SMH4804 Datasheet, PDF (22/41 Pages) Summit Microelectronics, Inc. – -48V Programmable Hot Swap Sequencing Power Controller

Timing Diagram
SMH4804
not all of the supplies turn on, RESET# is not released and
the SMH4804 disables the PG[4:1]# outputs. This
termination timer function can be programmed to abort the
sequence after PG1#, PG2#, PG3# or PG4#.
Soft Start Slew Rate Control
The –48V turn on time is controlled by the SMH4804 and by
the values of R4, C1 and C2 in Figures 21, 22, and 23. The
turn on time is approximately 10ms with the component
values shown in Figure 15. Increasing the capacitance
reduces the output slew rate and increases the turn on time.
The capacitors prevent the MOSFET from turning on
simultaneously with the application of –48V. Resistor R4 is
specified to limit the current into and the rate of charge of
C1. The ratio of C1 to C2 (10:1) limits the MOSFET’s V_GS to
approximately 5V once the –48V supply is connected and
C1 is fully charged.
Configuring the SMH4804 for Independent
Control of DC-DC Converters for Power-on-
LAN IEEE 802.3
Certain systems employing live card insertion or ‘hot-
swapping’ require independent control of the individual
secondary-side voltages. The SMH4804 Quad Hot Swap
Controller is easily configured for independent on/off control
of up to 4 individual DC-DC converters. A simplified
schematic displaying the SMH4804 enable pins together
with their respective output enabling pins is shown in
Figure 14.
The SMH4804 asserts each of its output enabling pins
(PG[4:1]#) independently of one another as shown in
Figure 14. Applying a logic high (3.5V - 5V) to any of the
‘ENABLE_PGx#’ nodes forces the corresponding output to
a logic low.
For example, to turn on the first DC-DC converter
(assuming its Enable pin requires a low to turn it on),
‘ENABLE_PG1#’ must be high. Taking this node low forces
the SMH4804 output to a high impedance (open-drain)
state. Please refer to Application Brief AB-01 for more
details.
FS#
PG1#
ENPGA
PG2#
SMH4804
ENPGA
PG3#
ENPGA
PG4#
ENABLE PG1#
ENABLE PG1#
ENABLE PG1#
ENABLE PG1#
To DC-DC #1
To DC-DC #2
To DC-DC #3
To DC-DC #4
Figure 14. Configuring the SMH4804 as a Quad Independent Hot-Swap Controller.
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2050 3.7 10/30/02
Summit Microelectronics