Datasheet UCC1913, UCC2913, UCC3913 Datasheet (UNITRODE)

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Page 1

查询UCC1913供应商

Negative Voltage Hot Swap Power Manager

UCC1913 UCC2913 UCC3913

FEATURES

• Precision Fault Threshold

• Programmable Average Power

Limiting

• Programmable Linear Current Control

• Programmable

• Overcurrent Limit

• Programmable Fault Time

• Fault Output Indication

• Shutdown Control

• Undervoltage Lockout

• 8-Pin SOIC

DESCRIPTION

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 V

IMAX/RSENSE

desired, a controlled current startup can be programmed with a capacitor on the IMAX pin.

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.

.If

BLOCK DIAGRAM

LOGIC

SUPPLY

9.5V SHUNT REGULATOR

SD/FLT

SLUS274 - JANUARY 1999

20µA

Other features of the UCC1913 family include undervoltage lockout, and 8-pin small outline (SOIC) and Dual-In-Line (DIL) packages.

VDD

5.0V REF

SOURCE

ONLY

UVLO

1= UNDERVOLTAGE

OVERLOAD COMPARATOR

ON-TIME

CONTROL

0.2V +

IMAX

DISABLE

OVERCURRENT COMPARATOR

5.0V

LINEAR CURRENT AMPLIFIER

50mV

50Ω

7OUT

6 SENSE

5 VSS

4CT

UDG-99001

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ABSOLUTE MAXIMUM RATINGS

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50mA

VCC

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

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.

CONNECTION DIAGRAMS

DIL-8, SOIC-8 (Top View) N or J, D Package

SD/FLT

IMAX

VDD

UCC1913 UCC2913 UCC3913

OUT

SENSE

VSS

ELECTRICAL CHARACTERISTICS: Unless otherwise stated these specifications apply for T

UCC1913; –40°C to +85°C for UCC2913; 0°C to +70°C for UCC3913; I

= 2mA, CT = 4.7pF, TA= T

VDD

= –55°C to +125°C for

PARAMETER TEST CONDITIONS MIN TYP MAX UNITS

VDD Section

IDD 1.0 2.0 mA Regulator Voltage I

SOURCE

= 2mA to 10mA 8.5 9.5 10.5 V

UVLO Off Voltage 678V

Fault Timing Section

Overcurrent Threshold T

= 25°C 47.5 50 53 mV

Over Operating Temperature 46 50 53.5 mV Overcurrent Input Bias 50 500 nA CT Charge Current VCT= 1.0V, IPL= 0 –50 –36 –22 µA

Overload Condition, V

SENSE

– V

= 300mV –1.7 –1.2 –0.7 mA

IMAX

CT Discharge Current VCT= 1.0V, IPL= 0 0.6 1 1.5 µA CT Fault Threshold 2.2 2.4 2.6 V CT Reset Threshold 0.32 0.5 0.62 V Output Duty Cycle Fault Condition, IPL= 0 1.7 2.7 3.7 %

Output Section

Output High Voltage I

Outut Low Voltage I

= 0A 8.5 10 V

OUT

= –1mA 6 8 V

OUT OUT

OUT

= 0A; V = 2mA; V

SENSE

– V

= 100mV 0 0.01 V

IMAX

– V

= 100mV 0.2 0.6 V

IMAX

Linear Amplifier Section

Sense Control Voltage IMAX = 100mV 85 100 115 mV

IMAX = 400mV 370 400 430 mV Input Bias 50 500 nA

Shutdown/Fault Section

Shutdown Threshold 1.4 1.7 2.0 V Input Current Shutdown = 5V 15 25 45 µA Fault Output High 6 7.5 9 V Fault Output Low 0 0.01 V Delay to Output (Note 1) 150 300 ns

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UCC1913 UCC2913 UCC3913

ELECTRICAL CHARACTERISTICS:

UCC1913; –40°C to +85°C for UCC2913; 0°C to +70°C for UCC3913; I

PARAMETER TEST CONDITIONS MIN TYP MAX UNITS

Power Limiting Section

V Duty Cycle Control IPL= 64µA 0.6 1.2 1.7 %

Overload Section

Delay to Output (Note 1) 300 500 ns Output Sink Current V Threshold Relative to IMAX 140 200 260 mV

Note 1: Guaranteed by design. Not 100% tested in production.

Regulator Voltage IPL= 64 A 4.35 4.85 5.35 V

SENSE

Unless otherwise stated these specifications apply for TA= –55°C to +125°C for

= 2mA, CT = 4.7pF, TA= T

VDD

= 1mA 0.045 0.1 0.17 %

SENSE

= V

= 300mV 40 100 mA

IMAX

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:

()

FAULT

•2

where

IAI

=+36µ

CH PL

and I

is the current into the power limit pin. Once the

fault time is reached the output will shutdown for a time given by:

TCT

=• •2 106

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.

OUT: Output drive to the MOSFET pass element. PL: This feature ensures that the average MOSFET

power dissipation is controlled. A resistor is connected

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 I

>>36µA then the average MOSFET

power dissipation is given by:

−

PIMAX R

FET avg PL

=•••

()

110

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.

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.

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.

VSS: Ground reference for the IC and the most negative voltage available.

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APPLICATION INFORMATION

LOAD

5.0V

SENSE

50mV

VSS

OUTPUT

VSS

INPUT VOLTAGE

OVERCURRENT

COMPARATOR

OVERLOAD COMPARATOR

36µA

H=CLOSE

1µA

1mA

2.5V

H=CLOSE

0.5V

UCC1913 UCC2913 UCC3913

0.2V +

FAULT TIMING CIRCUITRY

SENSE IMAX

TO OUTPUT DRIVE H=OFF

VSS

Figure 1. Fault timing circuitry for the UCC1913, including power limit overload.

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, R

, 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 I is related to the voltage across the FET with the following expression:

−5

FET

Where V

is the voltage across the NMOS pass de-

FET

vice. Later it will be shown how this feature will limit average

power dissipation in the pass device. Note that under a

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 cy-

cle to begin. Under a constant fault, the duty cycle is given by:

DutyCycle

+136µµ

Average power dissipation in the pass element is given by:

PVIMAX

FET avg FET

=• •

()

condition where the output current is more than the fault level, but less than the max level, V

~ VSS (input

OUT

where V

>> 5V IPLcan be approximated as :

FET

voltage), IPL= 0, the CT charging current is 36µA.

and where IPL>>36µA, the duty cycle can be approximated as :

UDG-99004

+136µµ

FET

Page 5

APPLICATION INFORMATION (cont.)

IOUT

IMAX

Output

Current

IFAULT

Io(nom)

UCC1913 UCC2913 UCC3913

2.5V

Voltage

(w/respectt oVSS)

0.5V

OUT

Output

Voltage

(w/respecttoGND)

VSS

t1 t2 t3 t4 t5 t6 t7 t8 t9 t10

t0: safe condition – output current is nominal, output

voltage is at the negative rail, VSS.

t1: fault control reached – output current rises above

the programmed fault value, CT begins to charge at ≅ 36µA.

t2: max current reached – output current reaches the

programmed maximum level and becomes a constant current with value I

MAX

t3: fault occurs – CT has charged to 2.5V, fault output

goes high, the FET turns off allowing no output current to flow, V

floats up to ground.

OUT

t4: retry – CT has discharged to 0.5V, but fault current

is still exceeded, CT begins charging again, FET is on, V

pulled down to VSS.

OUT

t5: t5 = t3: illustrates 3%duty cycle. t6: t6 = t4 t7: output short circuit - if V

is short circuited to

OUT

ground, CT charges at a higher rate depending upon the values for VSS and R

t8: fault occurs – output is still short circuited, but the

occurrence of a fault turns the FET off so no current is conducted.

t9: t9 = t4; output short circuit released, still in fault

mode.

t10: t10 = t0; fault released, safe condition – return to

normal operaton of the circuit breaker.

Figure 2. Typical timing diagram.

Page 6

APPLICATION INFORMATION (cont.)

UCC1913 UCC2913 UCC3913

1µ

•

FET

Therefore, the maximum average power dissipation in the MOSFET can be approximated by:

FET avg

VIMAX

FET

()

••

11µ

•

FET

IMAX A R

=••

Figure 3.

∞

Figure 4. Plot average power vs. FET voltage for increasing values of R

LOCAL VDD

SHUTDOWN

FAULT OUT

LOCAL GND

LEVEL SHIFT

SD/FLT7

VSS

Notice that in the approximation, V

cancels. therefore,

FET

average power dissipation is limited in the NMOS pass element.

Overload Comparator

The linear amplifier in the UCC1913 ensures that the output NMOS does not pass more than I V

IMAX/RS

programmed I

). In the event the output current exceeds the

by 0.2V/RS, which can only occur if

MAX

(which is

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 R

the following

VDD

must be achieved:

()

min

VDD

()

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 C

Now, given the values of C

, Load, R

OUT

SENSE

, VSS, and

T(min)

the resistors determining the voltage on the IMAX pin, the user can calculate the approximate startup time of the node V

. This startup time must be faster than the

OUT

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, R rent, R

, assuming the user has determined the fault cur-

SENSE

can be calculated by:

SENSE

FAULT

Figure 5. Possible level shift circuitry to interface to the UCC1913.

Page 7

APPLICATION INFORMATION (cont.)

Next, the variable I 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

where:

MAX

where V

IMAX

SENSE

= voltage on pin IMAX.

IMAX

Given this information, calculation of the startup time is now possible via the following:

Current Source Load:

must be calculated. I

MAX

is the

UCC1913 UCC2913 UCC3913

CVSS

•

START

Resistive Load:

TCRn

START OUT OUT

Once T

START

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, R easily determined by the following:

OUT

−

MAX LOAD



=••



IRVSS



MAX OUT

•

MAX OUT

•−

is calculated, the power limit feature of the

, can be

 

 

SD/FLT

20µA

5.0V REF

LOGIC

SUPPLY

9.5V SHUNT REGULATOR

VDD

SOURCE

ONLY

UVLO

1= UNDERVOLTAGE

ON-TIME

CONTROL

VDD

IMAX

CSS

DISABLE

VSS

LINEAR CURRENT AMPLIFIER

50Ω

FAULT=

50mV

OUT

SENSE

VSS

OUTPUT

Figure 6. Typical application diagram.

VSS

UDG-99002

Page 8

APPLICATION INFORMATION (cont.)

()

FET avg

•1µ

MAX

exists defined by

()

min

VSS

where a minimum R Finally, after computing the aforementioned variables,

the minimum timing capacitor can be derived as such: Current Source Load:

()

TARVSSV

•••+−

()

min

362 10

START PL

•

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

UCC1913 UCC2913 UCC3913

Resistive Load:

331 5

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.

()

min

TARVSSVIR

••+−−•

•

()

START PL MAX OUT

TOUT

VSS C

••

•5

•

UNITRODE CORPORATION 7 CONTINENTALBLVD. • MERRIMACK, NH 03054 TEL. (603) 424-2410 FAX (603) 424-3460

Page 9

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