LTC4244IGN datasheet(19/28 Pages) LINER

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LTC4244/LTC4244-1

42441f

APPLICATIO S I FOR ATIO

BD_SEL# voltage drops below 4.4V thus causing the bus

switch OE to be pulled high by Q2.

The CompactPCI specification assumes that there is a

diode to 3.3V on the circuit that is driving the BD_SEL# pin.

The 1.2k resistor pull-up to 5VIN on the plug-in card will be

clamped by the diode to 3.3V. If the BD_SEL# pin is being

driven high, the actual voltage on the pin will be approxi-

mately 3.9V. This is still above the high TTL threshold of

the LTC4244 OFF/ON pin, but low enough for Q2 to disable

the bus switches and thus disconnect the 10k precharge

resistors from the I/O lines. Since the power to the bus

switch is derived from a front-end power plane, a 100

Ω

resistor should be placed in series with the power supply

of the bus switch.

When the plug-in card is removed from the connector, the

BD_SEL# connection is broken first, and the BD_SEL#

voltage pulls up to 5VIN. This causes Q2 to turn off, which

re-enables the bus switch, and the precharge resistors are

again connected to the LTC4244 PRECHARGE pin for the

remainder of the extraction process.

TIMER/Auxiliary VCC

Once the TIMER pin voltage has ramped to within 1.6V of

12VIN, the auxiliary VCC function is enabled. In the event

the 12VIN supply voltage collapses, the LTC4244 will

continue to draw power from the charge stored on the

TIMER pin capacitor until the internal VCC node drops

below its undervoltage lockout threshold or the 12VIN

supply voltage recovers, whichever happens first.

Other CompactPCI Applications

The LTC4244-1 is designed for CompactPCI designs

where the –12V supply is not being used on the plug-in

board. The VEEOUT power good comparator, VEEIN UVL,

and VEE circuit breaker functions are disabled. The VEEIN

pin should be connected to GND and the VEEOUT pin left

floating if a –12V output is not needed.

If no 3.3V supply input is required, Figure 10 illustrates

how the LTC4244 should be configured: 3.3VSENSE and

3.3VIN are connected to 5VIN and 3.3VOUT is connected to

5VOUT.

For applications where the BD_SEL# connector pin is

typically connected to ground on the backplane, the circuit

in Figure 11 allows the LTC4244 to be reset simply by

pressing a pushbutton switch on the CPCI plug in board.

This arrangement eliminates the requirement to extract

and reinsert the CPCI board in order to reset the LTC4244’s

circuit breaker.

0.33

µF

5VIN

Ω

5VOUT

4244 F10

0.007

Ω

IRF7457

Z4: SMAJ5.0A

*ADDITIONAL PINS OMITTED FOR CLARITY

PCB EDGE

BACKPLANE

CONNECTOR

BACKPLANE

CONNECTOR

LONG 5V

GROUND

GND

5VIN

5VSENSE

3.3VOUT

3.3VIN

LTC4244*

5VOUT

3.3VSENSE

GATE

Figure 10. No 3.3V Supply Application Circuit

1.2k

PUSHBUTTON

SWITICH

100

Ω

0.25W

V(I/O)

GROUND

BD_SEL#

4244 F11

*ADDITIONAL PINS OMITTED FOR CLARITY

PCB EDGE

BACKPLANE

CONNECTOR

BACKPLANE

CONNECTOR

GND

LTC4244*

OFF/ON

Figure 11. BD_SEL# Pushbutton Toggle Switch

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