Advanced Analog Technology, Inc.
OPERATION (CONT.)
3. COM2 (Over Discharge Detector)
COM2 monitors the cell voltage at the
pin. When
drops below the over discharge threshold VD1 during the
VDD
VDD
discharging process, COM1 detects an over charging condition and after delay time ( tD1 ) elapses, the DOUT pin falls to a low
level and thus turning off the external discharge control N-channel MOSFET. As soon as this happens, the VN pin will be changed
to high level by an internal PMOS and the AAT8636 series will enter the standby mode.
Connecting the battery pack to a charger is the required condition for AAT8636 series to recover from standby mode. With the
charger connected, the charge current can flow through the parasitic diode of the external discharge control N-channel MOSFET
while
is still lower than the over-discharge threshold. Once
is charged up to a value higher than VD1 , the DOUT pin
VDD
VDD
goes to a high level. This leads to the “ON” state of both the charge and discharge control MOSFETs, and the charging process
proceeds on as long as the charger is connected. Connecting a charger to the battery pack when
will make DOUT instantaneously high.
is already higher than VD1
VDD
4. COM3 (Over Current Detector, Short Circuit Protector)
The over current detector and short circuit protector function normally when both the charge and discharge control N-channel
MOSFETs are “ON”.
In standard operation, voltage on VN pin will be either slightly higher or lower than GND, depending on the impedance of the two
MOSFETs. However, when the VN pin voltage rises to a value between the short circuit detection voltage Vshort and over current
detection voltage VOC , the AAT8636 series detect an over current condition. As a result, the external discharge control N-channel
MOSFET goes to “OFF” with DOUT pin at the low state. An output delay time for the over current detection is internally fixed. A
quick recovery of VN from a value between Vshort and VOC to the normal value within the delay time keeps the discharge control
FET staying at the “ON” state.
Short circuit may as well be explained as a “serious” over current condition. When the VN pin voltage rises to a value not only
higher than VOC but also higher than Vshort , the short circuit protector will shut down the discharge MOSFET immediately to
protect battery pack from being damaged or exploding.
The VN pin has a built-in pull down resistor. Thus once the factors that cause over current or short circuit is removed, the VN pin
will be pulled down to ground level through the internal resistor. Therefore, with VN lower than the over current and short circuit
protection threshold, DOUT will be turned back on and the AAT8636 series can continue normal charge or discharge operation.
When over current or short circuit occurs, the AAT8636 series will not enter a standby mode.
– 台灣類比科技股份有限公司–
– Advanced Analog Technology, Inc. –
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AAT [ ADVANCED ANALOG TECHNOLOGY, INC. ]
