bq24030, bq24031, bq24032,
bq24032A, bq24035, bq24038, bq24039
www.ti.com
SLUS618C–AUGUST 2004–REVISED JUNE 2005
Break Before Make
V
AC
V
USB
V
V
OUT
BAT
System Capacitance
Powering System
DPPM Mode
USB is Charging System Capacitance
Hi
PSEL
Low
Figure 6. Toggle PSEL Low
Figure 7 illustrates when AC is removed, power transfers to USB; PSEL = H (AC primary source); channel 1
(CH1) VAC = 5.4 V; channel 2 (CH2) V(USB) = 5 V; channel 3 (CH3) VOUT; output current, IOUT = 0.25 A; channel
4 (CH4) VBAT = 3.5 V; and I(PGM-CHG) = 1 A. The power transfer from AC to USB only takes place after the primary
source (AC) is considered bad (too low, VAC<=VBAT + 125 mV) indicated by the ACPG FET turning off (open
drain not shown). Thus, the output drops down to the battery voltage before the USB source is connected (6th
div). The output starts to recover when the USB FET starts to limit the input current (7th div) and the output drops
to the DPPM voltage threshold.
USB Input Current Limit is Reached.
DPPM Mode
V
USB
OUT
V
V
AC
V
BAT
AC Declared Not Present, USB Power Applied
Figure 7. Remove AC – PWR XFER to USB
17
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