LINEAR TECHNOLOGY LTC4244, LTC4244-1 Technical data

FEATURES

■

Controls –12V, 3.3V, 5V and 12V Supplies

■

±14.4V Absolute Maximum Rating for 12V

IN

and –12VIN Input Pins

■

Insensitive to Supply Voltage Transients

■

Adjustable Foldback Current Limit with Circuit Breaker

■

LOCAL_PCI_RST# Logic On-Chip

■

PRECHARGE Output Biases I/O Pins During Card Insertion and Extraction

■

LTC4244-1 Designed for Applications without –12V

■

Available in 20-Lead Narrow SSOP Package

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APPLICATIO S

■ Hot Board Insertion into CompactPCI Bus

, LTC and LT are registered trademarks of Linear Technology Corporation.

Hot Swap is a trademark of Linear Technology Corporation. CompactPCI is a trademark of the PCI Industrial Computer Manufacturers Group.

LTC4244/LTC4244-1

Rugged, CompactPCI Bus

Hot Swap Controllers

U

DESCRIPTIO

The LTC®4244/LTC4244-1 are Hot SwapTM controllers that allow a board to be safely inserted into and removed from a CompactPCITM bus slot. External N-channel transistors control the 5V and 3.3V supplies while on-chip switches control the ±12V supplies. The 3.3V and 5V supplies can be ramped up at an adjustable rate. Electronic circuit breakers protect all four supplies against overcurrent faults. After the power-up cycle is complete, the TIMER pin capacitor serves as auxiliary VCC allowing the LTC4244/ LTC4244-1 to function without interruption in the presence of voltage spikes on the 12VIN supply. The PWRGD output indicates when all four supplies are within tolerance. The OFF/ON pin is used to cycle board power or reset the circuit breaker. The PRECHARGE output can be used to bias the bus I/O pins during card insertion and extraction. PCI_RST# is combined on-chip with HEALTHY# in order to generate LOCAL_PCI_RST#.

TYPICAL APPLICATIO

5V

LONG 5V

3.3V

LONG 3.3V

12V

–12V

BD_SEL#

LONG V(I/O)

HEALTHY#

PCI_RST#

R15 1Ω

C4

GROUND

I/O PIN 1

I/O PIN 128

•

0.01µF

I/O DATA LINE 1

I/O DATA LINE 128

Z1, Z2: SMAJ12A Z3, Z4: SMAJ5.0A

U

C8

0.01µF PER POWER PIN

C6

0.01µF

R17 10k

Z2Z1

R16 1Ω

C5

0.01µF

R22

2.7Ω

R21

1.8Ω

C7

0.01µF

R20

1.2k

C9

0.01µF PER POWER PIN

R19 1k

R18 10k

•

3.3V

Z3

5V

IN

Z4

3.3V 12V V

EEIN

OFF/ON

FAULT

PWRGD RESETIN

GND PRECHARGE

R13 10Ω

R14 10Ω

0.005Ω

IN

R10 18Ω

R1

Q1

IRF7457

R3 10Ω

3.3V

SENSE

3.3V

GATE 5V

LTC4244

C3 4.7nF

R12

R11

10k

OUT

5V

IN5VSENSE

R9 24Ω

1V

±10%

R2

0.007Ω

DRIVE

MMBT2222A

IRF7457

Q3

Q2

R4 10Ω

12V

V

TIMER

RESETOUT

R8 1k

R7 12Ω

OUT OUT

EEOUT

•

+

C

LOAD(5VOUT)

+

C

LOAD(3.3VOUT)

C1

R5

0.33µF

1k

+

C

LOAD(12VOUT)

C

LOAD(VEEOUT)

+

C2

0.082µF

LOCAL_PCI_RST#

V

IN

3.3V

I/O #1

I/O #128

R6

10k

RESET#

PCI

BRIDGE

CHIP

4244 F01

V

OUT

5V 5A

V

OUT

3.3V 7A

V

OUT

12V 500mA

V

EEOUT

–12V 100mA

V

OUT

3.3V

Figure 1. Typical Compact PCI Application

42441f

1

LTC4244/LTC4244-1

WWWU

ABSOLUTE AXI U RATI GS

(Notes 1, 2, 3)

Supply Voltages

12VIN................................................................ 14.4V

V

.............................................................. –14.4V

EEIN

Input Voltages (OFF/ON, RESETIN) ........–0.3V to 13.5V

Output Voltages (FAULT, PWRGD, RESETOUT)

...........................................................–0.3V to 13.5V

Analog Voltages and Currents

5V

, DRIVE, 5VIN, 3.3V

OUT

...........................................................–0.3V to 13.5V

PRECHARGE, GATE ....................................... ±20mA

V TIMER, 12V

................................................–14.4V to 0.3V

EEOUT

...........................................

OUT

Operation Temperature Range

LTC4244C/LTC4244C-1........................... 0°C to 70°C

LTC4244I/LTC4244I-1 ........................ –40°C to 85°C

Storage Temperature Range ................. –65°C to 150°C

Lead Temperature (Soldering, 10 sec).................. 300°C

, 3.3VIN, 3.3V

SENSE

, 5V

OUT

SENSE

–0.3V to 14.4V

UU

W

PACKAGE/ORDER I FOR ATIO

TOP VIEW

1

12V

V

EEIN

5V

OUT

TIMER

OFF/ON

FAULT

PWRGD

GND

RESETIN

RESETOUT

IN

2 3 4 5 6 7 8 9

10

GN PACKAGE

20-LEAD PLASTIC SSOP

T

= 140°C, θJA = 135°C/W

JMAX

12V

20

V

19

3.3V

18

3.3V

17

3.3V

16

GATE

15

5V

14 13

5V

12

PRECHARGE

11

DRIVE

OUT

EEOUT

OUT

IN

SENSE

IN

Consult LTC Marketing for parts specified with wider operating temperature ranges.

ORDER PART

NUMBER

LTC4244CGN LTC4244CGN-1 LTC4244IGN LTC4244IGN-1

ELECTRICAL CHARACTERISTICS

temperature range, otherwise specifications are at TA = 25°C. V

The ● denotes the specifications which apply over the full operating

12VIN

= 12V, V

= –12V, V

EEIN

3.3VIN

= 3.3V, V

= 5V, unless

5VIN

otherwise noted.

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

I

DD

V

LKO

V

FB

V

CB

t

OC

I

GATE(UP)

I

GATE(DN)

I

GATE(FAULT)

∆V

GATE

∆V

12V

∆V

VEE

V

Supply Current OFF/ON = 0V ● 410 mA

12VIN

Undervoltage Lockout 12VIN, Ramping Down ● 8 9 10 V

, Ramping Down ● 4 4.25 4.5 V

5V

IN

3.3V

, Ramping Down ● 2.25 2.5 2.75 V

IN

, Ramping Up (LTC4244 Only) ● –8.25 –9.25 –10.25 V

V

EEIN

TIMER, Ramping Down, V

Foldback Current Limit Voltage VFB = (V

V

FB

V

FB

V

FB

Circuit Breaker Trip Voltage VCB = (V

V

CB

Overcurrent Fault Response Time (V

(V

5VIN

3.3VIN

= (V = (V = (V

= (V

– V

5VIN 5VIN

3.3VIN

5VIN

3.3VIN

5VSENSE

3.3VSENSE

– V – V

– V

GATE Pin Output Current OFF/ON = 0V, V

V

= 5V, OFF/ON = 4V ● 20 60 100 µA

GATE

OFF/ON = 0V, V

External Gate Voltage ∆V Internal Switch Voltage Drop ∆V

∆V

GATE

12V

VEE

= (V = (V = (V

12VIN

EEOUT

5VSENSE 5VSENSE

3.3VSENSE

5VSENSE

3.3VSENSE

) = 100mV, TIMER = FLOAT ● 17 25 35 µs

= 2V, TIMER = 0V ● –20 –67 –100 µA

GATE

= 2V, TIMER = FLOAT, FAULT = 0V ● 4 8 16 mA

GATE

– V

GATE

– V

12VOUT

– V

EEIN

= 6V ● 8.25 9.25 10.25 V

12VIN

), V ), V

= 0V, TIMER = 0V ● 11 16 21 mV

5VOUT

= 3V, TIMER = 0V ● 46 51 56 mV

5VOUT

), V ), V

= 0V, TIMER = 0V ● 11 16 21 mV

3.3VOUT

= 2V, TIMER = 0V ● 46 51 56 mV

3.3VOUT

), TIMER = FLOAT ● 45 52 57 mV

), I

= –1µA ● 0.6 1 V

GATE

), I = 500mA ● 225 600 mV

), IEE = 100mA ● 110 250 mV

2

42441f

LTC4244/LTC4244-1

ELECTRICAL CHARACTERISTICS

temperature range, otherwise specifications are at TA = 25°C. V

The ● denotes the specifications which apply over the full operating

12VIN

= 12V, V

= –12V, V

EEIN

3.3VIN

= 3.3V, V

= 5V, unless

5VIN

otherwise noted.

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

I

CL

T

TS

V

TH

V

IL

V

IH

I

IN

I

TIMER

V

TIMER

∆V R

DIS

V

OL

V

PXG

Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired.

Note 2: All currents into device pins are positive; all currents out of device pins are negative. All voltages are referenced to ground unless otherwise specified.

Current Foldback 12VIN = 12V, 12V

= 12V, 12V

12V

IN

V

= –12V, V

EEIN

= –12V, V

V

EEIN

= 0V, TIMER = 0V ● –100 –360 –1000 mA

OUT

= 10V, TIMER = 0V ● –550 –850 –1500 mA

OUT

= 0V, TIMER = 0V ● 50 225 350 mA

EEOUT

= –10V, TIMER = 0V ● 350 610 870 mA

EEOUT

Thermal Shutdown Temperature Junction Temperature, Ramping Up 150 °C Power Good Threshold Voltage 12V

, Ramping Down ● 10.8 11.1 11.4 V

OUT

, Ramping Down ● 4.50 4.61 4.75 V

5V

OUT

3.3V

, Ramping Down ● 2.80 2.90 3.00 V

OUT

, Ramping Up, LTC4244 Only ● –10.8 –11.1 –11.4 V

V

EEOUT

Logic Input Low Voltage OFF/ON, RESETIN, FAULT ● 0.8 V Logic Input High Voltage OFF/ON, RESETIN, FAULT ● 2V OFF/ON, RESETIN Input Current OFF/ON, RESETIN = 0V ● ±10 µA

OFF/ON, RESETIN = 12V

● ±10 µA

RESETOUT, FAULT Leakage RESETOUT, FAULT = 5V, OFF/ON = 0V, RESETIN = 3.3V ● ±10 µA Current

PWRGD Output Current PWRGD = 5V, OFF/ON = 4V ● ±10 µA 5V

Input Current 5V

SENSE

3.3V

Input Current 3.3V

SENSE

= 5V, 5V

OUT

= 3.3V, 3.3V

= 0V ● 57 100 µA

= 0V ● 56 100 µA

OUT

5VIN Input Current 5VIN = 5V, TIMER = 0V ● 0.8 1.5 mA

3.3VIN Input Current 3.3VIN = 3.3V, TIMER = FLOAT ● 510 700 µA

= 3.3V, TIMER = 0V ● 400 550 µA

3.3V

IN

5V

Input Current 5V

OUT

3.3V

Input Current 3.3V

OUT

PRECHARGE Input Current V TIMER Pin Current OFF/ON = 0V, V

TIMER Threshold Voltage TIMER_HI, (V

External Timer Voltage ∆V

TIMER

12V

Discharge Resistance OFF/ON = 4V ● 440 1000 Ω

OUT

5V

Discharge Resistance OFF/ON = 4V ● 200 500 Ω

OUT

Discharge Resistance OFF/ON = 4V ● 200 500 Ω

3.3V

OUT

Discharge Resistance OFF/ON = 4V ● 390 1000 Ω

V

EEOUT

= 5V, OFF/ON = 0V, TIMER = 0V ● 107 200 µA

OUT

= 3.3V, OFF/ON = 0V, TIMER = 0V ● 170 300 µA

OUT

PRECHARGE

OFF/ON = 5V, V

TIMER_LO, V

= 1V ● 0.1 10 µA

= 0V ● 16 21 26 µA

TIMER

= 5V ● 25 45 70 mA

TIMER

= (V

– V

12VIN

, Ramping Down ● 0.5 0.8 1.1 V

TIMER

– V

12VIN

), FAULT = 0V, Ramping Up ● 1.3 1.6 1.9 V

TIMER

), I

TIMER

= –1µA ● 1V

TIMER

Output Low Voltage PWRGD, RESETOUT, FAULT, I = 1mA ● 0.4 V PRECHARGE Reference Voltage V

= 2V ● 0.95 1 1.05 V

DRIVE

Note 3: The 12VIN and V

pins will withstand transient surges up to

EEIN

±15V, respectively, upon hot insertion.

42441f

3

LTC4244/LTC4244-1

VOLTAGE (V)

0

CURRENT (A)

–2 –4 –6 –10–8

4244 G03

–12

–0.6

–0.5

–0.3

–0.4

–0.2

–0.1

0

TEMPERATURE (°C)

–50

VOLTAGE (V)

–25 0 25 7550

4244 G06

100

0.30

0.25

0.15

0.20

0.10

0.05

0

I

12VOUT

= 550mA

TEMPERATURE (°C)

–50

VOLTAGE (mV)

–25 0 25 7550

4244 G09

100

60

50

30

40

20

10

0

3.3V

OUT

= 2V

3.3V

OUT

= 0V

UW

TYPICAL PERFOR A CE CHARACTERISTICS

3.3V and 5V Current Foldback Profile

60

50

3.3V

40

30

VOLTAGE (mV)

20

10

0

5V

234

1

VOLTAGE (V)

12V Foldback Current Limit vs Temperature

0.9

12V

0.8

0.7

0.6

0.5

0.4

CURRENT (A)

0.3

0.2

0.1

0

–50

= 10V

OUT

12V

= 0V

OUT

–25 0 25 7550

TEMPERATURE (°C)

4244 G01

4244 G04

100

12V

Current vs 12V

OUT

Voltage

1.0

0.9

0.8

0.7

0.6

0.5

0.4

CURRENT (A)

0.3

0.2

0.1

5

0

246 108

0

VOLTAGE (V)

VEE Foldback Current Limit vs Temperature

0.6

0.5

0.4

0.3

CURRENT (A)

0.2

0.1

0

–50

V

EEOUT

V

EEOUT

–25 0 25 7550

TEMPERATURE (°C)

= 10V

= 0V

OUT

4244 G02

4244 G05

12

100

V

Current vs V

EEOUT

Voltage

12V Internal Switch Voltage Drop vs Temperature

VEE Internal Switch Voltage Drop vs Temperature

0.14 I

= 100mA

VEEIN

0.12

0.10

0.08

0.06

VOLTAGE (V)

0.04

0.02

4

0

–25 0 25 7550

–50

TEMPERATURE (°C)

4244 G07

100

5VIN Foldback Current Limit Voltage vs Temperature

60

5V

= 3V

50

40

30

VOLTAGE (mV)

20

10

0

–50

–25 0 25 7550

OUT

5V

= 0V

OUT

TEMPERATURE (°C)

3.3VIN Foldback Current Limit Voltage vs Temperature

100

4244 G08

42441f

UW

TEMPERATURE (°C)

–50

CURRENT (mA)

–25 0 25 7550

4244 G12

100

3.94

3.93

3.92

3.90

3.91

3.89

3.88

3.87

TEMPERATURE (°C)

–50

VOLTAGE (V)

–25 0 25 7550

4244 G15

100

4.34

4.32

4.30

4.26

4.28

4.24

4.22

4.20

RAMPING-UP

RAMPING-DOWN

TEMPERATURE (°C)

–50

VOLTAGE (V)

–25 0 25 7550

4244 G18

100

–11.050

–11.055

–11.060

–11.070

–11.065

–11.075

–11.080

TYPICAL PERFOR A CE CHARACTERISTICS

LTC4244/LTC4244-1

3.3VIN and 5VIN Circuit Breaker Trip Voltage vs Temperature

52.0

51.8

51.6

51.4

51.2

51.0

50.8

VOLTAGE (mV)

50.6

50.4

50.2

50.0

–50

–25 0 25 7550

5V

IN

3.3V

IN

TEMPERATURE (°C)

12VIN Undervoltage Lockout vs Temperature

9.30

9.25

9.20

9.15

RAMPING-UP

4244 G10

100

3.3VIN and 5VIN Circuit Breaker Trip Filter Time vs Temperature

25.0

24.5

24.0

23.5

23.0

TIME (µs)

22.5

22.0

21.5 –25 0 25 7550

–50

V

EEIN

TEMPERATURE (°C)

Undervoltage Lockout vs

Temperature

–9.22

–9.24

–9.26

–9.28

RAMPING-UP

12VIN Supply Current vs Temperature

100

4244 G11

5VIN Undervoltage Lockout vs Temperature

9.10

VOLTAGE (V)

9.05

9.00

8.95 –50

–25 0 25 7550

RAMPING-DOWN

TEMPERATURE (°C)

3.3VIN Undervoltage Lockout vs Temperature

2.54

2.53

2.52

2.51

2.50

2.49

VOLTAGE (V)

2.48

2.47

2.46

2.45 –50

RAMPING-UP

RAMPING-DOWN

–25 0 25 7550

TEMPERATURE (°C)

4244 G13

4244 G16

100

–9.30

VOLTAGE (V)

–9.32

–9.34

–9.36

–25 0 25 7550

–50

12V

TEMPERATURE (°C)

Powergood Threshold

OUT

Voltage vs Temperature

11.090

11.085

11.080

11.075

11.070

VOLTAGE (V)

11.065

11.060

11.055 –25 0 25 7550

–50

TEMPERATURE (°C)

RAMPING-DOWN

4244 G14

4244 G17

100

V

Powergood Threshold

EEIN

Voltage vs Temperature

42441f

5

LTC4244/LTC4244-1

TEMPERATURE (°C)

–50

CURRENT (µA)

–25 0 25 7550

4244 G21

100

80

60

40

0

20

–20

–40

–80

–60

OFF/ON = 0V

OFF/ON = 4V

TEMPERATURE (°C)

–50

CURRENT (mA)

–25 0 25 7550

4244 G24

100

60

50

40

20

30

10

0

UW

TYPICAL PERFOR A CE CHARACTERISTICS

5V

Powergood Threshold

OUT

Voltage vs Temperature

4.603

4.602

4.601

4.600

4.599

4.598

VOLTAGE (V)

4.597

4.596

4.595

4.594 –25 0 25 7550

–50

TEMPERATURE (°C)

100

4244 G19

3.3V

Powergood Threshold

OUT

Voltage vs Temperature

2.902

2.901

2.900

2.899

2.898

VOLTAGE (V)

2.897

2.896

2.895

2.894 –25 0 25 7550

–50

TEMPERATURE (°C)

Gate Pin Current vs Temperature

100

4244 G20

Gate Pin Fault Current vs Temperature

16

FAULT = 0V

14

12

10

8

6

CURRENT (mA)

4

2

0

–25 0 25 7550

–50

TEMPERATURE (°C)

Timer Threshold Voltage vs Temperature

1.66

1.64

1.62

1.60

1.58

1.56

1.54

VOLTAGE (V)

1.52

1.50

1.48

1.46

6

–25 0 25 7550

–50

TEMPERATURE (°C)

12VIN – V

4244 G22

TIMER

4244 G25

100

Timer Pin On Current vs Temperature

20.30

20.25

20.20

20.15

CURRENT (µA)

20.10

20.05 –25 0 25 7550

–50

TEMPERATURE (°C)

100

4244 G23

Timer Pin Off Current vs Temperature

Discharge Resistance vs Temperature VOL vs Temperature

700

600

500

400

300

RESISTANCE (Ω)

200

100

0

–25 0 25 7550

–50

TEMPERATURE (°C)

12V

3.3V

OUT

V

EEOUT

5V

OUT

100

4244 G26

250

200

150

100

RESISTANCE (Ω)

50

0

–25 0 25 7550

–50

RESETOUT

PWRGD

FAULT

100

TEMPERATURE (°C)

4244 G27

42441f

LTC4244/LTC4244-1

U

UU

PI FU CTIO S

12VIN (Pin 1): 12V Supply Input. A 0.5Ω switch is con- nected between 12VIN and 12V limit. An undervoltage lockout circuit prevents the switches from turning on while the 12VIN pin voltage is less than 9V. 12VIN also provides power to the LTC4244’s internal V node.

V

(Pin 2): –12V Supply Input. A 1Ω switch is con-

EEIN

nected between V limit. An undervoltage lockout circuit prevents the switches from turning on while the V –9.25V. The V abled for the LTC4244-1.

5V

(Pin 3): 5V Output Sense. The PWRGD pin will not

OUT

pull low until the 5V active pull-down discharges 5V power switches are turned off.

TIMER (Pin 4): Current Fault Inhibit Timing Input and Auxiliary VCC. Connect a capacitor from TIMER to GND. When the LTC4244 is turned on, a 21µA pull-up current source is connected to TIMER. Current limit faults will be ignored until the voltage at the TIMER pin rises to within

1.6V of 12VIN. After the TIMER pin has completed ramping up, the TIMER capacitor serves as an auxiliary charge reservoir for VCC in the event the 12VIN pin voltage momentarily drops below the undervoltage lockout threshold voltage. When the LTC4244 is turned off (OFF/ON > 2V), the TIMER pin is pulled down to GND. After the TIMER pin voltage drops to within 0.8V of GND, the TIMER latch is reset and the part is ready for another power cycle.

EEIN

and V

EEIN

undervoltage lockout function is dis-

pin voltage exceeds 4.61V. A 200Ω

OUT

with a foldback current

OUT

with a foldback current

EEOUT

pin voltage is greater than

to ground when the

OUT

CC

OFF/ON (Pin 5): Digital Input. Connect the CPCI BD_SEL# signal to the OFF/ON pin. When the OFF/ON pin is pulled low, the GATE pin is pulled high by a 67µ A current source and the internal 12V and –12V switches are turned on. When the OFF/ON pin is pulled high, the GATE pin will be pulled to ground by a 60µ A current source and the 12V and –12V switches turn off.

FAULT (Pin 6): Open-Drain Digital I/O. FAULT is pulled low when a current limit fault is detected. Current limit faults are ignored until the voltage at the TIMER pin is within 1.6V of 12VIN. Once the TIMER cycle is complete, FAULT will pull low and the LTC4244 latches off in the event of an overcurrent fault. The part will remain in the latched off state until the OFF/ON pin is cycled high then low. Forcing the FAULT pin low with an external pull-down will cause the part to latch into the off state after a 25µs deglitching time.

PWRGD (Pin 7): Open-Drain Digital Power Good Output. Connect the CPCI HEALTHY# signal to the PWRGD pin. PWRGD remains low while V

2.9V, V the supplies falls below its power good threshold voltage, PWRGD will go high after a 14µs deglitching time.

GND (Pin 8): Device Ground. RESETIN (Pin 9): Digital Input. Connect the CPCI PCI_RST#

signal to the RESETIN pin. Pulling the RESETIN pin low will cause RESETOUT to pull low. RESETOUT will also pull low when PWRGD is high.

≥ 4.61V, and V

5VOUT

12VOUT

EEOUT

≥ 11.1V, V

≤ –11.1V. When any of

3.3VOUT

≥

42441f

7

LTC4244/LTC4244-1

U

UU

PI FU CTIO S

RESETOUT (Pin 10): Open-Drain Digital Output. Connect the CPCI_LOCAL_RST# signal to the RESETOUT pin. RESETOUT is the logical combination of the RESETIN and PWRGD.

DRIVE (Pin 11): Precharge Base Drive Output. Provides base drive for an external NPN emitter-follower that in turn biases the PRECHARGE node.

PRECHARGE (Pin 12): Precharge Monitor Input. An internal error amplifier servos the DRIVE pin voltage to keep the PRECHARGE node at 1V. See Applications Information for generating voltages other than 1V. If not used, tie the PRECHARGE pin to ground.

5VIN (Pin 13): 5V Supply Sense Input. An undervoltage lockout circuit prevents the switches from turning on when the voltage at the 5VIN pin is less than 4.25V.

5V

resistor placed in the supply path between 5VIN and 5V a constant 51mV across the sense resistor and a constant current through the switch while the TIMER pin is low. A foldback feature makes the current limit decrease as the voltage at the 5V TIMER pin is high, the circuit breaker function is enabled. If the voltage across the sense resistor exceeds 52mV, the circuit breaker is tripped after a 25µs time delay. In the event of a short-circuit or large overcurrent transient condition, the GATE pin voltage will be adjusted to maintain a constant 150mV across the sense resistor and a constant current through the switch.

(Pin 14): 5V Current Limit Sense. With a sense

SENSE

, the GATE pin voltage will be adjusted to maintain

SENSE

pin approaches GND. When the

OUT

GATE (Pin 15): High Side Gate Drive for the External 3.3V and 5V N-Channel Pass Transistors. An external series RC network is required for current limit loop compensation and setting the minimum ramp-up time. During power-up, the slope of the voltage rise at the GATE is set by the 67µ A current source connected through a Schottky diode to 12VIN and the external capacitor connected to GND (C1 in Figure 1) or by the 3.3V or 5V current limit and the bulk capacitance in the 3.3V power down, the slew rate of the GATE voltage is set by the 60µ A current source connected to GND and the external GATE capacitor (C1 in Figure 1).

The voltage at the GATE pin will be modulated to maintain a constant current when either the 5V or 3.3V supplies go into current limit. In the event of an overcurrent fault, the GATE pin is immediately pulled to GND.

3.3V

sense resistor placed in the supply path between 3.3V and 3.3V maintain a constant 51mV across the sense resistor and a constant current through the switch while the TIMER pin is low. A foldback feature makes the current limit decrease as the voltage at the 3.3V the TIMER pin is high, the circuit breaker function is enabled. If the voltage across the sense resistor exceeds 52mV, the circuit breaker is tripped after a 25µ s time delay. In the event of a short-circuit or large overcurrent transient condition, the GATE pin voltage will be adjusted to maintain a constant 150mV across the sense resistor and a constant current through the switch.

(Pin 16): 3.3V Current Limit Sense. With a

SENSE

, the GATE pin voltage will be adjusted to

SENSE

or 5V

OUT

pin approaches GND. When

OUT

supply lines. During

OUT

IN

8

If no 3.3V input supply is available, short the 3.3V to the 5VIN pin.

SENSE

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LTC4244/LTC4244-1

U

UU

PI FU CTIO S

3.3VIN (Pin 17): 3.3V Supply Sense Input. An undervoltage lockout circuit prevents the switches from turning on when the voltage at the 3.3VIN pin is less than 2.5V. If no

3.3V input supply is available, short the 3.3VIN pin to the 5VIN pin.

3.3V

Output Supply Voltage. The PWRGD pin cannot pull low until the 3.3V supply is available, tie the 3.3V 200Ω active pull-down discharges 3.3V when the power switches are turned off.

(Pin 18): Analog Input Used to Monitor the 3.3V

OUT

pin voltage exceeds 2.9V. If no 3.3V input

OUT

pin to the 5V

OUT

to ground

OUT

pin. A

V

connected between V than –11.1V before the PWRGD pin pulls low. The V power good comparator is disabled for the LTC4244-1. A 390Ω active pull-up discharges V the power switches are turned off.

12V

connected between 12VIN and 12V exceed 11.1V before the PWRGD pin can pull low. A 440Ω active pull-down discharges 12V power switches are turned off.

(Pin 19): -12V Supply Output. A 1Ω switch is

EEOUT

and V

EEIN

(Pin 20): 12V Supply Output. A 0.5Ω switch is

OUT

. V

EEOUT

to ground when the

OUT

must be less

EEOUT

to ground when

. 12V

OUT

EEOUT

must

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LINEAR TECHNOLOGY LTC4244, LTC4244-1 Technical data

Specifications and Main Features

Frequently Asked Questions

User Manual