Datasheet

136
8024A–AVR–04/08
ATmega8HVA/16HVA
24.2 FET Driver
24.2.1 Features
•
Charge-pump for generating suitable gate drive for N-Channel FET switch on high side
• Deep Under-voltage Recovery mode that allows normal operation while charging a Deeply Over-
discharged battery from 0-volt
24.2.2 Overview
The ATmega8HVA/16HVA includes a FET Driver. The FET Driver is designed for driving N-
channel FETs used as high side switch in 1- or 2-Cell Li-Ion battery pack. A block diagram of the
FET driver is shown in Figure 24-2 on page 136.
When charging deeply over-discharged cells, the FET Driver will be operated in Deep Under-
Voltage Recovery (DUVR) mode. In DUVR mode the FET Driver regulates the voltage at the
VFET pin to typically 2.0 Volts in 1-Cell applications and typically 4.0 Volts in 2-Cell applications.
This is done by operating the Charge FET at a point where the drain-source voltage is equal to
the voltage difference between the cell voltage and the required VFET operating voltage. As the
cell voltage increases, the drain-source voltage of the Charge FET will decrease until the
Charge FET is completely on. See Table 29-5 on page 170 for details.
In normal operation (DUVRD = 1), the Charge FET/Discharge FET is switched on by pumping
OC/OD sufficiently above the VFET supply voltage. To turn off the Charge FET/Discharge FET,
OC/OD is pulled quickly low. See Figure 24-3 on page 137 and Table 29-5 on page 170 for
details.
Figure 24-2. FET Driver block diagram.
Discharge FETCharge FET
OD
OC
BATT
+
BATT
-
VFET
NFET DRIVER
DUVRD
D-FET
Charge
Pump
CHARGE_EN
DISCHARGE_EN
FET
CONTROL
C-FET
Charge
Pump
DUALC_MODE
LDO
_VREG
DVDD
VREF
BANDGAP
REF.
CLK
CLK_OSC
1k
1k
14V clamp
14V clamp