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UCC3916
SCSI Termpower Manager
FEATURES
* Integrated Circuit Breaker Function * Integrated 0.2 Power FET * SCSI, SCSI-2, SCSI-3 Compliant * 1A ICC When Disabled * Programmable On Time * Accurate 1.65A Trip Current and 2.0A Max Current * Fixed 3% Duty Cycle * Uni-Directional Switch * Thermal Shutdown
DESCRIPTION
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. 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 220m. 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. 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 1A of supply current. Other features include thermal shutdown and low thermal resistance Small Outline Power package.
BLOCK DIAGRAM
1 REVERSE VOLTAGE COMPARATOR CHARGE PUMP MAXIMUM CURRENT LEVEL 2A LINEAR CURRENT AMPLIFIER CURRENT TRIP LEVEL 1.65A OVER CURRENT COMPARATOR 50mV + OUTPUT CURRENT SENSE H=OPEN POWER FET VIN 4V TO 6V
ON TIME CONTROL 3% DUTY CYCLE THERMAL SHUTDOWN INTERNAL BIAS 2 3 6 7 4 + - 5 SHTDWN
UDG-99172
1.5V
8
OUTPUT
GND GND GND GND CT 4 HEATSINK PINS
SLUS206A - JANUARY 2000
UCC3916
ABSOLUTE MAXIMUM RATINGS
VIN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . +6V Output Current DC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Self Limiting Pulse (Less than 100ns). . . . . . . . . . . . . . . . . . . . . . . . . 20A Storage Temperature . . . . . . . . . . . . . . . . . . . -65C to +150C Junction Temperature . . . . . . . . . . . . . . . . . . . -55C to +150C Lead Temperature (Soldering, 10 sec.) . . . . . . . . . . . . . +300C
CONNECTION DIAGRAM
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 = 0C to +70C; VIN = 5V,
SHTDWN = 2.4V, TA = TJ. PARAMETER Supply Current Section ICC ICC - Sleep Mode Output Section Voltage Drop IOUT = 1A IOUT = 1.5A IOUT = 1.65A Trip Current Max Current Reverse Leakage Soft Start Time Short Circuit Response Fault Section CT Charge Current CT Discharge Current Output Duty Cycle CT Charge Threshold CT Discharge Threshold Thermal Shutdown Thermal Hysteresis Shutdown Section Shutdown Threshold Shutdown Hysteresis Shutdown Bias Current SHTDWN = 1.0V 1.5 150 100 3.0 300 500 V mV nA VCT = 1.0V VCT = 1.0V VOUT = 0V -45 0.90 2.00 0.4 1.2 -36.0 1.0 3.00 0.5 1.4 170 10 -27 1.50 6.00 0.6 1.8 A A % V V C C VIN = 4.5V, VOUT = 5V VIN = 0V, VOUT = 5V Initial Startup -1.8 -2.4 0.22 0.33 0.40 -1.65 -2 6 0.50 50 100 0.33 0.50 0.60 -1.5 -1.65 20 9 V V V A A A A s ns SHTDWN = 0.2V 1.00 0.50 2.00 5 mA A TEST CONDITIONS MIN TYP MAX UNITS
Note 1: All voltages are with respect to ground.
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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: TFAULT= 28 * 103 * CT. Once the fault time is reached the output will shutdown for a time given by: TSD = 1 * 106 * CT this results in a 3% duty cycle. 0.1F is recommended for SCSI applications to achieve the normal maximum capacitance on the Termpwr line. 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. VOUT: Output voltage of the circuit breaker. When switched, the output voltage is approximately: VOUT = VIN - (220m) * IOUT.
TYPICAL APPLICATION
VIN
1
VIN
UCC3916
OUTPUT
8
TERMPOWER BUS CLOAD
5 D1 CIN
SHTDWN GND 2 GND 3 GND 6
CT GND 7
4 CT
UDG-99169
APPLICATION INFORMATION
Protecting The UCC3916 From Voltage Transients 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: * 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 1F 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
SAFETY RECOMMENDATIONS 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 (c) 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.
3
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Copyright (c) 2000, Texas Instruments Incorporated

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