33990_06 Datasheet, PDF (13/16 Pages) Freescale Semiconductor, Inc – Enhanced Class B Serial Transceiver

TYPICAL APPLICATIONS
FUNCTIONAL PIN DESCRIPTION
transition before 96 µs, one logic state is inferred. If there is a
bus transition after 96 µs, the other logic state is inferred. The
“end of data” bit is a logic [0] and lasts 200 µs. If there is no
activity on the bus for 280 µs to 320 µs following a broadcast
message, multiple unit nodes may arbitrate for control of the
next message. During an arbitration, after the “start of frame”
bit has been transmitted, the secondary node transmitting the
most consecutive logic [0] bits will be granted sole
transmission access to the bus for that message.
Loss of Assembly Ground Connection
The definition of a loss of assembly ground condition at the
device level is that all pins of the 33990, with the exception of
BUS and LOAD, see a very low impedance to V_BAT.
The LOAD pin of the device has an internal transistor
switch connected to it that is normally saturated to ground.
This pulls the LOAD-side of the external resistor (tied from
BUS to LOAD) to ground under normal conditions. The LOAD
pin switch is essentially that of an “upside down” FET, which
is normally biased “on” so long as module ground is present
and biased “off” when loss-of-ground occurs. When a loss of
assembly ground occurs, the load transistor switch is self-
biased “off”, allowing no more than 100 µA of leakage current
to flow in the LOAD pin. During such a loss of assembly
ground condition, the BUS and LOAD pins exhibit a high
impedance to V_BAT; all other pins will exhibit a low impedance
to V_BAT. During this condition the BUS pin is prevented from
sourcing any current or loading the bus, which would cause a
corruption of any data being transmitted on the bus. While a
particular assembly is experiencing a loss of ground, all other
assembly nodes are permitted to function normally. It should
be noted that with other nodes existing on the bus, the bus
will always have some minimum / maximum impedance to
ground as shown in Table 6, page 11.
Loss of Assembly Battery Connection
The definition of a loss of assembly battery condition at the
device level is that the V_BAT pin of the 33990 sees an infinite
impedance to V_BAT, but there is some undefined impedance
between these pins and ground.
V_BAT
33990
+VBAT
BUS
SLEEP
47µH
470pF
10.6kΩ
MCU
TX
LOAD
RX
4X/LOOP
GND
Figure 14. Typical Application
Primary
Node
Secondary
Nodes
Analog Integrated Circuit Device Data
Freescale Semiconductor
33990
13