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| Cool-ORing TM PI2002 Series Active ORing Controller IC with Load Disconnect Feature Description The PI2002 Cool-ORingTM solution is a high-speed Active ORing controller IC with a load disconnect feature designed for use with back-to-back Nchannel MOSFETs in redundant power system architectures. The PI2002 Cool-ORing controller enables an extremely low power loss solution with fast dynamic response to fault conditions, critical for high availability systems. The PI2002 controls backto-back MOSFETs providing true bi-directional switch capabilities to protect against both power source and load fault conditions. The gate drive output turns the MOSFETs on in normal steady state operation, while achieving highspeed turn-off during input power source fault conditions, that cause reverse current flow, with auto-reset once the fault clears. The PI2002 has the added benefit of being able to protect against output load fault conditions that may induce excessive forward current and device over-temperature by removing gate drive from the back-to-back MOSFETs with an auto-retry programmable off-time. The back-to-back MOSFETs drain-to-drain voltage is monitored to detect normal forward, excessive forward, light load and reverse current flow. The PI2002 provides an active low fault flag output to the system during fault condition. A temperature www..com sensing function turns off the MOSFETs and indicates a fault if the junction temperature exceeds 145C. Features * * * * * * * * * Power Source & Load Fault Protection Fast Dynamic Response, with 120ns reverse & 150ns forward over-current turn-off delay time 4A gate discharge current Accurate back-to-back MOSFETs drain-to-drain voltage sensing to indicate system level fault conditions Programmable under & over-voltage detection Over temperature fault detection Programmable over-current Gate off time Programmable short circuit load detection function Active low fault flag output Applications * * * * * N+1 Redundant Power Systems Servers & High End Computing Telecom Systems Active ORing with Load Disconnect High current Active ORing Package Options The PI2002 is offered in the following packages: * 3mm x 3mm 10 Lead TDFN package * 8 Lead SOIC Typical Applications: Figure 1a: PI2002 High Side ORing with load disconnect Figure 1b: PI2002 Low Side Disconnect Switch Picor Corporation * picorpower.com PI2002 Rev1.1 Page 1 of 23 Pin Description Pin Name GND GATE Pin Number 10-Pin DFN 1 2 SO-8 1 2 Ground: This pin is ground for the gate driver and control circuitry. Gate Drive Output: This pin drives the gates of the external Back-to-Back Nchannel MOSFETs. Under normal operating conditions, the GATE pin pulls high to 10V (typ) with respect to the SN pin. The controller turns the gate off during all fault conditions except the Low Forward Current condition. Controller Input Supply: This pin is the supply pin for the control circuitry and gate driver. Connect a 1F capacitor between VC pin and the GND pin. Voltage on this pin is limited to 15.5V by an internal shunt regulator. For high voltage auxiliary supply applications connect a shunt resistor between VC and the auxiliary supply. Over-Current Timer Input: Connecting a capacitor ( 20nF) sets the gate off time once an over-current condition is detected. No capacitor on this pin will result in minimum off time, 40s. Pulling this input low will disable Gate drive. Short Circuit Detect Input: This input pin is for setting the load voltage where a short circuit level is defined and detected. To enable slow MOSFET turn-on mode, connect SCD to VC. Connect to load point for minimum threshold (0.335V) or use resistor divider to increase threshold. Grounding pin enables the fast MOSFET turn on mode. This pin is not available in the SO-8 package and the controller is set for low Gate source current, 300A. Fault State Output: This open collector output pulls low 40s after a fault condition occurs. Fault logic inputs are VC Under-Voltage, input Under-Voltage, input OverVoltage, Forward Over-Current, Reverse Current, Low Forward Current (or shorted switches) and Over-Temperature. Leave this pin open if unused. Positive Sense Input & Clamp: Connect SP pin to the input power source side of the MOSFETs. The polarity and magnitude of the voltage difference between SP and SN provides an indication of current flow through the MOSFETs. Negative Sense Input & Clamp: Connect SN to the output load side of the MOSFET. The polarity and magnitude of the voltage difference between SP and SN provides an indication of current flow through the MOSFETs. Input Under-Voltage Input: The UV pin is used detects when the input is less than the Under-Voltage threshold resulting in a low Fault pin. The input voltage UV threshold is programmable through an external resistor divider. During an UnderVoltage fault, the Gate is pulled low. Connect UV to VC to disable this function. Input Over-Voltage Input: The OV pin detects when the input is greater than the Over-Voltage threshold resulting in a low Fault pin. OV "AND" a Forward Current condition turns the MOSFETs off. The input voltage OV threshold is programmable through an external resistor divider. Connect OV to GND to disable this function. This pin is not available in the SO-8 package and OV function is disabled. Description VC 3 3 OCT 4 4 SCD 5 n/a FT SP SN 6 5 7 8 6 7 www..com9 UV 8 OV 10 n/a Package Pin-Outs 10 Lead TDFN (3mm x 3mm) Top view 8 Lead SOIC (5mm x 6mm) Top view Picor Corporation * picorpower.com PI2002 Rev1.1 Page 2 of 23 Absolute Maximum Ratings VC SP, SN, OV, OCT UV, SCD, FT GATE GND Storage Temperature Operating Junction Temperature Lead Temperature (Soldering, 20 sec) ESD Rating -0.3V to 17.3V / 40mA -0.3V to 8.0V / 10mA -0.3V to 17.3V / 10mA -0.3V to 17.3V / 5A -0.3V / 5A peak -65oC to 150oC -40oC to Thermal shutdown 250oC 2kV HBM Electrical Specifications Unless otherwise specified: -40C < TJ < 125C, VC =12V, CVc = 1uF, COCT = 2nF, CGATE = 4nF Parameter VC Supply Operating Supply Range(3) Quiescent Current Clamp Voltage VC Clamp Shunt Resistance VC Under-Voltage Rising Threshold VC Under-Voltage Falling Threshold VC Under-Voltage Hysteresis FAULT www..com Under-Voltage Symbol VVC-GND IVC VVC-CLM RVC VVCUVR VVCUVF VVCUVHS VUVR VUVF VUVHS IUV VOVR VOVF VOV-HS IOV VFTL I FT-LC tFT-DEL TFT (1) Min 4.5 Typ Max 13.2 Units V mA V V V mV Conditions No VC Limiting Resistors Normal Operating Conditions No Faults IVC=10mA Delta IVC=10mA 3.7 15 15.5 4.3 4.0 4.15 150 500 440 -1 500 440 -1 200 20 40 145 -10 475 25 475 25 4.2 16 7.5 4.5 Rising Threshold 540 mV mV mV Under-Voltage Falling Threshold Under-Voltage Threshold Hysteresis Under-Voltage Bias Current Over-Voltage Rising Threshold Over-Voltage Falling Threshold Over-Voltage Threshold Hysteresis Over-Voltage Bias Current Fault Output Low Voltage Fault Output High Leakage Current Fault Delay Time Over Temperature Fault (1) Over Temperature Fault Hysteresis 1 540 A mV mV mV 1 500 10 60 A mV A s C C IFT=2mA, VC>4.5V VFT=14V Includes output glitch filter TFT-HS Picor Corporation * picorpower.com PI2002 Rev1.1 Page 3 of 23 Electrical Specifications Unless otherwise specified: -40C < TJ < 125C, VC =12V, CVc = 1uF, COCT = 2nF, CGATE = 4nF Parameter GATE DRIVER Gate Source Current Gate Source Current Pull Down Peak Current(1) Gate Pull-down Resistance AC Gate Pull-down Voltage Gate Voltage @ VC UVLO Gate Fault Condition Clear Gate to SN Clamp Voltage Gate Voltage High Gate Fall Time Common Mode Input Voltage VC to SN differential(1) Differential Operating Input Voltage SP Input Bias Current SN Input Bias Current SN (SP) Voltage Reverse Comparator www..com Off Threshold Reverse Comparator Hysteresis Reverse Fault to Gate Turn-off Delay Time Forward Comparator On Threshold Forward Comparator Hysteresis Forward Over-Current Comparator Threshold Forward Over-Current Comparator Hysteresis Forward Over-Current to Gate Turnoff Delay (1) (1) (1) Symbol Min Typ Max Units Conditions VG = 1V, Normal Operating Conditions, No Faults VSCD=0V VG = 1V, Normal Operating Conditions, No Faults VSCD=Vc VG = 1.5V @ 25C TRVS-DLY + 50nsec IG=100mA, in reverse fault IG =10A, 1.5 -1.5 -0.30 4.0 0.3 0.2 0.8 0.7 45 10 VC0.25V 10 11 1.2 1 mA mA A V V V % V V 15 5.5 125 ns V V mV A A 5.5 V mV mV ns mV mV mV mV ns -2 5 150 9 -2 120 -4 180 DC Gate Pull-down Voltage to GND DIFFERENTIAL AMPLIFIER AND COMPARATORS 3.5 -37 -6 3 120 5 -3 112 -6 150 VCM =3.3V VCM =3.3V VCM =3.3V VCM =3.3V Picor Corporation * picorpower.com PI2002 Rev1.1 Page 4 of 23 Electrical Specifications Unless otherwise specified: -40C < TJ < 125C, VC =12V, CVc = 1uF, COCT = 2nF, CGATE = 4nF OCT OCT Source Current OCT Clamp Voltage OCT Threshold Voltage High OCT Threshold Voltage Low OCT OFF OCT Gate Drive Disable OCT Sink Current SCD SCD Bias Current SCD Threshold Voltage High ;SCD Threshold Voltage Low SCD Hysteresis Iscd VThSCDR VThSCDF VThSCDR VThSCDF 25 -1 300 340 310 50 75 1 380 A mV mV mV VSP-SN=20mV, VG=1V VSCD=0V VSP-SN=20mV, VG=1V IOCTSC VOCT-CL VOCT-Hi VOCT-Lo TOCT-OFF VOCT-Lo IOCTSK 5 10 2.2 -10 3.2 1.75 0.875 350 500 4.2 A V V V s mV mA VOCT = 1.25V No Fault SP=3.3V, SN=0V SP=3.3V, SN=0V FOC fault condition IOCT = -100uA VOCT =2.25V SP-SN=125mV Note 1: These parameters are not production tested but are guaranteed by design, characterization and correlation with statistical process control. Note 2: Current sourced by a pin is reported with a negative sign. Note 3: Refer to the Auxiliary Power Supply section in the Application Information section for details on the VC requirement to meet the MOSFET Vgs requirement. www..com Picor Corporation * picorpower.com PI2002 Rev1.1 Page 5 of 23 Functional Description: The PI2002 controller IC product is designed to drive back-to-back N-channel MOSFETs in Active ORing applications that also require a load disconnect feature. The PI2002 used with external back-toback MOSFETs can function as an ideal ORing diode in the high-side of a redundant power system coupled with a load disconnect switch, significantly reducing power dissipation and eliminating the need for heatsinking. The PI2002 provides the ability to block current in both directions by driving two MOSFETs in a backto-back configuration as shown in Figure 1a. This configuration offers the ability to protect the load and the MOSFET, by pulling the gate low, during Reverse Current, Forward Over-Current, UnderVoltage, Over-Voltage and Over-Temperature faults. The fault flag is also issued during these fault conditions. Differential Amplifier: The PI2002 integrates a high-speed low offset voltage differential amplifier to sense the difference between the Sense Positive (SP) pin voltage and Sense Negative (SN) pin voltage with high accuracy. The amplifier output is connected to three comparators: Reverse comparator, Forward comparator, and Forward over-current comparator. Reverse Current Comparator: RVS The reverse current comparator provides the most critical function in the controller, detecting negative voltage caused by reverse current. When the SN pin is 6mV higher than the SP pin, the reverse comparator will enable the gate discharge circuit and www..com turn off the MOSFETs in typically 120ns. The reverse comparator has typically 3mV of hysteresis referenced to SP-SN. Forward Current Comparator: FWD The FWD comparator detects when a forward current condition exists and SP is 5mV (typical) positive with respect to SN. When SP-SN is less than 5mV it will indicate a fault condition on the FT pin during a light load while maintaining gate drive to the MOSFETs. The PI2002 will initiate a gate shutdown if the Forward "AND" the over-voltage (OV) condition are true. Forward Over-Current Comparator: FOC The FOC comparator indicates an excessive forward current condition when SP is 112mV higher than SN. The PI2002 controller will initiate a fault condition when the GATE output voltage is more than 45% of the regulated gate to SN voltage and SP-SN is higher than 112mV, the MOSFETs will turn off then Picor Corporation * picorpower.com retry after a controlled off-time determined by the capacitor value on the OCT input pins. Over-Current Timer: OCT OCT off-time is set by the OCT a capacitor as shown in Figure 3. The OCT block will control the off-time of the MOSFETs after a FOC fault condition has occurred. The equivalent block diagram is shown in Figure 2. As the Set input at the OCT timer goes high, Out will go low, pulling the GATE pin low. At the same time a one shot of 40s discharges the OCT capacitor, then releases it charging the capacitor again. Out and GATE pins stay low until the OCT pin reaches the OCT high threshold (VOCT-Hi), then Out goes high and the GATE pin sources current to charge the MOSFET gates. As soon as the GATE voltage reaches 45% of the GATE to SN clamp voltage, or 45% of {VC-V(SN) -0.25V}, the Clamp Detector asserts a low signal again at the NOR gate. If FOC is still low then the GATE pin will be pulled low and will start a new off-time cycle of the OverCurrent timer. Figure 2: OCT block and timing diagram PI2002 Rev1.1 Page 6 of 23 when VC is lower than the VC Under-Voltage Threshold. UV: The Under-Voltage (UV) input trip point can be programmed through an external resistive divider to monitor the input voltage. The UV comparator initiates a gate low condition turning the MOSFETs off and initiates a fault condition pulling the FT pin low, when UV falls below the Under-Voltage Falling Threshold. OV: The Overvoltage (OV) input trip point (for 10L-TDFN package only) can be programmed through an external resistive divider to monitor the input voltage. The OV comparator initiates a fault condition and pulls the FT pin low when OV rises above the Overvoltage Rising Threshold. The PI2002 will turn the Gate output off if the OV and the Forward Current conditions are both true. The low resistance redundant paths of an Active ORing system tend to force all the input sources to the same voltage making it difficult to identify the noncompliant source. By ANDing OV with the Forward Current Threshold the noncompliant source is identified and disconnected from the system. The OV pin is not available in the SO-8 package version and is disabled. Over-Temperature Detection: The internal Over-Temperature block monitors the junction temperature of the controller. The OverTemperature threshold is set to 145C with -10C of hysteresis. When the controller temperature exceeds this threshold, the Over-Temperature circuit pulls GATE pin low and initiates a fault condition and pulls the FT pin low. By maintaining proper thermal matching between the controller and the power MOSFETs, this function can be used to protect the MOSFETs from thermal runaway conditions. Gate Driver: The gate driver (GATE) output is configured to drive external N-channel MOSFETs. In the high state, the gate driver applies a current source that is dependent on the SCD pin voltage. The controller regulates the gate voltage to 10V above the SN pin when the VC voltage is 10.5V higher than the SN pin. Otherwise the gate voltage (VG) to VSN will be {VG-SN = VC - VSN - 0.5V}. Note that VC is the controller internal regulated voltage. When a reverse current fault is initiated, the gate driver pulls the GATE pin low and discharges the FET gate with 4A peak capability. PI2002 Rev1.1 Page 7 of 23 Figure 3: OCT Off time vs. OCT capacitor value Short Circuit Detect: SCD This comparator block input (for 10L-TDFN package only) can be connected to the load directly or programmed to a higher voltage with a resistor divider. The SCD function allows the user to define the (Hard Short) voltage level expected if a non-ideal short circuit occurs at the load. To prevent damage of the MOSFETs under this condition (VSCD<335mV) the gate charge current (IG-SC) is increased by a factor of approximately 5 times resulting in fast charging of the MOSFET gates. This feature enables the capability to distinguish between a faulted load versus powering capacitive and low resistive loads without entering the OCT mode. This pin can be grounded to provide a fast gate charging www..com or pulled to VC for lower gate current to drive highly capacitive loads with resulting slow gate charge under the fault condition. If the resulting temperature rise of the MOSFETs is thermally coupled to the controller, invoking a thermal shutdown, the thermal time constant of the system will determine the average duty cycle further protecting the MOSFETs. The SCD pin is not available in the SO-8 package version and is internally preset for slow gate charge, where the Gate source current is 300A. VC and Internal Voltage Regulator: The PI2002 has a separate input (VC) that provides power to the control circuitry and the gate driver. An internal regulator clamps the VC voltage to 15.5V. For high side applications, the VC input should be high enough above the bus voltage to properly enhance the external N-channel MOSFETs. The internal regulator circuit has a comparator to monitor VC voltage and initiates a FAULT condition Picor Corporation * picorpower.com When the input source voltage is applied and before the MOSFET is fully enhanced, a voltage greater than the Forward Over-Current (FOC) Threshold may be present across the MOSFET. To avoid an erroneous FOC detection, a VGS detector blanks the FOC and FWD comparators from initiating a fault, until the GATE pin reaches 45% of VG-CLMP. If VC is too low to establish the Gate Clamp condition the reference for detection is 45% of {VC-V(SN) 0.25V}. The GATE pin pulls low under the following fault conditions: * * * * * * Reverse Current Forward Over-Current "AND" clamp detector is cleared Over Temperature Input Under-Voltage Input Over-Voltage "AND" nominal Forward Current VC pin Under-Voltage will be pulled low when any of the following faults occurs: * Reverse Current * Forward Over-Current "AND" clamp detector is cleared * Forward Low Current "AND" clamp detector is cleared * Over Temperature * Input Under-Voltage * Input Over-Voltage "AND" nominal Forward Current * VC pin Under-Voltage The Forward Current fault condition occurs when the MOSFETs gates are high but are not conducting a significant level of forward current or may indicate the MOSFETs are shorted either internally or externally (VD1-D2 < 6mV). The VGS detector prevents FOC or FWD from initiating a fault when the MOSFET gate is low. The gate to SN voltage has to reach sufficient voltage to establish the Rds(on) condition before these faults are detected. Fault: The fault circuit output is an open collector with 40s delay to prevent any false triggering. The FT pin www..com Picor Corporation * picorpower.com PI2002 Rev1.1 Page 8 of 23 Figure 4: PI2002 Controller Internal Block Diagram (10 Lead TDFN package pin out shown) www..com Figure 5: Comparator hysteresis, values are for reference only, please refer to the electrical specifications Picor Corporation * picorpower.com PI2002 Rev1.1 Page 9 of 23 www..com Figure 6: PI2002 State Diagram Picor Corporation * picorpower.com PI2002 Rev1.1 Page 10 of 23 www..com Figure 7: Timing diagram for two PI2002 controllers in an Active ORing and Load Disconnect application Picor Corporation * picorpower.com PI2002 Rev1.1 Page 11 of 23 Typical Characteristics: Figure 8: Controller bias current vs. temperature Figure 9: VC UVLO threshold vs. temperature www..com Figure 10: Reverse condition gate turn-off delay time vs. temperature. Figure 11: Forward Over-Current condition gate turn-off delay time vs. temperature. Figure 12: Reverse comparator threshold vs. temperature. VCM: Common Mode Voltage. Figure 13: FOC comparator threshold vs. temperature. VCM: Common Mode Voltage. Picor Corporation * picorpower.com PI2002 Rev1.1 Page 12 of 23 Typical Characteristics: Continued Figure 14: Gate to SP clamp voltage vs. temperature. Figure 15: Gate output source current vs. temperature Figure 16: Gate output source current vs. temperature www..com Picor Corporation * picorpower.com PI2002 Rev1.1 Page 13 of 23 Application Information: The PI2002 is designed to replace ORing diodes and load disconnect switches in high current redundant power architectures. Replacing a traditional diode with a PI2002 controller IC and two low on-state resistance back-to-back N-channel MOSFETs will result in significant power dissipation reduction as well as board space reduction, efficiency improvement, input power source and output load protection and additional protection features. This section describes in detail the procedure to follow when designing with the PI2002 Active ORing controller and two back-toback N-Channel MOSFETs. Two design examples are presented, one Active ORing with load disconnect design example and one low side disconnect switch example. Fault Indication: FT output pin is an open collector and should be pulled up to the logic voltage or to the controller VC via a resistor (10K) Over-Current Timer: OCT Connect a capacitor, equal or less than 20nF, to set off time after over-current shutdown (see Figure 3). Short Circuit Detect: SCD Connect SCD pin to VC to avoid inrush current into a high capacitive load, or connect SCD to GND pin for fast MOSFET turn on. Note: The SCD pin is not available in the SO-8 package and the controller is set for low Gate source current, 300A. Auxiliary Power Supply (Vaux): Vaux is an independent power source required to www..com to the PI2002 VC input. The Vaux supply power voltage should be higher than Vin (redundant power source output voltage) by the required gate-to-source voltage (Vgs) to fully enhance the MOSFET, plus 0.5V maximum gate to VC headroom (VHDVC-G) Vaux = Vin + Vgs + VHDVC-G Where, VHDVC-G is defined as the 0.5V maximum drop from VC in the Gate Voltage High (VG) specification in the Gate Driver section of the Electrical Specification. For example, if the bus voltage is 3.3V and the MOSFET requires 4.5V of Vgs to fully enhance the MOSFET, then Vaux should be at least 3.3V + 4.5V + 0.5V = 8.3V. If Vaux is higher than 15V then a bias resistor (Rbias) is required, and should be connected between the PI2002 VC pin and Vaux. The resistor is selected based on the input voltage range. Minimize the resistor value for low Vaux voltage levels to avoid a voltage drop that may reduce the VC voltage lower than required to drive the gate of the MOSFET. Select the value of Rbias using the following equations: Rbias = Vaux min - VC clamp IC max (Vaux max - VC clamp ) 2 Rbias maximum power dissipation: Pd Rbias = Rbias Rbias maximum power dissipation is at maximum input voltage and minimum clamp voltage (15V). Where: Vauxmin : Vaux minimum voltage Vauxmax : Vaux maximum voltage VC Clamp : Controller clamp voltage, 15.5V IC max : Controller maximum bias current (4.2mA) N-Channel MOSFET Selection: There are several factors that affect the MOSFET selection including cost, on-state resistance (Rds(on)), current rating, power dissipation, thermal conductivity, drain-to-source breakdown voltage (BVdss), gate-tosource voltage rating (Vgs), and gate threshold voltage (Vgs(TH)). The first step is to select suitable MOSFETs based on the BVdss requirement for the application. The BVdss voltage rating should be higher than the applied Vin voltage plus expected transient voltages. Stray parasitic inductance in the circuit can also contribute to significant transient voltage conditions, particularly during MOSFET turn-off after a reverse current fault has been detected. In Active ORing applications when one of the input power sources is shorted, a large reverse current is sourced from the circuit output through the MOSFET. Depending on the output impedance of the system, the reverse current may reach over 60A in some conditions before the MOSFET is turned off. Such high current conditions will store energy even in a small parasitic element. For example, a 1nH parasitic inductance with 60A reverse current will store 1.8J (1/2Li2). When the MOSFET is turned off, the stored energy will be released and will produce high negative voltage ringing at the MOSFETs input. This event will create a high voltage difference across the MOSFETs. Note: Since the two MOSFETs are connected in to back-toback configuration, the maximum breaking voltage is BVdss of one MOSFET plus one diode forward voltage. PI2002 Rev1.1 Page 14 of 23 Picor Corporation * picorpower.com The MOSFET current rating and maximum power dissipation are closely related. Generally the lower the MOSFET Rds(on), the higher the current capability and the lower the resultant power dissipation. This leads to reduced thermal management overhead, but will ultimately be higher cost compared to higher Rds(on) parts. It is important to understand the primary design goal objectives for the application in order to effectively trade off the performance of one MOSFET versus another. Power dissipation in active ORing circuits is derived from the total source current and the on-state resistance of the selected MOSFET. MOSFET power dissipation: should be adequate for protecting MOSFETs with maximum Vgs ratings of 12V or greater. OV/UV resistor selection: The UV and OV comparator inputs are used to monitor the input voltage and will indicate a fault condition when this voltage is out of range. The UV and OV pins can be configured in two different ways, either with a divider on each pin, or with a threeresistor divider to the same node, enabling the elimination of one resistor. Under-Voltage is monitored by the UV pin input and Over-Voltage is monitored with the OV pin input. Note: The OV pin is not available in the SO-8 package and OV function is disabled. The Fault pin ( FT ) will indicate a fault (active low) when the UV pin is below the threshold or when the OV pin is above the threshold. The UV and OV thresholds are 0.50V typical with 25mV hysteresis and their input current is less than 1A. It is important to consider the maximum current that will flow in the resistor divider and maximum error due to UV and OV input current. Set the resistor current to 100A or higher to maintain 1% accuracy for UV and OV due to the bias current. The three-resistor voltage divider configuration for both UV and OV to monitor the same voltage node is shown in Figure 17: Pd MOSFET = Is 2 Rds(on) Where : Is : Source Current Rds(on) : MOSFET on-state resistance Note: In the calculation use Rds(on) at maximum MOSFET temperature because Rds(on) is temperature dependent. Refer to the normalized Rds(on) curves in the MOSFET manufacturers datasheet. Some MOSFET Rds(on) values may increase by 50% at 125C compared to values at 25C. The Junction Temperature rise is a function of power dissipation and thermal resistance. Ra = V (OVTH ) I Ra TriseMOSFET = RthJA PdMOSFET = RthJA Is 2 Rds(on) , Where: RthJA : Junction-to-Ambient www..com thermal resistance Figure 17: UV & OV three-resistor divider configuration. Rds(on) and PI2002 sensing: The PI2002 senses voltage across the ORing MOSFETs via the SP and SN pins to determine the status of the current through the MOSFETs. Refer Figure 1a. When the MOSFETs are fully enhanced, the total drop across the back to back MOSFETs (and between SP and SN) is; VSD=Rds(on)*Is * 2. The reverse current threshold is set for -6mV and when the differential voltage between the SP & SN pins is more negative than -6mV, i.e. SP-SN-6mV, the PI2002 detects a reverse current fault condition and pulls the MOSFET gate pin low to turn off the MOSFET and prevent further reverse current. The reverse current fault protection disconnects the power source fault condition from the redundant bus and allows the system to keep running. The GATE pin output voltage is clamped to 11V maximum with respect to the SN pin. The 11V clamp Picor Corporation * picorpower.com Ra = V (OVTH ) I Ra V (OVTH ) I Ra Set Ra value based on system allowable current I Ra Ra = V (OV ) Rb = Ra * V (UV ) - 1 V (UV ) Rc = (Ra + Rb ) * - 1 V TH Where: V (UVTH ) : UV threshold voltage V (OVTH ) : OV threshold voltage V(UV) PI2002 : UV voltage Rev1.1 Page 15 of 23 I Ra : Ra current. Alternatively, a two-resistor voltage divider configuration can be used and is shown in (Figure 18). Typical application Example 1: High Side Active ORing: Requirement: Redundant Bus Voltage = 3.3V Load Current = 15A (assume through each redundant path) Maximum Ambient Temperature = 75C Auxiliary Voltage = 12V (11V to 13V) Solution: 1. A single PI2002 with two suitable external MOSFETs for each redundant 3.3V power source should be used, configured as shown in the circuit schematic in Figure 19 2. Select a suitable N-Channel MOSFET: Most industry standard MOSFETs have a Vgs rating of +/-12V or higher. Select an N-Channel MOSFET with a low Rds(on) which is capable of supporting the full load current with some margin, so a MOSFET capable of at least 18A in steady state is reasonable. An exemplary MOSFET having these characteristic is FDS6162N7 from Fairchild. From FDS6162N7 datasheet: * N-Channel MOSFET * VDS= 20V * ID = 23A continuous drain current * VGS(MAX)= 12V * RJA= 40C/W * RDS(on)=2.9m typical at ID=23A, VGS4.5V, TJ=25C Reverse current threshold is: Figure 18: Two-resistor divider configuration The UV resistor voltage divider can be obtained from the following equations: R1UV = V (UVTH ) I RUV Set R1UV value based on system allowable current I RUV 100 A V (UV ) R 2UV = R1UV V (UV ) - 1 TH Where: V (UVTH ) : UV threshold voltage : R1UV current I RUV R1UV = V (UVTH ) I RUV Set R1OV value based on system allowable current I RUV 100 A V (OV ) R 2 OV = R1OV V (OV ) - 1 TH www..com Where: I RVS = V RVS -TH - 6mV = -1.03 A = 2 * Rds(on) 2 * 2.9m V FOC -TH 114mV = = 19.66 A 2 * Rds(on) 2 * 2.9m Forward over-current threshold is: V (OVTH ) : OV threshold voltage I ROV : R1OV current I FOC = Power dissipation final junction temperature for each MOSFET: Rds(on) is 3.5m maximum at 25C & 4.5Vgs and will increase as the temperature increases. Add 25C to maximum ambient temperature to compensate for the temperature rise due to power dissipation. At 100C (75C + 25C) Rds(on) will increase by 28%. Rds(on) = 3.5m 1.28 = 4.48m maximum at 100C Trise= RthJA Is2 Rds(on) Maximum Junction temperature TJ max = TA + Trise 40C TJ max = 75C + (15A)2 4.48m = 115C W Picor Corporation * picorpower.com PI2002 Rev1.1 Page 16 of 23 Recalculate based on calculated Junction temperature, 115C. At 115C Rds(on) will increase by 32%. V (OV ) 3.6V Rb = Ra V (UV ) - 1 = 2.49k 3.0V - 1 = 498 or 499 1% Rds(on) = 3.5m 1.32 = 4.62m 40C TJ max = 75C + (15A)2 4.62m = 116.5C W 3. Vaux: Make sure Vaux voltage is higher than Vin (power source output) by the voltage required to fully enhance the MOSFET. Minimum required Vaux = Vin + Vgs + 0.5V = 3.3V + 4.5V + 0.5V = 8.3V. Since 8.3V is less than the 11V minimum Aux supply voltage, there is sufficient voltage available to drive the gate of the MOSFET. 4. SP and SN pins: Connect the SP pin to the MOSFET drain pin at the input and the SN pin to the MOSFET drain pin at the load side. 5. OCT pin: Connect 18nF capacitor between OCT pin and the GND pin to achieve the maximum off time after forward over-current condition occurs. 6. SCD pin: Connect the SCD pin to the GND pin for fast MOSFET enhancement. 7. V (UV ) Rc = (Ra + Rb ) V (UV ) - 1 TH 3.0V = (2.49k + 499 ) - 1 = 14.95k 500mV or 15k 1% FT pin: Connect to the logic input and to the logic power supply via a 10K resistor. 8. Program UV and OV to monitor input voltage: Program UV at 3.0V and OV at 3.6V Use the three-resistor divider configuration: I Ra = 200A V (UVTH ) 500mV = = 2.5k or 2.49k 1% I Ra 200A www..com Ra = Figure 19: High side Active ORing function. Figure 20: PI2002 performance in example 1, applied short at Vin1. Picor Corporation * picorpower.com PI2002 Rev1.1 Page 17 of 23 Typical application Example 2: Low side disconnect switch Requirement: Bus Voltage = -48V (-36V to -60V, 100V for 100ms transient) Maximum operating load current = 5A Load current shutdown set at = 6A Maximum Ambient Temperature = 60C Solution: 1. A PI2002 with a suitable MOSFET for -48V power source should be used and configured as shown in Figure 22. The VC is biased from the return line through a bias resistor. 2. Select a suitable N-Channel MOSFET: Select the N-Channel MOSFET with voltage rating higher than the input voltage, Vin, plus any expected transient voltages, with a low Rds(on) that is capable of supporting the full load current with margin. For instance, a 100V rated MOSFET with 10A current capability is suitable. An exemplary MOSFET having these characteristic is Si4486EY from Vishay Siliconix. From Si4486EY datasheet: * * * * * * N-Channel MOSFET VDS= 100V ID = 23A continuous drain current at 125C VGS(MAX) = 20V RJA= 50C/W RDS(on)=20m typical at VGS=10V, TJ=25C At 111C Rds(on) will increase by 71%. Rds(on) = 25m 1.71 = 4.75m maximum at 111C 50C (5.0 A)2 42.75m = 113C TJ max = 60C + W Vaux: Connect each controller to the return path with a separate bias resistor, Rbias. To reduce Rbias power dissipation, VC clamp is selected at 13V which is less than the actual PI2002 clamp voltage (15V typical). 13V is higher than PI2002 maximum gate clamp voltage (11V). Rbias = Vaux min - VC clamp IC max = 36V - 13V = 5.48K 4.2mA or 5.49K Rbias maximum power dissipation is at maximum input voltage and minimum clamp voltage Pd Rbias = (Vaux max - VC clampMIN ) 2 Rbias = (60V - 15V ) 2 = 369mW 5.49 K 3. Select sense resistor: Sense resistor is selected based on load current shutdown. Where R Sense = V FOC -TH 114mV = = 19m I Shutdown 6A Select 20m resistor 20m Sense Resistor power dissipation at maximum operating current www..com Reverse current threshold is: Pd RSense = I max * R Sense = (5 A) 2 20m = 0.5W As an exemplary selected 1206 20m/1W/1% sense resistor from Vishay-Dale: Part Number: WSL1206R0200FEK Maximum current turn off: 2 Is.reverse = Vth.reverse - 6mV = = -300mA Rds(on) 20m Power dissipation: Rds(on) is 25m maximum at 25C & 10Vgs and will increase as the temperature increases. Add 40C to maximum ambient temperature to compensate for the temperature rise due to power dissipation. At 100C (60C + 40C) Rds(on) will increase by 63%. Isd MAX = V FOC -TH - MAX 121mV = = 6.05 A R Sense 20m V FOC -TH - MIN 107mV = = 5.35 A R Sense 20m Minimum current turn off: Rds(on) = 25m 1.63 = 41m maximum at 100C Maximum Junction temperature Isd MIN = 50C (5.0 A)2 41m = 111C TJ max = 60C + W Recalculate based on calculated Junction temperature, 111C. Picor Corporation * picorpower.com 4. SP and SN pins: Connect the SP pin to the MOSFET source and controller GND pin, and connect the SN pin to Vin- and the drain of the MOSFET. PI2002 Rev1.1 Page 18 of 23 5. OCT pin: Connect 18nF capacitor between OCT pin and the GND pin to achieve the maximum off time after forward over-current condition occurs. 6. SCD pin: Connect the SCD pin to the VC pin for slow MOSFET turn on to avoid over-current shutdown due to inrush current. 7. FT pin: Connect the FT pin to logic input and to the logic power supply or to the VC pin via a resistor. UV and OV inputs: UV and OV are not used in this example. Connect UV pin to VC pin and OV pin to GND pin do not leave them unconnected. Figure 22: PI2002 (10L-TDFN package) in low side disconnect switch application www..com Picor Corporation * picorpower.com PI2002 Rev1.1 Page 19 of 23 Layout Recommendation: Use the following general guidelines when designing printed circuit boards. An example of the typical land pattern for a TDFN PI2002 and SO-8/PowerPak MOSFET is shown in Figure 23: * It is best to connect the gate of the MOSFETs to the GATE pin of the controller with a short and wide trace. The GND pin of the controller carries high peak current and it should be returned to the ground plane through a low impedance path. Connections from the SP and SN pins to Vin and Vout respectively very close to the MOSFETs, SP to Q1 drain pin and SN to Q2 drain pin. The VC bypass capacitor should be located as close as possible to the VC and GND pins. Place the PI2002 and VC bypass capacitor on the same layer of the board. The VC pin and CVC PCB trace should not contain any vias. Connect all MOSFET Q1 Drain pins together with a wide trace to reduce trace parasitics and to accommodate the high current input. Similarly, connect all MOSFET Q2 Drain pins together with a wide trace to accommodate the high current output. Q1 and Q2 Sources should * be very close from each other and their pins should be connected with a short trace. Connect the power source very close to the Q1 drain connection to reduce the effects of stray parasitics. If a short trace is not possible, connect C3 (typically 1F) as shown in Figure 23. * * * * Figure 23: PI2002 and MOSFET layout recommendation www..com Figure 24: PI2002 Mounted on PI2002-EVAL1 Please visit www.picorpower.com for information on PI2002-EVAL1 Picor Corporation * picorpower.com PI2002 Rev1.1 Page 20 of 23 Package Drawings: 8 Lead SOIC www..com Picor Corporation * picorpower.com PI2002 Rev1.1 Page 21 of 23 Package Drawings: 10 Lead TDFN www..com Ordering Information Part Number PI2002-00-QEIG PI2002-00-SOIG Package Transport Media 3mm x 3mm 10L TDFN 8L SOIC Tape &Reel Tape &Reel Picor Corporation * picorpower.com PI2002 Rev1.1 Page 22 of 23 Warranty Vicor products are guaranteed for two years from date of shipment against defects in material or workmanship when in normal use and service. This warranty does not extend to products subjected to misuse, accident, or improper application or maintenance. Vicor shall not be liable for collateral or consequential damage. This warranty is extended to the original purchaser only. EXCEPT FOR THE FOREGOING EXPRESS WARRANTY, VICOR MAKES NO WARRANTY, EXPRESS OR LIMITED, INCLUDING, BUT NOT LIMITED TO, THE WARRANTY OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Vicor will repair or replace defective products in accordance with its own best judgment. For service under this warranty, the buyer must contact Vicor to obtain a Return Material Authorization (RMA) number and shipping instructions. Products returned without prior authorization will be returned to the buyer. The buyer will pay all charges incurred in returning the product to the factory. Vicor will pay all reshipment charges if the product was defective within the terms of this warranty. Information published by Vicor has been carefully checked and is believed to be accurate; however, no responsibility is assumed for inaccuracies. Vicor reserves the right to make changes to any products without further notice to improve reliability, function, or design. Vicor does not assume any liability arising out of the application or use of any product or circuit; neither does it convey any license under its patent rights nor the rights of others. Vicor general policy does not recommend the use of its components in life support applications wherein a failure or malfunction may directly threaten life or injury. Per Vicor Terms and Conditions of Sale, the user of Vicor components in life support applications assumes all risks of such use and indemnifies Vicor against all damages. Vicor's comprehensive line of power solutions includes high density AC-DC and DC-DC modules and accessory components, fully configurable AC-DC and DC-DC power supplies, and complete custom power systems. Information furnished by Vicor is believed to be accurate and reliable. However, no responsibility is assumed by Vicor for its use. Vicor components are not designed to be used in applications, such as life support systems, wherein a failure or malfunction could result in injury or death. All sales are subject to Vicor's Terms and Conditions of Sale, which are available upon request. Specifications are subject to change without notice. www..com Vicor Corporation 25 Frontage Road Andover, MA 01810 USA Picor Corporation 51 Industrial Drive North Smithfield, RI 02896 USA Customer Service: custserv@vicorpower.com Technical Support: apps@vicorpower.com Tel: 800-735-6200 Fax: 978-475-6715 Picor Corporation * picorpower.com PI2002 Rev1.1 Page 23 of 23 |
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