MIC2040/2041 Micrel MIC2040/2041 Single Channel Low Voltage Power Distribution Switch General Description Features The MIC2040 and MIC2041 are high side MOSFET switches optimized for general purpose power distribution applications that require circuit protection. The devices switch up to 5.5V and as low as 0.8V while offering both programmable current limiting and thermal shutdown to protect the device and the load. A fault status output is provided in order to detect overcurrent and thermal shutdown fault conditions. Both devices employ soft start circuitry to minimize the inrush current in applications that employ highly capacitive loads. Additionally, the MIC2040/41 is suited for multi-port USB applications to satisfy upstream/downstream power requirements. The MIC2041 features a auto-reset circuit breaker mode that latches the output off upon detecting an overcurrent condition lasting more than 28ms. The output is reset by removing or reducing the load. Data sheets and support documentation can be found on Micrel’s web site at www.micrel.com. • • • • • • • • • 75mΩ max. on-resistance 0.8V to 5.5V operating range Adjustable current limit Up to 1.5A continuous output current Short circuit protection with thermal shutdown Circuit breaker mode (MIC2041) Fault status flag Undervoltage lockout Output MOSFET reverse current flow block when disabled • Very fast reaction to short-circuits • Low quiescent current Applications • • • • • • • Docking stations Notebook PCs PDAs Board hot swap RAID controllers USB peripherals ACPI power distribution Ordering Information Part Number Standard Pb-Free Enable MIC2040-1BMM MIC2040-1YMM Active-High Circuit Breaker Package MIC2040-2BMM MIC2040-2YMM Active-Low MIC2041-1BMM MIC2041-1YMM Active-High X 10-Pin MSOP MIC2041-2BMM MIC2041-2YMM Active-Low X 10-Pin MSOP 10-Pin MSOP 10-Pin MSOP Typical Application C2 0.1µF +3.3V Power Supply C3 4.7µF MIC2040-1BM 6 7, 9 ON/OFF IN C1 0.1µF R1 20kΩ 1 Logic Controller Note: BothVIN pins (7, 8) must be externally tied together. BothVOUT pins (8, 10) must be externally tied together. ILIMIT = 1A. RSET 340Ω VOUT 3.3V@ 1A 8,10 CLOAD 33µF VIN EN 2 /FAULT 5 ILIM OVERCURRENT VOUT VBIAS UVLOIN 3 (OPEN) GND 4 Micrel, Inc. • 1849 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 944-0970 • http://www.micrel.com January 2005 1 M9999-012004 MIC2040/2041 Micrel Pin Configuration EN 1 10 VOUT /FAULT 2 9 VIN UVLOIN 3 8 VOUT GND 4 7 VIN ILIM 5 6 VBIAS MIC2040/MIC2041 10-Pin MSOP (MM) Pin Description Pin Number Pin Name 1 EN Switch Enable Input: Gate control pin of the output MOSFET available as an active high (–1) or active low (–2) input signal. 2 /FAULT Fault Status Output: Open drain N-Channel device, active low. This pin indicates an overcurrent, or thermal shutdown condition. For an overcurrent event, /FAULT is asserted if the duration of the overcurrent condition lasts longer than 28ms. 4 GND Ground Connection: Tie to analog ground. 5 ILIM Current Limit Set: A resistor, RSET, connected to this pin sets the current limit threshold as CLF/RSET, where CLF is the current limit factor specified in the electrical characteristics table. For the MIC2040/41, the continuous output current range is 0.25A to 1.5A. 7, 9 VIN Switch Input Supply: The drain of the output MOSFET. The range of input for the switch is 0.8V to 5.5V. These pins must be externally connected together. 8, 10 VOUT Switch Output: The source of the output MOSFET. These pins must be externally connected together. 6 VBIAS Bias Supply Input: This input pin supplies bias to operate the switch with range from 1.6V to 5.5V. When switching voltage (VIN) is between 1.6V to 5.5V and the use of a single supply is desired, connect VBIAS to VIN externally. 3 UVLOIN M9999-012004 Pin Function Undervoltage Lockout Adjust Input: With this pin left open, the UVLO threshold is internally set to 1.45V. When the switching voltage (VIN) is at or below 1.6V, connecting an external resistive divider to this input will lower the UVLO threshold. The total resistance must be less than 200kΩ. See “Applications Information” for further detail. 2 January 2005 MIC2040/2041 Micrel Absolute Maximum Ratings(1) Operating Ratings(2) VIN and VBIAS .................................................................................. 6V /FAULT, PWRGD Output Voltage ................................... 6V /FAULT, PWRGD Output Current .............................. 25mA Junction Temperature Range ................... Internally Limited ESD Rating(3) Human Body Model ................................................... 2kV Machine Model ........................................................ 200V Supply Voltage VIN ............................................................... 0.8V to 5.5V VBIAS ........................................................... 1.6V to 5.5V Continuous Output Current ........................... 0.25A to 1.5A Ambient Temperature (TA) ........................... –40°C to 85°C Package Thermal Resistance (Rθ(J-A)) MSOP ................................................................ 160°C/W Electrical Characteristics(4) VIN = VBIAS = 5V. TA = 25°C unless specified otherwise. Bold indicates –40°C to +85°C. Symbol Parameter Condition Min VIN Switch Input Voltage VIN ≤ VBIAS VBIAS Bias Supply Voltage IBIAS VBIAS Supply Current - Switch OFF VBIAS Supply Current - Switch ON Note 5 Max Units 0.8 5.5 V 1.6 5.5 V 0.1 250 5 400 µA µA VEN Enable Input Voltage 2.4 1.5 V No load No load VIL(max) VIH(min) 3.5 VENHYS Enable Input Threshold Hysteresis IEN Enable Input Current VEN = 0V to 5.5V RDS(ON) Switch Resistance VIN = VBIAS = 3V, 5V IOUT = 500mA ILEAK Output Leakage Current Output off Factor(6) VIN = 3V, 5V; 0.5V ≤ VOUT < 0.5VIN 0.25A ≤ IOUT ≤ 1.5A CLF Current Limit VLATCH Output Reset Threshold VIN = 0.8V to 5.5V VOUT rising (MIC2041) ILATCH Latched Output Off Current Output latched off (MIC2041) VOL Output low voltage (/FAULT) IOL (/FAULT) = 15mA IOFF /FAULT Off Current VFAULT = 5V VUV Undervoltage Lockout Threshold VIN rising VIN falling VUVHYS Undervoltage Lockout Threshold Hysteresis VUVINTH UVLO Adjust Pin Threshold Voltage VUVINHYS UVLO Adjust Pin Threshold Hysteresis Overtemperature Threshold –1 280 Typ 2.5 V 100 mV .01 1 µA 50 75 mΩ 10 µA 400 A•Ω 340 VIN–.0.2 1 1.30 1.20 3 1.45 1.35 V 5 mA 0.4 V 1 µA 1.58 1.50 V V 100 VIN rising VIN falling 200 180 TJ increasing TJ decreasing 220 200 mV 240 220 mV mV 20 mV 140 120 °C °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. OFF is VEN < 1.0V for MIC2040/MIC2041–1 and VEN > 4.0V for MIC2040/MIC2041 –2. ON is VEN > 4.0V for MIC2040/MIC2041–1 and VEN < 1.0V for MIC2040/MIC2041 –2. 6. The current limit is determined as follows: ILIM = CLF/RSET. January 2005 3 M9999-012004 MIC2040/2041 Micrel Electrical Characteristics(7) Symbol Parameter Condition Min Typ Max Units tFLAG Flag Response Delay VIN = VBIAS = 3V, 5V 21 28 35 ms tON Output Turn-on Delay, RLOAD = 10Ω, CLOAD = 1µF 400 600 800 µs tR Output turn-on Rise Time RLOAD = 10Ω, CLOAD = 1µF 0.5 1 1.5 ms tOFF Output Turn-off Delay RLOAD = 10Ω, CLOAD = 1µF 1 5 µs tF Output Turn-off Fall Time RLOAD = 10Ω, CLOAD = 1µF 24 µs Note: 7. Specification for packaged product only. Timing Diagrams Figure 1. Turn-On/Turn-Off Delay VEN Increase the load 0 VIN 0.2V VOUT 0 ILIMIT IOUT 0 tFLAG /FAULT 0 Figure 2. Overcurrent Fault Response — MIC2040-2 M9999-012004 4 January 2005 MIC2040/2041 Micrel Test Circuit VDD C1 0.1mF MIC2040/41-xBM C2 0.1mF 6 VBIAS VOUT 8,10 CLOAD R1 20kW 7, 9 VIN R3 75kW R2 20kW R4 68kW January 2005 VIN 1 EN 2 /FAULT 3 ILIM UVLOIN GND 4 5 VOUT 5 RSET M9999-012004 MIC2040/2041 Micrel Typical Characteristics Supply Current vs. Temperature 250 1.5 200 VBIAS = 1.6V 1 VIN = VBIAS = 1.6V 2 Output Leakage Current vs. Temperature ON Resistance (RDS(ON)) vs. Temperature 2400 1200 900 VBIAS = 1.6V 400 CURRENT LIMIT FACTOR (V) 400 RSET = 0.85A 390 380 370 360 V VBIAS = 3V = 1.6V BIAS 350 340 330 320 310 VBIAS = 5.5V 300 -40 -20 0 20 40 60 80 100 TEMPERATURE (°C) UVLO Threshold vs. Temperature UVLO (V) 1.35 UVLO– 1.25 1.2 -40 -20 0 20 40 60 80 100 TEMPERATURE (°C) 300 RSET = 1.5A Output Low Voltage vs. Temperature IOL (/FAULT) = 15mA 250 380 370 360 VBIAS = 5.5V 350 VBIAS = 1.6V 330 320 200 VBIAS = 5.5V 150 VBIAS = 3V 310 240 235 230 225 UVLO+ 220 215 210 205 200 195 UVLO– 190 185 180 -40 -20 0 20 40 60 80 100 TEMPERATURE (°C) 6 VBIAS = 1.6V 100 50 VBIAS = 3V 0 -40 -20 0 20 40 60 80 100 TEMPERATURE (°C) UVLO Adjust PinThreshold vs. Temperature UVLO+ 1.4 Current Limit Factor vs. Temperature 390 340 400 RSET = 0.4A 390 380 370 VBIAS = 1.6V 360 VBIAS = 3V 350 340 330 320 310 VBIAS = 5.5V 300 -40 -20 0 20 40 60 80 100 TEMPERATURE (°C) 300 -40 -20 0 20 40 60 80 100 TEMPERATURE (°C) 1.45 M9999-012004 VIN = VBIAS = 5V 0 -40 -20 0 20 40 60 80 100 TEMPERATURE (°C) Current Limit Factor vs. Temperature 1.3 VIN = VBIAS = 3V 30 10 300 1.5 40 20 600 1.55 50 Current Limit Factor vs. Temperature VOL (mV) VBIAS = 3V 0 -40 -20 0 20 40 60 80 100 TEMPERATURE (°C) 50 Flag Response Delay vs. Temperature 45 T FLAG (ms) 1800 1500 VIN = VBIAS = 1.6V 60 VBIAS = 5.5V RDS(mΩ) 2100 VBIAS = 1.6V 1 CURRENT LIMIT FACTOR (V) 100 -40 -20 0 20 40 60 80 100 TEMPERATURE (°C) 70 VBIAS = 3V 0.5 0 -40 -20 0 20 40 60 80 100 TEMPERATURE (°C) 80 VBIAS = 5.5V 1.5 0.5 150 Enable Input Threshold (Rising) vs. Temperature 2.5 VBIAS = 3V V EN (V) 300 VIN = VBIAS = 3V 2 2700 CURRENT LIMIT FACTOR (V) 3 2.5 VIN = VBIAS = 5.5V 350 0 -40 -20 0 20 40 60 80 100 TEMPERATURE (°C) UVLO (V) 3.5 3 V BIAS = 5.5V 400 3000 OUTPUT LEAKAGE (nA) 3.5 450 V EN (V) SUPPLY CURRENT (µA) 500 Enable Input Threshold (Falling) vs. Temperature 40 35 TFLAG = 5V 30 25 TFLAG = 3V 20 -40 -20 0 20 40 60 80 100 TEMPERATURE (°C) January 2005 MIC2040/2041 Micrel Typical Characteristics (continued) Turn On Delay vs. Temperature 800 800 750 700 700 VIN = VBIAS = 5.5V 650 600 VIN = VBIAS = 3V 500 VIN = VBIAS = 1.6V 650 TON (µs) TURN ON DELAY (µs) 750 550 Output Rise Time vs. Temperature VIN = VBIAS = 5.5V 600 550 500 VIN = VBIAS = 3V VIN = VBIAS = 1.6V 450 450 400 400 350 -40 -20 0 20 40 60 80 100 TEMPERATURE (°C) 350 -40 -20 0 20 40 60 80 100 TEMPERATURE (°C) January 2005 7 M9999-012004 MIC2040/2041 Micrel Functional Diagram ! + 5067 3# (8! % 8"#06 ' ' ' )* + "# 0$ . # 0#0% 5067 3# 8 5"! ( + #8 24 "# $!$# + 0 /## 0 % 0$ 8 ' %$ &! /% 1 2)!34 M9999-012004 ,*- & &( .'/ January 2005 MIC2040/2041 Micrel Functional Characteristics EN (5V/div.) VOUT (2V/div.) VIN = VBIAS =5V RLOAD = 5Ω CLOAD = 47µF TIME (500µs/div.) Latched Output - MIC2041 Latched Output Reset - MIC2041 VOUT (2V/div.) VIN = VBIAS = 5V RLOAD = 35Ω CLOAD = 57µF VIN = VBIAS = 5V RLOAD = 35Ω CLOAD = 57µF TIME (5ms/div.) TIME (50ms/div.) Current-Limit Response UVLO Response VOUT (1V/div.) /FAULT (5V/div.) VIN (1V/div.) EN (5V/div.) IOUT (1A/div.) VOUT (5V/div.) /FAULT (5V/div.) /FAULT (5V/div.) EN (5V/div.) EN (5V/div.) TIME (1ms/div.) VOUT (5V/div.) VIN = VBIAS = 5V RLOAD = 3.5Ω CLOAD = 47µF IOUT (500mA/div.) IOUT (1A/div.) January 2005 VIN = VBIAS = 5V RLOAD = 5Ω CLOAD = 47µF IOUT (1A/div.) IOUT (1A/div.) EN (5V/div.) Turn-Off Response VOUT (2V/div.) Turn-On Response TIME (5ms/div.) VEN ramps 0 to 1.6V RLOAD = 1.6Ω CLOAD = 47µF TIME (10ms/div.) 9 M9999-012004 MIC2040/2041 Micrel IOUT (1A/div.) VOUT (5V/div.) /FAULT (5V/div.) EN (5V/div.) Thermal Shutdown Response M9999-012004 TIME (100ms/div.) 10 January 2005 MIC2040/2041 Micrel Programmable Current Limit The MIC2040/41 is designed to prevent damage to the external load by limiting the maximum amount of current it can draw. The current limit is programmed by an external resistor (RSET) connected from ILIM to ground and becomes active when the output voltage is at least 200mV below the voltage at the input to the device. The limiting current value is defined by the current limit factor (CLF) divided by RSET, and the MIC2040/41 will limit from 0.25A to 1.5A with a set point accuracy of ±18%. In programming the nominal current limit, the value of RSET is determined using the following equation: Functional Description The MIC2040 and MIC2041 are high-side N-Channel switches equipped with programmable current limit up to 1.5A for use in general purpose power distribution applications. The switches, available with active-high or active-low enable inputs, operate down to 0.8V and provide circuit protection via thermal shutdown and an optional output latch during overcurrent conditions. Input and Output VBIAS supplies power to the internal circuitry of the switch and must be present for the switch to operate. VIN is connected to the drain of the output MOSFET and sources power to the switched load. VIN must be less than or equal to VBIAS. VOUT is the source terminal of the output MOSFET and attaches to the load. In a typical circuit, current flows from VIN to VOUT toward the load. If VOUT is greater than VIN, current will flow from VOUT to VIN since the switch is bi-directional when the device is enabled. When disabled (OFF), the switch will block current flow from either direction. RSET = CLF (340A × Ω) = ILIM ILIM (1) And given the ±18% tolerance of the current limit factor (CLF), the external resistor is bound by: 187Ω ≤ RSET ≤ 1.6kΩ (2) The graph below (Figure 3) displays the current limit factor characteristic over the full temperature and voltage range indicated on the graph. This curve can be used as a point of reference in determining the maximum variation in the device’s current limit over the full temperature range. For example: With VIN = VBIAS = 3.0V and a nominal 1A current limit (RSET = 340Ω), the low and high current limit settings for the MIC2040/41 would be approximately 0.82A and 1.18A, respectively, as shown on the graph using the 340Ω reference. The MIC2041 is equipped with an internal circuit breaker for overcurrent protection. During an overcurrent event which exceeds the flag delay, the /FAULT output is asserted and the MIC2041 latches the output off. Once the overcurrent load is removed, the output automatically resets. Enable Input Enable, the ON/OFF control for the output switch, is a digital input available as an active-high (–1) or active-low (–2) signal. The EN pin, referenced to approximately 0.5 × VBIAS, must be driven to a clearly defined logic high or logic low. Failure to observe this requirement, or allowing EN to float, will cause the MIC2040/41 to exhibit unpredictable behavior. EN should not be allowed to go negative with respect to ground, nor allowed to exceed VBIAS. Failure to adhere to these conditions may result in damage to the device. Undervoltage Lockout When the switch is enabled, undervoltage lockout (UVLO) monitors the input voltage, VIN, and prevents the output MOSFET from turning on until VIN exceeds a predetermined level, nominally set at 1.45V. The UVLO threshold is adjustable and can be varied by applying an external resistor divider to the UVLOIN pin from VIN to GND. The resistive divider network is required when the input voltage is below 1.5V. The UVLO threshold is internally preset to 1.45V if the UVLOIN pin is left open. See “Applications Information.” VIN = 1.6V to 5V –40°C to +85°C CLF (HI) 1500 1350 1200 900 1050 750 600 450 CLF (LO) 300 1.25 1 0.75 0.5 0.25 0 150 I LIM (A) Current Limit vs. RSET 2.5 2.25 2 1.75 1.5 RSET (Ω) Figure 3. Current Limit Factor January 2005 11 M9999-012004 MIC2040/2041 Micrel Depending on PCB layout (including thermal considerations such as heat sinking), package, and ambient temperature, it may take several hundred milliseconds from the incidence of the fault to the output MOSFET being shut off. Circuit Breaker Function (MIC2041) The MIC2041 is designed to shut off all power to the load when a fault condition occurs, just as a circuit breaker would do. A fault condition is deemed to be anytime the output current exceeds the current limit for more than the flag delay period, nominally 28ms. Once the output shuts off, it remains off until either the fault load is removed from VOUT or the EN input is cycled ON-OFF-ON. If the fault is still present after EN has been cycled, the MIC2041 will again shut off all power to the load after 28ms. Once the fault has been removed, then normal operation will resume. /FAULT The /FAULT signal is an N-Channel, open-drain MOSFET output. An external pull-up resistor tied to a maximum 6V rail is required for the /FAULT pin. The /FAULT pin is asserted (active-low) when either an overcurrent or thermal shutdown condition occurs. During a hot insert of a PCB or when turning on into a highly capacitive load, the resulting high transient inrush current may exceed the current limit threshold of the MIC2040/41. In the case where an overcurrent condition occurs, /FAULT will assert only after the flag delay time has elapsed, typically 28ms. This ensures that /FAULT is asserted only upon valid overcurrent conditions and that nuisance error reporting is prevented. Thermal Shutdown For the MIC2040, thermal shutdown is employed to protect the device from damage should the die temperature exceed safe margins due to a short circuit or an excessive load. Thermal shutdown shuts off the output MOSFET and asserts the /FAULT output if the die temperature exceeds 140°C. The MIC2040 automatically resets its output and resumes supplying current to the load when the die temperature drops to 120°C. If the fault is still present, the MIC2040 will quickly reheat and shut down again. This process of turning ON-OFF-ON is called thermal cycling and will continue as long as the power switch is enabled while the fault or excessive load is present. M9999-012004 Open Load Detection The MIC2041 will automatically reset its output when the fault load is cleared. This is accomplished by applying a small current to VOUT and watching for the voltage at VOUT to rise to within 200mV of VIN. This current is supplied by an internal resistor connected to VIN and is connected to VOUT when MIC2041 latches off. 12 January 2005 MIC2040/2041 Micrel Reverse Current Block Applications Information The MIC2040/41 provides reverse current flow block through the output MOSFET if the voltage at VOUT is greater than VIN when the device is disabled. The VBIAS supply has a limited reverse current flow if the voltage at VOUT is pulled above VBIAS when the device is disabled. The reverse current for VBIAS can be completely blocked by inserting a Schottky diode from the VBIAS pin (cathode) to the supply (anode). However, the minimum voltage of 1.6V must be supplied to VBIAS after accounting for the voltage drop across the diode. UVLO Threshold Setting With Low Input Voltages When the switching voltage is below 1.6V, the device’s standard UVLO threshold (1.45V nominal) will hinder the output MOSFET in switching VIN to VOUT. In this case, the use of the UVLOIN pin is required to override the standard UVLO threshold and set a new, lower threshold for the lower input operating voltages. An external resistive divider network connected at the UVLOIN pin is used to set the new threshold. Due to the ratio of the internal components, the total series resistance of the external resistive divider should not exceed 200kΩ. The circuit shown in Figure 4 illustrates an application that switches 0.8V while the device is powered from a separate 2.5V power supply. The UVLO threshold is set by the following equation. Input and Output Supply Bypass Filtering The need for input supply bypass is brought about due to several factors, most notably the input/output inductance along the power path, operating current and current limit, and output capacitance. A 0.1µF to 0.47µF bypass capacitor positioned very close to the VIN pin to GND of the device is strongly recommended to filter high frequency oscillations due to inductance. Also, a sufficient bypass capacitor positioned close to the input source to the switch is strongly advised in order to suppress supply transient spikes and to limit input voltage droop. Inrush current increases with larger output capacitance, thus the minimum value of this capacitor will require experimental determination for the intended application and design. A good starting point is a capacitor between 4.7µF to 15µF. Without these bypass capacitors, an extreme overload condition such as a short circuit, or a large capacitive load, may cause either the input supply to exceed the maximum rating of 6V and possibly cause damage to the internal control circuitry or allow the input supply to droop and fall out of regulation and/or below the minimum operating voltage of the device. Output Capacitance R2 VUVTH = 0.23V × 1 + R3 When the MIC2040 die exceeds the overtemperature threshold of approximately 140°C, the device can enter into a thermal shutdown mode if the die temperature falls below 120°C and then rises above 140°C in a continuous cycle. With the VOUT and /FAULT outputs cycling on and off, the MIC2040 will reset the /FAULT while in an overtemperature fault condition if the output voltage is allowed to swing below ground. The inductance present at the output must be neutralized by capacitance in order to ensure that the output does not fall below ground. In order to counter the board parasitic inductance and the inductance of relatively short-length (<1 ft., 16 - 20 gauge wire), a minimum output capacitance of 22µF is strongly recommended and should be placed close to the VOUT pin of the MIC2040. For applications that use more than a foot of cable, an additional 10µF/ft. is recommended. (3) In substituting the resistor values from Figure 4, the resulting UVLO threshold (VUVTH) is calculated as 0.6V for this 0.8V switching application. When using the UVLOIN pin to set a new UVLO threshold, an optional 0.1µF to 1.0µF capacitor from UVLOIN to GND may be used as a glitch filter in order to avoid nuisance tripping of the UVLO threshold. If the UVLOIN pin is not in use, this pin should be left open (floating). The use of a pull-down resistor to ground will offset the ratio of the internal resistive divider to this pin resulting in a shift in the UVLO threshold. To bypass (disable) UVLO, connect the UVLOIN pin directly to the VIN pin of the MIC2040/41. MIC2040-1BM VDD 2.5V 8 C2 0.1µF VIN 0.8V C3 10µF R2 95.3kΩ 1% R3 59kΩ 1% C1 0.1µF R1 47kΩ 7,9 1 RSET 220Ω VBIAS VOUT 8,10 VIN R6 47kΩ EN 3 UVLOIN 5 ILIM /FAULT GND 10 R4 75kΩ 1% R5 36.5kΩ 1% VOUT CLOAD 0.8V @1.25A 22µF Digital Output Signal 2 Note: Both VIN pins (7, 9) must be externally tied together. Both VOUT pins (8, 10) must be externally tied together. Undervoltage Lockout = 0.6V. Figure 4. Lower UVLO Setting January 2005 13 M9999-012004 MIC2040/2041 Micrel Power Dissipation Power dissipation depends on several factors such as the load, PCB layout, ambient temperature, and package type. The following equations can be used to calculate power dissipation and die temperature. Calculation of power dissipation can be accomplished by the following equation: PD = RDS(on) × (IOUT)2 (4) To relate this to junction temperature, the following equation can be used: TJ = PD × Rθ(J-A) + TA (5) where TJ = junction temperature, TA = ambient temperature and Rθ(J-A) is the thermal resistance of the package. Printed Circuit Board Hot-Plug The MIC2040/41 are ideal inrush current limiting power switches suitable for hot plug applications. Due to the integrated charge pump, the MIC2040/41 present a high impedance when in the off state and the device slowly becomes a low impedance as it turns on. This effectively isolates power supplies from highly capacitive loads by reducing inrush current during hot plug events. This same feature also can be used for soft-start requirements. Bus-Powered Hub (USB) Figure 5 illustrates a bus-powered hub application where the MIC2040 provides ganged power switching to multiple downstream ports. A low-cost MIC5203 (SOT-143) or MIC5207 (TO-92) 3.3V low-dropout (LDO) regulator provides power from the bus to the USB controller. PCB Layout Recommendations The MIC2040 and MIC2041 have very low on-resistance, typically 50mΩ, and the switches can provide up to 1.5A of continuous output current. Under maximum load, the power consumed by the devices may cause the devices to heat up considerably. The following list contains some useful suggestions for PCB layout design of the MIC2040/41 in order to prevent the die from overheating under normal operating conditions. VBUS D+ C3 4.7µF MIC5203-3.3 IN OUT C4 1µF LDO Regulator C1 0.1µF GND DGND R1 20kΩ IN C2 0.1µF MIC2040-1BM 7, 9 6 1 ON/OFF 3.3V USB D+ Controller OC DGND 1. Supply additional copper area under the device to remove heat away from the IC. See “Application Hint 17” for a general guideline in calculating the suggested area. 2. Provide additional pad area on the corner pins of the MIC2040/41 IC for heat distribution. 3. Tie the common power pins (VIN = pins 7 and 9 and VOUT = pins 8 and 10) together in a manner such that the traces entering and leaving the device have a uniform width sufficient for the application’s current requirements plus added margin (25% minimum recommended). Ex: For 1A maximum current, design traces for 1.25A capability. 4. For PCB trace width calculations, there are numerous calculator programs available on the internet and elsewhere. As a general rule of thumb, 15-20 mils for every 1A of current when using 1oz. copper. However, the trace width calculators often take into account maximum temperature increase constraints, as well as layer arrangement, in determining the PCB trace widths. R2 20kΩ 2 5 Note: BothVIN pins (7, 9) must be externally tied together. BothVOUT pins (8, 10) must be externally tied together. ILIMIT = 1.5A. RSET 220Ω VIN VOUT 8,10 VOUT 5V@ 1A Downstream port CLOAD (100mA max.) 10µF VBIAS EN /FAULT UVLOIN CLOAD 10µF 3 (OPEN) ILIM GND 4 CLOAD 10µF Downstream port (100mA max.) Downstream port (100mA max.) Figure 5. Multi-Port Bus-Powered Hub M9999-012004 14 January 2005 MIC2040/2041 Micrel Package Information I Rev. 00 10-Pin MSOP (MM) MICREL, INC. 1849 FORTUNE DRIVE SAN JOSE, CA 95131 USA TEL + 1 (408) 944-0800 FAX + 1 (408) 944-0970 WEB http://www.micrel.com The information furnished by Micrel in this datasheet is believed to be accurate and reliable. However, no responsibility is assumed by Micrel for its use. Micrel reserves the right to change circuitry and specifications at any time without notification to the customer. 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 at Purchaser’s own risk and Purchaser agrees to fully indemnify Micrel for any damages resulting from such use or sale. © 2003 Micrel, Incorporated. January 2005 15 M9999-012004