Atmel ATA6264 - Manual (Page 24)

24
4929B–AUTO–01/07
ATA6264 [Preliminary]
9. EVZ Step-up Regulator
A boost converter generates the supply voltage for energy reserve and firing capacitors in the
system. Using a voltage divider at pin FBEVZ, this voltage can be adjusted between 15V and
40V. Thus, high-voltage charged capacitors will be used to supply the whole system during the
stand-alone time (for example, broken K30 line after a crash). The step-up regulator has to start
running as soon as a certain threshold voltage at the K15 pin is exceeded. The regulator has to
stop running again if the voltage at the K15 pin falls below a voltage level (or voltage at pin K30
is missing, see
Section 5.3 ”Start-up and Power-down Procedure” on page 14 ).
An inductor is PWM-switched by an external n-channel power FET with a fixed frequency of
100 kHz. A driver stage for the external FET is integrated into the ATA6264. The current limita-
tion of the external FET is implemented by using an external resistor in series between the
source connection of the external FET and GND, sensing the voltage drop at this resistor via the
pins OCEVZ and GNDA.
The reference section provides a reference voltage of 1.24V for the regulation loop. An error
amplifier compares the reference voltage with the feedback signal, which is provided either from
two different serial-interface-programmable internal dividers (VEVZ1 = 22V, VEVZ2 = 31.5V) or
an external voltage divider network (VEVZExt). These dividers determine the output voltage
EVZ.
Figure 9-1. EVZ Regulator With External Divider
GNDA
-
+
-
+
Low battery
SPI
GEVZ
L
COMEVZO
FBEVZ
SPI
EVZ
OCEVZ
Logic and
driver
PWM
comp. Error
amp.
Bandgap
reference
Sawtooth oscillator
Overcurrent
EVZ
overvoltage
K30
Max. duty-cycle
SPI
R
VZ2
C +
R
VZ1