UCC2918 UCC3918 application INFO available Low On Resistance Hot Swap Power Manager FEATURES DESCRIPTION • Integrated 0.06Ω Power MOSFET The UCC3918 Low on Resistance Hot Swap Power Manager provides complete power management, hot swap capability, and circuit breaker functions. The only components needed to operate the device, other than supply bypassing, are a timing capacitor, and 2 programming resistors. All control and housekeeping functions are integrated, and externally programmable. These include the fault current level, maximum output sourcing current, maximum fault time, and startup delay. In the event of a constant fault, the internal fixed 3% duty cycle ratio limits the average output power. The IFAULT pin allows linear programming of the fault level current from 0A to 4A. • 3V to 6V Operation • External Analog control of Fault Current from 0A to 4A • Independent Analog Control of Current Limit up to 5A • Fast Overload Protection • Uni-directional Switch • Minimal External Components • 1µA ICC when Disabled • Programmable On Time Fast overload protection is accomplished by an additional overload comparator. Its threshold is internally set above the maximum sourcing current limit setting. In the event of a short circuit or extreme current condition, this comparator is tripped, shutting down the output. This function is needed since the maximum sourcing current limit loop has a finite bandwidth. When the output current is below the fault level, the output MOSFET is switched on with a nominal resistance of 0.06Ω. When the output current exceeds the fault level or the maximum sourcing level, the output remains on, but the fault timer starts charging CT. Once CT charges to a preset threshold, the switch is turned off, and remains off for 30 times the programmed fault time. When the output current reaches the maximum sourcing level, the MOSFET transitions form a switch to a constant current source. • Programmable Start Delay • Fixed 3% Duty Cycle (continued) BLOCK DIAGRAM CHARGE PUMP REVERSE COMPARATOR OVERLOAD COMPARATOR + 20mV 1 VIN 2 VIN 3 VIN VOUT CURRENT SENSE + H = OPEN IMAX 9 MAXIMUM CURRENT LEVEL CURRENT FAULT LEVEL IFAULT OVERCURRENT COMPARATOR 14 VOUT ON TIME CONTROL 8 15 VOUT 3% DUTY CYCLE 16 VOUT THERMAL SHUTDOWN 1.5V INTERNAL BIAS 5 GND SLUS384A - NOVEMBER 1999 4 13 12 HEAT SINK GND PINS 10 6 CT FAULT + – 7 SHTDWN UDG-99153 UCC2918 UCC3918 CONNECTION DIAGRAM DESCRIPTION (continued) The UCC3918 is designed for unidirectional current flow, emulating an ideal diode in series with the power switch. This feature is particularly attractive in applications where many devices are powering a common bus, such as with SCSI Termpwr. The UCC3918 can also be put into the sleep mode, drawing only 1µA of supply current. DIL-16, SOIC-16 (Top View) N Package, DP Package Other features include an open drain fault output indicator, thermal shutdown, undervoltage lockout, 3V to 6V operation, and a low thermal resistance small outline power package. ABSOLUTE MAXIMUM RATINGS Input Supply Voltage (VIN) . . . . . . . . . . . . . . . . . . . . . . . . . . 8V SOIC Power Dissipation . . . . . . . . . . . . . . . . . . . . . . . . . . 2.5W Fault Output Sink Current. . . . . . . . . . . . . . . . . . . . . . . . . 50mA Fault Output Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . VIN Output Current (DC) . . . . . . . . . . . . . . . . . . . . Internally Limited Input Voltage SHTDWN, IFAULT, IMAX . . . . . . . . . . . . . . . . . –0.3V to VIN Storage Temperature Range . . . . . . . . . . . . . –65°C to +150°C Operating Junction Temperature Range . . . . –55°C to +150°C Lead Temperature (Soldering, 10 sec.) . . . . . . . . . . . . . +300°C Unless otherwise indicated, voltages are reference to ground and currents are positive into, negative out of the specified terminal. Pulsed is defined as a less than 10% duty cycle with a maximum duration of 500µS. Consult Packaging Section of Databook for thermal limitations and considerations of package. * Pin 5 serves as the lowest impedance to the electrical ground. Pins 4, 12, and 13 serve as heat sink/ground. These pins should be connected to large etch PCB areas to help dissipate heat. For N Package, pins 4, 12, and 13 are N/C. TSSOP-24 (Top View) PWP Package VIN 1 24 VOUT VIN 2 23 VOUT VIN 3 22 VOUT VIN 4 21 VOUT GND* 5 20 GND* GND* 6 19 GND* GND* 7 18 GND* GND* 8 17 GND* GND* 9 16 GND* FAULT 10 15 N/C SHTDWN 11 14 CT IFAULT 12 13 IMAX * Pin 9 serves as the lowest impedance to the electrical ground. Pins 5, 6, 7, 8, 16, 17, 18, 19 and 20 serve as heat sink/ground. 2 UCC2918 UCC3918 ELECTRICAL CHARACTERISTICS: Unless otherwise specified, TA = 0°C to 70°C for the UCC3918, –40°C to 85° for the UCC2918, VIN = 5V. RIMAX = 42.2k, RIFAULT = 52.3k, SHTDWN = 2.4. TA = TJ. PARAMETER TEST CONDITIONS MIN TYP 3 5 MAX UNITS Supply Section Voltage Input Range, VIN VDD Supply Current No Load Sleep Mode Current SHTDWN = 0.2V 6 V 1 2 mA 0.5 5 µA 0.075 0.095 Ω Output Section RDSON IOUT = 1A to 4A, VIN = 5V, TA = 25°C IOUT = 1A to 4A, VIN = 3V, TA = 25°C 0.09 0.116 Ω IOUT = 1A to 4A, VIN = 5V 0.75 0.125 Ω IOUT = 1A to 4A, VIN = 3V 0.09 0.154 Ω 20 A Reverse Leakage Current VIN = 0V, VOUT = 5V, SHTDWN = 0V Initial Startup Time (Note 1) 100 µS Thermal Shutdown (Note 1) 170 DEG Thermal Hysteresis (Note 1) 10 DEG Output Leakage SHTDWN = 0.2V 20 µA Trip Current RIFAULT = 105k 0.75 1 1.25 A RIFAULT = 52.3k 1.7 2 2.3 A RIFAULT = 34.8k 2.5 3 3.5 A RIFAULT = 25.5k 3.3 4 4.7 A RIMAX = 118k 0.3 1 1.7 A RIMAX = 60.4k 1 2 3 A Output Section (cont) Maximum Output Current RIMAX = 42.2k 2 3 4 A RIMAX = 33.2k 2.5 3.8 5.1 A RIMAX = 27.4k 3.0 4.6 6.2 A CT Charge Current VCT = 1V –50 –36 –22 µA CT Discharge Current VCT = 1V 0.5 1.2 2.0 µA VOUT = 0V 1.5 3 6 % Fault Section Fault Section (cont.) Output Duty Cycle CT Fault Threshold 0.8 1.3 1.8 V CT Reset Threshold 0.25 0.5 0.75 V 1.1 1.5 2.0 V Shutdown Section Shutdown Threshold Shutdown Hysteresis 100 mV Input Low Current SHTDWN = 0V –500 0 500 nA Input High Current SHTDWN = 2V –2 –1 –0.5 µA 1 µA 0.4 0.9 V Open Drain Fault Output High Level Output Current Low Level Output Voltage IOUT = 1mA Note 1: Guaranteed by design. Not 100% tested in production. 3 UCC2918 UCC3918 PIN DESCRIPTIONS CT: A capacitor connected to this pin sets the maximum fault time. The maximum must be more than the time to charge external load capacitance. The maximum fault time is defined as R FAULT = 105k ITRIP IMAX: A resistor connected from this pin to ground sets the maximum sourcing current. The resistor vs the output sourcing current is set by the formula, T FAULT = 27.8 • 10 3 • CT Once the fault time is reached the output will shutdown for a time given by R FAULT = T SD = 0.833 • 10 6 • CT , 126k Maximum Sourcing Current SHTDWN: When this pin is brought low, the IC is put into sleep mode. The input threshold is hysteretic, allowing the user to program a startup delay with an external RC circuit. this equates to a 3% duty cycle. FAULT: Open drain output, which pulls low upon any condition which causes the output to open; Fault, Thermal Shutdown, Shutdown, and maximum sourcing current greater than the fault time. VIN: This is the input voltage to the UCC3918. The recommended operating voltage range is 3V to 6V. All VIN pins should be connected together and to the power source. GND: This is the most negative voltage in the circuit. All 4 ground pins should be used, and properly heat sunk on the PCB. VOUT: Output voltage for the circuit breaker. When switched the output voltage will be approximately VIN – 0.06Ω • IOUT. All VOUT pins should be connected together and to the load. IFAULT: A resistor connected from this pin to ground sets the fault threshold. The resistor vs fault current is set by the formula APPLICATION INFORMATION HEAT SINK GND PINS 4 VIN D1 R1 CIN 1 VIN 2 VIN 3 VIN 6 FAULT 10 CT 12 GND 13 5 VOUT 14 VOUT 15 VOUT 16 VOUT RL COUT RSD CT SHTDWN IFAULT IMAX 8 9 RIFAULT 7 S6 VIN CSD RIMAX UDG-99152 Figure 1. Evaluation circuit. 4 UCC2918 UCC3918 APPLICATION INFORMATION (cont.) Protecting The UCC3918 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 UCC3918. It is important to limit the peak of this spike to less than 6V to prevent damage to the UCC3918. 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, locate the power supply close to the UCC3918 or use a PCB ground plane). • Decoupling VIN with a capacitor, CIN (refer to Fig. 1), located close to the VIN pin. This capacitor is typically less than 1µF to limit the inrush current. • Clamping the voltage at VIN below 6V with a Zener diode, D1 (refer to Fig. 1), located close to the VIN pin. To guarantee recovery of a duty-cycle of the current-limited circuit breaker from a short-circuited load condition, there is a maximum total output capacitance which can be charged for a given unit ON time (Fault time). The design value of ON or Fault time can be adjusted by changing the timing capacitor CT. For worst-case constant-current load of value just less than the trip limit; COUT(max) can be estimated from: 28 • 10 3 • CT COUT (max) ≈ (I MAX – I LOAD ) VOUT Where VOUT is the output voltage and IMAX is the maximum, sourcing current. For a resistive load of value RI, the value of COUT(max) can be estimated from: 28 • 10 3 • CT COUT (max) ≈ 1 R • In L 1 − VOUT I MAX • R L Estimating Maximum Load Capacitance For circuit breaker applications, the rate at which the total output capacitance can be charged depends on the maximum output current available and the nature of the load. For a constant-current current-limited circuit breaker, the output will come up if the load asks for less than the maximum available short-circuit current. COUT 22µF UDG-97071 Figure 2. Load current, timing capacitor voltage and output voltage of the UCC3918 under fault. RL 5Ω CIN 5µF RIFAULT 52.3k RIMAX 42.0k Input driven with a pulse generator, shows COUT discharging through RL and conducting through UCC3918 FET in the reverse direction. Figure 3. 5 UCC2918 UCC3918 APPLICATION INFORMATION (cont.) VOUT 0V RL SHORT CIN 5µF RIFAULT 52.3k COUT 0µF RIMAX 42.2k Figure 4. UCC3918 in shorted condition. COUT 22µF RL 5Ω CIN 5µF RIFAULT 52.3k RL 5Ω CIN 5µF RIFAULT 52.3k RIMAX 42.4k CT OPEN Figure 6. CT to VOUT delay (fault condition). RIMAX 60.4k COUT 0µF Input switched on through external FET. VOUT shows IMAX linear amplifier limiting the changing current of COUT. Figure 5. Input hot swap. RL 5Ω CIN 5µF RIFAULT 52.3k Figure 7. Shutdown delay to VOUT off. 6 RIMAX 42.4k UCC2918 UCC3918 APPLICATION INFORMATION (cont.) 110 VIN = 5V, I = 1A RDS ON mOhms 100 90 VIN = 3V, I = 1A 80 70 AVERAGE VIN = 5V, I = 4A 60 50 VIN = 3V, I = 4A 40 -60 -40 -20 0 20 40 60 80 100 120 TEMPERATURE (°C) COUT 0µF RL 5Ω CIN 5µF RIFAULT 52.3k Figure 10. RDSON vs temperature. RIMAX 42.4k Figure 8. Shutdown delay to VOUT on. SAFETY RECOMMENDATIONS RDS ON mOhms Although the UCC3918 is designed to provide system protection for all fault conditions, all integrated circuits can ultimately fail short. For this reason, if the UCC3918 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 power device. The UCC3918 will prevent the fuse from blowing for virtually all fault conditions, increasing system reliability and reducing maintenance cost, in addition to providing the hot swap benefits of the device. IOUT(A) Figure 9. RDSON vs IOUT . UNITRODE CORPORATION 7 CONTINENTAL BLVD. • MERRIMACK, NH 03054 TEL. (603) 424-2410 FAX (603) 424-3460 7