Live Insertion Module Replacement
To allow a system module to be replaced without disturbing
signals passing between other operating modules requires
careful design of operating systems, applications software
and hardware. ETL supports live insertion module replace-
ment with features that minimize backplane signal distur-
bance while a module is inserted. As specified by VITA, live
insertion requires several backward-compatible system en-
hancements including: an improved backplane connector
with an embedded ground plane and differential length con-
nector pins. The differential length connector pins allow
power sequencing to the module so that the signal pins can
be controlled to a biased high impedance before they make
contact with the backplane.
VITA’s ETL modules will use an early VCC power input,
called VCC Bias, to control the ETL transceivers to a high
impedance to minimize insertion disturbance. In addition,
VCC Bias is used to precharge the backplane driver output
capacitance including the module connector pin and mod-
ule etch. The precharge voltage is to 1.5V using a switched
40 kXresistor. This precharge will minimize the capacitive
discharge onto an active backplane as the signal connec-
tion is made. To allow designers to maintain this condition until
after a module is fully powered and initialized, the OE pin
can be used to maintain outputs in the high impedance,
precharged state. Contact bounce during live insertion will
charge each output pin to a logic ONE or ZERO. If the con-
tact bounces open, the 40 kXresistor will reestablish the
1.5V level in a few microseconds.
When applying power to a PCB containing ETL transceivers,
the system VCC can be connected to VCC Bias without dam-
age to the device.
If the advantages of Live Insertion are to be included in the
system, then VCC Bias should be allowed to reach normal
operating levels before VCC becomes higher than 2.2 volts.
In addition, when removing a module, or turning off system
power, VCC should be reduced below 2.2 volts before
VCC Bias is allowed to drop below normal operating limits.
This sequencing is shown below.
The figure VCC Power-up Critical Voltages shows the rela-
tionship between OE and VCC while power is being applied
and removed. This relationship holds if VCC Bias is within
normal operating conditions or if VCC Bias is equal to VCC.
TL/F/11658– 13
Power Sequencing to Achieve Live Insertion Precharging
TL/F/11658– 6
VCC and OE Power-Up Critical Relations
6