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ISL6112EVAL1Z 데이터시트(PDF) 10 Page - Intersil Corporation |
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ISL6112EVAL1Z 데이터시트(HTML) 10 Page - Intersil Corporation |
10 / 31 page 10 FN6456.0 September 28, 2007 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 15m Ω 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 rDS(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. ISL6112 |
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