Rainbow-electronics ATmega8HVD Manuel d'utilisateur télécharger pdf (Page 115)

115

8052B–AVR–09/08

ATmega4HVD/8HVD

21.2 FET Driver

21.2.1 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

21.2.2 Overview

The ATmega4HVD/8HVD includes a FET Driver. The FET Driver is designed for driving N-

channel FETs used as high side switch in 1-Cell Li-Ion battery pack. A block diagram of the

FET driver is shown in Figure 21-2.

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 2.3 Volts in 1-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 26-6 on page 146 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 21-3 on page 116 and Table 26-6 on page 146

for details..

Figure 21-2. FET Driver block diagram.

Discharge FETCharge FET

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

14V clamp

1 2 ... 110 111 112 113 114 115 116 117 118 119 120 ... 167 168

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