bq24070
bq24071
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SLUS694B–MARCH 2006–REVISED AUGUST 2006
FUNCTIONAL DESCRIPTIONS (continued)
(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. When the Mode went low (1st div), the AC FET opened, and the
output fell until the USB FET turned on. Turning off the active source before turning on the replacement source
is referred to as break-before-make switching. The rate of discharge on the output is a function of system
capacitance and load. Note the cable IR drop in the AC and USB inputs when they are under load. At the 4th
division, the output has reached steady-state operation at the DPPM voltage level (charge current has been
reduced due to the limited USB input current). At the 6th division, the Mode goes high and the USB FET turns off
followed by the AC FET turning on. The output returns to its regulated value, and the battery returns to its
programmed current level.
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 Mode Low
Figure 7 illustrates when a battery is inserted for power up; channel 1 (CH1) VAC = 0 V; channel 2 (CH2) VUSB
0 V; channel 3 (CH3) VOUT; output current, IOUT = 0.25 A for VOUT > 2 V; channel 4 (CH4) VBAT = 3.5 V; C(DPPM)
=
=
0 pF. When there are no power sources and the battery is inserted, the output tracks the battery voltage if there
is no load (<10 mA of load) on the output, as shown. If a load is present that keeps the output more than 200
mV below the battery, a short-circuit condition is declared. At this time, the load has to be removed to recover. A
capacitor can be placed on the DPPM pin to delay implementing the short-circuit mode and get unrestricted (not
limited) current.
15
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