ETC UCC3918N

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
4
13
12
HEAT SINK GND
PINS
SLUS384A - NOVEMBER 1999
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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
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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
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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
12
13
5
VOUT
14
VOUT
15
VOUT
16
VOUT
RL
COUT
RSD
CT
CT
GND
SHTDWN
IFAULT
IMAX
8
9
RIFAULT
7
S6
VIN
CSD
RIMAX
UDG-99152
Figure 1. Evaluation circuit.
4
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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
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



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
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
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RL
5Ω
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
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