UJA1076 datasheet(20/47 Pages) NXP

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UJA1076_2

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Product data sheet

Rev. 02 — 27 May 2010

20 of 47

NXP Semiconductors

UJA1076

High-speed CAN core system basis chip

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

Vth(act)Ilim, the PNP current limiting activation threshold voltage, the transistor current will

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 UJA1076 and the

external PNP doesn’t affect the stability of the regulator loop because the loop is realized

within the UJA1076. Therefore, it is recommended that the distance between the

UJA1076 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 (Vuvd; see Table 10). The reset

threshold (90 % or 70 % of the nominal value) is set via the Reset Threshold Control bit

(RTHC) in the Int_Control register (Table 6). In addition, an undervoltage warning (a V1UI

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 (Table 4).

6.6.3 Voltage regulator V2

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 5). An undervoltage warning (a V2UI interrupt) is generated when the output

voltage drops below 90 % of its nominal value. The status of V2 can be read via bit V2S in

the WD_and_Status register (Table 4) in Normal mode (V2S = 1 in all other modes).

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.

6.7 CAN transceiver

The analog section of the UJA1076 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.

6.7.1 CAN operating modes

6.7.1.1

Active mode

The CAN transceiver is in Active mode when:

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