iC-GF
TRANSCEIVER
Rev C1, Page 13/26
DESCRIPTION OF FUNCTIONS
iC-GF has two independent switching channels which responds to the free-wheeling circuit activated. The
enables digital sensors to drive peripheral elements. switching channels are designed so that QNx can only
They are designed to cope with high driver currents. sink current and QPx can only source current (no re-
The switches are reverse-polarity protected, feature a verse current).
free-wheeling circuit for inductive loads and a satura-
tion voltage minimising system.
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
Reverse polarity protection
The pins VBO, QPx, QNx, VN and CFI on the line side by voltages higher than 36 V at QNx referenced to VN
of the chip are reverse polarity protected. As far as the or lower than -36 V at QPx referenced to VBO. In that
maximum voltage ratings are not exceeded, no possi- case the correspondent channel will switch on without
ble supply combination at the line side pins can dam- current limitation (see Figure 4).
age the chip.
I(Qx)
I(Qx)
36V
VBO-36V
V(Qx)
Ipeak
Isc()lo
VN
VBO
VN+36V
VAR
VN
V(Qx)
36V
4V
VBO
A
B
C
36V
Figure 4: Free-wheeling characteristic
Dead time
Figure 2: QNx characteristic when active
In order to avoid current flow between high- and low-
side switch in push-pull configuration, a dead time tdead
is implemented as shown in Figure 5 (cf. Electrical
Characteristics Nos. 112 and 212).
I(Qx)
VBO-36V
C
VN
B
A
V(Qx)
VBO
Isc()hi
Ipeak
ttrig
tdead
INx
36V
QNx
QPx
Figure 3: QPx characteristic when active
Output characteristics of Q1, Q2
Figure 5: Propagation delay
The switching channels are current limited to a value
set by the external resistor RSET (cf. Electrical Char-
acteristics 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 re-
duced in order to minimise the saturation voltages with-
out increasing the power dissipation. Figures 2 and
3 show the characteristic of the switching channels
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.
when activated. Region "A" is the saturation range, The level of power dissipation depends on the cur-
where the current limitation is not fully active yet and rent and the time during which this current flows. A
region "B" is the current limited range. Region "C" cor- current which fails to trigger the overload detection
ICHAUS [ IC-HAUS GMBH ]
