UCC3912 application INFO available Programmable Hot Swap Power Manager FEATURES DESCRIPTION • Integrated 0.15Ω Power MOSFET The UCC3912 Hot Swap Power Manager provides complete power management, hot swap capability, and circuit breaker functions. The only component required to operate the device, other than supply bypassing, is the fault timing capacitor, CT. All control and housekeeping functions are integrated, and externally programmable. These include the fault current level, maximum output sourcing current, maximum fault time,and start-up delay. In the event of a constant fault, the Internal fixed 3% duty cycle ratio limits average output power. • 3V to 8V Operation • Digital Programmable Current Limit from 0 to 3A • Electronic Circuit Breaker Function • 1µA ICC when Disabled • Programmable on Time The internal 4 bit DAC allows programming of the fault level current from 0 to 3A with 0.25A resolution. The IMAX control pin sets the maximum sourcing current to 1A above the fault level when driven low, and to a full 4A when driven high for applications which require fast output capacitor charging. • Programmable Start Delay • Fixed 3% Duty Cycle • Uni-Directional Switch When the output current is below the fault level, the output MOSFET is switched on with a nominal on resistance of 0.15 . When the output current exceeds the fault level, but is less than the maximum sourcing level, the output remains switched 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 from a switch to a constant current source. • Thermal Shutdown • Fault Output Indicator • Maximum Output Current can be set to 1A above the Programmed Fault Level or to a full 4A • Power SOIC, Low Thermal Resistance Packaging (continued) BLOCK DIAGRAM 2 VIN 3 VOUT MAX CURRENT LEVEL 4A 30mV + CHARGE PUMP H = 4A IMAX 10 REVERSE VOLTAGE COMPARATOR CURRENT SENSE H = OPEN POWER FET LINEAR CURRENT AMPLIFIER 1A ABOVE FAULT 14 OVER CURRENT COMPARATOR CURRENT FAULT LEVEL 0–3 AMPS VOUT ON TIME CONTROL 15 3% DUTY CYCLE THERMAL SHUTDOWN 0–3A 0.25 RES INTERNAL BIAS 6 7 8 9 5 B3 B2 B1 B0 GND 4 BIT DAC SLUS241A - NOVEMBER 1999 4 13 12 HEAT SINK GND PINS 11 16 CT FAULT 1.5V + – 1 SHTDWN UDG-99146 UCC3912 ABSOLUTE MAXIMUM RATINGS DESCRIPTION (cont.) VIN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . +8 V FAULT Sink Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50mA FAULT Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . –0.3 to VIN Output Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . Self Limiting Input Voltage (B0, B1, B2, B3, IMAX, SHTDWN) . . . . . . . . . . . –0.3 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 The UCC3912 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 UCC3912 can be put into sleep mode drawing only 1µA of supply current. The SHTDWN pin has a preset threshold hysteresis which allows the user the ability to set a time delay upon start-up to achieve sequencing of power. Other features include an open drain FAULT output indicator, Thermal Shutdown, Under Voltage Lockout, and a low thermal resistance Small outline package. Currents are positive into, negative out of the specified terminal. Consult Packaging Section of Databook for thermal limitations and considerations of packages. CONNECTION DIAGRAMS TSSOP-24 (Top View) PWP Package DIL-16, SOIC-16 (Top View) N, DP Package *Pin 5 serves as lowest impedance to the electrical ground; Pins 4, 12, and 13 serve as heat sink/ground. These pins should be connected to large etch areas to help dissipate heat. For N package, pins 4, 12, and 13 are N/C. SHTDWN 1 24 FAULT VIN 2 23 VOUT VIN 3 22 VOUT N/C 4 21 N/C GND* 5 20 GND* GND* 6 19 GND* GND* 7 18 GND* GND* 8 17 GND* EGND* 9 16 GND* B3 10 15 CT B2 11 14 IMAX B1 12 13 B0 *Pin 9 serves as lowest impedance to the electrical ground; other GND pins serve as heat sink/ground. These pins should be connected to large etch areas to help dissipate heat. ELECTRICAL CHARACTERISTICS: Unless otherwise stated, these specifications apply for TJ = 0°C to 70°C, VIN = 5V, IMAX = 0.4V, SHTDWN = 2.4V. PARAMETER Supply Section Voltage Input Range Supply Current Sleep Mode Current Output Section Voltage Drop TEST CONDITIONS MIN TYP 3.0 MAX UNITS SHTDWN = 0.2V 1.0 0.5 8.0 2.0 5.0 V mA µA IOUT = 1A IOUT = 2A IOUT = 3A IOUT = 1A, VIN = 3V IOUT = 2A, VIN = 3V IOUT = 3A, VIN = 3V 0.15 0.3 0.45 0.17 0.35 0.5 0.22 0.45 0.68 0.27 0.56 0.8 V V V V V V 2 UCC3912 ELECTRICAL CHARACTERISTICS: Unless otherwise stated, these specifications apply for TJ = 0°C to 70°C, VIN = 5V, IMAX = 0.4V, SHTDWN = 2.4V. PARAMETER Output Section (cont.) Reverse Leakage Current Initial Start-up Time Short Circuit Response Thermal Shutdown Thermal Hysteresis DAC Section Output Leakage Trip Current Max Output Current Max Output Current Over Trip (Current Source Mode) Max Output Current (Current Source Mode) Timer Section CT Charge Current CT Discharge Current Output Duty Cycle CT Fault Threshold CT Reset Threshold TEST CONDITIONS MIN VIN < VOUT , SHTDWN = 0.2V, VOUT = 5V (Note 2) (Note 2) (Note 2) (Note 2) Code = 0000-0011 Code = 0100 Code = 0101 Code = 0110 Code = 0111 Code = 1000 Code = 1001 Code = 1010 Code = 1011 Code = 1100 Code = 1101 Code = 1110 Code = 1111 Code = 0000 to 0011 Code = 0100 to 1111, IMAX = 0V Code = 0100 to 1111, IMAX = 2.4V VCT = 1.0V VCT = 1.0V VOUT = 0V TYP 5 1.0 3.0 4.0 5.2 A −45.0 0.72 2.0 1.3 0.4 −36.0 1.2 3.0 1.5 0.5 −22.0 1.5 6.0 1.7 0.6 µA µA % V V 1.1 1.9 500 V mV nA 500 0.8 nA V 0.8 10 1 V V µA µA 0.5 SHTDWN = 1V IOUT = 10mA 0.4 2.0 3 Note 1: All voltages are with respect to Ground. Current is positive into and negative out of the specified terminal. Note 2: Guaranteed by design. Not 100% tested in production. 3 µs ns °C °C µA A A A A A A A A A A A A mA A 0 0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00 2.25 2.50 2.75 3.0 Fault Output Section Output Leakage Current Low Level Output Voltage VIH = 2.4V VIL = 0.4V µA 20 0.45 0.75 1.0 1.25 1.5 1.75 2.0 2.3 2.58 2.9 3.2 3.5 0.02 1.8 0.1 0.25 0.5 0.75 1.0 1.25 1.5 1.7 1.9 2.1 2.3 2.5 1.5 100 100 (can be connected to VIN) 20 100 100 170 10 Shutdown Section Shutdown Threshold Shutdown Hysteresis Input Current TTL Input DC Characteristics Section TTL Input Voltage High TTL Input Voltage Low TTL Input High Current TTL Input Low Current MAX UNITS UCC3912 PIN DESCRIPTIONS grammed fault level. When set to logic high, the maximum sourcing current will be a constant 4A for applications which require fast charging of load capacitance. B0 - B3: These pins provide digital input to the DAC which sets the fault current threshold. They can be used to provide a digital soft-start, adaptive current limiting. CT: A capacitor connected to ground sets the maximum fault time. The maximum fault time must be more than the time to charge the external capacitance in one cycle. 3 The maximum fault time is defined as FAULT = 27.8 •10 • CT. Once the fault time is reached the output will shut3 down for a time given by: TSD = 833 •10 • CT, this equates to a 3% duty cycle. SHTDWN: When this pin is brought to a logic low, the IC is put into a sleep mode drawing typically less than 1µA of ICC. The input threshold is hysteretic, allowing the user to program a start-up delay with an external RC circuit. VIN: Input voltage to the UCC3912. The recommended voltage range is 3 to 8 volts. Both VIN pins should be connected together and to the power source. FAULT: Open drain output which pulls low upon any condition which causes the output to open: Fault, Thermal Shutdown, or Shutdown. VOUT: Output voltage from the UCC3912. When switched the output voltage will be approximately VIN (0.15Ω • IOUT). Both VOUT pins should be connected together and to the load. IMAX: When this pin is set to logic low the maximum sourcing current will always be 1A above the pro- APPLICATION INFORMATION 4 VIN 2 R1 12 13 HEAT SINK GND PINS 5 GND VIN CIN VOUT 3 D1 VOUT 14 15 RL COUT UCC3912 LED S6 16 FAULT SHTDWN VIN 1 11 CT CT RSD CSD B0 B1 B2 B3 IMAX 6 7 8 9 5 VIN S1 S2 S3 Note: For demonstration board schematic see Design Note DN-58. S4 S5 DIP SWITCH UDG-99171 Figure 1. Evaluation circuit. • Reducing the power distribution inductance (e.g., twist the “+” and “–” leads of the power supply feeding VIN, locate the power supply close to the UCC3912, use a PCB ground plane,...etc.). Protecting The UCC3912 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 UCC3912. It is important to limit the peak of this spike to less than 8V to prevent damage to the UCC3912. This voltage spike can be minimized by: • Decoupling VIN with a capacitor, CIN (refer to Fig. 1), located close to pins 2 and 3. This capacitor is typically less than 1µF to limit the inrush current. • Clamping the voltage at VIN below 8V with a Zener diode, D1(refer to Fig. 1), located close to pins 2 and 3. 4 UCC3912 APPLICATION INFORMATION (cont.) UDG-93019-4 Figure 2. Load current, timing capacitor voltage, and output voltage of the UCC3912 under Fault conditions. Estimating Maximum Load Capacitance where VOUT is the output voltage. For hot swap 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 controller, the output will come up if the load asks for less than the maximum available short-circuit current. For a resistive load of value RL, the value of COUT(max) can be estimated from: To guarantee recovery of a duty-cycle 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 28 • 10 3 • CT COUT (max ) ≈ 1 RL • ln VOUT 1− I MAX • RL 5 UCC3912 APPLICATION INFORMATION (cont.) The overcurrent comparator senses both the DAC output and a representation of the output current. When the output current exceeds the programmed level the timing capacitor CT charges with 36µA of current. If the fault occurs for the time it takes for CT to charge up to 1.5V, the fault latch is set and the output switch is opened. The output remains opened until CT discharges to 0.5V with a 1.2µA current source. Once the 0.5V is reached the output is enabled and will either appear as a switch, if the fault is removed, or a current source if the fault remains. If the over current condition is still present then CT will begin charging, starting the cycle over, resulting in approximately a 3% on time. UDG-94019-1 Figure 3. UCC3912 on time control circuitry. SAFETY RECOMMENDATIONS Although the UCC3912 is designed to provide system protection for all fault conditions, all integrated circuits can ultimately fail short. For this reason, if the UCC3912 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 UCC3912 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. UDG-94101 Figure 4. RDS(on) vs temperature at 2A load current. UNITRODE CORPORATION 7 CONTINENTAL BLVD. • MERRIMACK, NH 03054 TEL. (603) 424-2410 FAX (603) 424-3460 6