Rainbow Electronics ATmega8HVD - Manual (Page 104)

104
8052B–AVR–09/08
ATmega4HVD/8HVD
20. Battery Protection
20.1 Features
• Short-circuit Protection
• Discharge Over-current Protection
• Charge Over-current Protection
• External Protection Input
• Programmable and Lockable Detection Levels and Reaction Times
• Autonomous Operation Independent of CPU
20.2 Overview
The Current Battery Protection circuitry (CBP) monitors the charge and discharge current and
disables C-FET and D-FET if a Short-circuit, Over-current or High-current condition is
detected. There are three different programmable detection levels: Short-circuit Detection
Level, Discharge Over-current Detection Level, and Charge Over-current Detection Level.
There are two different programmable delays for activating Current Battery Protection: Short-
circuit Reaction Time and Over-current Reaction Time. After Current Battery Protection has
been activated, the application software must re-enable the FETs. The Battery Protection
hardware provides a hold-off time of 1 second nominally before software can re-enable the
discharge FET. This provides safety in case the application software should unintentionally re-
enable the discharge FET too early.
The activation of a protection also issues an interrupt to the CPU. The battery protection inter-
rupts can be individually enabled and disabled by the CPU.
In addition, the module offers an External Protection Input. The activation of the External Pro-
tection Input operates independently of the rest of the battery protection mechanisms. The
activation/deactivation of this protection is instantaneously controlled from the External Protec-
tion Input port, and will not deactivate or affect the other battery protection mechanisms.
The effect of the various battery protection types is given in Table 20-1 .
In order to reduce power consumption, Short-circuit and Discharge Over-current Protection
are automatically deactivated when the D-FET is disabled. The Charge Over-current is dis-
abled when the C-FET is disabled. Note that Charge Over-current Protection is never
automatically disabled when the chip is operated in DUVR mode. Also note that none of the
current protections are deactivated by External Protection Input. To save power during an
External Protection event, DFE and CFE should be cleared in the FCSR register. Make also
sure that the chip is not operated in DUVR mode.
Table 20-1. Effect of Battery Protection Types
Battery Protection Type Interrupt Requests C-FET D-FET MCU
Short-circuit Protection Entry Disabled Disabled Operational
Discharge Over-current
Protection
Entry Disabled Disabled Operational
Charge Over-current
Protection
Entry Disabled Disabled Operational
External Protection Input Entry and/or Exit Disabled Disabled Operational