ATmega16HVB datasheet(149/273 Pages) ATMEL

149 / 273 page

149

8042A–AVR–07/09

ATmega16HVB/32HVB

For safe operation the FET driver automatically turns off both the Charge and Discharge FET if

the autonomous Battery Protection circuitry (see ”Battery Protection” on page 135) detects an

illegal current condition. If such conditions occur, software is not allowed to turn on the FETs

until the current condition has normalized.

To charge deeply discharged cells the ATmega16HVB/32HVB can be configured to run in Deep

Under Voltage Recovery (DUVR) mode. Using chargers with pre-charge current functionality,

this allows charging of deeply discharge cells without an additional pre-charge FET. For char-

gers without a pre-charge limitation current, an optional pre-charge FET in parallel with a charge

FET is supported to be able to charge deeply discharge cells.

25.3

Operation and Usage

25.3.1

Normal Operation

In normal operation (DUVRD=1), the FET control is used to enable and disable the Charge FET

and Discharge FET. Normally, the FETs are enabled and disabled by SW writing to the FET

Control and Status Register (FCSR). However, the autonomous Battery Protection circuitry will if

necessary override SW settings to protect the battery cells from too high Charge- or Discharge

currents. Note that the CPU is never allowed to enable a FET that is disabled by the battery pro-

tection circuitry. The FET control is shown in Figure 25-1 on page 148.

Figure 25-2. FET Control module.

If Current Protection is activated by the Battery Protection circuitry both the Charge-FET and

Discharge FET will be disabled by hardware. When the protection condition disappears the Cur-

rent Protection Timer will ensure a hold-off time of 1 second before software can re-enable the

external FETs.

To turn on the Charge and Discharge FET a minimum VFET supply voltage is required. When

the C-FET/D-FET is off with a total cell voltage lower than 6V, SW should not turn on the C-

FET/D-FET unless a charger is connected. If the total cell voltage is higher than 6V, SW could

turn-on the C-FET or D-FET. Note however, if the FETs are already turned-on, the FET driver

can operate in the entire supply operating range of the device.

FET

Control

and

Status

DFE

CFE

CURRENT_PROTECTION

Power-off Mode

CHARGE_EN

DISCHARGE_EN

DUVRD

DUVR_OFF

Current Protection

Timer

External_Protection_Input

ATmega16HVB 数据表(PDF) 149 Page - ATMEL Corporation

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