Preliminary
CBC910 Detailed Description
CBC910
The CBC910 uses a charge pump to generate the supply voltage for charging a battery. An internal FET switch
with low RDS
ON
is used to route V
DD
to V
OUT
during normal operation when main power is above the battery
switchover threshold voltage. When V
DD
is below the battery switchover threshold voltage, the FET switch
is shut off and V
OUT
is supplied by the battery through a silicon diode in series between VBAT and VOUT. An
interrupt signal is asserted low prior to the switchover.
Operating Modes
The EnerChip CC can be operated from various power supplies such as a primary source or a non-rechargeable
battery. With the ENABLE pin asserted high, the charge pump is active and charges the integrated EnerChip.
The EnerChip CC will be 80% charged within 10 minutes. Due to the rapid recharge it is recommended that,
once the EnerChip CC is fully charged, the user de-assert the ENABLE pin (i.e., force low) to reduce power
consumption. A signal generated from the MCU could be used to enable and disable the EnerChip CC.
When controlling the ENABLE pin by way of an external controller - as opposed to fixing the ENABLE line to VDD
- ensure that the ENABLE pin is forced low by the controller anytime the RESET line is low, which occurs when
the switchover threshold voltage is reached and the device is placed in backup mode. Although the internal
charge pump is designed to operate below the threshold switchover level when the ENABLE line is active, it
is recommended that the ENABLE pin be forced low whenever RESET is low to ensure no parasitic loads are
placed on the EnerChip while in this mode. If ENABLE is high or floating while VDD is in an indeterminate
state, bias currents within the EnerChip CC could flow, placing a parasitic load on the EnerChip that could
dramatically reduce the effective backup operating time.
Mode 1 Operation
For use in 3.3 volt systems. The V
MODE
pin should be tied directly to GND. This will set the battery switchover
threshold at approximately 3.0 volts.
Mode 2 Operation
To adjust the user-selectable battery switchover threshold to a value between 2.5 and 5.0 volts, refer to Figure
6 to determine the value of R1. To determine the amount of hysteresis from the backup battery switchover
threshold, use Figure 7.
DS-72-11 Rev 5
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