SMS64
Preliminary
APPLICATIONS INFORMATION (CONTINUED)
Power-Off
Power-On
Sequence
Position 0
Sequence Sequence
Position 2 Position 1
Sequence
Position 0
Sequence
Position 1
Sequence
Position 2
VCCA
PUPA
tDPONA
tDPOFFA
VPTHA
VOFF
VMA,D
VCCB
tDPONB
VPTHB
PUPB
tDPOFFB
VOFF
VMB,E
VCCC
tDPOFFC
PUPC
tDPONC
VPTHC
VOFF
VMC,F
PWR_ON/OFF
HEALTHY#
RST_A#
RST_B#
IRQ#
tPRTO
Figure 10 - The SMS64 sequencing the supplies off then sequencing the supplies back on.
Additional Considerations
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
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
needs to be fully enhanced to minimize RDS(ON)
.
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 RDS(ON)
specifications.
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 0.01µF (10nF), 25V, ceramic capacitor on
each PUP output pin to ground.
Summit Microelectronics, Inc
2060 2.22 10/09/03
18
SUMMIT [ SUMMIT MICROELECTRONICS, INC. ]
