ISL6112 Datasheet, PDF (10/31 Pages) Intersil Corporation – Dual Slot PCI-Express Power Controller

ISL6112
Functional Description
The ISL6112 protects the power supplies in PCI-Express
systems that utilize hot-pluggable add-in cards. This IC
together with two each of N-Channel and P-Channel
MOSFETs, four current sense resistors and a few external
passive components, provide a compliant hot plug power
control solution to any combination of two PCI-Express X1,
X4, X8 or X16 slots.
The ISL6112 primarily features start-up in-rush current
protection, maximum current regulated (CR) levels for each
of the MAIN and AUX outputs, programmable CR duration
so that both fault isolation protection and imperviousness to
electrical transients are provided. The ISL6112 also offers
input and output voltage supervisory functions and two
operational system interfaces for implementation flexibility.
In-Rush Current Protection
When any electronic circuitry is powered up, there is an
in-rush of current due to the charging of bulk capacitance
that resides across the circuit board’s supply pins. This
transient in-rush current may cause the systems supply
voltages to temporarily droop out of regulation, causing data
loss or system lock-up. The ISL6112 addresses these issues
by limiting the in-rush currents to the PCI-Express add-in
cards, and thereby controlling the rate at which the loads
circuits turn-on. See Figures 2, 3, 4, 5, 6 and 7 for AUX and
MAIN turn-on examples illustrating the current limiting
capabilities across a variety of compensation component
values.
MAIN Supply Overcurrent Protection
For each of the 3VMAIN and 12VMAIN supplies, the current
regulated (CR) levels are set by a sub ohm value sense
resistor. The value for the 12VMAIN is dependant on the size
of the PCI-Express connector (X1, X4/X8 or X16) to be
powered. The voltage across this resistor is compared to a
50mV internal reference providing a nominal CR protection
level which would be set above the maximum specified slot
limits. The 3.3VMAIN supply can use a 15mΩ sense resistor
compared to a 50mV reference to provide a nominal
regulated current limit of 3.3A, as this supply has a common
3A maximum across all slot sizes. For both MAIN supplies,
there is a Way Overcurrent (WOC) shutdown protocol that is
without a CR duration. WOC is invoked if the load current
causes the RSENSE voltage to be >100mV. See Figures 10
and 11.
VAUX Supply Overcurrent Protection
The VAUX load current is internally monitored and controlled
via an internal power FET. This FET has a typical r_DS(ON) of
320mW at a VAUX current of 375mA to minimize distribution
losses to typically <100mV through the IC. Using active
monitoring and control, the ISL6112 provides nominal
limiting to ~1000mA of load current across the temperature
range and for various loading conditions. See Figures 2, 12
and 13 for examples of this performance.
Current Regulation (CR) Duration
The CR duration for each slot is set by an external capacitor
between the associated CFILTER pin and ground. This
feature masks current transients and overcurrents prior to
supply turn-off. Once the CR duration has expired, the IC
then quickly turns-off the associated MAIN outputs via its
external FETs or the failed AUX output, unloading the faulted
load card from the supply voltage rails.
UVLO, Power Good and FAULT
The ISL6112 incorporates undervoltage lock out (UVLO)
protections on each of the four MAIN VIN and two VSTBY
supplies to prevent operation during a ‘brown out’ condition.
Likewise on the outputs are minimum voltage compliances
that must be satisfied for the Power Good output, PWRGD to
be asserted. There is some hysteresis on the UVLO levels
as the voltage on VIN decreases to ensure IC operation
below the minimum operating supply standards. The FAULT
output is asserted (low) whenever there is an OC, OT or UV
condition. The FAULT is cleared once the appropriate enable
is deasserted.
Operational System Interfaces
The ISL6112 employs two system interfaces: the hardware
Hot-Plug Interface (HPI) and the System Management
Interface (SMI). The HPI I/O includes ON, AUXEN, FAULT
and PWRGD]; the SMI I/O consists of SDA, SCL, and INT,
whose signals conform to the levels and timing of the SMBus
specification; see “SMI only Control Applications” on
page 17 The ISL6112 can be operated exclusively from
either the SMI or HPI, 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 ISL6112
accessible by the HPI, the SMI also gives the host access to
the following information from the part:
• Fault conditions occurring on each supply. These faults
include Overcurrent, Over-Temperature and undervoltage
• GPI pin status when using the System
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, AUXEN,
and FORCE_ON) should be configured, as shown in Figure 1
(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 1.
10
FN6456.0
September 28, 2007