MIC2544A-2YM

MIC2544A/2548A Programmable Current Limit High-Side Switch General Description Features The MIC2544A and MIC2548A are integrated, high-side power switches optimized for low loss DC power switching and other power management applications, including Advanced Configuration and Power Interface (ACPI). The MIC2544A/48A is a cost-effective, highly integrated solution that requires few external components to satisfy USB and ACPI requirements. Load current management features include a precision resistor-programmable output current-limit and a soft-start circuit which minimizes inrush current when the switch is enabled. Thermal shutdown, along with current-limit, protects the switch and the attached device. The MIC2544A/48A’s open-drain flag output is used to indicate current-limiting or thermal shutdown to a local controller. The MIC2548A has an additional internal latch which turns the output off upon thermal shutdown providing robust fault control. The enable signal is compatible with both 3V and 5V logic, and is also used as the thermal shutdown latch reset for the MIC2548A The MIC2544A and MIC2548A are available in active-high and active-low enable versions in the 8-pin SOIC (small-outline integrated circuit) and 8-pin MSOP (microsmall-outline package). • • • • • • • • • • • 2.7V to 5.5V input Adjustable current-limit up to 1.5A Reverse current flow blocking (no “body diode”) 90µA typical on-state supply current 1μA typical off-state supply current 120mΩ maximum on-resistance Open-drain fault flag Thermal shutdown Thermal shutdown output latch (MIC2548A) 2ms (slow) turn-on and fast turn-off Available with active-high or active-low enable Applications • • • • • • USB power distribution PCI bus power switching Notebook PC ACPI power distribution PC card hot swap applications Inrush current-limiting _________________________________________________________________________________________________________ Typical Application Typical Advanced Configuration and Power Interface (ACPI) Application Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com April 2010 M9999-043010 Micrel, Inc. MIC2544A/2548A Ordering Information* Part Number Temperature Range Package Pb-Free MIC2544A-1YM Active High -40°C to +85°C 8-pin SOIC „ MIC2544A-1YMM Active High -40°C to +85°C 8-pin MSOP „ MIC2544A-2YM Active Low -40°C to +85°C 8-pin SOIC „ MIC2544A-2YMM Active Low -40°C to +85°C 8-pin MSOP „ MIC2548A-1YM Active High „ -40°C to +85°C 8-pin SOIC „ MIC2548A-1YMM Active High „ -40°C to +85°C 8-pin MSOP „ MIC2548A-2YM Active Low „ -40°C to +85°C 8-pin SOIC „ Active Low „ 8-pin MSOP „ MIC2548A-2YMM Enable Latch* -40°C to +85°C *Thermal Shutdown Latch April 2010 2 M9999-043010 Micrel, Inc. MIC2544A/2548A Pin Configuration 8-pin SOIC 8-Pin MSOP (MM) Note: 1. Pins 4 and 5 for SOIC and MSOP are different. Pin Description Pin Number MSOP-8 Pin Number SOIC-8 Pin Name 1 1 EN Enable (Input): Logic-compatible enable input. Active-high (-1) or activelow (-2). High input >1.7V typical; low input VIN) when the switch is disabled. In this situation, the MIC2544A/48A avoids undesirable current flow from OUT to IN. Both OUT pins must be connected together. Enable Input EN must be driven logic high or logic low, or be pulled high or low for a clearly defined input. Floating the input may cause unpredictable operation. EN should not be allowed to go negative with respect to GND, and VEN should be less than or equal to VIN. Thermal Shutdown Thermal shutdown shuts off the output MOSFET and signals the fault flag if the die temperature exceeds 150°C. 5°C of hysteresis prevents the switch from turning on until the die temperature drops to 145°C. Over-temperature detection functions only when the April 2010 14 M9999-043010 Micrel, Inc. MIC2544A/2548A Giving one a maximum ILIMIT variation over-temperature of: ILIMIT_MIN ILIMIT_TYP ILIMIT_MAX 0.79A (-21%) 1.0A 1.19A (+19%) Setting ILIMIT The MIC2544A/2548A’s current limit is user programmable and controlled by a resistor connected between the ILIMIT pin and ground. The value of this resistor is determined by the following equation: I LIMIT = CurrentLimitFactor(CLF) R SET or R SET = CurrentLim itFactor(V) ILIMIT (A) For example: Set ILIMIT = 1.0A Looking in the Electrical specifications we will find CLF at ILIMIT = 1 A. Min Typ Max Units 184 230 276 V Table 1. CLF at ILIMIT = 1A For the sake of this example, we will say the typical value of CLF at an IOUT of 1A is 230V. Applying the equation above: R SET (Ω ) = 230V = 230Ω 1.0A RSET = 232Ω (the closest standard 1% value) Designers should be aware that variations in the measured ILIMIT for a given RSET resistor, will occur because of small differences between individual ICs (inherent in silicon processing) resulting in a spread of ILIMIT values. In the example above a typical value of CLF was used to calculate RSET. One can determine ILIMIT’s spread by using the minimum and maximum values of CLF and the calculated value of RSET. ILIMIT_MIN = April 2010 R_SET I_OUT_Min I_OUT_Max 0.2 1150 0.140 0.260 0.3 767 0.210 0.390 0.4 575 0.280 0.520 0.5 460 0.350 0.650 0.6 383 0.480 0.720 0.7 329 0.560 0.840 0.8 288 0.640 0.960 0.9 256 0.720 1.080 1 230 0.800 1.200 1.1 209 0.880 1.320 1.2 192 0.960 1.440 1.3 177 1.040 1.560 1.4 164 1.120 1.680 1.5 153 1.200 1.800 Table 2. MIC2544A/2548A RSET Table Short-Circuit Protection In the event of a short circuit, the output current will fold back to approximately 70% of the short-circuit currentlimit. Fault Flag FLG is an N-channel, open-drain MOSFET output. The fault flag is active (low) for current-limit or thermal shutdown conditions. The flag output MOSFET is capable of sinking a 10mA load to typically 100mV above ground. The FLG response delay time tD is typically 5µs. 184V = 0.79 A 232Ω ILIMIT _ MAX = I_OUT 276V = 1.19 A 232Ω 15 M9999-043010 Micrel, Inc. MIC2544A/2548A Application Information Supply Filtering A minimum 1μF bypass capacitor from IN-to-GND, located near the MIC2544A and MIC2548A, is strongly recommended to control supply transients. Without a bypass capacitor, an output short may cause sufficient ringing on the input (from supply lead inductance) to damage internal control circuitry. An additional 22µF input capacitor placed close to the IC is required if a bulk input capacitor is further than 3 inches away from the IC. Input transients must not exceed the absolute maximum supply voltage (VIN max = 6V) even for a short duration. Figure 4. Flag Glitch with COUT = 120µF Adding an optional series resistor-capacitor (RSET2), in parallel with RSET, and as shown in Figure 8, allows the transient current-limit to be set to a different value than steady-state. A typical USB hot-plug inrush is 2A to 3A for 10μs to 20μs. If RSET is 309Ω (525mA), an RSET2 of 100Ω (2.3A) and CSET of 1μF (RC = 100μs) allows transient surge of 3A to pass for 100μs without tripping the over current flag (FLG), as shown in Figure 5. Figure 3. Supply Bypassing Power Dissipation The device's junction temperature depends upon several factors such as the load, PCB layout, ambient temperature, and package type. Equations that can be used to calculate power dissipation and junction temperature are found below. Calculation of power dissipation can be accomplished by the following equation: PD = RDS(on) × (IOUT)2 To relate this to junction temperature, the following equation can be used: Tj = PD × θJA + TA where: Tj = junction temperature TA = ambient temperature θJA = is the thermal resistance of the package Figure 5. ILIMIT Filter with COUT = 120µF Figure 6 circuit can also be used to filter out transient FLG assertion. The value of the RC time constant should be selected to match the length of transient. Figure 7 shows the FLAG pin waveform due to the inrush of current surge. Transient Over Current Filter The inrush current from the connection of a heavy capacitive load may cause the fault flag to fall for 10μs to 200μs while the switch is in a constant-current mode, charging the capacitance, as shown in Figure 4. Figure 6. Flag Filter Circuit April 2010 16 M9999-043010 Micrel, Inc. MIC2544A/2548A Figure 7. Flag Filter with COUT = 100µF USB Power Distribution The MIC2544A is ideal for meeting USB power distribution requirements. Figure 8 depicts a USB Host application. RSET should be set to a value providing a current-limit >500mA. The accurate current-limit of the MIC2544A will reduce power supply current requirements. Also, fast reaction to short circuit faults prevent voltage droop in mobile PC applications. Printed Circuit Board Hot-Plug The MIC2544A/48A are ideal inrush current-limiters suitable for hot-plug applications. Due to the integrated charge pump, the MIC2544A/48A presents high impedance when off and slowly becomes low impedance as it turns on. This “soft start” feature effectively isolates power supplies from highly capacitive loads by reducing inrush current during hot-plug events. Figure 9 shows how the MIC2544A may be used in a hot-plug application. April 2010 17 M9999-043010 Micrel, Inc. MIC2544A/2548A Figure 8. USB Host Application Note: MSOP package option uses pin 5 for ILIM. Pin 4 is not connected (NC). Bold lines indicate 0.1” wide, 1-oz. copper high-current traces. Figure 9. Hot Plug Application April 2010 18 M9999-043010 Micrel, Inc. MIC2544A/2548A Package Information 8-pin SOIC (M) 8-Pin MSOP (MM) 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 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 a Purchaser’s own risk and Purchaser agrees to fully indemnify Micrel for any damages resulting from such use or sale. © 2010 Micrel, Incorporated. April 2010 19 M9999-043010