LTC4216
20
4216fa
For more information www.linear.com/LTC4216
the plug-in boards, the LTC4216 provides two separate
pins for bias supply input and load supply sensing. With
this configuration, an RC network, R
Y
and C
Y
, shown
in Figure 13, can be used with the V
CC
pin to ride out
supply glitches during output short or adjacent board
short. The RC network shown has a time constant of 7µs
and this is good enough for the supply to ride out most
supply glitches, preventing the device from entering an
undervoltage lockout condition unnecessarily. When V
CC
and SENSEP pins are connected together, the R
Y
value
should be chosen such that V
CC
pin voltage is lower than
V
SENSEP
– 70mV; otherwise, part of V
CC
pin current will
be diverted through SENSEP pin.
This unique scheme of separating the device’s supply input
and sensing also provides the flexibility of operating the
load supply from ground to its supply rail with a minimum
bias supply voltage of 2.3V. For proper operation, the load
supply is required to be equal to or less than the bias sup
-
ply voltage (maximum 6V).
Supply T
ransients Protection
There are two methods used in most applications to
eliminate supply transients:
1. Transient voltage suppressor to
clip the transient to
a safe level.
2. Snubber (series RC) network.
For
applications with load supply voltages of 3.3V or
higher, the ringing and overshoot during hot-swapping
or output short-circuit events can easily exceed the
absolute maximum rating of the LTC4216. To minimize
the risk, a transient voltage suppressor and snubber
network are highly recommended at the SENSEP pin.
For applications with load supply voltages of 2.5V or
below, usually a snubber network is adequate to reduce
the supply ringing.
Figure 13 shows the connections of the supply transient
protection devices, Z1, R
X
and C
X
, around the LTC4216.
The RC network, R
Y
and C
Y
, at the V
CC
pin also serve
as a snubber circuit for the load supply
(V
IN
)
. On the
PCB layout, these transient protection devices should
be mounted very close to the LTC4216’s load supply rail
using short lead lengths to minimize lead inductance.
Staggered Pins Connections
The LTC4216 can be used on either the backplane side of
the connector or a printed circuit board, and examples for
both are shown in Figure 14 and 15. Printed circuit board
edge connectors with staggered pins are recommended as
the insertion and removal of
circuit boards will sequence
the
pin connections. Supplies (V
CC
and SENSEP) and
ground connections on the printed circuit board should
be wired to the long pins or blades of the edge connector.
Control signal (ON) and status signals (RESET and FAULT)
passing through the edge connector should be wired to
short pins or blades.
Backplane and PCB Connection Sensing
The LTC4216’s ON pin can be used in various ways to
detect whether the printed circuit board is seated properly
in the backplane connector before the LTC4216 begins a
start-up cycle.
An example is shown in Figure 14, in which the LTC4216
is mounted on the PCB and the R1/R2 resistive divider
is connected to the ON pin. On the edge connector, R2
is wired to a short pin. Before the connectors are mated,
the ON pin is held low by R1, keeping the LTC4216 in an
off state. When the connectors are mated, the resistive
divider is connected to the load supply (V
IN
) and the ON
pin voltage rises above 0.8V, turning the LTC4216 on.
Figure 13. Connecting Transient Protection
Devices to the LTC4216’s Load Supply Rail
SENSEP SENSEN
GATE
V
CC
GND
GND
FB
FILTERTIMER
LTC4216**
C
Y
0.33µF
C
X
0.1µF
R4
R3
SS
C1
Z1
Z1: SMAJ6.0A
**ADDITIONAL DETAILS
OMITTED FOR CLARITY
C2
M1
C3
V
OUT
5V
C
LOAD
R
SENSE
R
Y
22Ω
R
X
10Ω
+
4216 F13
V
IN
5V
applicaTions inForMaTion
