ETC UCC1913J

UCC1913
UCC2913
UCC3913
Negative Voltage Hot Swap Power Manager
FEATURES
DESCRIPTION
• Precision Fault Threshold
The UCC1913 family of negative voltage circuit breakers provides complete power management, hot swap, and fault handling capability. The IC is
referenced to the negative input voltage and is driven through an external
resistor connected to ground, which is essentially a current drive as opposed to the traditional voltage drive. The on-board 10V shunt regulator
protects the IC from excess voltage and serves as a reference for programming the maximum allowable output sourcing current during a fault. All
control and housekeeping functions are integrated, and externally programmable. These include the fault current level, maximum output sourcing current, maximum fault time, soft start time, and average power limiting. In the
event of a constant fault, the internal timer will limit the on-time from less
than 0.1% to a maximum of 3%. The duty cycle modulates depending on
the current into the PL pin, which is a function of the voltage across the
FET, and will limit average power dissipation in the FET. The fault level is
fixed at 50mV across the current sense amplifier to minimize total dropout.
The fault current level is set with an external current sense resistor. The
maximum allowable sourcing current is programmed with a voltage divider
from VDD to generate a fixed voltage on the IMAX pin. The current level,
when the output appears as a current source, is equal to VIMAX/RSENSE. If
desired, a controlled current startup can be programmed with a capacitor
on the IMAX pin.
• Programmable Average Power
Limiting
• Programmable Linear Current Control
• Programmable
• Overcurrent Limit
• Programmable Fault Time
• Fault Output Indication
• Shutdown Control
• Undervoltage Lockout
• 8-Pin SOIC
When the output current is below the fault level, the output device is
switched on. When the output current exceeds the fault level, but is less
than the maximum sourcing level programmed by the IMAX pin, the output
remains switched on, and the fault timer starts charging CT. Once CT
charges to 2.5V, the output device is turned off and performs a retry some
time later. When the output current reaches the maximum sourcing current
level, the output appears as a current source, limiting the output current to
the set value defined by IMAX.
Other features of the UCC1913 family include undervoltage lockout, and
8-pin small outline (SOIC) and Dual-In-Line (DIL) packages.
BLOCK DIAGRAM
VDD
IMAX
3
2
UVLO
LOGIC
SUPPLY
5.0V
REF
1=
UNDERVOLTAGE
0.2V
7
OUT
6
SENSE
5
VSS
4
CT
5.0V
VDD
LINEAR
CURRENT
AMPLIFIER
OVERLOAD COMPARATOR
SD/FLT
PL
VDD
VDD
+
9.5V SHUNT REGULATOR
8
50Ω
DISABLE
1
+
20µA
SOURCE
ONLY
ON-TIME
CONTROL
50mV
OVERCURRENT
COMPARATOR
1/99
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UDG-99001
UCC1913
UCC2913
UCC3913
CONNECTION DIAGRAMS
ABSOLUTE MAXIMUM RATINGS
IVCC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50mA
SHUTDOWN Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10mA
PL Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10mA
IMAX Input Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . VCC
Storage Temperature . . . . . . . . . . . . . . . . . . . –65°C to +150°C
Junction Temperature . . . . . . . . . . . . . . . . . . . –55°C to +150°C
Lead Temperature (Soldering, 10 sec.) . . . . . . . . . . . . . +300°C
DIL-8, SOIC-8 (Top View)
N or J, D Package
SD/FLT
1
8
PL
IMAX
2
7
OUT
VDD
3
6
SENSE
CT
4
5
VSS
All voltages are with respect to VSS (The most negative voltage). All currents are positive into, negative out of the specified
terminal. Consult Packaging Section of Databook for thermal
limitations and considerations of packages.
ELECTRICAL CHARACTERISTICS: Unless otherwise stated these specifications apply for TA = –55°C to +125°C for
UCC1913; –40°C to +85°C for UCC2913; 0°C to +70°C for UCC3913; IVDD = 2mA, CT = 4.7pF, TA = TJ
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX UNITS
VDD Section
IDD
Regulator Voltage
ISOURCE = 2mA to 10mA
UVLO Off Voltage
1.0
2.0
mA
8.5
9.5
10.5
V
6
7
8
V
47.5
50
53
mV
50
53.5
mV
50
500
nA
Fault Timing Section
Overcurrent Threshold
TJ = 25°C
Over Operating Temperature
46
Overcurrent Input Bias
CT Charge Current
CT Discharge Current
VCT = 1.0V, IPL = 0
–50
–36
–22
µA
Overload Condition, VSENSE – VIMAX = 300mV
–1.7
–1.2
–0.7
mA
VCT = 1.0V, IPL = 0
CT Fault Threshold
CT Reset Threshold
Output Duty Cycle
0.6
1
1.5
µA
2.2
2.4
2.6
V
0.32
0.5
0.62
V
Fault Condition, IPL = 0
1.7
2.7
3.7
%
IOUT = 0A
8.5
10
Output Section
Output High Voltage
IOUT = –1mA
Outut Low Voltage
6
IOUT = 0A; VSENSE – VIMAX = 100mV
IOUT = 2mA; VSENSE – VIMAX = 100mV
V
8
V
0
0.01
V
0.2
0.6
V
Linear Amplifier Section
Sense Control Voltage
IMAX = 100mV
85
100
115
mV
IMAX = 400mV
370
400
430
mV
50
500
nA
1.4
1.7
2.0
V
15
25
45
µA
6
7.5
9
V
0
0.01
V
150
300
ns
Input Bias
Shutdown/Fault Section
Shutdown Threshold
Input Current
Shutdown = 5V
Fault Output High
Fault Output Low
Delay to Output
(Note 1)
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2
UCC1913
UCC2913
UCC3913
ELECTRICAL CHARACTERISTICS: Unless otherwise stated these specifications apply for TA = –55°C to +125°C for
UCC1913; –40°C to +85°C for UCC2913; 0°C to +70°C for UCC3913; IVDD = 2mA, CT = 4.7pF, TA = TJ
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX UNITS
4.35
4.85
5.35
Power Limiting Section
VSENSE Regulator Voltage
IPL = 64 A
V
Duty Cycle Control
IPL = 64µA
0.6
1.2
1.7
%
IPL = 1mA
0.045
0.1
0.17
%
300
500
ns
Overload Section
Delay to Output
(Note 1)
Output Sink Current
VSENSE = VIMAX = 300mV
40
100
Threshold
Relative to IMAX
140
200
mA
260
mV
Note 1: Guaranteed by design. Not 100% tested in production.
PIN DESCRIPTIONS
CT: A capacitor is connected to this pin in order to set the
maximum fault time. The maximum fault time must be
more than the time to charge external load capacitance.
The maximum fault time is defined as:
TFAULT =
from this pin to the drain of the NMOS pass element.
When the voltage across the NMOS exceeds 5V, current
will flow into the PL pin which adds to the fault timer
charge current, reducing the duty cycle from the 3%
level. When IPL>>36µA then the average MOSFET
power dissipation is given by:
( 2 • CT )
ICH
PFET ( avg ) = IMAX • 1 • 10 −6 • RPL
where
ICH = 36µA + IPL ,
SENSE: Input voltage from the current sense resistor.
When there is greater than 50mV across this pin with respect to VSS, then a fault is sensed, and CT starts to
charge.
and IPL is the current into the power limit pin. Once the
fault time is reached the output will shutdown for a time
given by:
SD/FLT: This pin provides fault output indication and
shutdown control. Interface into and out of this pin is usually performed through level shift transistors. When 20µA
is sourced into this pin, shutdown drives high causing the
output to disable the NMOS pass device. When opened,
and under a non-fault condition, the SD/FLT pin will pull
to a low state. When a fault is detected by the fault timer,
or undervoltage lockout, this pin will drive to a high state,
indicating the output FET is off.
TSD = 2 • 106 • CT
IMAX: This pin programs the maximum allowable sourcing current. Since VDD is a regulated voltage, a voltage
divider can be derived from VDD to generate the program level for the IMAX pin. The current level at which
the output appears as a current source is equal to the
voltage on the IMAX pin over the current sense resistor.
If desired, a controlled current startup can be programmed with a capacitor on the imax pin, and a programmed start delay can be achieved by driving the
shutdown with an open collector/drain device into an RC
network.
VDD: Current driven with a resistor to a voltage at least
10V more positive than VSS. Typically a resistor is connected to ground. The 10V shunt regulator clamps VDD
at 10V above the VSS pin, and is also used as an output
reference to program the maximum allowable sourcing
current.
OUT: Output drive to the MOSFET pass element.
PL: This feature ensures that the average MOSFET
power dissipation is controlled. A resistor is connected
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VSS: Ground reference for the IC and the most negative
voltage available.
3
UCC1913
UCC2913
UCC3913
APPLICATION INFORMATION
LOAD
PL
RPL
+
0.2V
OVERLOAD COMPARATOR
VDD
SENSE
IMAX
8
I1
36µA
5.0V
OUTPUT
6
RS
+
SENSE
I3
1mA
OVERCURRENT
COMPARATOR
2.5V
50mV
H=CLOSE
VSS
H=CLOSE
I2
1µA
5
S
Q
R
Q
TO OUTPUT
DRIVE
H=OFF
0.5V
VSS
INPUT VOLTAGE
CT
FAULT TIMING CIRCUITRY
4
CT
UDG-99004
VSS
Figure 1. Fault timing circuitry for the UCC1913, including power limit overload.
During a fault, CT will charge at a rate determined by the
internal charging current and the external timing capacitor. Once CT charges to 2.5V, the fault comparator
switches and sets the fault latch. Setting of the fault latch
causes both the output to switch off and the charging
switch to open. CT must now discharge with the 1µA current source, I2, until 0.5V is reached. Once the voltage at
CT reaches 0.5V, the fault latch resets, which re-enables
the output and allows the fault circuitry to regain control
of the charging switch. If a fault is still present, the fault
comparator will close the charging switch causing the cycle to begin. Under a constant fault, the duty cycle is
given by:
Figure 1 shows the detailed circuitry for the fault timing
function of the UCC1913. For the time being, we will discuss a typical fault mode, therefore, the overload comparator, and current source I3 does not work into the
operation. Once the voltage across the current sense resistor, RS, exceeds 50mV, a fault has occurred. This
causes the timing capacitor to charge with a combination
of 36µA plus the current from the power limiting amplifier.
The PL amplifier is designed to only source current into
the CT pin and to begin sourcing current once the voltage across the output FET exceeds 5V. The current IPL
is related to the voltage across the FET with the following
expression:
IPL =
VFET − 5V
RPL
DutyCycle =
1 µA
IPL + 36 µA
Average power dissipation in the pass element is given
by:
Where VFET is the voltage across the NMOS pass device.
Later it will be shown how this feature will limit average
power dissipation in the pass device. Note that under a
condition where the output current is more than the fault
level, but less than the max level, VOUT ~ VSS (input
voltage), IPL = 0, the CT charging current is 36µA.
PFET ( avg ) = VFET • IMAX •
1 µA
IPL + 36 µA
where VFET >> 5V IPL can be approximated as :
VFET
RPL
and where IPL>>36µA, the duty cycle can be approximated as :
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4
UCC1913
UCC2913
UCC3913
APPLICATION INFORMATION (cont.)
IOUT
Output
Current
IMAX
IFAULT
Io(nom)
t
0A
VCT
2.5V
CT
Voltage
(w/respect to VSS)
0.5V
t
0V
VOUT
0V
Output
Voltage
(w/respect to GND)
VSS
t0 t1 t2
t3
t4
t5
t6 t7 t8
t9 t10
t
t0: safe condition – output current is nominal, output
voltage is at the negative rail, VSS.
t5: t5 = t3: illustrates 3%duty cycle.
t1: fault control reached – output current rises above
the programmed fault value, CT begins to charge at
≅ 36µA.
t7: output short circuit - if VOUT is short circuited to
ground, CT charges at a higher rate depending
upon the values for VSS and RPL.
t2: max current reached – output current reaches the
programmed maximum level and becomes a constant current with value IMAX.
t8: fault occurs – output is still short circuited, but the
occurrence of a fault turns the FET off so no current
is conducted.
t3: fault occurs – CT has charged to 2.5V, fault output
goes high, the FET turns off allowing no output current to flow, VOUT floats up to ground.
t9: t9 = t4; output short circuit released, still in fault
mode.
t6: t6 = t4
t10: t10 = t0; fault released, safe condition – return to
normal operaton of the circuit breaker.
t4: retry – CT has discharged to 0.5V, but fault current
is still exceeded, CT begins charging again, FET is
on, VOUT pulled down to VSS.
Figure 2. Typical timing diagram.
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5
UCC1913
UCC2913
UCC3913
APPLICATION INFORMATION (cont.)
1µA • RPL
VFET
Therefore, the maximum average power dissipation in
the MOSFET can be approximated by:
PFET ( avg ) =
VFET • IMAX •
1 µA • RPL
= IMAX • 1µA • R PL
VFET
Notice that in the approximation, VFET cancels. therefore,
average power dissipation is limited in the NMOS pass
element.
Overload Comparator
Figure 3.
The linear amplifier in the UCC1913 ensures that the
output NMOS does not pass more than IMAX (which is
VIMAX/RS). In the event the output current exceeds the
programmed IMAX by 0.2V/RS, which can only occur if
the output FET is not responding to a command from the
IC, the CT pin will begin charging with I3, 1mA, and continue to charge to approximately 8V. This allows a constant fault to show up on the SD/FLT pin, and also since
the voltage on CT will only charge past 2.5V in an overload fault mode, it can be used for detection of output
FET failure or to build in redundancy in the system.
∞
Determining External Component Values
Referring now to Figure 3. To set RVDD the following
must be achieved:
VIN (min )
RVDD
10 V
(R1 + R 2)
+ 2 mA
In order to estimate the minimum timing capacitor, CT,
several things must be taken into account. For example,
given the schematic below as a possible (and at this
point, a standard) application, certain external component values must be known in order to estimate CT(min).
Figure 4. Plot average power vs. FET voltage for
increasing values of RPL.
Now, given the values of COUT, Load, RSENSE, VSS, and
the resistors determining the voltage on the IMAX pin,
the user can calculate the approximate startup time of
the node VOUT. This startup time must be faster than the
time it takes for CT to charge to 2.5V (relative to VSS),
and is the basis for estimating the minimum value of CT.
In order to determine the value of the sense resistor,
RSENSE, assuming the user has determined the fault current, RSENSE can be calculated by:
LOCAL VDD
R3
SHUTDOWN
FAULT OUT
R4
LOCAL GND
LEVEL SHIFT
>
7
R SENSE =
SD/FLT
VSS
Figure 5. Possible level shift circuitry to interface to
the UCC1913.
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6
50mV
IFAULT
UCC1913
UCC2913
UCC3913
APPLICATION INFORMATION (cont.)
Next, the variable IMAX must be calculated. IMAX is the
maximum current that the UCC1913 will allow through
the transistor, M1, and it can be shown that during
startup with an output capacitor the power MOSFET, M1,
can be modeled as a constant current source of value
IMAX where:
IMAX =
TSTART =
COUT • VSS
IMAX − ILOAD
Resistive Load:
IMAX • ROUT

TSTART = COUT • ROUT • n 
 IMAX • ROUT − VSS
VIMAX
R SENSE



Once TSTART is calculated, the power limit feature of the
UCC1913 must be addressed and component values derived. Assuming the user chooses to limit the maximum
allowable average power that will be associated with the
circuit breaker, the power limiting resistor, RPL, can be
easily determined by the following:
where VIMAX = voltage on pin IMAX.
Given this information, calculation of the startup time is
now possible via the following:
Current Source Load:
CVDD
R1
R2
VSS
RVDD
CSS
VDD
IMAX
3
OUTPUT
2
PL R
T
UVLO
LOGIC
SUPPLY
5.0V
REF
8
1=
UNDERVOLTAGE
VDD
VDD
9.5V SHUNT REGULATOR
+
OUT
VDD
SD/FLT
LINEAR
CURRENT
AMPLIFIER
7
50Ω
DISABLE
1
SENSE
+
20µA
SOURCE
ONLY
ON-TIME
CONTROL
6
FAULT=
50mV
RS
VSS
5
CT
CT
4
VSS
UDG-99002
Figure 6. Typical application diagram.
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7
UCC1913
UCC2913
UCC3913
APPLICATION INFORMATION (cont.)
RPL =
PFET (avg )
Resistive Load:
CT (min ) =
1µA • IMAX
where a minimum RPL exists defined by RPL (min ) =
3 • TSTART (31 µA • RPL + VSS − 5V − IMAX • ROUT
5 • RPL
VSS
5mA
)
+
3 • ROUT • VSS • COUT
5 • RPL
Finally, after computing the aforementioned variables,
the minimum timing capacitor can be derived as such:
Current Source Load:
CT (min ) =
(3 • TSTART
• 62µA • RPL + VSS − 10V )
10 • RPL
SAFETY RECOMENDATION
Although the UCC3913 is designed to provide system
protection for all fault conditions, all integrated circuits
can ultimately fail short. For this reason, if the UCC3913
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 UCC3913 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.
UNITRODE CORPORATION
7 CONTINENTAL BLVD. • MERRIMACK, NH 03054
TEL. (603) 424-2410 FAX (603) 424-3460
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