MIC2537 Micrel MIC2537 Quad Power Distribution Switch Preliminary Information General Description Features The MIC2537 is a cost-effective high-side power switch with four independently controlled channels, optimized for buspowered Universal Serial Bus (USB) applications. Few external components are necessary to satisfy USB requirements. The MIC2537 satisfies the following USB requirements: each switch channel supplies up to 100mA as required by USB bus-powered downstream devices; fault current is limited to typically 250mA, well below the UL 25VA safety requirements; and a flag output is available to indicate fault conditions to the local USB controller. Soft start eliminates the momentary voltage drop on the upstream port that may occur when the switch is enabled in bus-powered applications. Additional features include thermal shutdown to prevent catastrophic switch failure from high-current loads and 3.3V and 5V logic compatible enable inputs. The MIC2537 is available in active-high and active-low versions in a 16-lead SOP package. • • • • • • • • • • • • Compliant to USB specifications 3V to 5.5V input 100mA minimum continuous load current per port 425mΩ typical on-resistance < 400mA current limit Individual open-drain fault flag leads 3V/5V-compatible enable inputs Active-high (-1) and active-low (-2) versions 100µA max. on-state supply current <1µA typical off-state supply current 16-lead SOP package –40°C to 85°C operation Applications • • • • • • USB keyboards USB bus-powered docking stations Notebook docking stations Notebook PCs PDA General power distribution Typical Application Upstream VBUS 4.75V to 5.25V 500mA max. Ferrite Bead 10k MIC5207-3.3 LDO Regulator IN 4.7 µF 3.3V USB Controller EN OC V+ OUT 1µF GND EN OC EN D+ D– Bold lines indicate 0.1" wide, 1-oz. copper high-current traces. VBUS 10k 10k 10k GND ENA 0.01µF IN FLGA ENB NC OUTA FLGB OUTB OUTC ENC OC FLGC EN END OC FLGD D+ 33µF* MIC2537 D– GND 0.1 µF VBUS D+ 33µF* 0.01µF OUTD Downstream USB Port 1 100mA max. D– GND NC Downstream USB Port 2 100mA max. GND VBUS D+ 33µF* 0.01µF * 33µF, 16V tantalum or 100µF, 10V electrolytic per port D– GND Downstream USB Port 3 100mA max. VBUS D+ 33µF* 0.01µF D– GND Downstream USB Port 4 100mA max. Typical Bus-Powered Hub Micrel, Inc. • 1849 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 944-0970 • http://www.micrel.com December 1999 1 MIC2537 MIC2537 Micrel Ordering Information Part Number Enable Temperature Range Package MIC2537-1BM Active High –40°C to +85°C 16-Lead SOP MIC2537-2BM Active Low –40°C to +85°C 16-Lead SOP Pin Configuration MIC2537-x FLGA 1 16 FLGD ENA 2 15 END OUTA 3 14 OUTD GND 4 13 IN NC 5 12 NC OUTB 6 11 OUTC ENB 7 10 ENC FLGB 8 9 FLGC 16-Lead SOP (M) Pin Description Pin Number Pin Name 1 FLGA Flag A: (Output): Channel A open-drain fault flag output. 2 ENA Enable A (Input): Channel A control input. 3 OUTA Output A: Channel A switch output. 4 GND Ground: Supply return. Connect both leads to ground. 5, 12 NC 6 OUTB 7 ENB Enable B (Input): Channel B control input. 8 FLGB Flag B (Output): Channel B open-drain fault flag output. 9 FLGC Flag C (Output): Channel C open-drain fault flag output. 10 ENC Enable C (Input): Channel C control input. 11 OUTC 13 IN 14 OUTD 15 END Enable D (Input): Channel D control input. 16 FLGD Flag D (Output): Channel D open-drain fault flag output. December 1999 Pin Function Not internally connected Output B: Channel B switch output. Output C: Channel C switch output. Positive Supply Input Output D: Channel D switch output. 2 MIC2537 MIC2537 Micrel Absolute Maximum Ratings (Note 1) Operating Ratings (Note 2) Supply Voltage (VIN) ..................................................... +6V Fault Flag Voltage (VFLG).............................................. +6V Fault Flag Current (IFLG) ............................................ 25mA Output Voltage (VOUT) .................................................. +6V Output Current (IOUT) ............................... Internally Limited Control Input (VEN) ......................................... –0.3V to 12V Storage Temperature (TS) ....................... –65°C to +150°C Lead Temperature (Soldering 5 sec.) ....................... 260°C ESD Rating, Note 3 ....................................................... 2kV Supply Voltage (VIN) ...................................... +3V to +5.5V Ambient Operating Temperature (TA) ........ –40°C to +85°C Thermal Resistance SOP (θJA) .......................................................... 120°C/W Electrical Characteristics VIN = +5V; TA = 25°C; unless noted. Parameter Condition Supply Current Note 4, switch off, OUTA–D = open Enable Input Threshold Min Typ Max Units 0.75 5 µA Note 4, all switches on, OUTA–D = open 70 100 µA low-to-high transition 1.8 2.4 V high-to-low transition, Note 4 Enable Input Current 0.8 1.6 V VEN = VOH(min) = 2.4V 0.01 1 µA VEN = VOL(max) = 0.8V 0.01 1 µA Enable Input Capacitance 1 pF Switch Resistance single switch, 100mA load 425 Output Turn-On Delay RL = 50Ω, CL = 1µF, Note 5 0.51 ms Output Turn-On Rise Time RL = 50Ω, CL = 1µF, Note 5 0.5 ms Output Turnoff Delay RL = 50Ω, CL = 1µF, Note 5 150 300 µs Output Turnoff Fall Time RL = 50Ω, CL = 1µF, Note 5 148 300 µs Output Leakage Current each output (switch off) 1 10 µA Current Limit Threshold ramped load applied to enable output, Note 6 300 500 mA Continuous Load Current each output, FLG not active 100 Short Circuit Current Limit each output (enabled into load), VOUT = 4.0V 150 Overtemperature Shutdown TJ increasing 135 °C Threshold TJ decreasing 125 °C Error Flag Output Resistance VIN = 5V, IL = 10mA 10 Ω VIN = 3.3V, IL = 10mA 12 Ω Error Flag Off Current 0.2 VFLAG = 5V Exceeding the absolute maximum rating may damage the device. Note 2. The device is not guaranteed to function outside its operating rating. mΩ mA 250 0.01 Note 1. 700 400 mA µA 1 Note 3. Devices are ESD sensitive. Handling precautions recommended. Human body model, 1.5kΩ in series with 100pF. Note 4. Off is ≤ 0.8V and on is ≥ 2.4V for the MIC2537-1. Off is ≥ 2.4V and on is ≤ 0.8V for the MIC2537-2. The enable input has approximately 200mV of hysteresis. See control threshold charts. Note 5. See “Timing Diagrams.” Note 6. See “Functional Characteristics: Current-Limit Response” graph. December 1999 3 MIC2537 MIC2537 Micrel Typical Characteristics Supply Current vs. Supply Voltage 60 40 TA = 25°C RL = ∞ 3 4 5 SUPPLY VOLTAGE (V) 60 40 CURRENT (mA) 200 VIN = 5V IL = 100mA 100 0 2 Control Threshold vs. Supply Voltage 2.0 2.0 THRESHOLD VOLTAGE (V) ENABLE VOLTAGE (V) VIH 1.5 VIL 1.0 0.5 TA = 25°C 2 3 4 5 SUPPLY VOLTAGE (V) ILIM 100 0 -40 -20 0 20 40 60 80 100 TEMPERATURE ( °C) 6 TA = 25°C IL = 100mA 100 3 4 5 SUPPLY VOLTAGE (V) 250 200 3 4 5 SUPPLY VOLTAGE (V) 6 ITHR 200 ILIM 150 100 TA = 25°C 50 200 300 ITHR 150 300 Overcurrent Threshold , and Current Limit vs. Te mperature 300 250 400 0 2 Overcurrent Threshold and Current Limit vs. Supply Voltage 300 1.5 RL = ∞ 0 -40 -20 0 20 40 60 80 100 TEMPERATURE (°C) 400 0 VIN = 3.3V 20 6 Ouput On-Resistance Variation vs. Temperat ure 500 VIN = 5V CURRENT (mA) 2 80 VIN = 5V 50 0 -40 -20 6 0 20 40 60 80 100 TEMPERATURE ( °C) Control Threshold vs. Temperature Output Rise Time vs. Temperature 500 VIH 400 1.5 VIL 1.0 0.5 VIN = 5V 0 -40 -20 0 20 40 60 80 100 TEMPERATURE (°C) TIME (µs) 20 TIME (µs) Ouput On-Resistance Variation vs. Supply Voltage 500 ON-RESISTANCE (mΩ) 80 0 ON RESISTANCE ( mΩ) Supply Current vs. Temperature 100 SUPPLY CURRENT (µA) SUPPLY CURRENT (µA) 100 300 200 100 VIN = 5V CL = 0.01µF RL = 44Ω 0 -40 -20 0 20 40 60 80 100 TEMPERATURE (°C) Output Fall Time vs. Temperature 1.0 0.5 VIN = 5V CL = 0.01µF RL = 44Ω 0 -40 -20 0 20 40 60 80 100 TEMPERATURE (°C) December 1999 4 MIC2537 MIC2537 Micrel Functional Characteristics Input Voltage Response (Input Voltage Decreasing: MIC2537-2) VOUT VFLG VIN IOUT (100mA/div.) (2V/div.) (2V/div.) (2V/div.) VOUT VFLG VIN IOUT (100mA/div.) (2V/div.) (2V/div.) (2V/div.) Input Voltage Response (Input Voltage Rising: MIC2537-2) EN = 0V RL = 24Ω EN = 0V RL = 24Ω Current Limit Transient Response (Heavy Load Applied to Output: MIC2537-2) Current Limit Response (Ramped Load: MIC2537-2) VOUT VFLG VEN (5V/div.) (10V/div.)(5V/div.) TIME (25ms/div.) VOUT VFLG VEN (5V/div.) (10V/div.)(5V/div.) TIME (25ms/div.) 1V TIME (25µs/div.) December 1999 250mA Current Limit Threshold IOUT (100mA/div.) IOUT (500mA/div.) VIN = 5V 1V 180mA Short Circuit Current Limit VIN = 5V TIME (5ms/div.) 5 MIC2537 MIC2537 Micrel Test Circuit VOUT Device Under OUT Test RL CL Timing Diagrams tR tF 90% VOUT 90% 10% 10% Output Rise and Fall Times VEN 50% tOFF tON 90% VOUT 10% Active-Low Switch Delay Times (MIC2537-2) VEN 50% tOFF tON VOUT 90% 10% Active-Low Switch Delay Times (MIC2537-1) December 1999 6 MIC2537 MIC2537 Micrel Functional Diagram FLGA OUTA ENA GATE CONTROL CHARGE PUMP CURRENT LIMIT FLG B ENB OUTB GATE CONTROL CHARGE PUMP CURRENT LIMIT 1.2V REFERENCE THERMAL SHUTDOWN OSC. IN CURRENT LIMIT CHARGE PUMP GATE CONTROL ENC OUTC FLGC CHARGE PUMP CURRENT LIMIT GATE CONTROL END OUTD FLGD MIC2537 GND December 1999 7 MIC2537 MIC2537 Micrel Current Sensing and Limiting The current-limit threshold is preset internally. The preset level prevents damage to the output MOSFET and external load but allows a minimum current of 0.15A through the output MOSFET of each channel. The current-limit circuit senses a portion of the output FET switch current. The current sense resistor shown in the block diagram is virtual and has no voltage drop. The reaction to an overcurrent condition varies with the following three scenarios: Functional Description The MIC2537-1 and MIC2537-2 are quad high-side switches with active-high and active-low enable inputs, respectively. Fault conditions turn off or inhibit turn-on of one or more of the output transistors, depending upon the type of fault, and activate the open-drain error flag transistors making them sink current to ground. Input and Output IN (input) is the power supply connection to the logic circuitry and the drain of each output MOSFET. OUTx (output) is the source of each respective MOSFET. In a typical circuit, current flows through the switch from IN to OUTx toward the load. If VOUT is greater than VIN, current will flow from OUT to IN since the MOSFET is bidirectional when on. The output MOSFET and driver circuitry are also designed to allow the MOSFET source to be externally forced to a higher voltage than the drain (VOUTx > VIN) when the output is off. In this situation, the MIC2537 prevents reverse current flow. Thermal Shutdown Thermal shutdown shuts off the affected output MOSFET and signals the corresponding fault flags if the die temperature exceeds 135°C. 10°C of hysteresis prevents the switch from turning on until the die temperature drops to 125°C. Overtemperature detection functions only when at least one switch is enabled. Current-Limit Induced Thermal Shutdown Internal circuitry increases the output MOSFET on-resistance until the series combination of the MOSFET on-resistance and the load impedance limits output current to approximately 200mA. The resulting increase in power dissipation may cause the shorted channel to go into thermal shutdown. In addition, even though individual channels are thermally isolated, it is possible they may shut down when an adjacent channel is shorted. When this is undesirable, shutdown of the channels not shorted can be avoided by externally responding to the fault and disabling the current limited channel before the shutdown temperature is reached. The delay between the flag indication of a current limit fault and thermal shutdown will vary with ambient temperature, board layout, and load impedance, but is typically several seconds. The USB controller must therefore recognize a fault and disable the appropriate channel within this time. December 1999 Switch Enabled into Short Circuit If a switch is powered on or enabled into an excessive load or short circuit, the switch immediately goes into a constantcurrent mode, slowly increasing the output voltage. The fault flag goes low until the load is reduced. Short Circuit Applied to Output When a heavy load or short circuit is applied to an enabled switch, a large transient current may flow until the currentlimit circuitry responds. Once this occurs, the device limits current to less than the short circuit current-limit specification. See the “Functional Characteristics: Current-Limit Transient Response graph for details. Current-Limit Response The MIC2537 current-limit profile exhibits a small foldback effect of approximately 100mA. Once this current-limit threshold is exceeded the device enters constant-current mode. This constant current is specified as the short-circuit current limit in the “Electrical Characteristics” table. It is important to note that the MIC2537 will deliver load current up to the current-limit threshold. See the “Functional Characteristics: Current-Limit Response” graph for details. Fault Flag FLGx is an open-drain N-channel MOSFET output. Fault flags are active (low) for current limit or thermal shutdown. Each flag output MOSFET is capable of sinking a 10mA load to approximately 200mV above ground. Several FLGx pins may be wired-NOR connected to a common pull-up resistor. 8 MIC2537 MIC2537 Micrel In USB applications it is required that output bulk capacitance shown in “Typical Application” is utilized to meet transient regulation requirements during hot-plug events. When the MIC2537 is enabled, the flag will go active for about 5ms depending on output capacitance. Additionally, during hotplug events, inrush currents may cause the flag to go active for approximately 30µs. If these “false” overcurrent indications are a system problem, they can be masked by an RC filter on the flag output (see Figure 2). Alternatively, a 15ms debounce routine may be programmed into the USB logic controller to eliminate the need for an RC filter. Bus-Powered Hub Port Switching The USB Specification requires that bus-powered hubs implement port switching on either a ganged or individual basis. The specific implementation must be reported via the Hub Descriptor Status Register. Individual port switching has advantages in that a fault on one port will not prevent the other ports from operating correctly. In addition, a soft-start circuit must be included in order to reduce inrush currents when the switch is enabled. To meet this requirement, the MIC2537 has been designed to slowly ramp its output. Suspend Current For hubs, Universal Serial Bus Specification Revision 1.1 section 7.2.3, stipulates that the maximum suspend current for a configured hub is 2.5mA. This number is derived by allocating 500µA for up to four downstream ports plus 500µA for the hub’s internal functions. A nonconfigured hub is considered a low-power device and cannot consume more than 500µA. In a nonconfigured state all downstream devices will be switched off. In most cases, a nonconfigured hub is not a practical state for the system. Therefore, the 2.5mA specification is the applicable target specification for the suspend state. In a bus-powered hub with less than 4 ports, the hub may use the additional current for internal functions. The 500µA worst case suspend current must be further divided among the data port termination resistors and internal functions. The termination resistors will consume 3.6V ÷ (16.5KΩ – 5%) = 230µA. This leaves only 270µA for internal functions. Assuming 100µA as the maximum USB controller suspend current, 170µA remains for the rest of the system. The MIC2537 will consume 100µA maximum, leaving a margin of 70µA. Applications Information Supply Filtering A 0.1µF to 1µF bypass capacitor from IN to GND, located at the device, 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. Input or output transients must not exceed the absolute maximum supply voltage (VIN(max) = 6V) even for a short duration. VIN 3V to 5.5V 0.1µF to 1µF MIC2537 FLGA FLGB ENA ENB OUTA OUTB GND NC IN NC OUTC OUTD ENC END FLGC FLGD Figure 1. Supply Bypassing Enable Input EN must be driven logic high or logic 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. Soft Start The MIC2537 presents a high impedance when off and slowly becomes a low impedance as it turns on. This reduces inrush current and related voltage drop that results from charging a capacitive load, satisfying the USB voltage droop requirements. Transient Overcurrent Fault-Flag Filter When the MIC2537 is enabled, large values of capacitance at the output of the device will cause inrush currents to flow that exceed the short circuit current-limit threshold of the device and cause the flag to activate. The duration of this time depends on the size of the output capacitance. See “Functional Characteristics: Switch Turn-On and Turnoff Charcteristics” for details. During the charging time, the device enters into constant-current mode and the flag is activated. As the capacitance is charged the current decreases below the short circuit current-limit threshold and the flag will be deasserted. USB Controller OVERCURRENT 10k FLGA 50k 0.3µF FLGB FLGC FLGD Figure 2. Transient Filter December 1999 9 MIC2537 MIC2537 Micrel USB Voltage Regulation USB specifications require a minimum downstream voltage supply of 4.40V from a bus-powered hub port (See Application Note 17 for details). The USB specification allows for a 100mV drop across the hub, leaving 250mV for PCB, upstream cable, and connector resistance. Therefore, the onresistance of the switch for each port, not including PCB resistance, must be about 100mV ÷ 100mA = 1Ω. The MIC2537 has a maximum on-resistance of 700mΩ, which easily satisfies this requirement. December 1999 Overcurrent Indication The USB Specification does not require bus-powered hubs to report overcurrent conditions to the host since the hub is already current-limited at the upstream port. However, if it is desired to report overcurrent, the Hub Descriptor Status Register must be programmed to indicate this. The MIC2537 provides a flag output for this application. 10 MIC2537 MIC2537 Micrel Package Information PIN 1 0.157 (3.99) 0.150 (3.81) DIMENSIONS: INCHES (MM) 0.020 (0.51) REF 0.050 (1.27) BSC 0.0648 (1.646) 0.0434 (1.102) 0.020 (0.51) 0.013 (0.33) 0.0098 (0.249) 0.0040 (0.102) 0.394 (10.00) 0.386 (9.80) SEATING PLANE 45° 0°–8° 0.050 (1.27) 0.016 (0.40) 0.244 (6.20) 0.228 (5.79) 16-Lead SOP (M) December 1999 11 MIC2537 MIC2537 Micrel MICREL INC. 1849 FORTUNE DRIVE SAN JOSE, CA 95131 TEL + 1 (408) 944-0800 FAX + 1 (408) 944-0970 WEB USA http://www.micrel.com This information is believed to be accurate and reliable, however no responsibility is assumed by Micrel for its use nor for any infringement of patents or other rights of third parties resulting from its use. No license is granted by implication or otherwise under any patent or patent right of Micrel Inc. © 1999 Micrel Incorporated December 1999 12 MIC2537