B10011S Datasheet, PDF (8/11 Pages) ATMEL Corporation – CAN TRANSCEIVER IC

All the logical and sensing functions in the device are powered by V_DD = 5 V. Therefore,
the filter section also acts as a level shifter to the input comparator range (approximately
1 to 3.3 V). The diagram (see Figure 7) shows how the battery voltage, V_CC, influences
the comparator input voltages, F₀ and F₁, in relation to the internal reference voltage,
V_ref, in the recessive state. The lower V_CC, the lower the bus level. Taking this into
account the comparator input levels are F₁ - V_ref for single-wire H respectively F₁ - F₀ for
two-wire operation. The comparator’s offset voltage is ≤10 mV. Matching the filter bias-
ing to the internal reference is essentially for safe operation even at low battery voltages
during motor start.
The level investigations and tests described in the following description have been car-
ried out within the temperature range of -40°C to +105°C with two B10011S on a bus
line, one of them always in the recessive state (see Figure 8 on page 9).
In case of line shorts to V_CC or to ground or in case of H to L shorts, all participants on
the bus are intended to switch to single-wire operation and to disable their drivers not in
use.
The dynamic behavior of the circuit depends on the line capacitances to ground.
Approximately 200 pF/m and a maximum of 6 nF have to be taken into account. The
transition from the dominant to the recessive state enables the bias network to recharge
the line through a driving resistor of approximately 300 Ω. The transition from the reces-
sive to the dominant state is approximately twice as fast. This is probably the source of
emitted radiation having no capacitance on the line. The choke coil enables the sup-
pression of this radiation in the frequency range above 5 MHz to 7 MHz. Care should be
taken not to feed noise from V_DD or V_CC to the line. Therefore, they should be properly
blocked by low-inductance capacitors.
Data loss by externally induced interference is avoided by careful PCB layout and EMC
design for this circuit as well as by providing appropriate overvoltage protection. It is
very essential to separate battery ground and filter ground as indicated in the application
circuit (see Figure 5 on page 6). Especially important is that the filter ground must be
connected to pin 8 by a short connection not subject to disturbing currents from external
sources. The ground wire of the “starquad” cable may introduce such currents and
should be connected to battery ground via a 0.1-µF capacitor in a way as short as possi-
ble, perhaps to the metal housing.
In order to avoid thermal problems, the voltage divider and driving resistors should be
kept away from the IC. Otherwise they would heat up the environment of the small IC
and might reduce its life expectancy.
Figure 7. Comparator Thresholds
V
not ER
5
RxN
4
3
F₀
U_ref
2
1
F₁
0
5
10
15
20
25
30
35
V_CC
8 B10011S
4749B–AUTO–09/04