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UCC3912
Programmable Hot Swap Power Manager
FEATURES
* Integrated 0.15 Power MOSFET * 3V to 8V Operation * Digital Programmable Current Limit from 0 to 3A * Electronic Circuit Breaker Function * 1A ICC when Disabled * Programmable on Time * Programmable Start Delay * Fixed 3% Duty Cycle * Uni-Directional Switch * 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
DESCRIPTION
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. 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. 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. (continued)
BLOCK DIAGRAM
2 CHARGE PUMP MAX CURRENT LEVEL LINEAR CURRENT AMPLIFIER REVERSE VOLTAGE COMPARATOR 30mV + 3 CURRENT SENSE H = OPEN POWER FET VIN
IMAX 10
H = 4A
VOUT
4A
1A ABOVE FAULT
14 OVER CURRENT COMPARATOR CURRENT FAULT LEVEL 0-3 AMPS ON TIME CONTROL 3% DUTY CYCLE THERMAL SHUTDOWN INTERNAL BIAS + - 1 SHTDWN 1.5V VOUT 15
0-3A 0.25 RES
6 B3
7 B2
8 B1
9 B0
5 GND
4
13
12
11 CT
16 FAULT
UDG-99146
4 BIT DAC
HEAT SINK GND PINS
SLUS241A - NOVEMBER 1999
UCC3912
ABSOLUTE MAXIMUM RATINGS
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 . . . . . . . . . . . . . -65C to +150C Operating Junction Temperature Range . . . . -55C to +150C Lead Temperature (Soldering, 10 sec.) . . . . . . . . . . . . . +300C
DESCRIPTION (cont.)
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 1A 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
DIL-16, SOIC-16 (Top View) N, DP Package TSSOP-24 (Top View) PWP Package
SHTDWN VIN VIN N/C GND* GND* GND* GND* EGND* B3 B2 B1 1 2 3 4 5 6 7 8 9 10 11 12 24 23 22 21 20 19 18 17 16 15 14 13 FAULT VOUT VOUT N/C GND* GND* GND* GND* GND* CT IMAX B0
*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.
*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 = 0C to 70C, 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 3.0 SHTDWN = 0.2V IOUT = 1A IOUT = 2A IOUT = 3A IOUT = 1A, VIN = 3V IOUT = 2A, VIN = 3V IOUT = 3A, VIN = 3V 1.0 0.5 0.15 0.3 0.45 0.17 0.35 0.5 TYP MAX UNITS 8.0 2.0 5.0 0.22 0.45 0.68 0.27 0.56 0.8 V mA A V V V V V V
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UCC3912
ELECTRICAL CHARACTERISTICS: Unless otherwise stated, these specifications apply for TJ = 0C to 70C, 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 TEST CONDITIONS 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 MIN TYP 5 100 100 170 10 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 1.0 4.0 -36.0 1.2 3.0 1.5 0.5 1.5 100 100 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 5.2 -22.0 1.5 6.0 1.7 0.6 1.9 500 500 0.8 MAX UNITS 20 A s ns C C A A A A A A A A A A A A A mA A A A A % V V V mV nA nA V V V A A
0.1 0.25 0.5 0.75 1.0 1.25 1.5 1.7 1.9 2.1 2.3 2.5 0.5 3.0 -45.0 0.72 2.0 1.3 0.4 1.1
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 Shutdown Section Shutdown Threshold Shutdown Hysteresis Input Current Fault Output Section Output Leakage Current Low Level Output Voltage TTL Input DC Characteristics Section TTL Input Voltage High TTL Input Voltage Low TTL Input High Current TTL Input Low Current
SHTDWN = 1V
IOUT = 10mA (can be connected to VIN) VIH = 2.4V VIL = 0.4V 2.0
0.4
3
0.8 10 1
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.
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UCC3912
PIN DESCRIPTIONS
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. FAULT: Open drain output which pulls low upon any condition which causes the output to open: Fault, Thermal Shutdown, or Shutdown. IMAX: When this pin is set to logic low the maximum sourcing current will always be 1A above the programmed 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. SHTDWN: When this pin is brought to a logic low, the IC is put into a sleep mode drawing typically less than 1A 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. VOUT: Output voltage from the UCC3912. When switched the output voltage will be approximately VIN (0.15 * IOUT). Both VOUT pins should be connected together and to the load.
APPLICATION INFORMATION
4 VIN 2 R1 VIN CIN D1 3
12
13
5 GND 14 VOUT 15 RL COUT RSD VIN VOUT
HEAT SINK GND PINS
LED 16 FAULT 11 CT CT B0 6 B1 7
UCC3912 S6 SHTDWN 1 CSD B2 8 B3 9 IMAX 5 VIN DIP SWITCH
S1
S2
S3
S4
S5
Note: For demonstration board schematic see Design Note DN-58.
UDG-99171
Figure 1. Evaluation circuit.
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: * 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.). * Decoupling VIN with a capacitor, CIN (refer to Fig. 1), located close to pins 2 and 3. This capacitor is typically less than 1F 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 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. 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 where VOUT is the output voltage. For a resistive load of value RL, the value of COUT(max) can be estimated from: 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 36A 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 1.2A 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
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Copyright (c) 2000, Texas Instruments Incorporated

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