MIC2593 Datasheet, PDF (11/26 Pages) STMicroelectronics – Dual-Slot PCI Hot Plug Controller

MIC2593
Functional Description
Hot Swap Insertion
When circuit boards are inserted into systems carrying live
supply voltages (“hot-plugged”), high inrush currents often
result due to the charging of bulk capacitance that resides
across the circuit board’s supply pins. This transient inrush
current can cause the system’s supply voltages to tempo-
rarily go out of regulation, causing data loss or system
lock-up. In more extreme cases, the transients occurring
during a hot plug event may cause permanent damage to
connectors or on-board components.
The MIC2593 addresses these issues by limiting the inrush
currents to the load (PCI Board), and thereby controlling the
rate at which the load’s circuits turn-on. In addition to this
inrush current control, the MIC2593 offers input and output
voltage supervisory functions and current limiting to provide
robust protection for both the system and circuit board.
System Interface
The MIC2593 employs two system interfaces: the hardware
Hot Plug Interface (HPI) and the System Management Inter-
face (SMI). The HPI includes ON[A/B], AUXEN[A/B], as well
as /FAULT[A/B]; the SMI consists of SDA, SCL, and /INT,
whose signals conform to the levels and timing of the SMBus
specification. The MIC2593 can be operated exclusively from
the SMI, or can employ the HPl for power control while
continuing to use the SMI for access to all but the power
control registers.
In addition to the basic power control features of the MIC2593
accessible by the HPI, the SMI also gives the host access to
the following information from the part:
• Fault conditions occurring on each supply
• GPI[A/B] pin status
When using the System Management Interface for power
control, do not use the Hot Plug Interface. Conversely, when
using the Hot Plug Interface for power control, do not execute
power control commands over the System Management
Interface bus (all other register accesses via the SMI bus
remain permissible while in the HPI control mode). When
utilizing the SMI exclusively, the HPI input pins ON[A/B] and
AUXEN[A/B] should be tied to ground as shown below in
Figure 6 (Disabling HPI when SMI control is used). This
configuration safeguards the power slots in the event that the
SMBus communication link is disconnected for any reason.
V_STBY
100k
100k
100k
/INT
MIC2593
47 _SCL
48 _SDA
37 _/INT
39 _A2
40 _A1
41 _A0
Micrel
Additionally, when utilizing the HPI exclusively, the SMBus
(or SMI) will be inactive if the input pins (SDA, SCL, A0, A1,
and A2) are configured as shown in Figure 6 below (disabling
SMI when HPI Control is used).
Power-On Reset and Power Cycling
The MIC2593 utilizes VSTBY[A/B] as the main supply input
source. VTSBY[A/B] is required for proper operation of the
MIC2593 SMBus interface and registers and must be applied
at all times. A Power-On Reset (POR) cycle is initiated after
VSTBY[A/B] rises above its UVLO threshold and remains
valid at that voltage for 500µs. All internal registers are
cleared after POR. If VSTBY[A/B] is recycled, the MIC2593
enters a new power-on reset cycle. VSTBY[A/B] must be the
first supply input applied followed by the MAIN supply inputs
of 12V_IN, 12MV_IN, 5V_IN, and 3V_IN. The MAIN supply inputs
may be applied in any order. The SMBus is ready for access
at the end of the POR interval (500µs after VSTBY[A/B] is
valid). All outputs remain off during t_POR.
Power-Up Cycle
When a slot is off, the 5VGATE and 3VGATE pins are held
low with an internal pull-down current source. When a slot’s
MAIN outputs are enabled by applying a rising-edge signal at
the ON[A/B] control input and all input voltages are above
their respective undervoltage lockout thresholds, all four
main supplies will then execute a controlled turn on. The
5VGATE and 3VGATE pins are each connected to a constant
current source of 25µA, nominal. Both the 5V and 3.3V
outputs act as source followers, where:
V_SOURCE = [V_GATE – V_TH(ON)]
until the associated output is equal to its input. The voltages
on the gates of the external MOSFETs for the 5V and 3.3V
MAIN supplies will continue to rise to approximately 11.5V,
ensuring minimum R_DS(ON) of the MOSFET. Note that a
delay exists between the ON command to a slot and the
appearance of voltage at the slot’s 3.3V or 5V MAIN output.
This delay is the time required to charge the 3V or 5V GATE
output up to the threshold voltage of the external MOSFET
(typically about 4V). For the 5V and 3.3V MAIN supplies, the
source (output) side of the external MOSFET will reach the
drain (input) voltage in a time given by:
( ) ^CGATE ^{× V}DRAIN
( ) ^{tDELAY = IGATE SOURCE}
Table 1 provides a reference list of the expected GATE
output slew rate for the 3.3V and 5V supplies using several
MIC2593
45 _AUXENA
42 _AUXENB
44 _ONA
43
ONB
April 2004
Disabling SMI when
HPI Control is used
Disabling HPI when
SMI Control is used
Figure 6. Input Pin Configuration for Disabling HPI/SMI Control
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