UCC3916 SCSI Termpower Manager FEATURES DESCRIPTION • Integrated Circuit Breaker Function The UCC3916 SCSI termpower manager provides complete power management, hot swap capability, and circuit breaker functions with minimal external components. For most applications, the only external component required to operate the device, other than supply bypassing, is a timing capacitor which sets the fault time. • Integrated 0.2 Power FET • SCSI, SCSI-2, SCSI-3 Compliant • 1µA ICC When Disabled The current trip level is internally set at 1.65A, and the maximum current level is also internally programmed for 2A. While the output current is below the trip level of 1.65A, the internal power MOSFET is switched on at a nominal 220mΩ. When the output current exceeds the trip level but remains less than the maximum current level, the MOSFET remains switched on, but the fault timer starts charging CT. Once the fault time is reached, the circuit will shut off for a time which equates to a 3% duty cycle. Finally, when the output current reaches the maximum current level, the MOSFET transitions from a switch to a constant current source. • Programmable On Time • Accurate 1.65A Trip Current and 2.0A Max Current • Fixed 3% Duty Cycle • Uni-Directional Switch • Thermal Shutdown The UCC3916 is designed for uni-directional current flow, emulating a diode in series with the power MOSFET. The UCC3916 can be put in a sleep mode, drawing only 1µA of supply current. Other features include thermal shutdown and low thermal resistance Small Outline Power package. BLOCK DIAGRAM REVERSE VOLTAGE COMPARATOR 1 VIN 4V TO 6V 8 OUTPUT 50mV + OUTPUT CHARGE PUMP CURRENT SENSE MAXIMUM CURRENT LEVEL 2A H=OPEN POWER FET LINEAR CURRENT AMPLIFIER CURRENT TRIP LEVEL 1.65A ON TIME CONTROL 3% DUTY CYCLE OVER CURRENT COMPARATOR THERMAL SHUTDOWN INTERNAL BIAS 2 3 6 7 4 GND GND GND GND CT 4 HEATSINK PINS SLUS206A - JANUARY 2000 1.5V + – 5 SHTDWN UDG-99172 UCC3916 ABSOLUTE MAXIMUM RATINGS CONNECTION DIAGRAM VIN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . +6V Output Current DC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Self Limiting Pulse (Less than 100ns). . . . . . . . . . . . . . . . . . . . . . . . . 20A Storage Temperature . . . . . . . . . . . . . . . . . . . –65°C to +150°C Junction Temperature . . . . . . . . . . . . . . . . . . . –55°C to +150°C Lead Temperature (Soldering, 10 sec.) . . . . . . . . . . . . . +300°C SOIC-8 (Top View) DP Package Currents are positive into, negative out of the specified terminal. Consult Packaging Section of Databook for thermal limitations and considerations of packages. ELECTRICAL CHARACTERISTICS: Unless otherwise stated, these parameters apply for TJ = 0°C to +70°C; VIN = 5V, SHTDWN = 2.4V, TA = TJ. PARAMETER TEST CONDITIONS MIN TYP MAX UNITS 1.00 2.00 mA SHTDWN = 0.2V 0.50 5 µA IOUT = 1A 0.22 0.33 V IOUT = 1.5A 0.33 0.50 V Supply Current Section ICC ICC - Sleep Mode Output Section Voltage Drop IOUT = 1.65A Trip Current Max Current Reverse Leakage 0.40 0.60 V –1.8 –1.65 –1.5 A –2.4 –2 –1.65 A 6 20 µA 0.50 9 µA VIN = 4.5V, VOUT = 5V VIN = 0V, VOUT = 5V Soft Start Time Initial Startup Short Circuit Response 50 µs 100 ns Fault Section CT Charge Current VCT = 1.0V –45 –36.0 –27 µA CT Discharge Current VCT = 1.0V 0.90 1.0 1.50 µA Output Duty Cycle VOUT = 0V 2.00 3.00 6.00 % CT Charge Threshold 0.4 0.5 0.6 V CT Discharge Threshold 1.2 1.4 1.8 V Thermal Shutdown 170 °C Thermal Hysteresis 10 °C Shutdown Section Shutdown Threshold 1.5 3.0 V Shutdown Hysteresis 150 300 mV 100 500 nA Shutdown Bias Current SHTDWN = 1.0V Note 1: All voltages are with respect to ground. 2 UCC3916 PIN DESCRIPTIONS CT: A capacitor is applied between this pin and ground to set the maximum fault time. The maximum fault time must be more than the time to charge external capacitance. The maximum fault time is defined as: SHTDWN: The IC enters a low-power sleep mode when this pin is low and exits the sleep mode when this pin is high. VIN: Input voltage to the circuit breaker, ranging from 4V to 6V. TFAULT= 28 • 103 • CT. Once the fault time is reached the output will shutdown for a time given by: VOUT: Output voltage of the circuit breaker. When switched, the output voltage is approximately: TSD = 1 • 106 • CT VOUT = VIN – (220mΩ) • IOUT. this results in a 3% duty cycle. 0.1µF is recommended for SCSI applications to achieve the normal maximum capacitance on the Termpwr line. TYPICAL APPLICATION VIN D1 CIN 1 VIN 5 SHTDWN UCC3916 OUTPUT 8 CT 4 TERMPOWER BUS CLOAD GND GND GND GND 2 3 6 7 CT UDG-99169 APPLICATION INFORMATION Protecting The UCC3916 From Voltage Transients SAFETY RECOMMENDATIONS The parasitic inductance associated with the power distribution can cause a voltage spike at VIN if the load current is suddenly interrupted by the UCC3916. It is important to limit the peak of this spike to less than 6V to prevent damage to the UCC3916. This voltage spike can be minimized by: Although the UCC3916 is designed to provide system protection for all fault conditions, all integrated circuits can ultimately fail short. For this reason, if the UCC3916 is intended for use in safety critical applications where © UL or some other safety rating is required, a redundant safety device such as a fuse should be placed in series with the device. The UCC3916 will prevent the fuse from blowing virtually all fault conditions, increasing system reliability and reducing maintainence cost, in addition to providing the hot swap benefits of the device. • Reducing the power distribution inductance (e.g., twist the positive (+) and negative (–) leads of the power supply feeding VIN pin, locate the power supply close to the UCC3916 or use a PCB ground plane). • Decoupling VIN with a capacitor, CIN, located close to the VIN. This capacitor is typically less than 1µF to limit the inrush current. • Clamping the voltage at VIN below 6V with a Zener diode, D1, located close to the VIN pin. UNITRODE CORPORATION 7 CONTINENTAL BLVD. • MERRIMACK, NH 03054 TEL. (603) 424-2410 FAX (603) 424-3460 3