BQ2205LYPWR Datasheet, PDF (7/14 Pages) Texas Instruments – POWER MONITORING AND SWITCHING CONTROLLER FOR 3.3-V SRAM

bq2205LY
FUNCTIONAL DESCRIPTION
SLUS581 − FEBRUARY 2004
During power up, VOUT is switched back to the main supply as VCC rises above the backup cell input voltage
sourcing VOUT. If V_PFD < BC_P on the bq2205 the switch to the main supply occurs at V_PFD. CE_CONx is held
inactive for time t_CER after the power supply has reached V_PFD, independent of the CE input, to allow for
processor stabilization.
Power-On Reset
The bq2205 provides a power-on reset, which pulls the RST pin low on power down and remains low on power
up for t_RST after V_CC passes V_PFD. With valid battery voltage on BC_P, RST remains valid for V_CC = V_SS. The
pull-up resistor on this pin should not exceed 10 kΩ if a push button reset is used.
Battery Low Warning
The bq2205 checks the battery voltage on power-up. The threshold for the battery warning comparator is V_BW,
and a low level is sensed after power valid on each power up and latched after t_CER time. The latched value
is presented at BW pin where a low indicates a low battery.
APPLICATION INFORMATION
PCB LAYOUT INFORMATION
It is important to pay special attention to the PCB layout. The following provides some guidelines:
D To obtain optimal performance, the decoupling capacitor from input terminals to V_SS should be placed as
close as possible to the bq2205, with short trace runs to both signal and V_SS pins.
D All low-current V_SS connections should be kept separate from the high-current paths from the inputs
supplies. Use a single-point ground technique incorporating both the small signal ground path and the
power ground path.
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