MIC2090/MIC2091 Current Limiting Power Distribution Switches General Description Features The MIC2090 and MIC2091 are high-side MOSFET power switches optimized for general-purpose 50mA or 100mA low power distribution in circuits requiring over-current limiting and circuit protection. Typical applications for these parts are for switching power in USB ports, portable consumer items, camera and camcorder motor protection, thermal printer head protection, and many other low current-load switching applications. * * * * The MIC2090 and MIC2091 come in two versions: autoretry current limit and output latch off on an over current fault. The MIC2090 and MIC2091 are offered in a space saving 5-pin SOT-23 package with an operating junction temperature range of -40C to +125C. Data sheets and support documentation can be found on Micrel's web site at: www.micrel.com. * * * * * * * * * 1.8V to 5.5V supply voltage 790 m typical RDSON at 3.3V MIC2090 is rated for 50mA minimum continuous current MIC2091 is rated for 100mA minimum continuous current Reverse current blocking (OGI) 20ns super fast reaction time to hard short at output 10ms fault flag delay (tD_FAULT/) eliminates false assertions Auto-retry overcurrent and short-circuit protection (-1 version) Latch-off on current limit (-2 version) Thermal shutdown Fault status flag indicates: over-current, overtemperature, or UVLO Under-voltage lockout (UVLO) Low quiescent current Applications * * * * * * USB peripherals Camcorder DSC MP3/iPod SD protection USB low-power hub _________________________________________________________________________________________________________________________ Typical Application MIC2091 USB Power Switch Startup into Short Circuit Micrel Inc. * 2180 Fortune Drive * San Jose, CA 95131 * USA * tel +1 (408) 944-0800 * fax + 1 (408) 474-1000 * http://www.micrel.com July 2011 M9999-070611-B Micrel, Inc. MIC2090/MIC2091 Ordering Information Marking Current Limit Current-Limit Recovery Junction Temperature Range Package MIC2090-1YM5 L1K 50mA Auto-Retry -40C to +125C SOT-23-5 MIC2091-1YM5 M1K 100mA Auto-Retry -40C to +125C SOT-23-5 MIC2090-2YM5 L2K 50mA Latch-Off -40C to +125C SOT-23-5 MIC2091-2YM5 M2K 100mA Latch-Off -40C to +125C SOT-23-5 Part Number Pin Configuration 5-Pin SOT-23 (M5) Pin Description Pin Number Pin Name Pin Function 1 VIN Supply (Input): +1.8V to +5.5V. Provides power to the output switch and the MIC2090/MIC2091 internal control circuitry. 2 GND Ground. 3 EN Enable (Input): Active-high TTL compatible control input. A high signal turns on the internal switch and supplies power to the load. This pin cannot be left floating. Fault Status (Output): Open drain output. Can be connected to other open drain outputs. Must be pulled high with an external resistor. When EN=0, FAULT/ pin is high 4 FAULT/ When EN=1, a low on the FAULT/ pin indicates one or more of the following conditions: 1. The part is in current limit and is turned off. 2. The part is in thermal limit and is turned off. 3. The part is in UVLO 5 July 2011 VOUT Switched Output (Output): The voltage on this pin is controlled by the internal switch. Connect the load driven by the MIC2090/MIC2091 to this pin. 2 M9999-070611-B Micrel, Inc. MIC2090/MIC2091 Absolute Maximum Ratings(1) Operating Ratings(2) Supply Voltage (VIN) ..................................... -0.3V to +6.0V Output Voltage (VOUT). ................................. -0.3V to +6.0V FAULT/ Pin Voltage (VFAULT/) ....................... -0.3V to +6.0V FAULT/ Pin Current (I FAULT/) .......................................25mA EN Pin Voltage (VEN)........................... -0.3V to (VIN + 0.3V) Power Dissipation (PD) ..............................Internally Limited Maximum Junction Temperature (TJ)......................... 150C Storage Temperature (TS)......................... -65C to +150C Lead Temperature (soldering, 10s)............................ 260C ESD HBM Rating(3)......................................................... 3kV ESD MM Rating(3) .........................................................200V Supply Voltage (VIN)..................................... +1.8V to +5.5V Output Voltage (VOUT) .................................. +1.8V to +5.5V EN Pin Voltage (VEN).............................................. 0V to VIN FAULT/ Pin Voltage (VFAULT/) .............................. 0V to 5.5V FAULT/ Pin Current (I FAULT/) .........................................1mA Ambient Temperature (TA) .......................... -40C to +85C Junction Temperature (TJ) ........................ -40C to +125C Package Thermal Resistance SOT23-5 (JA) ...............................................252.7C/W Electrical Characteristics(4) VIN = 5V; TA = 25C, bold values indicate -40C TA +85C, unless noted. Symbol Parameter Condition Min. Typ. Max. Units 5.5 V Power Input Supply VIN 1.8 Input Voltage Range Shutdown Current VEN 0.5V (switch off), VOUT = open 5 10 Supply Current VEN 1.5V (switch on), VOUT = open 70 110 VUVLO Under-Voltage Lockout Threshold VIN rising VUVLO_HYS Under-Voltage Lockout Threshold Hysteresis IVIN 1.75 100 A V mV Enable Input VEN Enable Logic Level High(5) (5) 1.5 VIH (MIN) 0.5 V Enable Logic Level Low VIL (MAX) IEN Enable Bias Current VEN = 5V 0.1 A tON Output Turn-On Delay RL = 500, CL = 0.1F See "Timing Diagrams" 215 s tR Output Turn-On Rise Time RL = 500, CL = 0.1F See "Timing Diagrams" 5 s tOFF Output Turn-Off Delay RL = 500, CL = 0.1F See "Timing Diagrams" 125 s tF Output Turn-Off Fall Time RL = 500, CL = 0.1F See "Timing Diagrams" 115 s MIC2090 VIN = 5.0V, IOUT = 50mA 700 1200 MIC2090 VIN = 3.3V, IOUT = 50mA 790 1200 MIC2090 VIN = 1.8V, IOUT = 50mA 1300 MIC2091 VIN = 5.0V, IOUT = 100mA 700 1200 MIC2091 VIN = 3.3V, IOUT = 100mA 790 1200 MIC2091 VIN = 1.8V, IOUT = 100mA 1300 Internal Switch RDSON On Resistance RDS(ON) Input-to-Output Leakage Current (Forward leakage Current) July 2011 MIC2090 and MIC2091, VEN 0.5V, (output off), VIN = 5.5V, VOUT = 0V 3 10 m A M9999-070611-B Micrel, Inc. MIC2090/MIC2091 Electrical Characteristics(4) (Continued) VIN = 5V; TA = 25C, bold values indicate -40C TA +85C, unless noted. Symbol Parameter Condition Min. Output to Input Leakage Current (Reverse Leakage Current) MIC2090 and MIC2091, VEN 0.5V, (output off), VOUT = 5.5V, VIN = 0V Typ. Max. Units 10 A Current Limit ILIMIT Current-Limit Threshold tSC_RESP Short-Circuit Response Time TAUTORESTART Time After Switch Shuts Down From An OverCurrent Condition Before It Tries To Turn On Again. MIC2090 @ VOUT = 4.5V 50 75 100 MIC2090 @ VOUT = 0V 50 100 150 MIC2091 @ VOUT = 4.5V 100 150 200 MIC2091 @ VOUT = 0V 100 175 250 Short circuit applied to output after switch is turned on, see "Timing Diagrams". VIN = 3.3V. 20 30 60 mA ns 90 ms 0.4 V 20 ms FAULT/ Flag Error Flag Output Voltage Output voltage high (1mA Sinking) tD_FAULT/ Time After Switch Comes Into Current Limit Before The PIN FAULT/ Is Pulled Low. When an over-current condition happens, the part will go into constant output current for this time. After this time it will turn off the output and pull low the PIN FAULT/. The MIC2090-1 and MIC2091-1 will automatically restart themselves after the auto restart time TAUTORESTART. tR_FAULT/ FAULT/ Rising Time FAULT/ is connected to VIN = 5V through 10k and 100pF in parallel. See "Timing Diagrams" tF_FAULT/ FAULT/ Falling Time 5 10 5 s 1 s If the output voltage is greater than the input voltage by this amount, the part will shut down. The enable pin must be recycled to reset. 85 mV Time that the output voltage can be greater than the input voltage before the chip is shut down. 10 ms TJ Rising 150 TJ Falling 140 Reverse Voltage Protection (OGI) OGI Output Voltage Greater Than Input Voltage (OGI) OGITIME Thermal Protection TOVERTEMP Over-Temperature Shutdown C Notes: 1. Exceeding the absolute maximum rating may damage the device. 2. The device is not guaranteed to function outside its operating rating. 3. Devices are ESD sensitive. Handling precautions recommended. Human body model, 1.5k in series with 100pF. 4. Specification for packaged product only. 5. VIL(MAX) = Maximum positive voltage applied to the input which will be accepted by the device as a logic low. VIH(MIN) = Minimum positive voltage applied to the input which will be accepted by the device as a logic high. July 2011 4 M9999-070611-B Micrel, Inc. MIC2090/MIC2091 Timing Diagrams Output Rise and Fall Times (tR, tF) Switch Delay Time (tON, tOFF) July 2011 5 M9999-070611-B Micrel, Inc. MIC2090/MIC2091 Typical Characteristics VIN Shutdown Current vs. Input Voltage VIN Supply Current vs. Input Voltage 1.3 8 6 4 2 ENABLE THRESHOLD (V) 80 SUPPLY CURRENT (A) SUPPLY CURRENT (A) 10 Enable Thresholds vs. Input Voltage 70 60 50 40 0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 2.0 2.5 1.0 VEN Falling 0.9 0.8 3.0 3.5 4.0 4.5 5.0 5.5 1.5 2.0 INPUT VOLTAGE (V) INPUT VOLTAGE (V) 110.0 VEN Rising 1.1 0.7 1.5 5.5 1.2 Current Limit vs. Input Voltage MIC2090 2.5 3.0 3.5 4.0 4.5 5.0 5.5 INPUT VOLTAGE (V) Auto-Reset Time vs. Input Voltage (MIC2090) FAULT/ Delay vs. Input Voltage (MIC2090) 61.0 100.0 7.8 60.5 90.0 ILIMIT @ VOUT = 0.9V * VOUT 80.0 7.6 DELAY (ms) DELAY (ms) CURRENT LIMIT (mA) 8.0 ILIMIT @ VOUT = 0V 7.4 CLOAD = 10F 7.2 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 7.0 59.0 58.0 1.5 INPUT VOLTAGE (V) 59.5 58.5 70.0 1.5 60.0 2.0 2.5 3.0 3.5 4.0 4.5 5.0 1.5 5.5 2.0 INPUT VOLTAGE (V) Current Limit vs. Input Voltage MIC2091 190.0 180.0 170.0 ILIMIT @ VOUT = 0.9V * VOUT 1.1 0.9 150.0 2.0 2.5 3.0 3.5 4.0 4.5 INPUT VOLTAGE (V) July 2011 5.0 5.5 5.5 CLOAD = 0.1F IOUT = 10mA RLOAD = 500 0.5 1.5 5.0 195 190 0.7 160.0 4.5 200 DELAY (s) 200.0 4.0 205 1.3 RESISTANCE () CURRENT LIMIT (mA) ILIMIT @ VOUT = 0V 3.5 Output Turn-On Delay vs. Input Voltage 1.5 210.0 3.0 INPUT VOLTAGE (V) Switch On Resistance vs. Input Voltage 220.0 2.5 185 1.5 2.0 2.5 3.0 3.5 4.0 4.5 INPUT VOLTAGE (V) 6 5.0 5.5 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 INPUT VOLTAGE (V) M9999-070611-B Micrel, Inc. MIC2090/MIC2091 Typical Characteristics (Continued) Output Rise Time vs. Input Voltage Output Turn-Off Delay vs. Input Voltage 8 5 4 3 2 CLOAD = 0.1F 33 32 31 RLOAD = 500 2.5 3.0 3.5 4.0 4.5 5.0 RLOAD = 500 1.5 5.5 3.0 3.5 4.0 4.5 OGI Delay vs. Input Voltage 80 70 50 5 3.5 4.0 4.5 5.0 2.0 2.5 3.0 3.5 4.0 4.5 INPUT VOLTAGE (V) INPUT VOLTAGE (V) VIN Supply Current vs.Temperature Enable Threshold vs. Temperature 1.40 75 1.35 ENABLE THRESHOLD (V) 80 VIN = 5V 70 65 60 55 V IN = 1.8V 50 45 RLOAD = 0 40 -15 10 35 TEMPERATURE (C) 5.0 1.25 1.20 1.15 VEN Falling VIN = 5.0V 85 -40 -15 10 35 3.5 4.0 4.5 5.0 5.5 5.5 VIN = 5V 5.0 4.5 4.0 3.5 VIN = 1.8V 3.0 2.5 -40 -15 10 35 60 85 Current Limit vs. Temperature (MIC2090) 96 94 92 90 ILIMIT @ VOUT = 0V 88 86 84 82 80 78 ILIMIT @ V OUT = 4.5V 76 74 72 70 V IN = 5.0V -40 1.00 60 3.0 TEMPERATURE (C) VEN Rising 1.05 2.5 2.0 5.5 1.30 1.10 2.0 VIN ShutdownCurrent vs. Temperature 6.0 1.5 5.5 1.5 INPUT VOLTAGE (V) 7 6 3.0 5.5 8 60 2.5 5.0 SHUTDOWN CURRENT (A) DELAY (ms) 9 July 2011 2.5 OGI Threshold vs. Input Voltage 90 -40 2.0 INPUT VOLTAGE (V) 10 2.0 70 INPUT VOLTAGE (V) 100 1.5 80 CLOAD = 0.1F CURRENT LIMIT (mA) 2.0 90 RLOAD = 500 29 1.5 100 CLOAD = 0.1F 30 0 OGI THRESHOLD (mV) FALL TIME (s) DELAY (s) RISE TIME (s) 34 6 1 SUPPLY CURRENT (A) 110 35 7 Output Fall Time vs. Input Voltage 60 85 -15 10 35 60 85 TEMPERATURE (C) TEMPERATURE (C) 7 M9999-070611-B Micrel, Inc. MIC2090/MIC2091 Typical Characteristics (Continued) Current Limit vs. Temperature (MIC2090) Auto-Reset Time vs. Temperature (MIC2090) FAULT/ Delay vs. Temperature (MIC2090) 8.5 110 66 65 8.0 95 90 ILIMIT @ V OUT = 1.6V 85 80 VIN = 5V 7.5 VIN = 1.8V 7.0 61 V IN = 5.0V 6.5 -40 -15 10 35 60 -40 85 -15 Current Limit vs. Temperature (MIC2091) 240 35 60 58 85 -40 1.6 190 ILIMIT @ VOUT = 1.6V 180 170 160 VIN = 1.8V 150 ILIMIT @ VOUT = 0V 170 160 ILIMIT @ VOUT = 4.5V 150 -40 -15 10 35 60 85 1.1 1.0 VIN = 5.0V 0.9 0.8 0.7 IOUT = 10mA 0.4 -40 -15 10 35 60 -40 85 -15 Output Rise Time vs. Temperature 35 60 85 Output Turn-Off Delay vs. Temperature 7 35 V IN = 5.0V VIN = 5.0V 6 210 10 TEMPERATURE (C) TEMPERATURE (C) Output Turn-On Delay vs. Temperature 215 1.2 0.5 140 TEMPERATURE (C) 85 1.3 0.6 VIN = 5.0V 140 60 VIN = 1.8V 1.4 180 RESISTANCE () CURRENT LIMIT (mA) 200 35 RDS(ON) vs. Temperature 1.5 210 10 TEMPERATURE (C) ILIMIT @ VOUT = 0V 220 -15 Current Limit vs. Temperature (MIC2091) 190 230 10 TEMPERATURE (C) TEMPERATURE (C) CURRENT LIMIT (mA) 62 59 70 33 205 VIN = 1.8V 200 195 CLOAD = 0.1F 190 10 35 TEMPERATURE (C) 60 85 31 V IN = 1.8V 29 2 CLOAD = 0.1F 27 RLOAD =500 CLOAD = 0.1F RLOAD =500 185 July 2011 3 1 VIN = 5.0V -15 4 VIN = 1.8V RLOAD =500 -40 5 DELAY (s) RISE TIME (s) DELAY (s) 63 60 VIN = 1.8V 75 VIN = 1.8V 64 DELAY (ms) ILIMIT @ VOUT = 0V 100 DELAY (ms) CURRENT LIMIT (mA) 105 25 0 -40 -15 10 35 TEMPERATURE (C) 8 60 85 -40 -15 10 35 60 85 TEMPERATURE (C) M9999-070611-B Micrel, Inc. MIC2090/MIC2091 Typical Characteristics (Continued) Output Fall Time vs. Temperature 120 OGI Threshold vs. Temperature 120 100 V IN = 1.8V 80 CLOAD = 0.1F 70 RLOAD =500 60 8.6 80 60 V IN = 1.8V 40 -15 10 35 60 85 TEMPERATURE (C) 8.4 8.2 8.0 20 VIN = 1.8V 7.8 0 -40 7.6 -40 -15 10 35 TEMPERATURE (C) 60 85 -40 -15 10 35 60 85 TEMPERATURE (C) VIN UVLO Thresholds vs. Temperature 1.4 VIN ULVO THRESHOLDS (V) VIN = 5.0V 8.8 100 DELAY (ms) OGI THRESHOLD (mV) FALL TIME (s) 110 90 9.0 VIN = 5.0V VIN = 5.0V OGI Delay vs. Temperature VIN Rising 1.3 1.2 V IN Falling 1.1 1.0 -40 -15 10 35 60 85 TEMPERATURE (C) July 2011 9 M9999-070611-B Micrel, Inc. MIC2090/MIC2091 Functional Characteristics July 2011 10 M9999-070611-B Micrel, Inc. MIC2090/MIC2091 Functional Characteristics (Continued) July 2011 11 M9999-070611-B Micrel, Inc. MIC2090/MIC2091 Functional Characteristics (Continued) July 2011 12 M9999-070611-B Micrel, Inc. MIC2090/MIC2091 Functional Characteristics (Continued) July 2011 13 M9999-070611-B Micrel, Inc. MIC2090/MIC2091 Functional Diagram MIC2090/MIC2091 Functional Diagram July 2011 14 M9999-070611-B Micrel, Inc. MIC2090/MIC2091 Functional Description Limitations on COUT The part may enter current limit when turning on with a large output capacitance, which is an acceptable condition. However, if the part remains in current limit for a time greater than tD_FAULT, the FAULT/ pin will assert low. The maximum value of COUT may be approximated by Equation 1: VIN and VOUT VIN is both the power supply connection for the internal circuitry driving the switch and the input (source connection) of the power MOSFET switch. VOUT is the drain connection of the power MOSFET and supplies power to the load. In a typical circuit, current flows from VIN to VOUT toward the load. When the switch is disabled, current will not flow to the load, except for a small unavoidable leakage current of a few microamps (forward leakage current). C OUT_MAX = CIN A minimum 1F bypass capacitor positioned close to the VIN and GND pins of the switch is both good design practice and required for proper operation of the switch. This will control supply transients and ringing. Without a sufficient bypass capacitor, large current surges or a short may cause sufficient ringing on VIN (from supply lead inductance) to cause erratic operation of the switch's control circuitry. For best performance, place a ceramic capacitor next to the IC. An additional 10F (or greater) capacitor, positioned close to the VIN and GND pins of the switch is necessary if the distance between a larger bulk capacitor and the switch is greater than three inches. This additional capacitor limits input voltage transients at the switch caused by fast changing input currents that occur during a fault condition, such as current limit and thermal shutdown. When bypassing with capacitors of 10F or more, it is good practice to place a smaller value capacitor in parallel with the larger to handle the high-frequency components of any line transients. Values in the range of 0.1F to 1F are recommended. Again, good quality, low-ESR capacitors, preferably ceramic, should be chosen. VIN_MAX Eq. 1 Where: ILIMIT_MIN and TD_FAULT_MIN are the minimum specified values listed in the Electrical Characteristic table and VIN_MAX is the maximum input voltage to the switch. Current Sensing and Limiting The MIC2090/MIC2091 protects the system power supply and load from damage by continuously monitoring current through the on-chip power MOSFET. Load current is monitored by means of a current mirror in parallel with the power MOSFET switch. Current limiting is invoked when the load exceeds the overcurrent threshold. When current limiting is activated in the -1 version, the output current is constrained to the limit value, and remains at this level until either the load/fault is removed, the load's current requirement drops below the limiting value, or the switch goes into thermal shutdown. If the overcurrent fault is large enough to drop VOUT below (typically) 1.8V, the internal MOSFET turns off very quickly (typically 20ns). This prevents excessive current from flowing through the device and damaging the internal MOSFET. The latch-off feature of the -2 version latches the output off when the output current exceeds the overcurrent threshold. VIN or the enable pin must be toggled to reset the latch. COUT An output capacitor is required to reduce ringing and voltage sag on the output during a transient condition. A value between 1F and 10F is recommended. A 10F or larger capacitor should be used if the distance between the MIC2090/MIC2091 and the load is greater than three inches. The internal switch in the MIC2090/MIC2091 turns off in (typically) 20ns. This extremely fast turn-off can cause an inductive spike in the output voltage when the internal switch turns off during an overcurrent condition. The larger value capacitor prevents the output from glitching too low. July 2011 ILIMIT_MIN x TD_FAULT_MIN Enable Input The EN pin is a TTL logic level compatible input which turns the internal MOSFET switch on and off. The FAULT/ pin remains high when the EN pin is pulled low and the output is turned off. Toggling the enable pin resets the output after an OGI (output greater than input) condition occurs. In the -2 version, toggling the enable pin resets the output after an overcurrent event. Fault Output The FAULT/ is an N-channel open-drain output, which is asserted LOW when the MIC2090/MIC2091 switch either begins current limiting or enters thermal shutdown. 15 M9999-070611-B Micrel, Inc. MIC2090/MIC2091 During an overcurrent or short circuit, The FAULT/ signal asserts after a brief delay period, tD_FAULT/, in order to filter out false or transient over-current conditions. The FAULT/ output is open-drain and must be pulled HIGH with an external resistor. The FAULT/ signal may be wire-OR'd with other similar outputs, sharing a single pull-up resistor. may exceed the package and PCB's ability to cool the device and the MIC2090/MIC2091 will shut down and signal a fault condition. Please see the "Fault Output" description for more details on the FAULT/ output. After the MIC2090/MIC2091 shuts down, and cools, it will re-start itself if the enable signal remains true. n Figure 2, die temperature is plotted against IOUT assuming a constant ambient temperature of 85C and a worst case internal switch on-resistance (RON). This plot is valid for both the MIC2090 and MIC2091. Power Dissipation and Thermal Shutdown Thermal shutdown is used to protect the MIC2090/MIC2091 switch from damage should the die temperature exceed a safe operating temperature. Thermal shutdown shuts off the output MOSFET and asserts the FAULT/ output if the die temperature reaches the over-temperature threshold, TOVERTEMP. The switch will automatically resume operation when the die temperature cools down to 140C. If resumed operation results in reheating of the die, another shutdown cycle will occur and the switch will continue cycling between ON and OFF states until the reason for the overcurrent condition has been resolved. Depending upon the PCB layout, package type, ambient temperature, etc., hundreds of milliseconds may elapse from the time a fault occurs to the time the output MOSFET will be shut off. This delay is caused because of the time it takes for the die to heat after the fault condition occurs. Power dissipation depends on several factors such as the load, PCB layout, ambient temperature, and supply voltage. Calculation of power dissipation can be accomplished by Equation 2: PD = RDS(ON) x (IOUT) 2 DIE TEMPERATURE (C) Die Temperature vs. Output Current (Ambient Temperature = 85C) 88 87 86 85 84 83 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1 Figure 2. Die Temperature vs. IOUT ILIMIT vs. IOUT Measured (-1 version only) When the MIC2090/MIC2091 is current limiting, it is designed to act as a constant current source to the load. As the load tries to pull more than the maximum current, VOUT drops and the input to output voltage differential increases. When VOUT drops below 1.8V, then the output switch momentarily turns off to insure the internal MOSFET switch is not damaged by a very fast short circuit event. When measuring IOUT in an overcurrent condition, it is important to remember voltage dependence, otherwise the measurement data may appear to indicate a problem when none really exists. This voltage dependence is illustrated in Figures 3 and 4. In Figure 3, output current is measured as VOUT is pulled below VIN, with the test terminating when VOUT is 2.5V below VIN. Observe that once ILIMIT is reached IOUT remains constant throughout the remainder of the test. Figure 4 repeats this test but simulates operation deeper into an overcurrent condition. When VOUT drops below 1.8V, the switch turns off for a few microseconds before turning back on. Eq.2 Eq. 3 Where: TJ = Junction Temperature TA = Ambient Temperature R(J-A) is the thermal resistance of the package. In normal operation, excessive switch heating is most often caused by an output short circuit. If the output is shorted, when the switch is enabled, the MIC2090/MIC2091 switch limits the output current to the maximum value. The heat generated by the power dissipation of the switch continuously limiting the current July 2011 89 IOUT (A) To relate this to junction temperature, Equation 3 can be used: TJ = PD x R(J-A) + TA 90 16 M9999-070611-B Micrel, Inc. MIC2090/MIC2091 Under-Voltage Lock Out (UVLO) The MIC2090/MIC2091 switches have an Under-Voltage Lock Out (UVLO) feature that will shut down the switch in a reproducible way when the input power supply voltage goes too low. The UVLO circuit disables the output until the supply voltage exceeds the UVLO threshold. Hysteresis in the UVLO circuit prevents noise and finite circuit impedance from causing chatter during turn-on and turn-off. While disable by the UVLO circuit, the output switch (power MOSFET) is OFF and no circuit functions, such as FAULT/ or EN, are considered to be valid or operative. OGI (Output Greater than Input) The internal MOSFET switch turns off when it senses an output voltage that is greater than the input voltage. This feature prevents continuous current from flowing from the output to the input. If the output voltage rises above VIN by the OGI threshold voltage (typically 85mV), the internal MOSFET switch turns off after a period of time, specified in the electrical characteristics table as OGITIME. The FAULT/ pin remains high during and after an OGI event. Figure 5 shows the output voltage, input current and FAULT/ pin voltage when the output voltage is raised above the input. Reverse current flows through the internal MOSFET switch for the OGITIME period, until the internal MOSFET switch is turned off and the input current goes to 0A. Figure 3. IOUT in Current Limiting for VOUT > 1.8V Figure 4. IOUT in Current Limiting for VOUT < 1.8V Figure 5. OGI Event July 2011 17 M9999-070611-B Micrel, Inc. MIC2090/MIC2091 MIC2090/MIC2091 Evaluation Board Schematic July 2011 18 M9999-070611-B Micrel, Inc. MIC2090/MIC2091 Bill of Materials Item C1, C2 Part Number 08056D106MAT2A Manufacturer (1) AVX C3, C4 R1, R3 CRCW06031002FRT1 Vishay Dale(2) R2 U1 MIC2090-1YM5 Description Qty. 10F, 6.3V Ceramic Capacitor, X5R 2 NF (No Fill) 2 10k, 1%, 0603 Resistor 2 NF (No Fill) 1 Micrel, Inc. (3) Current Limiting Power Distribution Switch 1 (3) U1 MIC2091-1YM5 Micrel, Inc. Current Limiting Power Distribution Switch 0 U1 MIC2090-2YM5 Micrel, Inc.(3) Current Limiting Power Distribution Switch 0 MIC2091-2YM5 (3) Current Limiting Power Distribution Switch 0 U1 Micrel, Inc. Notes: 1. AVX: www.avx.com. 2. Vishay Tel: www.vishay.com. 3. Micrel, Inc.: www.micrel.com. July 2011 19 M9999-070611-B Micrel, Inc. MIC2090/MIC2091 PCB Layout Recommendations Top Silk Screen Top Copper July 2011 20 M9999-070611-B Micrel, Inc. MIC2090/MIC2091 PCB Layout Recommendations (Continued) Bottom Copper Bottom Silk Screen July 2011 21 M9999-070611-B Micrel, Inc. MIC2090/MIC2091 Package Information 5-Pin SOT23 (SOT23-5) July 2011 22 M9999-070611-B Micrel, Inc. MIC2090/MIC2091 Recommended Landing Pattern MICREL, INC. 2180 FORTUNE DRIVE SAN JOSE, CA 95131 USA TEL +1 (408) 944-0800 FAX +1 (408) 474-1000 WEB http://www.micrel.com Micrel makes no representations or warranties with respect to the accuracy or completeness of the information furnished in this data sheet. This information is not intended as a warranty and Micrel does not assume responsibility for its use. Micrel reserves the right to change circuitry, specifications and descriptions at any time without notice. No license, whether express, implied, arising by estoppel or otherwise, to any intellectual property rights is granted by this document. Except as provided in Micrel's terms and conditions of sale for such products, Micrel assumes no liability whatsoever, and Micrel disclaims any express or implied warranty relating to the sale and/or use of Micrel products including liability or warranties relating to fitness for a particular purpose, merchantability, or infringement of any patent, copyright or other intellectual property right. Micrel Products are not designed or authorized for use as components in life support appliances, devices or systems where malfunction of a product can reasonably be expected to result in personal injury. Life support devices or systems are devices or systems that (a) are intended for surgical implant into the body or (b) support or sustain life, and whose failure to perform can be reasonably expected to result in a significant injury to the user. A Purchaser's use or sale of Micrel Products for use in life support appliances, devices or systems is a Purchaser's own risk and Purchaser agrees to fully indemnify Micrel for any damages resulting from such use or sale. (c) 2011 Micrel, Incorporated. July 2011 23 M9999-070611-B