SMS64

Preliminary

Summit Microelectronics, Inc

2060 2.22 10/09/03

18

Additional Considerations

An example application circuit is shown in Figure

11. Additional optional noise bypassing components

are shown for the VMX monitor pins.

These

components consist of ferrite bead inductors and

capacitors.

They may be necessary in very noisy

systems

where

tight

undervoltage/overvoltage

tolerances are needed.

The PUP output pins require series resistors to drive

the gates of the power mosfets. Gate capacitors (C27

thru C32) are also recommended to prevent initial

mosfet, LDO or dc-dc converter turn-on during the

SMS64 power on sequence. To minimize transient

power surges in hot-swappable line card designs,

place a 0.01

µF (10nF), 25V, ceramic capacitor on

each PUP output pin to ground.

The PUP output level is programmable to either

logic-level, 10.5V or 14V depending on the type of

power component used in the system. To minimize

the voltage drop across the power mosfets, the device

However, some mosfets have maximum VGS

specifications of 15V while others are 20V.

For

improved sequencing performance with the SMS64, it

is recommended to use the lower rated VGS devices

with the PUP outputs set to 10.5V instead of 14V. The

industry trend for power mosfets is toward lower VGS

specs

while

also

maintaining

low

specifications.

VM

B,E

VCC

A

VCC

B

PUP

A

VM

A,D

PUP

B

VM

C,F

PUP

C

RST_A#

RST_B#

IRQ#

HEALTHY#

PW R_ON/OFF

Sequence

Position 0

Sequence

Position 1

Sequence

Position 2

t

PRTO

Sequence

Position 0

Sequence

Position 1

Sequence

Position 2

t

DPOFFB

t

DPOFFC

V

OFF

V

OFF

V

OFF

Power-Off

Power-On

t

DPOFFA

VCC

C

t

DPONB

V

PTHB

t

DPONC

V

PTHC

t

DPONA

V

PTHA

Figure 10 - The SMS64 sequencing the supplies off then sequencing the supplies back on.

APPLICATIONS INFORMATION (CONTINUED)