TPS2420_技术文档

TPS2420

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SLUS903D –JANUARY 2009–REVISED SEPTEMBER 2011

3-V to 20-V INTEGRATED FET HOT SWAP CONTROLLER

Check for Samples: TPS2420

1

FEATURES

DESCRIPTION

The TPS2420 provides highly integrated load

protection for 3-V to 20-V applications. The TPS2420

protects loads, minimizes inrush current, and safely

shuts down in the event of a fault. The programmable

fault current threshold starts the fault timer while

allowing the current to pass to the load uninhibited.

The programmable current limit threshold sets the

maximum current allowed into the load, for both

inrush and severe load faults. Both events use the

programmable timer which inhibits all current to the

load when it expires.

2

•

Integrated 30-mΩ Pass MOSFET

3.0-V to 20-V Bus Operation

Programmable Fault Current

Programmable Hard Current Limit

Programmable Fault Timer

Internal MOSFET Power Limiting Foldback

Latching and Auto-Retry Operation

Analog Current Monitor Output

Powergood Output

The dual protection thresholds are useful in

applications such as disk drives. The start-up and

seek currents are typically higher than the nominal

current and during this time the load needs a low

impedance path to deliver the power. If a failure at

the load occurs, the current limit does not allow the

current to exceed the programmed threshold. This

protects both the load and the integrity of the power

supply. The internal MOSFET is protected by power

limit circuitry which ensures that the MOSFET

remains within its safe operating area (SOA) during

all operating states.

Fault Output Indicator

4 mm × 4 mm QFN

–40°C to 125°C Junction Temperature Range

UL Listed - File Number E169910

APPLICATIONS

•

RAID Arrays

Telecommunications

Plug-In Circuit Boards

Disk Drives

The TPS2420 also allows the system to monitor load

currents with no need for a shunt in the power path.

The gain of the current monitor can be scaled to the

application. Fault and power good outputs are

provided for improved system management and

sequencing control.

This device can be programmed to either latch-off or

retry in the event of a fault. All of this functionality is

packed into a 16-pin 4 × 4 mm QFN package.

3.0 V to 20.0 V

VOUT

1

2

3

4

VIN

12

11

10

15

14

13

VOUT

(A)

FLT

PG

Optional:

to system

monitor

C_LOAD

(A)

15-V

SMAJ15A

TPS2420

}

(A)

EN

16

C_VIN

IMON

LTCH GND IMAX

IFLT

8

CT

9

6

5

7

63.4 kW

40.2 kW

49.9 kW

0.1 mF

UDG-09017

(A) Required only in systems with lead and/or load inductance.

1

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.

2

PowerPad is a trademark of Texas Instruments.

PRODUCTION DATA information is current as of publication date.

Products conform to specifications per the terms of the Texas

Instruments standard warranty. Production processing does not

necessarily include testing of all parameters.

TPS2420

SLUS903D –JANUARY 2009–REVISED SEPTEMBER 2011

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This integrated circuit can be damaged by ESD. Texas Instruments recommends that all integrated circuits be handled with

appropriate precautions. Failure to observe proper handling and installation procedures can cause damage.

ESD damage can range from subtle performance degradation to complete device failure. Precision integrated circuits may be more

susceptible to damage because very small parametric changes could cause the device not to meet its published specifications.

PRODUCT INFORMATION⁽¹⁾

JUNCTION

TEMPERATURE

DEVICE

PACKAGE

MARKING

TPS2420

–40°C to 125°C

RSA (4-mm × 4-mm QFN)

TPS2420

(1) For the most current package and ordering information, see the Package Option Addendum at the end of this document, or visit the

device product folder on www.ti.com.

ABSOLUTE MAXIMUM RATINGS^{(1) (2)}

over operating free-air temperature range (unless otherwise noted)

VALUE

–0.3 to 25

–0.3 to 20

1.75

UNIT

V_IN, V_OUT

FLT, PG

I_FAULT, I_MAX, C_T

FLT, PG

EN

Voltage range

V

Voltage

Output sink current

10

mA

V

Input voltage range

–0.3 to 6

35

LTCH

Input current (LTCH internally clamped to 3 V) LTCH = 0 V

Voltage range CT⁽³⁾, IFLT⁽³⁾, IMAX, IMON⁽³⁾, LTCH

ESD rating, HBM

μA

–0.3 to 3

2500

V

ESD rating, CDM

400

T_J

Operating junction temperature range

Storage temperature range

Internally Limited

–65 to 150

°C

T_stg

(1) 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.

(2) All voltage values are with respect to GND.

(3) Do not apply voltage to these pins.

DISSIPATION RATINGS⁽¹⁾

θ_JA

PACKAGE

LOW K⁽²⁾, °C/W

HIGH K⁽³⁾, °C/W

BEST⁽⁴⁾, °C/W

RSA

211

55

50

(1) Tested per JEDEC JESD51, natural convection. The definitions of high-k and low-k are per JESD 51-7 and JESD 51-3.

(2) Low-k (2 signal – no plane, 3-inch by 3-inch board, 0.062 inch thick, 1 oz. copper) test board with the pad soldered, and an additional

0.12 inch 2 of top-side copper added to the pad.

(3) High-k is a (2 signal – 2 plane) test board with the pad soldered.

(4) The best case thermal resistance is obtained using the recommendations per SLMA002A (2 signal – 2 plane with the pad connected to

the plane).

RECOMMENDED OPERATING CONDITIONS

PARAMETER

Voltage range

Output sink current

Voltage range

MIN

3

MAX UNIT

VIN, VOUT

EN

20

5

V

0

FLT, PG

LTCH

CT

0

20

1

V

0

mA

V

0

3

0.1

–40

100

125

μF

°C

T_J

Junction temperature

2

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SLUS903D –JANUARY 2009–REVISED SEPTEMBER 2011

ELECTRICAL CHARACTERISTICS

over operating free-air temperature range (unless otherwise noted)

PARAMETER

TEST CONDITIONS

MIN

TYP

MAX

UNIT

INPUT SUPPLY (V_IN

)

V_UVLOUndervoltage lockout

V_INincreasing

Hysteresis

2.6

2.85

150

25

2.9

V

mV

μA

mA

Bias current

V _EN= 2.4 V

V _EN= 0 V

100

5

3.9

INPUT/OUTPUT

R_ON

On-resistance

R_VIN-VOUT, I_VOUT< I_IMAXor

_VOUT< (I_SET× 1.25), 1 A ≤ I_VOUT≤ 4.5 A

33

5

50

7.5

1.0

mΩ

I

P_LIMITPower limit

V_IN= 12 V, C_OUT= 1000 μF

EN: 3V → 0 V

3

W

V

Reverse diode voltage

FAULT CURRENT (_FLT

I _FLTFault current threshold

V_OUT> V_IN, EN = 5 V, I_IN= –1 A

0.77

)

I_VOUTincreasing, I_CTfrom sinking to sourcing,

pulsed test

R _FLT= 200 kΩ

R _FLT= 100 kΩ

R _FLT= 49.9 kΩ

0.8

1.8

3.6

1

2

4

1.2

2.2

4.4

A

CURRENT LIMIT (IMAX)

I_IMAXCurrent limit program I_VOUT

R_IMAX= 100 kΩ

R_IMAX= 66.5 kΩ

R_IMAX= 40.2 kΩ

1.6

2.6

4.6

2

3

5

2.4

3.4

5.4

↑ ,

V_VIN-VOUT= 0.3 V, pulsed

test

FAULT TIMER (CT)

Charge/Discharge current

I_CTsourcing, V_CT= 1 V, In current limit

29

35

41

μA

I_CTsinking, V_CT= 1 V, drive CT to 1 V, measure

current

1.0

1.4

1.8

Threshold voltage

V_CTincreasing

V_CTdecreasing

V_VOUT= 0 V

1.3

0.1

1.4

0.16

1.5

0.3

V

D

ON/OFF fault duty cycle

2.8%

3.7%

4.6%

ENABLE (_EN

)

Threshold voltage

V _ENdecreasing

0.8

50

1.0

150

0

1.5

250

0.5

V

Hysteresis

mV

Input bias current

V _EN= 2.4 V (sinking)

V _EN= 0.2 V (sourcing)

V_IN= 3.3 V, I_LOAD= 1 A,

–1.5

2

μA

1

0.5

Turn on propagation delay

350

500

V _EN

↑ 90% × V_IN

: 2.4 V → 0.2 V, VOUT:

: 0.2 V → 2.4V, V_OUT: ↓

μs

Turn off propagation delay

V_IN= 3.3 V, I_LOAD= 1 A,

V _EN

30

50

10% × V_IN

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ELECTRICAL CHARACTERISTICS (continued)

over operating free-air temperature range (unless otherwise noted)

PARAMETER

FAULT (IFLT)

TEST CONDITIONS

MIN

TYP

MAX

UNIT

V_OL

I_IFLT

Low-level output voltage

Leakage current

V_CT= 1.8 V, I _FLT= 1 mA

0.2

0.4

1

V

V _FLT= 18 V

μA

POWERGOOD (PG)

V _PG

PG threshold

V_(VIN-VOUT)decreasing

Hysteresis

0.4

0.1

0.5

0.25

0.2

0.65

0.4

1

V

V_OL

I _PG

Low-level output voltage

Leakage current

I _PG= 1 mA

V _PG= 18 V

μA

CURRENT MONITOR (IMON)

Ratio I_LOAD/I_IMON

I_OUT= 500 mA

I_OUT= 2.0 A

I_OUT= 4.50 A

I_VIN= 0 A

30

50

56

61

80

70

66

0

A/mA

56

61

Offset current (sourcing)

Clamp voltage

–10

2.6

–2

μA

2.75

2.9

V

LATCH FUNCTION (LTCH)

Low threshold voltage

High threshold

Auto retry mode

Latch mode

0.8

V

2.0

–1.0

–50

Input bias current

V_LTCH= 3.0 V

V_LTCH= 0.2 V

0.2

1.0

0

μA

–25

THERMAL SHUTDOWN

Thermal shutdown

Junction temperature increasing

Hysteresis

160

10

°C

4

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SLUS903D –JANUARY 2009–REVISED SEPTEMBER 2011

TPS2420 FUNCTIONAL BLOCK DIAGRAM

I_OUT

1

12

VIN

2

3

4

11 VOUT

10

V(DS) Detector

I(D)

Detector

-

+

S

10 uA

Q

Pump

Constant

Power

Engine

I_OUT/ 66k

IMON

13

GND 5

FT

LCA

1.0V

R

1.6 x I_LIM

+

15 FLT

IMAX

IFLT

7

8

+

I_OUT

______

200k

PWRG\

CT

Charge

THERMAL

SHUTDOWN

34 uA

FLT

S

R

Q

1.35 V

CT

9

+

FLT

1.25 uA 33 uA

+

200 mV

LTCH

6

VIN

1.5V

+

10M

V_OUT

14 PG

PWRG\

EN 16

+

Internal Rail

VIN

18M

V_IN-300mV

2.7 / 2.6

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DEVICE INFORMATION

PINOUT DIAGRAM

16

15

14

13

VIN

VOUT

CT

1

2

3

4

12

11

10

9

TPS2420

5

6

7

8

TERMINAL FUNCTIONS

NO.

NAME

I/O

DESCRIPTION

EN

16

1

I

Device is enabled when this pin is pulled low.

Power in and control supply voltage .

2

VIN

I

3

4

If low, the TPS2420 will attempt to restart after an overcurrent fault. If floating (high) the device will latch

off after an overcurrent fault and will not attempt to restart until EN or V_INis cycled off and on.

LTCH

6

I

GND

IMAX

IFLT

CT

5

—

I

Ground.

7

A resistor to ground sets the current limit level.

A resistor to ground sets the fault current level.

A capacitor to ground sets the fault time.

A scaled down current which indicates the current through the device.

8

I

9

I/O

O

IMON

13

10

11

12

14

15

VOUT

O

Output to the load.

PG

O

Power Good low represents the output voltage is within 300 mV of the input voltage.

Fault low indicated the fault time has expired and the FET is switched off.

FLT

6

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PIN DESCRIPTION

CT: Connect a capacitor form CT to GND to set the fault time. The fault timer starts when the fault current

threshold is exceeded, charging the capacitor with 36 μA from GND towards an upper threshold of 1.4 V. If the

capacitor reaches the upper threshold, the internal pass MOSFET is turned off. The MOSFET will stay off until

EN is cycled if a latching version is used. If an auto-retry version is used, the capacitor will discharge at 5 μA to

0.2 V and then re-enable the pass MOSFET. When the device is disabled, CT is pulled to GND through a

100-kΩ resistor.

The timer period must be chosen long enough to allow the external load capacitance to charge. The fault timer

period is selected using the following formula where T_FAULTis the minimum timer period in seconds and C_CTis in

Farads.

T_FAULT

38.9 ´10³

C_CT

=

(1)

This equation does not account for component tolerances. In autoretry versions, the second and subsequent

retry timer periods will be approximately 85% as long as the first retry period.

In autoretry versions, the fault timer discharges the capacitor for a nominal T_SDin seconds with C_CTin Farads per

the following equation.

6

= 1.0´10 ´C

T

SD

CT

(2)

The nominal ratio of on to off times represents about a 3% duty cycle when a hard fault is present on the output

of an autoretry version device.

FLT: Open-drain output that pulls low on any condition that causes the output to open. These conditions are

either an overload with a fault time-out, or a thermal shutdown. FLT becomes operational before UV, when V_INis

greater than 1 volt.

GND: This is the most negative voltage in the circuit and is used as reference for all voltage measurements

unless otherwise specified.

IFLT: A resistor connected from this pin to ground sets the fault current threshold (I_FAULT). Currents between the

fault current threshold and the current limit are permitted to flow unimpeded for the period set by the fault timer

programmed on C_T. This permits loads to draw momentary surges while maintaining the protection provided by a

lower average-current limit. IFLT may not be set below 1 A to maintain the Fault Current Limit threshold accuracy

listed in Electrical Characteristics. Some parts may not current limit or fault as expected.

The fault timer implemented by C_Tstarts charging C_Twhen current through V_INexceeds I_FAULT. If the current

doesn’t drop below the I_FAULTlevel before V_CTreaches its upper threshold, the output will be shut off. The fault

current resistor is set by the following formula where I_FAULTis in Amperes and R_RFLTis in ohms.

200kW

R

=

IFLT

I

FAULT

(3)

IMAX: A resistor connected from this pin to ground sets I_MAX. The TPS2420 will limit current to I_MAX. If the current

does not drop below the I_FAULTlevel before the timer times out then the output will be shut off. R_MAXis set by the

formula:

201kW

R

=

IMAX

I

IMAX

(4)

I_MAXmust be set sufficiently larger than I_FAULTto ensure that l_MAXcould never be less than I_FAULT, even after

taking tolerances into account.

EN: When this pin is pulled low, the device is enabled. The input threshold is hysteretic, allowing the user to

program a startup delay with an external RC circuit. EN is pulled to V_INby a 10-MΩ resistor, pulled to GND by

16.8 MΩ and is clamped to ground by a 7-V Zener diode. Because high impedance pullup/down resistors are

used to reduce current draw, any external FET controlling this pin should be low leakage.

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VIN: Input voltage to the TPS2420. The recommended operating voltage range is 3 V to 18 V. All VIN pins

should be connected together and to the power source.

VOUT: Output connection for the TPS2420. When switched on the output voltage will be approximately:

V

= V - 0.04´I

IN OUT

OUT

(5)

All V_OUTpins should be connected together and to the load.

LTCH: When pulled low the 2420 will attempt to restart after a fault. If left floating or pulled high the TPS2420 will

latch off after a fault. This pin is internally clamped at 3 V and is pulled to the internal 3-V supply by diode in

series with a 100-kΩ resistor.

PG: Active low, Open Drain output, Power Good indicates that there is no fault condition and the output voltage

is within 0.5 V of the input voltage. PG becomes operational before UV, whenever V_INis greater than 1 V.

IMON: This is a scaled analog output of I_VIN. Select R_IMONbased on the maximum allowed A/D input voltage

(V_{AD_FS}) and the desired full-scale current in VIN (I_{VIN_FS}) per the following equation

63kW ´ V_{AD _IN max}

(

)

R_IMON

=

I_{LOAD max}

(

)

(6)

This pin is clamped at 2.5 V to protect A/D converters. It is reccomended that I_MONbe ignored until after PG

asserts because the I_MONoutput is accurate only after V_OUT> 3 V.

8

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SLUS903D –JANUARY 2009–REVISED SEPTEMBER 2011

TYPICAL CHARACTERISTICS

CURRENT LIMIT

vs

FAULT CURRENT

vs

JUNCTION TEMPERATURE

2.20

R

= 100 k

R_MAX= 100 k

FLT

2.15

2.10

2.15

2.10

2.50

2.00

2.50

2.00

1.95

1.90

1.95

1.90

1.85

1.80

1.85

1.80

–50

0

50

100

150

–50

0

50

100

150

T – Junction Temperature – °C

J

T – Junction Temperature – °C

J

Figure 1.

Figure 2.

POWER LIMIT

vs

SUPPLY CURRENT

vs

JUNCTION TEMPERATURE

8.0

7.5

7.0

6.5

24

22

20

18

16

14

12

10

I

= 1 A

LOAD

Sleep Mode

6.0

5.5

5.0

4.5

4.0

3.5

3.0

–50

0

50

100

150

–50

0

50

100

150

T – Junction Temperature – °C

J

T – Junction Temperature – °C

J

Figure 3.

Figure 4.

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TYPICAL CHARACTERISTICS (continued)

OUTPUT CURRENT

FAULT TIMER THRESHOLD VOLTAGE

vs

JUNCTION TEMPERATURE

–32.0

–32.2

–32.4

–32.6

–32.8

–33.0

1.50

1.45

1.40

1.35

1.30

I

= 2 A

LOAD

–33.2

–33.4

–33.6

–33.8

–34.0

–50

0

50

100

150

–50

0

50

100

150

T – Junction Temperature – °C

J

T – Junction Temperature – °C

J

Figure 5.

Figure 6.

10

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TYPICAL CHARACTERISTICS

Figure 7. 12-V Startup into 15-Ω, 700-μF Load

Figure 8. 12-V Input Addded to an 8-Ω Load

Figure 9. Failed Startup into a 4-Ω Load

Figure 10. 12-V Soft Overload, 3-A to 4.2-A, Power Limit

Not Tripped

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TYPICAL CHARACTERISTICS (continued)

Figure 11. Firm Overload, 3-A to 5.4 A,

Power Limit Tripped

Figure 12. 12-V Hard Overload, 3.6-A Load then Short

Figure 13. Power Dissipation During 12-V Startup into a

Figure 14. Power Dissipation During 12-V Startup into a

60-Ω, 800-μF Load

15-Ω, 140-μF Load

12

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TYPICAL CHARACTERISTICS (continued)

Figure 15. Startup into a 1-Ω Load

Figure 16. Firm Overload, Load Stepped

From 3.8 A to 5.5 A

Figure 17. Hard Overload, Load Stepped

from 3.8 A to 7.1 A

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APPLICATION INFORMATION

If EN is tied to GND at startup and V_INdoes not ramp quickly the TPS2420 may momentarily turn off then on

during startup. This can happen if a capacitive load momentarily pulls down the input voltage below the UV

threshold. If necessary, this can be avoided by delaying EN assertion until V_INis fully up.

Maximum Load

The power limiting function of the TPS2420 provides very effective protection for the internal FET. Expectedly,

there is a supply voltage dependent maximum load which the device will be able to power up. Loads above this

level may cause the device to shut off current before startup is complete. Neglecting any load capacitance, the

maximum load ( minimum load resistance ) is calculated using the equation;

2

IN

V

R

=

MIN

12

(7)

Adding load capacitance may reduce the maximum load which can be present at start up.

Transient Protection

The need for transient protection in conjunction with hot-swap controllers should always be considered. When

the TPS2420 interrupts current flow, input inductance generates a positive voltage spike on the input and output

inductance generates a negative voltage spike on the output. Such transients can easily exceed twice the supply

voltage if steps are not taken to address the issue. Typical methods for addressing transients include;

•

Minimizing lead length/inductance into and out of the device

Voltage Suppressors (TVS) on the input to absorb inductive spikes

Shottky diode across the output to absorb negative spikes

A combination of ceramic and electrolytic capacitors on the input and output to absorb energy

Use PCB GND plane

The following equation estimates the magnitude of these voltage spikes:

L

V

= V

+ I

´

NOM LOAD

SPIKE absolute

(

)

C

where

•

V_NOMis the nominal supply voltage

I_LOADis the load current

C is the capacitance present at the input or output of the TPS2420

L equals the effective inductance seen looking into the source or the load

(8)

Calculating the inductance due to a straight length of wire is shown in Equation 9.

4´L

æ

ö

L_straightwire» 0.2´L ´ln

- 0.75 nH

÷

( )

ç

D

è

ø

where

•

L is the length of the wire

D is diameter of the wire

•

(9)

Some applications may require the addition of a TVS to prevent transients from exceeding the absolute ratings if

sufficient capacitance cannot be included.

14

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APPLICATION INFORMATION

Operation

When load current exceeds the user programmed fault limit (I_FAULT) during normal operation the fault timer starts.

If load current drops below the I_FAULTthreshold before the fault timer expires, normal operation continues. If load

current stays above the I_FAULTthreshold the fault timer expires and a fault is declared. When a fault is declared a

device operating in latch mode turns off and can be restarted by cycling power or toggling the EN signal. A

device operating in retry mode attempts to turn on at a 3% duty cycle until the fault is cleared. When the I_MAX

limit is reached during a fault the device goes into current limit and the fault timer keeps running. I_MAXcan be

programmed by the user by connecting a resistor from the IMAX pin to GND.

Startup

When power is first applied to a load with discharged capacitors there is a large inrush current. The inrush is

controlled by the TPS2420 by initially entering the power limit mode and turning on the fault timer. See Figure 19.

As the charge builds on the capacitor, the current increases to I_MAX. When the capacitor is fully charged, current

output is set by the dc load value, The fault timer is turned off. The FET is then fully enhanced and the power

good signal is true.

In order to start properly, the fault timer must be set to exceed the capacitor charge time.

When the load has a resistive component as well as capacitive, the fault time needs to be increased because

current to the resistive load is unavailable to charge the capacitor. The startup time for some selected loading is

given in Table 1.

Table 1 data was taken with I_FAULTset to 4 A and I_MAXset to 5 A. Lower current settings of TPS2420 do not have

a great influence on the start up timer because of operation at power limit. Load capacitance and dc resistance

was selected for a measured start time. The start time is measured from the assertion of the EN pin to the

assertion of the PG pin.

Table 1. Start Time for Input Voltage and Output Loading⁽¹⁾

LOAD CAPACITANCE

DC LOAD

RESISTANCE (Ω)

INPUT VOLTAGE (V)

START TIME (ms)

(μF)

OPEN

5

2.5

220

1000

220

2.7

12

2.6

5

OPEN

5

4

12

4

4.4

OPEN

5

No start

7

12

OPEN

5

14

1000

No start

23

12

(1) I_FAULT= 4 A, I_MAX= 5 A.

Some combinations of loading and current limit settings exceed the 5-W power limit of the internal MOSFET. The

output voltage will not turn on regardless of the fault time setting. One way to work with the physical limits that

create this problem is to allow the power manager to charge only the capacitive component of the load and use

the PG signal to turn on the resistive component. This is common usage in dc-to-dc converters and other

electrical equipment with power good inputs.

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Start Up Into a Short

The controller attempts to power on into a short for the duration of the timer. Figure 20 shows a small current

resulting from power limiting the internal MOSFET. This happens only once for the latch off mode. For the retry

mode, Figure 24 shows this cycle repeating at an interval based on the C_Ttime.

Shutdown Modes

Hard Overload - Fast Trip

When a hard overload causes the load current to exceed 1.6 × I_MAXthe TPS2420 immediately shuts off current

to the load without waiting for the fault timer to expire. After such a shutoff the TPS2420 enters into startup mode

and attempts to apply power to the load.

If the hard overload is caused by a current transient, then a normal startup can be expected with a low probability

of disruption to the load, assuming there is sufficient load capacitance to hold up the load during the fractions of

a millisecond that make up the fast trip/restart cycle.

If the hard overload is caused by a real, continuous failure then the TPS2420 goes into current limit during the

attempt at restart. The timer starts and eventually runs out, shutting off current to the load. See the fast trip

figures 22 and 23. When the hard overload occurs the current is turned off, the PG pin becomes false, and the

FLT pin stays false. The FLT pin becomes true only when the fault timer times out.

Overcurrent Shutdown

Overcurrent shutdown occurs when the output current exceeds I_MAXfor the duration of the fault timer.

Overcurrent shutdown is the circuit breaker type protection of equipment. Figure 23 shows the step rise in output

current. The increased current is on for the duration of the timer. At conclusion of the timer, the output is turned

off.

Design Example

The TPS2420 Design shown in Figure 25 supports 12 V to operate a hot plugged disk drive.

The 12 V specification for a disk drive is approximately 1-A operating current and 2-A typical spin-up. Selecting a

2.5 A setting for I_FAULTwould allow some margin for the operating current and satisfy the start current

requirements.

Calculate R_RFLTusing equation Equation 10 or select it using Table 2.

200kW 200,000

R

=

´

= 80 kW

( )

IFLT

I

2.5

FAULT

(10)

(11)

The I_MAXsetting, 3.5 A, is set by R_RMAXin Equation 11.

201kW 201,000

R

=

´

= 57.4 kW

( )

IMAX

I

3.5

IMAX

16

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Because I_FAULTsatisfies the spin up current, the timer can be set for the additional loading of charging the

capacitor. Estimate approximately 20 ms. Use either Equation 12 or Table 2 to estimate the capacitance.

-3

T

10

3

´10 = 0.514´10

-6

FAULT

C

=

= 20´

CT

3

38.9

38.9´10

(12)

For a scaled analog readback of the current from V_IN, set the I_MONresistor. In Equation 13 , the V_{AD_INMAX}is the

desired full scale A/D converter voltage. The largest value of V_{AD_INMAX}2.5 V. I_LOADMAXis the full scale current,

2.5 A.

63,000´ V

(

)

AD _IN max

(

63,000´ 2.5

( )

)

R

=

= 63 kW

( )

IMON

I

2.5

LOAD max

(

)

(13)

The read-back voltage at the IMON pin, V_IMON, indicates the instantaneous current output. Using equation

Equation 14 again, determine the current output for example, a 1.8-V V_IMON. Substitute V_IMONfor V_{AD_INMAX}and

I_LOADfor I_LOADMAXand solve for I_LOAD, (Equation 14).

63,000´ V

63,000´1.8

(

_IMON) (

)

I

=

= 1.81 A

( )

LOAD

R

62,500

IMON

(14)

Layout

Support Components

Locate all TPS2420 support components, R_SET, C_T, etc. or any input or output voltage clamps, close to their

connection pin. Connect the other end of the component to the inner layer GND without trace length.

PowerPad™

When properly mounted the PowerPad package provides significantly greater cooling ability than an ordinary

package. To operate at rated power the Power Pad must be soldered directly to the PC board GND plane

directly under the device. The PowerPad is at GND potential and can be connected using multiple vias to inner

layer GND. Other planes, such as the bottom side of the circuit board can be used to increase heat sinking in

higher current applications.

Refer to Technical Briefs: PowerPAD™ Thermally Enhanced Package (TI Literature Number SLMA002) and

PowerPAD™ Made Easy (TI Literature Number SLMA004) for more information on using this PowerPadTM

package.These documents are available at www.ti.com (Search by Keyword).

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APPLICATION PLOTS

Figure 18. Start Up Into an RC Load (PG)

Figure 19. Start Up Into an RC Load (CT)

Figure 20. Startup Into a Short Circuit Output

Figure 21. Device Output Short

18

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Figure 22. FLT on Device Output Short

Figure 23. Overcurrent Shutdown

Figure 24. Retry Into an Output Short Circuit

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12 V

V

1

2

3

4

5

6

7

8

VIN

EN

16

15

14

13

12

11

10

9

R1 10 kW

R2 10 kW

IN

C1

1 mF

VIN

FLT

PG

15 V

D1

SMAJ15A

VIN

IMON

VOUT

U1

TPS2420RSA

12 V

GND

LTCH

IMAX

IFLT

V

OUT

VOUT

CT

R

IMON

63.4 kW

PowerPAD

D2

MBR130LSFT1

R

IMAX

57.6 kW

R

IFLT

80.6 kW

CT

560 nF

GND

UDG-09018

Figure 25. TPS2420 Reference Design, 12-V, 2.5-A Steady State Current, 5-A Max Current

NOTE

D1, D2, and C1 are required only in systems with significant feed and/or load inductance.

To alter parameters I_IAX, I_FAULT, I_IMONor C_CTuse the formulas in the Pin Description section or use Table 2 .

Table 2. Typical Design Examples

I_FAULT(A)

R_IFLT(kΩ)

200

I_IMAX(A)

R_IMAX(kΩ)

100

C_CT(μF)

0.022

0.047

0.1

T_FAULT(ms)

0.86

T_SD(ms)

22

I_LOAD(max)(A) R_IMON(kΩ)

1

1.5

2

2.5

3

1

1.5

2

158

105

133

80.6

1.83

47

100

65.5

3.89

100

78.7

63.4

52.3

45.3

39.2

2.5

3

80.6

3.5

4

56.2

0.22

0.47

0.68

1

8.56

220

2.5

3

65.5

49.9

18.28

26.45

38.9

470

3.5

4

56.2

4.5

5

44.2

680

3.5

4

49.9

40.2

1000

20

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SLUS903D –JANUARY 2009–REVISED SEPTEMBER 2011

REVISION HISTORY

Changes from Revision A (March, 2010) to Revision B

Page

•

Changed PRODUCT INFORMATION Note 1 to: "For the most current package and ordering information, see the

Package Option Addendum at the end of this document, or visit the device product folder on www.ti.com." ..................... 2

Changed T_SD(ms) column values ...................................................................................................................................... 20

Changes from Revision B (July 2010) to Revision C

Page

•

Added UL Listed - File Number E169910 ............................................................................................................................. 1

Changes from Revision C (August 2010) to Revision D

Page

•

Changed CURRENT LIMIT (IMAX) to CURRENT IMAX ...................................................................................................... 3

Added IFLT may not be set below 1 A to maintain the Fault Current Limit threshold accuracy listed in the Electrical

Characteristics table. Some parts may not current limit or fault as expected. ..................................................................... 7

•

Changed I_ILIMto I_MAX........................................................................................................................................................... 15

Changed I_ILIMITto I_MAX......................................................................................................................................................... 16

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PACKAGE MATERIALS INFORMATION

www.ti.com

14-Jul-2012

TAPE AND REEL INFORMATION

*All dimensions are nominal

Device

Package Package Pins

Type Drawing

SPQ

Reel

A0

B0

K0

P1

W

Pin1

Diameter Width (mm) (mm) (mm) (mm) (mm) Quadrant

(mm) W1 (mm)

TPS2420RSAR

TPS2420RSAT

QFN

RSA

16

3000

250

330.0

180.0

12.4

4.25

1.15

8.0

12.0

Q2

Pack Materials-Page 1

PACKAGE MATERIALS INFORMATION

www.ti.com

14-Jul-2012

*All dimensions are nominal

Device

Package Type Package Drawing Pins

SPQ

Length (mm) Width (mm) Height (mm)

TPS2420RSAR

TPS2420RSAT

QFN

RSA

16

3000

250

367.0

210.0

367.0

185.0

35.0

Pack Materials-Page 2

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型号：	TPS2420
厂家：	TEXAS INSTRUMENTS
描述：	3-V to 20-V INTEGRATED FET HOT SWAP CONTROLLER 3 V至20 V集成FET热插拔控制器控制器
文件：	总29页 (文件大小：1462K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

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