LTC1643HIGN datasheet(13/16 Pages) LINER

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LTC1643L/LTC1643L-1/LTC1643H

APPLICATIONS INFORMATION

circuit, PCI bridge chip and the LOCAL_PCI_RESET# logic

circuitry. The BD_SEL# signal is connected to the ON pin

while the PWRGD pin is connected to the HEALTHY#

signal. The HEATHLY# signal is combined with the

PCI_RESET# signal to generate the LOCAL_PCI_RESET#

signal. Capacitors C6 and C7 provide chip bypassing on

the 12V and –12V inputs. Diode D2 protects the part from

voltage surges below –13.2V on the –12V supply.

The 1V precharge voltage for the data bus lines is gener-

ated by an LT1117 low dropout regulator. The output of the

LT1117 is set to 1.8V, then the voltage is dropped by a

1N4148 diode to generate 1V. The precharge circuit is

capable of sourcing and sinking 40mA.

0.005

Ω

V(I/O)

IRF7413

0.007

Ω

100

Ω

0.047

µF

MED 5V

MED 3.3V

BD_SEL#

LONG GND

PCI_RST#

I/O

3.3V

7.6A

–12V

100mA

12V

500mA

PRECHARGE OUT

±20%

IOUT = ±40mA

LOCAL_PCI_RESET#

DATA LINE EXAMPLE

DATA BUS

R10

R14

Ω, 5%

3VIN

12V

–12V

12VIN

VEEIN

FAULT

3VSENSE

5VSENSE

3VOUT

LTC1643L

5VOUT

12VOUT

VEEOUT

TIMER

5VIN

GATE

HEALTHY#

PWRGD

1643 F07

0.1

µF

GND

0.1

µF

0.01

µF

1N4148

0.1

µF

D2*

12V

*1SMA12CAT3

1.2k

R13

10k

RESET#

LONG

3.3V

LONG

3.3V

LONG

3.3V

PCI

BRIDGE

(21154)

OUT

ADJ

LT1117

R11

Ω

130

Ω

56.2

Ω

I/O

Figure 7. Typical CompactPCI Application

LTC1643L-1

The LTC1643L-1 is designed for CompactPCI designs

where the

±12V supplies are not being used on the board

or the supplies are not well regulated. The power good

comparators on the 12VOUT and VEEOUT pins are disabled.

The VEEIN pin can be connected to GND and the part will

still operate normally if a – 12VOUT output is not needed.

However, 12V is still required at the 12VIN pin for the part

to function. Refer to Figure 10 for a typical LTC1643L-1

application circuit.

Increasing 12V and – 12V Current Capability

The internal switches in the LTC1643 are designed for up

to 500mA loads on 12V and 200mA on – 12V. If more

current is needed, then the circuits in Figure 8 can be used.

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