.
SLUS241B – MARCH 1994 - REVISED - DECEMBER 2000
Integrated 0.15-Ω Power MOSFET
3-V to 8-V Operation
Digital Programmable Current Limit from 0
to 3 A
Electronic Circuit Breaker Function
1µA ICC When Disabled
Programmable on Time
Programmable Start Delay
Fixed 3% Duty Cycle
Unidirectional Switch
Thermal Shutdown
Fault-Output Indicator
Maximum-Output Current Can Be Set to 1 A
Above the Programmed Fault Level or to a
Full 4 A
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 startup 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 3 A with 0.25-A resolution. The
IMAX control pin sets the maximum sourcing current to 1 A above the fault level when driven low, and to a full
4 A 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 Ω. 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
H=4A
IMAX
2
VIN
3
VIN
14
VOUT
15
VOUT
1
SHTDWN
10
+
REVERSE VOLTAGE
COMPARATOR
CHARGE
PUMP
30 mV
–
+
V OUT
CURRENT SENSE
4A
POWER
FET
+
MAX CURRENT
LEVEL
–
LINEAR CURRENT AMPLIFIER
H = OPEN
1A
ABOVE
FAULT
CURRENT FAULT
LEVEL 0A TO 3 A
ON TIME
CONTROL
+
–
3% DUTY
CYCLE
THERMAL
SHUTDOWN
OVERCURRENT
COMPARATOR
0 A–3 A
0.25
RES
INTERNAL
BIAS
6
7
8
9
5
B3
B2
B1
B0
GND
4 BIT DAC
4
13
12
HEATSINK
GND PINS
11
16
CT
FAULT
1.5 V
+
–
UDG-99146
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of
Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
Copyright 2000, Texas Instruments Incorporated
!$%'#)!%$ !( *''$) ( % &*"!)!%$ )
'%*)( %$%'# )% (&!!)!%$( &' ) )'#( % ,( $()'*#$)(
()$' +''$)- '%*)!%$ &'%((!$ %( $%) $(('!"- !$"*
)()!$ % "" &'#)'(
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1
SLUS241B – MARCH 1994 - REVISED - DECEMBER 2000
description (continued)
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 1-µA of supply current. The SHTDWN pin has a preset
threshold hysteresis which allows the user the ability to set a time delay upon startup 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.
absolute maximum ratings over operating free-air temperature (unless otherwise noted)†
VIN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 V
FAULT sink current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 mA
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, Tstg . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -65°C to 150°C
Operating junction temperature range, TJ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -55°C to 150°C
Lead temperature (soldering, 10 sec.) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 300°C
† Stresses beyond those listed under “absolute maximum ratings” may cause permanent damage to the device. These are stress ratings only, and
functional operation of the device at these or any other conditions beyond those indicated under “recommended operating conditions” is not
implied. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
‡ Currents are positive into, negative out of the specified terminal. Consult Packaging Section of the Interface Products Data book (TI Literature
Number SLUD002) for thermal limitations and considerations of packages.
package information
TSSOP-24,
PWP Package
(TOP VIEW)
DIL-16, SOIC-16
N, DP Package
(TOP VIEW)
*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.
2
POST OFFICE BOX 655303
SHTDWN1
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.
• DALLAS, TEXAS 75265
SLUS241B – MARCH 1994 - REVISED - DECEMBER 2000
electrical characteristics, these specifications apply for TA = 0°C to 70°C, VIN = 5 V, IMAX = 0.4 V,
SHTDWN = 2.4 V, (unless otherwise stated)
supply section
PARAMETER
TEST CONDITIONS
Voltage input range
MIN
TYP
Supply current
Sleep mode current
MAX
3.0
SHTDWN = 0.2 V
UNITS
8.0
V
1.0
2.0
mA
0.5
5.0
µA
NOTE 1: All voltages are with respect to ground. Current is positive into and negative out of the specified terminal.
output section
PARAMETER
Voltage drop
TEST CONDITIONS
MIN
TYP
MAX
UNITS
IOUT = 1 A
IOUT = 2 A
0.15
0.22
V
0.3
0.45
V
IOUT = 3 A
IOUT = 1A,
0.45
0.68
V
VIN = 3 V
0.17
0.27
V
IOUT = 2 A,
IOUT = 3 A,
VIN = 3 V
0.35
0.56
V
VIN = 3 V
0.5
0.8
V
VIN < VOUT ,
See Note 2
SHTDWN = 0.2 V, VOUT = 5 V
5
20
µA
Initial startup time
Short circuit response
See Note 2
100
ns
Thermal shutdown
See Note 2
170
°C
Thermal hysteresis
See Note 2
10
°C
Reverse leakage current
µs
100
NOTE 1: All voltages are with respect to ground. Current is positive into and negative out of the specified terminal.
NOTE 2: Ensured by design. Not production tested.
DAC section
PARAMETER
Output leakage
Trip current
TEST CONDITIONS
MIN
TYP
MAX
UNITS
0
20
µA
Code = 0100
0.1
0.25
0.45
A
Code = 0101
0.25
0.50
0.75
A
Code = 0110
0.5
0.75
1.0
A
Code = 0111
0.75
1.00
1.25
A
Code = 1000
1.0
1.25
1.5
A
Code = 1001
1.25
1.50
1.75
A
Code = 1010
1.5
1.75
2.0
A
Code = 1011
1.7
2.00
2.3
A
Code = 1100
1.9
2.25
2.58
A
Code = 1101
2.1
2.50
2.9
A
Code = 1110
2.3
2.75
3.2
A
Code = 1111
2.5
3.0
3.5
A
0.02
mA
Code = 0000–0011
Max output current
Code = 0000 to 0011
Max output current over trip
(current source mode)
Code = 0100 to 1111,
IMAX = 0 V
0.5
1.0
1.8
A
Max output current
(current source mode)
Code = 0100 to 1111,
IMAX = 2.4 V
3.0
4.0
5.2
A
NOTE 1: All voltages are with respect to ground. Current is positive into and negative out of the specified terminal.
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SLUS241B – MARCH 1994 - REVISED - DECEMBER 2000
electrical characteristics, these specifications apply for TA = 0°C to 70°C, VIN = 5 V, IMAX = 0.4 V,
SHTDWN = 2.4 V, (unless otherwise stated)
timer section
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNITS
–45.0
-36.0
–22.0
µA
CT discharge current
VCT = 1.0 V
VCT = 1.0 V
0.72
1.2
1.5
µA
Output duty cycle
VOUT = 0 V
CT charge current
2.0
3.0
6.0
%
CT fault threshold
1.3
1.5
1.7
V
CT reset threshold
0.4
0.5
0.6
V
NOTE 1: All voltages are with respect to ground. Current is positive into and negative out of the specified terminal.
shutdown section
PARAMETER
TEST CONDITIONS
Shutdown threshold
MIN
TYP
1.1
Shutdown hysteresis
Input current
MAX
1.5
UNITS
1.9
100
SHTDWN = 1 V
100
V
mV
500
nA
fault output section
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
Output leakage current
Low level output voltage
IOUT = 10 mA
0.4
UNITS
500
nA
0.8
V
TTL input dc characteristics section
PARAMETER
TTL input voltage high
TEST CONDITIONS
(can be connected to VIN)
MIN
TYP
MAX
2.0
V
TTL input voltage low
TTL input high current
TTL input low current
UNITS
VIH = 2.4 V
VIL = 0.4 V
3
0.8
V
10
µA
1
µA
NOTE 1: All voltages are with respect to ground. Current is positive into and negative out of the specified terminal.
pin description
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. The maximum fault time is defined as
FAULT = 27.8 × 103 × CT. Once the fault time is reached the output will shutdown for a time given by:
TSD = 833 × 103 × 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 1 A above the programmed
fault level. When set to logic high, the maximum sourcing current will be a constant 4 A for applications which
require fast charging of load capacitance.
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SLUS241B – MARCH 1994 - REVISED - DECEMBER 2000
pin description (continued)
SHTDWN: When this pin is brought to a logic low, the IC is put into a sleep mode drawing typically less than
1 µA of ICC. The input threshold is hysteretic, allowing the user to program a startup delay with an external RC
circuit.
VIN: Input voltage to the UCC3912. The recommended voltage range is 3 V to 8 V. 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 Ω × IOUT). Both VOUT pins should be connected together and to the load.
APPLICATION INFORMATION
4
VIN
2
R1
CIN
12
13
HEAT SINK
GND PINS
VIN
5
GND
VOUT
3
D1
VOUT
14
15
RL
COUT
UCC3912
LED
S6
16 FAULT
VIN
SHTDWN 1
11 CT
CT
RSD
B3
B2
B1
B0
IMAX
6
7
8
9
10
CSD
VIN
S1
S2
S3
S4
S5
DIP
SWITCH
NOTE: For demonstration board schematic see Design Note DN-58 (TI Literature Number SLUA187).
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 8 V
to prevent damage to the UCC3912. 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 UCC3912, use a PCB ground plane,...etc.).
Decoupling VIN with a capacitor, CIN (refer to Figure 1), located close to pins 2 and 3. This capacitor is
typically less than 1 µF to limit the inrush current.
Clamping the voltage at VIN below 8 V with a zener diode, D1 (refer to Figure 1), located close to pins 2
and 3.
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SLUS241B – MARCH 1994 - REVISED - DECEMBER 2000
APPLICATION INFORMATION
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 ensure 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:
C
OUT(max)
MAX ILOAD I
28 10 3 CT
V
OUT
where VOUT is the output voltage.
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SLUS241B – MARCH 1994 - REVISED - DECEMBER 2000
APPLICATION INFORMATION
For a resistive load of value RL, the value of COUT(max) can be estimated from:
28 103 CT
C
OUT(max) RL n
1
V
1
OUT
I
MAXRL
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 36 µA of current. If the fault
occurs for the time it takes for CT to charge up to 1.5 V, the fault latch is set and the output switch is opened.
The output remains opened until CT discharges to 0.5 V with a 1.2-µA current source. Once the 0.5 V 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 Circuitry
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SLUS241B – MARCH 1994 - REVISED - DECEMBER 2000
APPLICATION INFORMATION
UDG-94019-1
Figure 4. RDS(on) vs. Temperature at 2-A Load Current.
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 for all fault conditions, increasing
system reliability and reducing maintenance cost, in addition to providing the hot swap benefits of the device.
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• DALLAS, TEXAS 75265
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TI warrants performance of its semiconductor products to the specifications applicable at the time of sale in
accordance with TI’s standard warranty. Testing and other quality control techniques are utilized to the extent
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Copyright 2000, Texas Instruments Incorporated