IC-GF_15 Datasheet, PDF (16/30 Pages) IC-Haus GmbH – TRANSCEIVER

iC-GF
TRANSCEIVER
DESCRIPTION OF FUNCTIONS
Rev F1, Page 16/30
iC-GF has two independent switching channels which
enables digital sensors to drive peripheral elements.
They are designed to cope with high driver currents.
The switches are reverse-polarity protected, feature a
free-wheeling circuit for inductive loads and a saturation
voltage minimising system.
Reverse polarity protection
The pins VBO, QPx, QNx, VN and CFI on the line side
of the chip are reverse polarity protected. As far as the
maximum voltage ratings are not exceeded, no possible
supply combination at the line side pins can damage
the chip.
I(Qx)
circuit activated. The switching channels are designed
so that QNx can only sink current and QPx can only
source current (no reverse current).
Free-wheeling circuit for inductive loads
The free-wheeling circuit is always present and does
not depend on the current output status. It is activated
by voltages higher than 36 V at QNx referenced to VN
or lower than -36 V at QPx referenced to VBO. In that
case the correspondent channel will switch on without
current limitation (see Figure 4).
I(Qx)
36V
Ipeak
Isc()lo
VN
4V
A
VBO
B
36V
V(Qx)
C
Figure 2: QNx characteristic when active
VBO-36V
C
I(Qx)
Isc()hi
VN B
Ipeak
36V
A VBO V(Qx)
VBO-36V
VN
36V
VBO
VAR
VN+36V
V(Qx)
Figure 4: Free-wheeling characteristic
Dead time
In order to avoid current flow between high- and low-
side switch in push-pull configuration, a dead time t_dead
is implemented as shown in Figure 5 (cf. Electrical
Characteristics Nos. 112 and 212).
ttrig
tdead
INx
QNx
QPx
Figure 3: QPx characteristic when active
Figure 5: Propagation delay
Output characteristics of Q1, Q2
The switching channels are current limited to a value
set by the external resistor RSET (cf. Electrical Charac-
teristics No. D03). If pin ISET is short circuited to GND,
the current limitation will be set to a maximum value (cf.
Electrical Characteristics Nos. 108, 208). The current
limitation works only for voltages higher than 4 V at QNx
resp. lower than VBO − 4 V at QPx. For smaller output
voltages the current limitation is reduced in order to
minimise the saturation voltages without increasing the
power dissipation. Figures 2 and 3 show the character-
istic of the switching channels when activated. Region
"A" is the saturation range, where the current limitation
is not fully active yet and region "B" is the current limited
range. Region "C" corresponds to the free-wheeling
Overload detection
To protect the device against excessive power dissipa-
tion due to high currents the switches are clocked if an
overload occurs. If a short circuit is detected, i.e. if the
voltage at the switch output overshoots or undershoots
Overload Detection Threshold off (cf. Electrical Char-
acteristics Nos. 104 and 204), the switches are shut
down for a typical 50 ms (cf. Electrical Characteristics
No. 302) and the current flow thus interrupted.
The level of power dissipation depends on the current
and the time during which this current flows. A current
which fails to trigger the overload detection is not criti-
cal; high current can also be tolerated for a short period