ATmega16HVB datasheet(136/273 Pages) ATMEL

136 / 273 page

136

8042A–AVR–07/09

ATmega16HVB/32HVB

24.3

Operation

The Current Battery Protections (CBP) monitors the cell current by sampling the shunt resistor

voltage at the PPI/NNI input pins. A differential operational amplifier amplifies the voltage with a

suitable gain. The output from the operational amplifier is compared to an accurate, programma-

ble 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, Over-current, and High-current Protection. This ensures a reliable clock source,

offset cancellation and low power consumption.

24.3.1

Short-circuit Protection

The Short-circuit detection is provided to enable a fast response time to very large discharge

currents. If the voltage at the PPI/NNI pins is above the Short-circuit Detection Level for a period

longer 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.

24.3.2

Discharge Over-current Protection

If the voltage at the PPI/NNI pins is above the Discharge Over-current Detection level for a time

longer 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.

24.3.3

Charge Over-current Protection

If the voltage at the PPI/NNI 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 acti-

vated again.

24.3.4

Discharge High-current Protection

If the voltage at the PPI/NNI pins is above the Discharge High-current Detection level for a time

longer than High-current Protection Reaction Time, the chip activates Discharge High-current

Protection.

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