MIC2593_08 Datasheet, PDF (11/26 Pages) Micrel Semiconductor – Dual-Slot PCI Hot Plug Controller

Micrel, Inc.
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 temporarily 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 Interfaces
The MIC2593 employs two system interfaces: the
hardware Hot Plug Interface (HPI) and the System
Management Interface (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:
1. Fault conditions occurring on each supply.
2. GPI[A/B] pin status.
V_STBY
100k
100k
100k
/INT
MIC2593
47 _SCL
48 _SDA
37 _/INT
39 _A2
40 _A1
41 _A0
MIC2593
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.
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.
MIC2593
45 _AUXENA
42 _AUXENB
44 _ONA
43
ONB
Disabling SMI when
HPI Control is used
Disabling HPI when
SMI Control is used
Figure 6. Input Pin Configuration for
Disabling HPI/SMI Control
September 2008
11
M9999-092208