Atmel ATA6264 - Manual (Page 58)

58
4929B–AUTO–01/07
ATA6264 [Preliminary]
18. Voltage/Current Sources (IASG
x
Sources)
For a variable resistance measurement and especially for buckle-switch detection, five constant
voltage sources, switchable between two different voltages (V1 and V2) are implemented. The
current delivered by these voltage sources is mirrored by a factor of 1 / 10 or 1 / 15 to the pin
ISENS and causes a voltage drop at the external resistor connected to this pin. This voltage
drop can be measured at pin UZP by choosing the corresponding AMUX command. The exter-
nal resistor at pin IASG
x
can be calculated using the following formulas:
or
The current through pin IASG
x
is internally limited to a value between I
IASGx
= –150 mA and
–50 mA. If the voltage at pin ISENS becomes higher than V
VPERI
, the voltage at pin IASG and,
consequently, the current at pin IASG
x
is reduced until V
ISENS
= V
VPERI
. This function can be
used to reduce the current limitation of pin IASG
x
to values lower than the internal limit by choos-
ing an adequate external resistor at pin ISENS. In this case, the maximum current through pin
IASG
x
can be calculated as:
or
For high accuracy, the IASGx current needs to be between 0.5 mA and 40 mA, and the maxi-
mum ISENS voltage must be < V
PERI
– 40%. Under a clamping condition, the voltage at pin
ISENS is clamped to V
PERI
+ 5%. Calculation of the resistor at pin ISENS:
In applications with one or more unused IASG channels, the IASG pins can be used as mea-
surement inputs. The five IASG pins are connected to the analog multiplexer block via different
dividers. Voltages applied to these IASG pins can be measured at the UZP pin, selected via SPI
commands.
R
IASGx
R
ISENS
10
------------------
V
V1
V
V2
–
V
ISENS1
V
ISENS2
–
----------------------------------------------- ×
=
R
IASGx
R
ISENS
15
------------------
V
V1
V
V2
–
V
ISENS1
V
ISENS2
–
----------------------------------------------- ×
=
I
IASGxlim
10
V
VPERI
R
ISENS
------------------
×
=
I
IASGxlim
15
V
VPERI
R
ISENS
------------------ ×
=
RSENS 0.96 V
PERI
×
CR1
I
ASGmax
-------------------- Ч
=