LTC1644IGN datasheet(10/24 Pages) LINER

10 / 24 page

LTC1644

1644f

BLOCK DIAGRA

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 45

µs 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).

PI FU CTIO S

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.

VEEIN

TIMER

VEEOUT

3VOUT

5VOUT

–

+–

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

225

µA

GATE

5VOUT

TIMER

51mV, TIMER LO

150mV, TIMER HI

55mV

12VIN

5VSENSE

12VIN

12VOUT

5VIN

–

+–

2.5V

UVL

8.3V

UVL

–

+–

3VOUT

55mV

CP3

REF

3VSENSE

3VIN

RESETOUT

–

+–

2.5V

UVL

Q12

CP4

REF

–

CP7

REF

–

CP5

REF

–

RESETIN 9

PWRGD 7

Q10

FAULT 6

Q11

OFF/ON 5

µA

12VIN

GND

DRIVE

PRECHARGE

1644 BD

LOGIC

TIMER

51mV, TIMER LO

150mV, TIMER HI

CP1

CP2

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