AOZ9004B
Theory of Operation
Please refer to the Timing Diagrams for more information.
Over-Discharge Status
When the battery voltage falls below over-discharge
detection voltage (V
DL
) for the over-discharge detection-
delay time (t
DL
) or longer, the IC turns off the discharging
control MOSFET to stop discharging. This condition is the
over-discharge status. Under the over-discharge
status, the VM pin voltage is pulled up by the resistor
between the VM pin and VDD pin in the IC (R
VMD
). When
voltage difference between the VM pin and VDD pin is
1.3V (Typ.) or lower, the productions with “Shut-down
Function Available” feature can enter the shut-down
status to save power. At this status, the current consump-
tion is reduced to the shut-down current consumption
(IPON). The shut-down status is released when a charger
is connected and the voltage difference between the VM
pin and VDD pin becomes 1.3V (Typ.) or higher.
When a battery in the over-discharge status is connected
to a charger and provides that the VM pin voltage is lower
than -0.7V (Typ.), the AOZ9004B releases the over-
discharge status and turns on the discharging MOSFET
when the battery voltage reaches over-discharge
detection voltage (V
DL
) or higher. If VM pin voltage is not
lower than -0.7V (Typ.), the AOZ9004B releases the over-
discharge status and turns on the discharging MOSFET
when the battery voltage reaches over-discharge
detection voltage (V
DU
) or higher.
Normal Status
The AOZ9004B monitors the voltage between the VDD
pin and VSS pin and the voltage difference between the
VM pin and VSS pin to control charging and discharging.
Since the device only draws a few microamperes of
current during operation and the voltage drop across the
low-pass filter R1 is negligible, the voltage between VDD
and VSS is equal to the battery voltage. When the battery
voltage is in the range between over-discharge detection
voltage (V
DL
) and overcharge detection voltage (V
CU
),
and the VM pin voltage is in the range between the charge
over-current detection voltage (V
CIOV
) and
discharge over-current detection voltage (V
DIOV
), the IC
turns both the charging and discharging control FETs on.
In this normal status, charging and discharging can be
carried out freely.
Caution:
Products with “Shut-down Function Available”
feature may not enable discharging when the battery is
connected for the first time. Connect the charger or short
VM pin to VSS can restore the normal status.
Overcharge Status
When the battery voltage rises higher than overcharge
detection voltage (V
CU
) for the overcharge detection delay
time (t
CU
) or longer in the normal status, the AOZ9004B
turns off the charging control MOSFET to stop charging.
This condition is the overcharge status. The resistance
(R
VMD
) between the VM pin and VDD pin, and the resis-
tance (R
VMS
) between the VM pin and VSS pin are not
connected. The overcharge status is released in the fol-
lowing two cases:
1. When the battery voltage falls below overcharge
release voltage (V
CL
) and VM pin voltage is higher
than -0.7V (Typ.) (charger is removed), the
AOZ9004B turns on the charging control MOSFET
and returns to the normal status.
2. When a load is connected and battery voltage is
below overcharge detection voltage (V
CU
), the
AOZ9004B turns on the charging control MOSFET
and returns to the normal status.
Caution:
When both charger and load are connected after
overcharge detection, charging control FET still remains
off and a portion of the load current may flow through body
diode of charging control FET if the charger can not sup-
ply the full load current. This condition may overheat the
charging control FET. Please refer to the Typical Charac-
teristics for more information.
Discharge Over-Current Status (Discharge
Over-current, Load Short-circuiting)
When a battery is in the normal status, and the discharge
current becomes higher than specified value and the
status lasts for the discharge over-current detection delay
time (t
DIOV
), the IC turns off the discharge control
MOSFET and stops discharging. This status is the
discharge over-current status. In the discharge over-
current status, the VM pin and VSS pin are shorted by the
resistor between VM pin and VSS pin (R
VMS
) in the IC.
When the load is disconnected, the VM pin returns to the
VSS potential. When the impedance between the EB+ pin
and EB- pin (Refer to Figure 1) increases and is equal to
the impedance that enables automatic restoration and the
voltage at the VM pin returns to discharge over-
current detection voltage (V
DIOV
) or lower, the discharge
over-current status is restored to the normal status. Even
if the connected impedance is smaller than automatic res-
toration level, the AOZ9004B will be restored to the nor-
mal status from discharge over-current detection
status when the voltage at the VM pin becomes the
discharge over-current detection voltage (V
DIOV
) or lower
by connecting the charger. The resistance (R
VMD
)
between the VM pin and VDD pin is not connected in the
discharge over-current detection status.
Page 9 of 17
Rev. 1.2 August 2008
www.aosmd.com
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