AT73C209 Datasheet, PDF (49/63 Pages) ATMEL Corporation – Power Management and Analog Companions PMAAC)

AT73C209
12.3
USB vs. DC/DC Power On/Off Operation
AT73C209 has a power selection priority. The USB pin powers the LDO1 and the IN pin powers
the DC/DC Converter. If the output value of the DC/DC is higher than the LDO1 output value,
then the LDO1 is stopped. If the output value of the LDO1 is higher than the DC/DC output
value, then the DC/DC is put in standby mode.
Figure 12-3. Power Supply Priority Diagram
USB
LDO1
Stop
DC/DC > LDO1
FB/VBOOST
Standby
IN
LDO1
Using default values (In the registers), the power-on and power-off sequences when both power
supplies are connected, should be as described below.
Power On Sequence:
A cell is connected to the IN pin. The DC/DC can be started by ONOFF pin activation and
latched by UPONOFF bit activation.
• FB output rises until 3.3V (default voltage value).
• Once FB reaches 2.4V, a counter is launched and after “Reset-Time”, a reset is generated on
RSTB pin.
• DC/DC is running.
A USB power supply is connected on the USB pin. The LDO1 starts automatically.
• FB/VBOOST rises to 3.4V (default voltage value).
• The DC/DC is in Standby Mode
Power Off Sequence:
The USB power supply is disconnected from the USB pin.
• The LDO1 is stopped
• The DC/DC is start (in case of UPONOFF bit activated)
• FB/VBOOST is falling down until 3.3V (default voltage value).
The DC/DC is stopped when the UPONOFF bit is set to Low.
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6365A–PMAAC–12-Mar-08