MIC2042/2043 Micrel MIC2042/2043 Single Channel, High Current, Low Voltage, Protected Power Distribution Switch General Description Features The MIC2042 and MIC2043 are high-side MOSFET switches optimized for general purpose power distribution applications which 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, for tighter control over inrush current during start-up, the output slew-rate may be adjusted by an external capacitor. The MIC2043 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. All support documentation can be found on Micrel’s web site at www.micrel.com. • • • • • • • • • • • 60mΩ max. on-resistance 0.8V to 5.5V operating range Adjustable current limit Power-Good detection Up to 3A continuous output current Short-circuit protection with thermal shutdown Adjustable slew-rate control Circuit breaker mode (MIC2043) 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 Hot swap board insertions RAID controllers USB hosts ACPI power distribution Typical Application +3.3V Power Supply OUT1 C2 0.1µF C1 0.1µF OUT2 MIC2042-1BTS 7 8, 12 ON/OFF IN C3 4.7µF R1 20kΩ Logic Controller 2 3 OVERCURRENT VBIAS VOUT VIN PGREF EN 13 R4 20kΩ /FAULT VOUT 3.3V@ 1.5A 10,11,14 R2 294kΩ 1% R3 24.3kΩ 1% CLOAD 33µF MIC39100-2.5BS IN C4* 0.022µF 9 SLEW PWRGD 1 6 ILIM 4 RSET 200Ω UVLOIN GND 5 2.5V OUT EN GND (OPEN) Note: All VIN pins (8, 12) must be externally tied together. All VOUT pins (10, 11, 14) must be externally tied together. ILIMIT ≅ 2A. Output Power-Good = 3.0V. *C4 is optional. See "Applications Information." 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 M0512-112603 MIC2042/2043 Micrel Ordering Information Part Number Standard Pb-Free Enable MIC2042-1BM MIC2042-1YM MIC2042-2BM MIC2042-2YM MIC2043-1BM MIC2043-1YM Active High MIC2043-2BM MIC2043-2YM Active Low MIC2042-1BTS MIC2042-1YTS Active High MIC2042-2BTS MIC2042-2YTS Active Low MIC2043-1BTS MIC2043-1YTS Active High MIC2043-2BTS MIC2043-2YTS Active Low Circuit Breaker VBIAS VIN Range Package Active High 1.6V to 5.5V 8-pin SOP Active Low 1.6V to 5.5V 8-pin SOP X 1.6V to 5.5V 8-pin SOP X 1.6V to 5.5V 8-pin SOP X 0.8V to 5.5V 14-pin TSSOP X 0.8V to 5.5V 14-pin TSSOP X X 0.8V to 5.5V 14-pin TSSOP X X 0.8V to 5.5V 14-pin TSSOP Pin Configuration EN 1 PWRGD 1 8 VOUT /FAULT 2 EN 2 7 VIN GND 3 6 VOUT ILIM 4 5 VIN /FAULT 3 8-Pin SOP (M) 14 VOUT 13 PGREF 12 VIN UVLOIN 4 11 VOUT GND 5 10 VOUT ILIM 6 9 SLEW VBIAS 7 8 VIN 14-Pin TSSOP (TS) M0512-112603 2 January 2005 MIC2042/2043 Micrel Pin Description Pin Number 8-Pin SOP Pin Number 14-Pin TSSOP Pin Name 1 2 EN 2 3 /FAULT 3 5 GND N/A 9 SLEW Slew-Rate Control Input: A capacitor connected between this pin and ground will reduce (slow) the output slew-rate. The output turn-on time must be less than the nominal flag delay of 28ms in order to avoid nuisance tripping of the /FAULT output since VOUT must be “fully on” (i.e., within 200mV of the voltage at the input) before the /FAULT signal delay elapses. The capacitor requires a 16V rating, or greater, 25V is recommended. See “Applications Information,” “Output Slew-Rate Adjustment” for further detail. 4 6 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 MIC2042/43, the continuous output current range is 0.5A to 3A. 5,7 8,12 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 to achieve rated performance. 6,8 10,11,14 VOUT Switch Output: The source of the output MOSFET. These pins must be externally connected together to achieve rated performance. N/A 7 VBIAS Bias Supply Input: This input pin supplies power to operate the switch and internal circuitry. The input range for VBIAS is 1.6V to 5.5V. When switched voltage (VIN) is between 1.6V to 5.5V and the use of a single supply is desired, connect VBIAS to VIN externally. N/A 13 PGREF Power-Good Threshold (Input): Analog reference used to specify the PWRGD threshold. When the voltage at this pin exceeds its threshold, VTH, PWRGD is asserted high. An external resistive divider network is used to determine the output voltage level at which VTH is exceeded. See “Functional Description” for further detail. When the PWRGD signal is not utilized, this input should be tied to VOUT. N/A 1 PWRGD Power-Good Output: Active high, open-drain. This pin asserts high when the voltage at PGREF exceeds its threshold. N/A 4 UVLOIN Undervoltage Lockout Adjust Input: With this pin left open, the UVLO threshold is internally set to 1.45V. When the switching voltage (VIN) is below 1.6V, connecting an external resistive divider to this input will lower the UVLO threshold. The total resistance of the divider must be less than 200kΩ. See “Applications Information” for further detail. January 2005 Pin Function Switch Enable Input: Gate control pin of the output MOSFET available as an active high (–1) or active low (–2) input signal. 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. Ground Connection: Tie to analog ground. 3 M0512-112603 MIC2042/2043 Micrel Absolute Maximum Ratings(1) Operating Ratings(2) Supply Voltage VIN and VBIAS ............................................................................. 6V /FAULT, PWRGD Output Voltage ................................... 6V /FAULT, PWRGD Output Current .............................. 25mA Junction Temperature (TJ) ...................... Internally Limited ESD Rating(3) Human Body Model ................................................... 3kV Machine Model ........................................................ 200V Supply Voltage VIN ............................................................... 0.8V to 5.5V VBIAS ........................................................... 1.6V to 5.5V Continuous Output Current ................................ 0.5A to 3A Ambient Temperature (TA) ........................... –40°C to 85°C Package Thermal Resistance SOP (θJA) .......................................................... 160°C/W TSSOP (θJA) ....................................................... 85°C/W Electrical Characteristics(4) VIN = VBIAS = 5V; TA = 25°C unless specified otherwise. Bold indicates –40°C to +85°C. Symbol Parameter Condition VIN Switch Input Voltage VIN ≤ VBIAS Min Typ Max Units 14-pin TSSOP 0.8 5.5 V 8-pin SOP 1.6 5.5 V 1.6 5.5 V VBIAS Bias Supply Voltage (14-pin TSSOP) IBIAS VBIAS Supply Current - Switch OFF VBIAS Supply Current - Switch ON Note 5 No load No load 0.1 300 5 400 µA µA VEN Enable Input Voltage VIL(max) 2.4 1.5 V VIH(min) 3.5 VENHYST 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 CLF Current Limit Factor(2) VIN = 5V, 0.5V ≤ VOUT < 0.5VIN 0.5A ≤ IOUT ≤ 3A 310 VIN = 3V, 0.5V ≤ VOUT < 0.5VIN 0.5A ≤ IOUT ≤ 3A VTH PGREF and UVLOIN Threshold VIN = VBIAS = 1.6V to 5.5V (14-pin TSSOP) VLATCH Output Reset Threshold VIN = 0.8V to 5.5V VOUT rising (MIC2043) ILATCH Latched Output Off Current Output latched off (MIC2043) VOL Output Low Voltage (/FAULT, PWRGD) IOL (/FAULT) = 15mA –1 2.5 V 100 mV .01 1 µA 40 60 mΩ 10 µA 395 485 A×Ω 320 385 450 A×Ω 205 225 245 mV VIN–.0.2 1 3 V 5 mA 0.4 V 1 µA IOL (PWRGD) = 5mA IOFF /FAULT, PWRGD Off Current VFAULT = VPWRGD = 5V VUV Undervoltage Lockout Threshold VIN rising 1.30 1.45 1.58 V VIN falling 1.20 1.35 1.50 V VUVHYST Undervoltage Lockout Threshold Hysteresis VUVINTH UVLO Adjust Pin Threshold Voltage VUVINHYST mV VIN rising 205 225 245 mV VIN falling 185 205 225 mV UVLO Adjust Pin Threshold Hysteresis Overtemperature Threshold M0512-112603 100 20 mV TJ increasing 140 °C TJ decreasing 120 °C 4 January 2005 MIC2042/2043 Micrel 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 600 800 1000 µs tR Output Turn-on Rise Time RLOAD = 10Ω, CLOAD = 1µF 1 1.5 2 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 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 MIC2042/MIC2043-1 and VEN > 4.0V for MIC2042/MIC2043-2. ON is VEN > 4.0V for MIC2042/MIC2043-1 and VEN < 1.0V for MIC2042/MIC2043-2. 6. The current limit is determined as follows: ILIM = CLF/RSET. Timing Diagrams tOFF 50% 0 VEN tON 10% 0 VOUT 90% (a) MIC2042/43-1 50% 0 VEN tOFF tON 90% 10% 0 VOUT (b) MIC2042/43-2 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 — MIC2042-2 January 2005 5 M0512-112603 MIC2042/2043 Micrel Test Circuit C1 0.1mF VDD C2 0.1mF R1 20kW VIN C3 10mF R3 75kW R2 20kW R4 68kW MIC2042/43-xBTS 7 VOUT VBIAS 8, 12 VIN PGREF M0512-112603 10,11,14 13 2 EN 3 /FAULT 4 UVLOIN PWRGD 1 9 SLEW ILIM GND 6 R7 20kW 5 *CSLEW uses multiple values (See specific response plots) ILOAD *CSLEW 6 VOUT R5 260kW CLOAD 47mF R6 24kW RSET 200W January 2005 MIC2042/2043 Micrel Typical Characteristics 500 2 1.5 VIN = VBIAS = 1.6V Power-Good Reference Threshold vs. Temperature 1.55 300 200 220 1.45 VTH @ 1.6V to 5.5V UVLO (V) VBIAS = 3V 1.35 1.25 210 -40 -20 0 20 40 60 80 100 TEMPERATURE (°C) UVLO Adjust PinThreshold vs. Temperature 70 VIN = VBIAS = 1.6V 600 550 500 -40 -20 0 20 40 60 80 100 TEMPERATURE (°C) January 2005 Flag Response Delay vs. Temperature 45 VIN = VBIAS = 3V 40 30 VIN = VBIAS = 5V T FLAG (ms) RDS(ON) 50 40 35 TFLAG = 5V 30 25 VBIAS Reverse Current Flow vs. Output Voltage 20 18 16 14 12 10 8 6 VIN = GND 4 VBIAS = 1.6V 2 0 2 2.5 3 3.5 4 4.5 5 5.5 6 V OUT (V) 7 TFLAG = 3V 20 -40 -20 0 20 40 60 80 100 TEMPERATURE (°C) 25 SLEW VOLTAGE (V) 650 50 VIN = VBIAS = 1.6V 0 -40 -20 0 20 40 60 80 100 TEMPERATURE (°C) VIN = VBIAS = 5.5V VIN = VBIAS = 3V On Resistance vs. Temperature 10 I R (mA) 700 1.2 -40 -20 0 20 40 60 80 100 TEMPERATURE (°C) 20 800 750 UVLO– 60 Turn-On Delay vs. Temperature 900 850 80 UVLO+ 1.3 VBIAS = 1.6V 250 245 240 UVLO+ 235 230 225 220 215 210 UVLO– 205 200 -40 -20 0 20 40 60 80 100 TEMPERATURE (°C) UVLO Threshold vs. Temperature 1.4 215 100 VBIAS = 1.6V 1.5 225 400 1.5 0 -40 -20 0 20 40 60 80 100 TEMPERATURE (°C) VBIAS = 5.5V 500 V TH (mV) OUTPUT LEAKAGE (nA) 230 VBIAS = 3V 0.5 0 -40 -20 0 20 40 60 80 100 TEMPERATURE (°C) Output Leakage Current vs. Temperature 2 1 0.5 150 0 -40 -20 0 20 40 60 80 100 TEMPERATURE (°C) UVLO (V) VBIAS = 1.6V 1 100 -40 -20 0 20 40 60 80 100 TEMPERATURE (°C) TURN ON DELAY (µs) 2.5 VBIAS = 3V V EN (V) VIN = VBIAS = 3V 200 600 3 VBIAS = 5.5V 2.5 VIN = VBIAS = 5.5V 300 250 3.5 3 V = 5.5V BIAS 400 350 Enable Input Threshold (Rising) vs. Temperature 3.5 450 V EN (V) SUPPLY CURRENT (µA) Enable Input Threshold (Falling) vs. Temperature Supply Current vs. Temperature 20 Slew Voltage vs. Temperature VIN = V BIAS = 5V 15 10 5 VIN = V BIAS = 3V VIN = V BIAS = 1.6V 0 -40 -20 0 20 40 60 80 100 TEMPERATURE (°C) M0512-112603 MIC2042/2043 Micrel Functional Characteristics W m 5V Turn-Off 5V Turn-On !"# $ W m $ %& W m ! " W m W ! m M0512-112603 m "#" W m ! "# $ % 8 January 2005 MIC2042/2043 Micrel W m m ! January 2005 W m 9 M0512-112603 MIC2042/2043 Micrel Functional Diagram 20-. 2- ' 2/78 5 )9 ! 9/7 ' + 0 1 # '*''*' $%& + '& # + # # ,*' " / - //! 2/78 5 ) ! " + .! 3 4,56 9 2 9 46 / . / ! / + ( ") $ -#. MIC2042/43 Block Diagram M0512-112603 10 January 2005 MIC2042/2043 Micrel Programmable Current Limit The MIC2042/43 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 MIC2042/43 will limit from 0.5A to 3A with a set point accuracy of ±22%. In programming the nominal current limit, the value of RSET is determined using the following equation: Functional Description The MIC2042 and MIC2043 are high-side N-Channel switches equipped with programmable current limit up to 3A for use in general purpose power distribution applications. The switches, available with active-high or active-low enable inputs, provide output slew-rate control and 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. 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 MIC2042/43 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. RSET = 4 (390A × Ω) 4 –40°C to +85°C VIN = VBIAS = 3V 3 2.5 2.5 1.5 1 CLF (HI) 1.5 1 0.5 CLF (LO) 0 2 0 120 240 360 480 600 720 840 960 R SET (Ω) 0.5 0 I LIM (A) 3 2.5 CLF (HI) Current Limit vs. RSET –40°C to +85°C VIN = VBIAS = 1.6V 3.5 3 2 (1) ILIMIT Current Limit vs. RSET 3.5 I LIM (A) I LIM (A) 4 –40°C to +85°C VIN = VBIAS = 5V 3.5 ILIMIT = And given the ±22% tolerance of the current limit factor (CLF), the external resistor is bound by: 103Ω ≤ RSET ≤ 970Ω (2) The graphs below (Figure 3) display the current limit factor characteristic over the full temperature range at the indicated voltage. These curves 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 V IN = V BIAS = 3.0V and a nominal 2A current limit (RSET = 192Ω), the low and high current limit settings for the MIC2042/43 would be 1.66A and 2.34A, respectively, as shown on the 3V graph using the 192Ω reference point. When current limiting occurs, the MIC2042 and MIC2043 respond differently. Upon first reaching the limiting current both devices restrict current flow, allowing the load voltage to drop below VIN. If the VIN-to-VOUT differential voltage exceeds 200mV, then a fault condition is declared and the fault delay timer is started. If the fault condition persists longer than the delay period, typically 28ms, then the /FAULT output asserts low. At this point, the MIC2042 will continue to supply current to the load at the limiting value (ILIMIT), whereas the MIC2043 will latch off its output. 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” section. Current Limit vs. RSET CLF CLF (HI) 2 1.5 1 0.5 CLF (LO) 0 120 240 360 480 600 720 840 960 R SET (Ω) 0 CLF (LO) 0 120 240 360 480 600 720 840 960 R SET (Ω) Figure 3. Current Limit Factor January 2005 11 M0512-112603 MIC2042/2043 Micrel /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 MIC2042/43. 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 MIC2042, 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 MIC2042 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 MIC2042 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. 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 (MIC2043) The MIC2043 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 M0512-112603 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 MIC2043 will again shut off all power to the load after 28ms. Once the fault has been removed, then normal operation will resume. Open Load Detection The MIC2043 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 MIC2043 latches off. Power-Good Detection The MIC2042/43 can detect when the output voltage is above or below a preset threshold that is monitored by a comparator at the PGREF input. The PWRGD signal is an N-Channel open-drain MOSFET output and an external pull-up resistor up to a 6V maximum rail is required for the PWRGD pin. Whenever the voltage at the PGREF pin exceeds its threshold (VTH), typically 230mV, the PWRGD output is asserted. Using the typical applications circuit from page 1 that switches 3.3V as an example, the output voltage threshold determining “power is good” is calculated by the following equation: R2 VOUT(GOOD) = VTH × 1 + R3 (3) In substituting the resistor values of the circuit and the typical PGREF threshold, the resulting VOUT(GOOD) is calculated as 3.0V for this 3.3V switching application. Slew The MIC2042/43’s output rise time is controlled at turn-on to a minimum of 1.5ms and is controlled by an internal slew-rate limiting circuit. A slew-rate adjustment control pin is available for applications requiring slower rise times. By placing a capacitor between SLEW and ground, longer rise times can be achieved. For further detail, see the “Applications Information” section. 12 January 2005 MIC2042/2043 Micrel linear response. See the “Functional Characteristics” plots. Table 1 shows the rise time for various standard capacitor values. Additionally, the output turn-on time must be less than the nominal flag delay of 28ms in order to avoid nuisance tripping of the /FAULT output. This limit is imposed by the current limiting circuitry which monitors the (VIN – VOUT) differential voltage and concludes a fault condition is present if the differential voltage exceeds 200mV for more than the flag delay period. For the MIC2043, the /FAULT will assert and the output will latch off if the output is not within 200mV of the input before the flag delay times out. When using the active-low (–2) option with the EN input tied to ground, slew control is functional during initial start-up but does not function upon resetting the input power to the device. In order for the SLEW control to operate during consecutive system restarts, the EN pin must reset (toggle OFF to ON). 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 voltage. 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: Applications Information Input and Output Supply Bypass Filtering The need for input supply bypass is necessary 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 When the MIC2042 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 MIC2042 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 power cable (≤ 1ft., 16 to 20 gauge wire), a minimum output capacitance of 22µF is strongly recommended and should be placed close to the VOUT pin of the MIC2042. For applications that use more than a foot of cable, an additional 10µF/ft. is recommended. R2 VUVTH = 0.23V × 1 + R3 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 MIC2042/43. Reverse Current Block The MIC2042/43 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 pin has a limited reverse current flow if the voltage at VOUT is pulled above VBIAS when the device is disabled. A graph of the VBIAS reverse current flow is shown in the “Functional Characteristics” plots. 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. Output Slew-Rate Adjustment The output slew-rate for the MIC2042/43 can be slowed down by the capacitor (16V rating, minimum; 25V suggested) between SLEW and GND. The slew-rate control circuitry is independent of the load capacitance and exhibits a non- January 2005 (4) Conditions: VIN = VBIAS = 5V/3V; CLOAD = 47µF; ILOAD = 1A CSLEW (µF) Rise Time (ms) 5V 3V 0.01 3 4.75 0.033 10.5 15 0.047 14 21 0.1 32 46 Table 1. Typical Output Rise Time for Various CSLEW 13 M0512-112603 MIC2042/2043 Micrel MIC2042-1BTS VDD 2.5V VIN 0.8V C3 10mF R2 95.3kW 1% R1 47kW C2 0.1mF C1 0.1mF 7 8, 12 2 4 R3 59kW 1% VBIAS VIN VOUT PGREF 10,11,14 13 EN R6 47kW UVLOIN 9 SLEW 6 ILIM RSET 200W PWRGD 1 /FAULT GND 3 5 R4 75kW 1% R5 36.5kW 1% R7 47kW CLOAD 22mF VOUT 0.8V @1.5A Digital Output Signals Note: All VIN pins (8, 12) must be externally tied together. All VOUT pins (10, 11, 14) must be externally tied together. Undervoltage Lockout = 0.6V. Output Power-Good = 0.7V. Figure 4. Lower UVLO Setting 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 (5) To relate this to junction temperature, the following equation can be used: TJ = PD × RθJA + TA (6) where TJ = junction temperature, TA = ambient temperature and RθJA is the thermal resistance of the package. Printed Circuit Board Hot-Plug The MIC2042/43 are ideal inrush current limiting power switches suitable for hot-plug applications. Due to the integrated charge pump, the MIC2042/43 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. PCB Layout Recommendations The MIC2042 and MIC2043 have very low on-resistance, typically 40mΩ, and the switches can provide up to 3A of continuous output current. Under such heavy loads, the power consumed by the devices may cause the devices to M0512-112603 14 heat up considerably. The following list contains some useful suggestions for PCB layout design of the MIC2042/43 in order to prevent the die from overheating under normal operating conditions: 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 MIC2042/43 IC for heat distribution. 3. Tie the common power pins (VIN = pins 8 and 12 and VOUT = pins 10, 11, 14 for the 14-pin TSSOP, VIN = pins 5 and 7 and VOUT = pins 6 and 8 for the 8-pin SOP) 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 2A maximum current, design traces for 2.5A capability. 4. For PCB trace width calculation, 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. January 2005 MIC2042/2043 Micrel Package Information 0.026 (0.65) MAX) PIN 1 0.157 (3.99) 0.150 (3.81) DIMENSIONS: INCHES (MM) 0.020 (0.51) 0.013 (0.33) 0.050 (1.27) TYP 0.064 (1.63) 0.045 (1.14) 45° 0.0098 (0.249) 0.0040 (0.102) 0°–8° 0.197 (5.0) 0.189 (4.8) SEATING PLANE 0.010 (0.25) 0.007 (0.18) 0.050 (1.27) 0.016 (0.40) 0.244 (6.20) 0.228 (5.79) 8-Pin SOP (M) 4.50 (0.177) 6.4 BSC (0.252) 4.30 (0.169) DIMENSIONS: MM (INCH) 0.30 (0.012) 0.19 (0.007) 5.10 (0.200) 4.90 (0.193) 0.20 (0.008) 0.09 (0.003) 1.10 MAX (0.043) 0.65 BSC (0.026) 1.00 (0.039) REF 8° 0° 0.15 (0.006) 0.05 (0.002) 0.70 (0.028) 0.50 (0.020) 14-Pin TSSOP (TS) MICREL, INC. TEL 1849 FORTUNE DRIVE SAN JOSE, CA 95131 USA + 1 (408) 944-0800 FAX + 1 (408) 944-0970 WEB http://www.micrel.com The information furnished by Micrel in this data sheet 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. © 2005 Micrel, Incorporated. January 2005 15 M0512-112603