BL2555 Load Switch with Adjustable Current Limit FEATURES DESCRIPTION The BL2555 is a load switch which provides full protection to systems and loads which may encounter large current conditions. BL2555 offers a 95mΩ current-limited switch which can operate over an input voltage range of 2.5-5.5V. The current limit can be externally programmed by a precision resistor, ranges from 75mA to 1.7A. Switch control is by a logic input (EN) capable of interfacing directly with low voltage control signals. Current is prevented from flowing when the switch is off and the output voltage is higher than the input voltage. Up to 1.5A Max Load current Accurate Current-limit threshold: +/-5% Programmable Current-limit : 75mA to 1.7A Fast Over-Current Response Reversed Current blocking Thermal Shutdown, UVLO protection Tiny DFN2x2-6L Package APPLICATIONS BL2555 also features thermal shutdown protection which shuts off the switch to prevent damage to the part when a continuous over-current condition causes excessive heating. When the switch current reaches the current limit, the parts operate in a constant-current mode to prohibit excessive currents from causing damage. USB ports/Hubs Hot Swaps Cellphones Tablet PC Set Top Box PC motherboard Handheld Devices BL2555 is in a tiny DFN2x2-6L package TYPICAL APPLICATION Output USB input IN OUT 120µF BL2555 ILIM 4.7uF RILIM EN www.belling.com.cn 1 GND BL2555 MARKING INFORMATION PIN ASSIGNMENT OUT 1 6 IN ILIM 2 5 GND NC 3 4 EN HL YW HL: product code Y: Year code, 1 for 2011, 2 for 2012… W: Week code, A-Z for 01-26, Ā- for 27-52 DFN2x2-6L Top View ABSOLUTE MAXIMUM RATINGS Parameter Value Input Voltage OUT, ILIM, EN to GND OUT to GND current Maximum Power Dissipation Operating Temperature Range Storage Temperature Lead Temperature & Time -0.3V to 5.5V -0.3V to VIN+0.3V Internally limited 1.0 W -40 - 85C -40C - 150C 260C, 10S Note: Exceed these limits to damage to the device. Exposure to absolute maximum rating conditions may affect device reliability. ELECTRICAL CHARACTERISTICS (Vin=5V Ta=25C, unless otherwise specified) Symbol Vin V_uvlo Iq Parameter Input Voltage Range Typ 2.5 Max Unit 5.5 V Rising, hysteresis=25mV 2.35 V Input Supply Current RILIM=20K 320 uA Input Shutdown Current Ron Power Switch On Resistance Ilim1 Min Input UVLO I_SD Ilim2 Conditions Second Current Limit Threshold First Current Limit Threshold T_lim1 First Current Limit Timeout V_enh EN Input Logic High Threshold V_enl EN Input Logic Low Threshold T_SD Thermal Shutdown www.belling.com.cn 0.5 Isw=500mA 1.5 95 Isw=500mA, Tj: -40C - 120C uA mohm 145 mohm RILIM=15K 1.705 A RILIM=20K 1.295 A RILIM=49.9K 0.520 A 50 % Percentage of Limit Current above Second Current Limit 0.8 1.2 0.66 ms 1 V V 160 2 1.6 C BL2555 PINOUT DESCRIPTION PIN # 1 NAME OUT 2 ILIM 3 4 5 6 NC EN GND IN DESCRIPTION Current limit Output. Bypass with a capacitor that is greater than 120F if used for USB Current limit threshold setting pin. Connect a resistor from this pin to GND to set different current limit values No Connect Enable pin Ground Power input. Bypass with a 4.7F capacitor to GND BLOCK DIAGRAM IN Current Limit + Reverse-Voltage Block - OUT ILIM UVLO Control Logic GND EN THERMAL SHUT DOWN FUNCTION DESCRIPTION The BL2555 is a load switch which provides full protection to systems and loads which may encounter large current conditions. BL2555 offers a 95mΩ current-limited switch which can operate over an input voltage range of 2.5-5.5V. The current limit can be externally programmed by a precision resistor, ranges from 75mA to 1.7A. limiting at less than a minimum value. The current at which the parts will limit is adjustable through the selection of an external resistor connected to ILIM. Information for selecting the resistor is found in the Application Info section. THERMAL PROTECTION BL2555 thermal cycles if an overload condition is present long enough to activate thermal limiting in any of the above cases. The device turns off when the junction temperature exceeds 135°C (typ) while in current limit. The device remains off until the junction temperature cools 10°C (typ) and then restarts BL2555 also features reverse voltage blocking, UVLO, and thermal shutdown to protect IC from overheating. CURRENT LIMITING The current limit ensures that the current through the switch doesn't exceed a maximum value while not www.belling.com.cn 3 BL2555 REVERSE-VOLTAGE BLOCKING The reverse-voltage protection feature turns off the Power MOSFET whenever the output voltage exceeds the input voltage by 150mV (typ) for 4-ms (typ). This prevents damage to devices on the input side of the BL2555 by preventing significant current from sinking into the input capacitance. The BL2555 allow the power MOSFET to turn on once the output voltage goes below the input voltage for the same 4-ms deglitch time. APPLICATION INFORMATION INPUT OUTPUT CAPACITANCE Input and output capacitance improves the performance of the device; the actual capacitance should be optimized for the particular application. For all applications, a 4.7µF or greater ceramic bypass capacitor between IN and GND is recommended as close to the device as possible for local noise de-coupling. This precaution reduces ringing on the input due to power-supply transients. Additional input capacitance may be needed on the input to reduce voltage overshoot from exceeding the absolute maximum voltage of the device during heavy transient conditions. This is especially important during bench testing when long, inductive cables are used to connect the evaluation board to the bench power-supply. Placing a high-value electrolytic capacitor on the output pin is recommended when large transient currents are expected on the output. SETTING THE CURRENT LIMIT THRESHOLD Typical Current Limit (mA) RILIM (K) 200 138 180 152 151 179 100 266 82 324 68 389 51 520 43 612 30 873 20 1295 15.1 1705 Current Limit Threshold VS RILIM Current Limit Threshold(mA) 1800 1600 1400 1200 1000 800 600 Ilim 400 200 0 0 50 100 150 Rset(Kohm) 200 250 THERMAL CONSIDERATIONS During normal operation as a switch, the power dissipated in the part will depend upon the level at which the current limit is set. The maximum allowed setting for the current limit is 1A and this will result in a power dissipation of, 2 2 P = (ILIM) x RDS = (1) x 0.10 = 100mW If the part goes into current limit the maximum power dissipation will occur when the output is shorted to ground. This is more power than the package can dissipate, but the thermal shutdown of the part will activate to protect the part from damage due to excessive heating. A short on the output will cause the part to operate in a constant current state dissipating a worst case power of, P(max) = VIN(max) x ILIM(max) = 5.5 x 1 = 5W This large amount of power will activate the thermal shutdown and the part will cycle in and out of thermal shutdown so long as the ON pin is active and the short is present. www.belling.com.cn 4 BL2555 TYPICAL PERFORMANCE CHARACTERISTICS T=25°C unless specified. The first and second current limit level nd st Constant current load on BL2555, with 2 current limit level set to 500mA. The 1 current limit level is 50% higher nd st than 2 level, and the 1 level current limiting duration is 1ms. Blue: Output Voltage Red: Current through BL2555 Output Short Response Short BL2552 to GND, and the internal short current limit is shown. Green: Input Voltage Blue: Output Voltage Red: Current through BL2555 www.belling.com.cn 5 BL2555 OUTPUT CAPACITANCE REDUCTION COMPARISION Test condition, Vin=5V, I_load=2A for 1.5ms, RIlimit=27K BL2555 response, with Cout=580uF, output voltage drop 2.4V. Blue: Output Voltage Red: Current through BL2555 TPS2553 (conventional single level current limit) response, with Cout=580uF, output voltage drop 3.2V. Blue: Output Voltage Red: Current through TPS2553 BL2555 response the same voltage drop (3.2V) with only 380uF output capacitance. 33% saved. Blue: Output Voltage Red: Current through BL2555 www.belling.com.cn 6 BL2555 PACKAGE OUTLINE Package DFN2x2-6L Devices per reel 5000 Package specification： www.belling.com.cn 7 Unit mm