Low On Resistance Hot Swap Power Manager
application
INFO
available
UCC2918
UCC3918
FEATURES
Integrated 0.06Ω Power
•
MOSFET
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 I
•
Programmable On Time
•
• Programmable Start Delay
• Fixed 3% Duty Cycle
when Disabled
CC
DESCRIPTION
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 tim
ing 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.
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 cur
rent 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.
-
-
BLOCK DIAGRAM
9
IMAX
FAULT LEVEL
IFAULT
8
COMPARATOR
+
MAXIMUM
CURRENT
LEVEL
CURRENT
OVERLOAD
OVERCURRENT
COMPARATOR
CHARGE
PUMP
REVERSE
COMPARATOR
ON TIME
CONTROL
3% DUTY
CYCLE
+
V
OUT
THERMAL
SHUTDOWN
INTERNAL
20mV
CURRENT SENSE
H = OPEN
BIAS
(continued)
VIN
1
VIN
2
VIN
3
14
VOUT
15
VOUT
16
VOUT
1.5V
+
–
7
SHTDWN
5
GND
SLUS384A - NOVEMBER 1999
4
13
HEAT SINK GND
PINS
12
10
6
FAU LTCT
UDG-99153
UCC2918
UCC3918
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.
Other features include an open drain fault output indica
tor, 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
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 500
Databook for thermal limitations and considerations of package.
, IFAULT, IMAX . . . . . . . . . . . . . . . . . –0.3V to VIN
µ
S. Consult Packaging Section of
CONNECTION DIAGRAM
DIL-16, SOIC-16 (Top View)
N Package, DP 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
VIN
2
VIN
3
4
VIN
5
GND*
6
GND*
7
GND*
8
GND*
9
GND*
FAU LT
SHTDWN
IFAULT IMAX
10
11
12
24
VOUT
23
VOUT
22
VOUT
21
VOUT
20
GND*
19
GND*
18
GND*
17
GND*
GND*
16
15
N/C
1413CT
* 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
UCC2918, VIN = 5V. R
IMAX
= 42.2k, R
: Unless otherwise specified, TA= 0°C to 70°C for the UCC3918, –40°C to 85° for the
= 52.3k, SHTDWN = 2.4. TA=TJ.
IFAULT
PARAMETER TEST CONDITIONS MIN TYP MAX UNITS
Supply Section
Voltage Input Range, VIN 356V
V
Supply Current No Load 1 2 mA
DD
Sleep Mode Current SHTDWN
= 0.2V 0.5 5 µA
Output Section
RDS
ON
Reverse Leakage Current V
I
= 1A to 4A, VIN = 5V, TA = 25°C 0.075 0.095 Ω
OUT
= 1A to 4A, VIN = 3V, TA = 25°C 0.09 0.116 Ω
I
OUT
= 1A to 4A, VIN = 5V 0.75 0.125 Ω
I
OUT
= 1A to 4A, VIN = 3V 0.09 0.154 Ω
I
OUT
= 0V, V
IN
= 5V, SHTDWN = 0V 20 A
OUT
Initial Startup Time (Note 1) 100 µS
Thermal Shutdown (Note 1) 170 DEG
Output Section (cont)
Thermal Hysteresis (Note 1) 10 DEG
Output Leakage SHTDWN
Trip Current R
Maximum Output Current R
IFAULT
R
IFAULT
R
IFAULT
R
IFAULT
IMAX
R
IMAX
R
IMAX
R
IMAX
R
IMAX
= 0.2V 20 µA
= 105k 0.75 1 1.25 A
= 52.3k 1.7 2 2.3 A
= 34.8k 2.5 3 3.5 A
= 25.5k 3.3 4 4.7 A
= 118k 0.3 1 1.7 A
= 60.4k 1 2 3 A
= 42.2k 2 3 4 A
= 33.2k 2.5 3.8 5.1 A
= 27.4k 3.0 4.6 6.2 A
Fault Section
C
Charge Current VCT= 1V –50 –36 –22 µA
T
Discharge Current VCT= 1V 0.5 1.2 2.0 µA
C
T
Fault Section (cont.)
Output Duty Cycle VOUT = 0V 1.5 3 6 %
Fault Threshold 0.8 1.3 1.8 V
C
T
Reset Threshold 0.25 0.5 0.75 V
C
T
Shutdown Section
Shutdown Threshold 1.1 1.5 2.0 V
Shutdown Hysteresis 100 mV
Input Low Current SHTDWN
Input High Current SHTDWN
= 0V –500 0 500 nA
= 2V –2 –1 –0.5 µA
Open Drain Fault Output
High Level Output Current 1 µA
Low Level Output Voltage I
= 1mA 0.4 0.9 V
OUT
Note 1: Guaranteed by design. Not 100% tested in production.
3
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
TC
=••27 8 10
FAULT T
Once the fault time is reached the output will shutdown
for a time given by
TC
=••0 833 10
.
SD T
this equates to a 3% duty cycle.
FAULT: Open drain output, which pulls low upon any
condition which causes the output to open; Fault, Ther
mal Shutdown, Shutdown, and maximum sourcing cur
rent greater than the fault time.
GND: This is the most negative voltage in the circuit. All
4 ground pins should be used, and properly heat sunk on
the PCB.
IFAULT: A resistor connected from this pin to ground
sets the fault threshold. The resistor vs fault current is
set by the formula
3
.
6
,
UCC2918
UCC3918
k
R
FAULT
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,
R
FAULT
SHTDWN:
sleep mode. The input threshold is hysteretic, allowing
the user to program a startup delay with an external RC
circuit.
VIN: This is the input voltage to the UCC3918. The rec
ommended operating voltage range is 3V to 6V. All VIN
pins should be connected together and to the power
source.
VOUT: Output voltage for the circuit breaker. When
switched the output voltage will be approximately VIN –
0.06Ω •I
gether and to the load.
105
=
I
TRIP
k
=
Maximum Sourcing Current
126
When this pin is brought low, the IC is put into
. All VOUT pins should be connected to-
OUT
-
APPLICATION INFORMATION
V
IN
D1
R1
C
IN
HEAT SINK GND
PINS
VIN
1
2
VIN
3
VIN
6
FAU LT
CT
10
C
T
IFAULT IMAX
98
R
IFAULT
GND
VOUT
VOUT
VOUT
SHTDWN
R
IMAX
54 1312
14
15
16
R
7
S6
C
SD
C
L
R
OUT
SD
V
OUT
V
IN
UDG-99152
Figure 1. Evaluation circuit.
4
APPLICATION INFORMATION (cont.)
Protecting The UCC3918 From Voltage Transients
The parasitic inductance associated with the power dis
tribution can cause a voltage spike at V
current is suddenly interrupted by the UCC3918.
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 V
, locate the power supply
IN
close to the UCC3918 or use a PCB ground plane).
if the load
IN
It is
UCC2918
UCC3918
To guarantee recovery of a duty-cycle of the cur
rent-limited circuit breaker from a short-circuited load con
dition, 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 C
For worst-case constant-current load of value just less
than the trip limit; C
CII
(max) ( – )≈
OUT MAX LOAD
OUT(max) can be estimated from:
.
T
••
28 10
V
3
OUT
C
T
-
-
Decoupling V
•
located close to the V
with a capacitor, CIN(refer to Fig. 1),
IN
pin. This capacitor is typically
IN
less than 1µF to limit the inrush current.
Clamping the voltage at V
•
diode, D1 (refer to Fig. 1), located close to the V
below 6V with a Zener
IN
IN
pin.
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.
Where V
is the output voltage and I
OUT
MAX
mum, sourcing current.
For a resistive load of value RI, the value of C
be estimated from:
28 10
C
(max) ≈
OUT
RIn
•
L
3
••
C
1
V
OUT
1
−
IR
MAX L
T
•
is the maxi
can
(max)
OUT
-
UDG-97071
Figure 2. Load current, timing capacitor voltage and
output voltage of the UCC3918 under fault.
C
OUT
22µF5Ω 5µF 52.3k 42.0k
Input driven with a pulse generator, shows C
ing through R
the reverse direction.
R
L
and conducting through UCC3918 FET in
L
C
IN
Figure 3.
5
R
IFAULT
OUT
R
IMAX
discharg
-
APPLICATION INFORMATION (cont.)
UCC2918
UCC3918
V
OUT
R
L
C
IN
R
IFAULT
0V SHORT 5µF 52.3k 42.2k
Figure 4. UCC3918 in shorted condition.
R
IMAX
C
OUT
R
L
C
R
IN
IFAULT
R
IMAX
0µF5Ω 5µF 52.3k 42.4k OPEN
Figure 6. CTto V
delay (fault condition).
OUT
C
T
C
OUT
R
L
C
IN
R
IFAULT
22µF5Ω 5µF 52.3k 60.4k
Input switched on through external FET. V
OUT
linear amplifier limiting the changing current of C
Figure 5. Input hot swap.
R
IMAX
shows I
.
OUT
MAX
C
OUT
R
L
0µF5Ω 5µF 52.3k 42.4k
Figure 7. Shutdown delay to V
6
C
IN
OUT
R
IFAULT
off.
R
IMAX
APPLICATION INFORMATION (cont.)
110
100
90
80
mOhms
ON
70
AVERAGE
RDS
60
50
40
-60 -40 -20 0 20 40 60 80 100 120
VIN=3V,I=1A
VIN=5V,I=1A
VIN = 5V, I = 4A
VIN = 3V, I = 4A
TEMPERATURE (°C)
UCC2918
UCC3918
C
OUT
R
L
C
IN
R
IFAULT
0µF5Ω 5µF 52.3k 42.4k
Figure 8. Shutdown delay to V
mOhms
ON
RDS
Figure 9. RDSONvs I
OUT
.
I
OUT
OUT
(A)
on.
R
IMAX
Figure 10. RDSONvs temperature.
SAFETY RECOMMENDATIONS
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
©
or some other safety rating is required, a redundant
UL
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, in
creasing system reliability and reducing maintenance
cost, in addition to providing the hot swap benefits of the
device.
-
UNITRODE CORPORATION
7 CONTINENTAL BLVD. • MERRIMACK, NH 03054
TEL. (603) 424-2410 FAX (603) 424-3460
7
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