bit (OT_INT) in the Common Status
Register.
Output Power-Good Status
For the MIC2593, “Power-is-Good” is valid on a slot when
the outputs of the four MAIN supplies (12V, –12V, 5V, and
3.3V) and the auxiliary supply output are all above their
respective power-good thresholds specified in the
“Electrical Characteristics” table. The power-good status
of either slot is verified by polling the CNTRL[A/B]
Register Bits D[7:6]. CNTRL[A/B] Register Bits D[7] and
D[6] indicate output power-good status for the AUX supply
and MAIN supplies, respectively. Figure7 below illustrates
an equivalent logic circuit that determines the output
power-good status for the MAIN and AUX supplies.
V_STBY[A/B]
AUX[A/B]PG⁽²⁾
September 2008
12VOUT_UV[A/B]⁽¹⁾
3VOUT_UV[A/B]⁽¹⁾
V_STBY[A/B]
MAIN[A/B]PG⁽³⁾
Notes:
1. Internal flag
2. CNTRL[A/B] Register Bit D[7]
3. CNTRL[A/B] Register Bit D[6]
Figure 7. Power-Good Status Logic Diagram
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