MIC2526-1BM TR

MIC2526 Micrel MIC2526 Dual USB Power Control Switch Not Recommended for New Designs Refer to MIC2026 General Description Features The MIC2526 is a dual integrated high-side power switch with independent enable and flag functions, optimized for selfpowered and bus-powered Universal Serial Bus (USB) applications. Few external components are necessary to satisfy USB requirements. The MIC2526 satisfies the following USB requirements: each switch channel supplies up to 500mA as required by USB downstream devices; the switch’s low on-resistance meets USB voltage drop requirements; fault current is limited to typically 750mA, 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, undervoltage lockout (UVLO) to ensure that the device remains off unless there is a valid input voltage present, and 3.3V and 5V logic compatible enable inputs. The MIC2526 is available in active-high and active-low versions in 8-pin DIP and SOIC packages. Compliant to USB specifications UL Recognized Component 2 independent switches 3V to 5.5V input 500mA minimum continuous load current per port 140mΩ maximum on-resistance 1.25A maximum short circuit current limit Individual open-drain fault flag pins 110µA typical on-state supply current 1µA typical off-state supply current Output can be forced higher than input (off-state) Thermal shutdown 2.4V typical undervoltage lockout (UVLO) 1ms turn-on (soft-start) and fast turnoff Active-high or active-low enable versions 8-pin SOIC and DIP packages Applications • • • • USB host and self-powered hubs USB bus-powered hubs Hot plug-in power supplies Battery-charger circuits Typical Application VCC 5.0V 4.50V to 5.25V Upstream VBUS 100mA max. VBUS 10k 100k 10k 100k 3.3V USB Controller MIC2526-2 Ferrite Beads VBUS D+ MIC5207-3.3 IN D+ 1µF D– GND VIN OUT GND 1µF ENA ON/OFF OUTA OVERCURRENT FLGA IN OVERCURRENT FLGB GND ENB OUTB ON/OFF D– 47µF USB Port 1 GND 0.1µF VBUS D+ D– 47µF USB Port 2 GND Data Data (Two Pair) to USB Controller 2-Port USB Self-Powered Hub UL Recognized Component Micrel, Inc. • 1849 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 944-0970 • http://www.micrel.com February 2000 1 MIC2526 MIC2526 Micrel Ordering Information Part Number Enable Temperature Range Package MIC2526-1BM Active High –40°C to +85°C 8-Pin SOIC MIC2526-2BM Active Low –40°C to +85°C 8-Pin SOIC MIC2526-1BN Active High –40°C to +85°C 8-pin DIP MIC2526-2BN Active Low –40°C to +85°C 8-pin DIP Pin Configuration MIC2526 ENA 1 8 OUTA FLGA 2 7 IN FLGB 3 6 GND ENB 4 5 OUTB 8-Pin SOIC (M) 8-Pin DIP (N) MIC2526 (ENA) 1 (FLGA) 2 LOGIC, CHARGE PUMP (FLGB) 3 (ENB) 4 LOGIC, CHARGE PUMP 8 (OUTA) 7 (IN) 5 (OUTB) 6 (GND) Pin Description Pin Number Pin Name 1/4 EN(A/B) Enable (Input): Logic-compatible enable input. High input > 2.1V typical. Low input VIN) when the output is off. In this situation, the MIC2526 avoids undesirable current flow from OUT to IN. If VIN < 2.5V, UVLO disables both switches. Thermal Shutdown Thermal shutdown shuts off the affected output MOSFETs and signals all 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 limit current to typically 850mA. The increase in power dissipation, in most cases, will cause the MIC2526 to go into thermal shutdown, disabling affected channels. When this is undesirable, thermal shutdown 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 hundred milliseconds. The USB controller must therefore recognize a fault and disable the appropriate channel within this time. If the fault is not removed or the switch is not disabled within this time, then the device will enter into a thermal oscillation of about 2Hz. This does not cause any damage to the device. Refer to “Functional Characteristics: Thermal Shutdown Response.” MIC2526 Switch Enabled into Short Circuit If a switch is powered on or enabled into a heavy load or shortcircuit, the switch immediately goes into a constant-current mode, reducing the output voltage. The fault flag goes low until the load is reduced. See the “Functional Characteristics: Short Circuit Response, Enabled into Short Circuit” photo. Short Circuit Applied to Output When a heavy load is applied, a large transient current may flow until the current limit circuitry will respond. Once this occurs, the device limits current to less than the short-circuit current limit specification. See the “Short Circuit Transient Response, Short Applied to Output” graph. Current-Limit Response The MIC2526 current-limit profile exhibits a small foldback effect of approximately 500mA. 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 MIC2526 will deliver load current up to the current-limit threshold which is typically 1.6A. Refer to “Functional Characteristics: Current-Limit Response” photo for details. Fault Flag FLG is an N-channel, open-drain MOSFET output. The faultflag is active (low) for one or more of the following conditions: undervoltage (while 2V < VIN < 2.7), current limit, or thermal shutdown. The flag output MOSFET is capable of sinking a 10mA load to typically 100mV above ground. Multiple FLG pins may be “wire NORed” to a common pull-up resistor. 8 February 2000 MIC2526 Micrel Soft Start The MIC2526 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 for bus-powered applications as shown in Figure 2. The soft start circuit shown in Figure 3 can be utilized to meet USB transient regulation specifications with large load capacitances (CBULK > 10uF). The MIC2526 will provide inrush current limiting for these applications. 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. 3.0V to 5.5V Transient Overcurrent Filter When the MIC2526 is enabled, large values of capacitance at the output of the device will cause inrush current to exceed the short circuit current-limit threshold of the device and assert the flag. The duration of this time will depend on the size of the output capacitance. Refer to the “Functional Characteristics” turn-on and turnoff behaviors for details. During the capacitance charging time, the device enters into constant-current mode. As the capacitance is charged, the current decreases below the short circuit current-limit threshold, and the flag will then be deasserted. MIC2526 ENA OUTA FLGA IN FLGB GND ENB OUTB 0.1µF to 1µF 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. USB Controller MIC2526-xBM VBUS USB Host 4.7 µF 1 ENA 2 FLGA IN 3 FLGB GND 6 4 ENB OUTB 5 OUTA 8 7 CBULK 0.1µF Capacitive Load GND Cable Cable Bus Powered Hub Downstream USB Device Figure 2. Soft Start (Single Channel) USB Controller MIC2526-2BM 1 VBUS 4.7 µF USB Hub ENA OUTA USB Function 8 2 7 FLGA IN 3 FLGB GND 6 4 ENB OUTB 5 CBULK USB Function CBULK GND Cable USB Peripheral Figure 3. Inrush Current-Limit Application February 2000 9 MIC2526 MIC2526 Micrel In USB applications, it is required that output bulk capacitance is utilized to support hot-plug events. When the MIC2526 is enabled, the flag may go active for about 1ms due to inrush current exceeding the current-limit setpoint. Additionally, during hot-plug events, inrush currents may also cause the flag to go active for 30µs. Since these conditions are not valid overcurrent faults, the USB controller must ignore the flag during these events. To prevent this erroneous overcurrent reporting, a 1ms RC filter as shown in Figure 4 may be used. Alternatively, a 1ms debounce routine may be programmed into the USB logic controller, eliminating the need for the RC filter. MIC2526 V+ USB Controller MIC2526 10k 1 10k OVERCURRENT 0.1 µF 2 3 4 ENA OUTA FLGA IN FLGB GND ENB OUTB 8 7 6 5 Figure 4. Transient Filter 10 February 2000 MIC2526 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) 0.197 (5.0) 0.189 (4.8) 0°–8° 0.010 (0.25) 0.007 (0.18) 0.050 (1.27) 0.016 (0.40) SEATING PLANE 0.244 (6.20) 0.228 (5.79) 8-Pin SOP (M) PIN 1 DIMENSIONS: INCH (MM) 0.380 (9.65) 0.370 (9.40) 0.255 (6.48) 0.245 (6.22) 0.135 (3.43) 0.125 (3.18) 0.300 (7.62) 0.013 (0.330) 0.010 (0.254) 0.018 (0.57) 0.100 (2.54) 0.130 (3.30) 0.380 (9.65) 0.320 (8.13) 0.0375 (0.952) 8-Pin Plastic DIP (N) February 2000 11 MIC2526 MIC2526 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. © 2000 Micrel Incorporated MIC2526 12 February 2000