uja1078a NXP Semiconductors, uja1078a Datasheet - Page 22

• Manufacturer Part Number: uja1078a
• Description: High-speed Can/dual Lin Core System Basis Chip
• Manufacturer: NXP Semiconductors

NXP Semiconductors
UJA1078A
Product data sheet
6.6.3 Voltage regulator V2
6.7 CAN transceiver
For short-circuit protection, a resistor needs to be connected between pins V1 and
VEXCC to allow the current to be monitored. This resistor limits the current delivered by
the external transistor. If the voltage difference between pins VEXCC and V1 reaches
V
not increase further.
The thermal performance of the transistor needs to be considered when calculating the
value of this resistor. A 3.3 Ω resistor was used with the BCP52-16 (NXP Semiconductors)
employed during testing. Note that the selection of the transistor is not critical. In general,
any PNP transistor with a current amplification factor (β) of between 60 and 500 can be
used.
If an external PNP transistor is not used, pin VEXCC must be connected to V1 while pin
VEXCTRL can be left open.
One advantage of this scalable voltage regulator concept is that there are no PCB layout
restrictions when using the external PNP. The distance between the UJA1078A and the
external PNP doesn’t affect the stability of the regulator loop because the loop is realized
within the UJA1078A. Therefore, it is recommended that the distance between the
UJA1078A and PNP transistor be maximized for optimal thermal distribution.
The output voltage on V1 is monitored continuously and a system reset signal is
generated if an undervoltage event occurs. A system reset is generated if the voltage on
V1 falls below the undervoltage detection voltage (V
threshold (90 % or 70 % of the nominal value) is set via the Reset Threshold Control bit
(RTHC) in the Int_Control register
interrupt) will be generated at 90 % of the nominal output voltage. The status of V1 can be
read via bit V1S in the WD_and_Status register
Voltage regulator V2 is reserved for the high-speed CAN transceiver, providing a 5 V
supply.
V2 can be activated and deactivated via the MC bits in the Mode_Control register
(Table
voltage drops below 90 % of its nominal value. The status of V2 can be read via bit V2S in
the WD_and_Status register
V2 can be deactivated (MC = 10) to allow the internal CAN transceiver to be supplied from
an external source or from V1. The alternative voltage source must be connected to pin
V2. All internal functions (e.g. undervoltage protection) will work normally.
The analog section of the UJA1078A CAN transceiver corresponds to that integrated into
the TJA1042/TJA1043. The transceiver is designed for high-speed (up to 1 Mbit/s) CAN
applications in the automotive industry, providing differential transmit and receive
capability to a CAN protocol controller.
th(act)Ilim
5). An undervoltage warning (a V2UI interrupt) is generated when the output
, the PNP current limiting activation threshold voltage, the transistor current will
All information provided in this document is subject to legal disclaimers.
Rev. 01 — 9 July 2010
(Table
(Table
5) in Normal mode (V2S = 1 in all other modes).
High-speed CAN/dual LIN core system basis chip
6). In addition, an undervoltage warning (a V1UI
(Table
uvd
; see
4).
Table
10). The reset
UJA1078A
© NXP B.V. 2010. All rights reserved.
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