Rainbow Electronics ATmega8HVD - Manual (Page 105)

105
8052B–AVR–09/08
ATmega4HVD/8HVD
The Current Battery Protection (CBP) monitors the cell current by sampling the shunt resistor
voltage (R
SENSE
) connected between the NI and GND pins. A differential operational amplifier
amplifies the voltage with a suitable gain. The output from the operational amplifier is com-
pared to an accurate, programmable On-chip voltage reference by an Analog Comparator. If
the shunt resistor voltage is above the Detection level for a time longer than the corresponding
Protection Reaction Time, the chip activates Current Protection. A sampled system clocked by
the internal ULP Oscillator is used for Short-circuit and Over-current. This ensures a reliable
clock source, offset cancellation and low power consumption.
20.3 Short-circuit Protection
The Short-circuit detection is provided to enable a fast response time to very large discharge
currents. If the voltage over R
SENSE
is above the Short-circuit Detection Level for a period lon-
ger than Short-circuit Reaction Time, the Short-circuit Protection is activated.
When the Short-circuit Protection is activated, the external D-FET and C-FET are disabled
and a Current Protection Timer is started. This timer ensures that the D-FET and C-FET are
disabled for at least one second. The application software must then set the DFE and CFE bits
in the FET Control and Status Register to re-enable normal operation. If the D-FET is re-
enabled before the cause of the short-circuit condition is removed, the Short-circuit Protection
will be activated again.
20.4 Discharge Over-current Protection
If the voltage over R
SENSE
is above the Discharge Over-current Detection level for a time lon-
ger than Over-current Protection Reaction Time, the chip activates Discharge Over-current
Protection.
When the Discharge Over-current Protection is activated, the external D-FET and C-FET are
disabled and a Current Protection Timer is started. This timer ensures that the FETs are dis-
abled for at least one second. The application software must then set the DFE and CFE bits in
the FET Control and Status Register to re-enable normal operation. If the D-FET is re-enabled
while the loading of the battery still is too large, the Discharge Over-current Protection will be
activated again.
20.5 Charge Over-current Protection
If the voltage at the GND/NI pins is above the Charge Over-current Detection level for a time
longer than Over-current Protection Reaction Time, the chip activates Charge Over-current
Protection.
When the Charge Over-current Protection is activated, the external D-FET and C-FET are dis-
abled and a Current Protection Timer is started. This timer ensures that the FETs are disabled
for at least one second. The application software must then set the DFE and CFE bits in the
FET Control and Status Register to re-enable normal operation. If the C-FET is re-enabled
and the charger continues to supply too high currents, the Charge Over-current Protection will
be activated again.
The Short-circuit and Over-current parameters are programmable to adapt to different types of
batteries. The parameters are set by writing to I/O Registers. The Parameter Registers can be
locked after the initial configuration, prohibiting any further updates until the next Hardware
Reset.
Refer to ”Register Description” on page 108 for register descriptions.