DS1336
current when V
CC
is out of tolerance. The DS1336 switches back to the higher current V
CC
from battery
current when PF and
PF
become inactive.
OPERATION
The required PF or
PF
input which controls the switching between the main V
CC
and backup battery can
be supplied by any of the devices listed in Table 1. All of the devices provide the DS1336 with a PF or
PF
signal, switching between a main supply V
CC
and backup supply V
BAT
when V
CC
falls out of
tolerance. For applications requiring switching from the V
CC
supply inputs to V
BAT
, the required PF or
PF
input to the DS1336 can be provided by the DS1236, DS1239, DS5001, or DS5340. For applications
requiring switching from the V
CC
inputs to the V
BAT
input when V
CC
begins falling out of tolerance, any
of the Dallas Semiconductor devices listed in Table 1 can provide the DS1336 with the required
switching input. A typical application is shown in Figure 1. For applications where switching between
V
CC
and V
BAT
must occur at a voltage level such that V
CC
is still greater than V
BAT
, the OUT5 pin is
recommended as it provides a diode path which will provide for a gradual transition between V
CC
and
V
BAT
. OUT5 can be tied to the other OUTPUT pins to provide a gradual transition for all five current
paths. In applications where tri-state switching is desired, OUT5 should be omitted. Only the PF/
PF
pin
is required for switching. In cases where the PF input will not be used, it should be connected to GND.
When either PF or
PF
is active, either of the V
BAT0X
outputs is available, although they should not be tied
together (Figure 2, 鈥淒S1336 Block Diagram鈥?. V
BAT01
is recommended for sensitive applications such as
providing backup current to timekeepers, because its diode isolated path provides for increased
protection. V
BAT02
is not recommended for applications where it would be tied to an OUTPUT pin
supplying a voltage greater than that of the backup battery because V
BAT02
is not a diode isolated current
path.
TYPICAL APPLICATION
Figure 1
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