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LTC1644IGN

CompactPCI Bus Hot Swap Controller

Linear Technology 

LTC1644

PI FU CTIO S

When the TIMER pin is high, the circuit breaker function is

enabled. If the voltage across the sense resistor exceeds

55mV but is less than 150mV, the circuit breaker is tripped

after a 45µs time delay. In the event the sense resistor

voltage exceeds 150mV, the circuit breaker trips immedi-

ately and the chip latches off. To disable the current limit,

3VSENSE and 3VIN can be shorted together.

3VIN (Pin 17): 3.3V Supply Sense Input. An undervoltage

lockout circuit prevents the switches from turning on

when the voltage at the 3VIN pin is less than 2.48V. If no

3.3V input supply is available, connect two series diodes

between 5VIN and 3VIN (tie anode of first diode to 5VIN and

cathode of second diode to 3VIN, see Figure 11).

3VOUT (Pin 18): Analog Input used to monitor the 3.3V

output supply voltage. The PWRGD pin cannot pull low

until the 3VOUT pin voltage exceeds 2.9V. If no 3.3V input

supply is available, tie the 3VOUT pin to the 5VOUT pin.

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

connected between VEEIN and VEEOUT. VEEOUT must ex-

ceed –10.5V before the PWRGD pin pulls low unless the

VEE PWRGD function is disabled by grounding the VEEIN

pin.

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

connected between 12VIN and 12VOUT. 12VOUT must

exceed 11.1V before the PWRGD pin can pull low.

BLOCK DIAGRA

5VIN

5VSENSE

13

14

5VOUT

TIMER

+–

51mV, TIMER LO

150mV, TIMER HI

55mV

+–

+– +

A1

–

+

CP1

–

2.5V

UVL

OFF/ON 5

FAULT 6

Q11

PWRGD 7

Q10

RESETIN 9

GATE

15

12VIN

65µA

Q1

225µA

3VOUT

A2

3VSENSE

3VIN

16

17

TIMER

51mV, TIMER LO

150mV, TIMER HI

CP2

55mV

2.5V

UVL

3VOUT 5VOUT

18 3

Q2

Q3

CP3

LOGIC

REF

CP4

10 RESETOUT

REF

Q4

8.3V

Q9

UVL

Q8

12VIN

+

CP7

21µA

Q7

–

REF

1

20

12VIN 12VOUT

NOTE: V12VIN – VTIMER < 1V = TIMER HI, V12VIN – VTIMER > 1V = TIMER LOW

4

TIMER

Q6

Q5

2

VEEIN

19

VEEOUT

10

REF

+

CP5

–

Q12

8 11

GND DRIVE

1V

A3

12 PRECHARGE

1644 BD

1644f

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