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L5951

Functional description

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2

Functional description

2.1

General features

The L5951 is an integrated circuit which provides a J1850 physical layer as well three

voltage regulators. The L5951 was developed to provide the power and Class 2/IDR

interface for a microcontroller.

2.2

REG1 output voltage

The REG1 regulator output is equal to 3.3V. The 3.3V regulator is non low drop out and can

handle currents up to 100mA with short circuit limit of 280mA.

2.3

REG2 output voltage

The REG2 regulator output is equal to 5V and can handle currents up to 100mA with short

circuit limit of 280mA. The output stage of the 5V regulator is low dropout.

2.4

REG3 output voltage

The REG3 regulator output is equal to 7.8 V and can handle currents up to 100mA with

short circuit limit of 280 mA. The output stage of the 7.8 V regulator is low dropout. REG3

regulator is controlled by the EN (enable) pin of the IC. REG3 can be turned on and off by

toggling the EN pin. A logic "1" on the EN pin enables REG3, while a logic "0" on the EN pin

disables REG3. The maximum voltage when REG3 is off must be less than 0.2 V.

Sleep(a) Input - The Class 2 transmitter can be turned on and turned off by the Sleep* pin.

Once the voltage level is above 2VDC, the transmitter is enabled. If the Sleep* pin drops

below 0.8 VDC, and EN is "0" the transceiver goes into a low power mode. In low power

mode, REG3 and the transceiver are disabled. The L5951 will still receive messages and

send them to the microcontroller out of the RX pin.

LVS input - Reg1 and Reg2 are supplied by Vbat pin. The device could then dissipate a lot

of power, causing thermal shutdown at high voltage. For this reason a secondary low

voltage supply (LVS) can be used to reduce power dissipation.

Reset(a) Output - The L5951 has low voltage or no voltage circuitry that is a warning to the

microcontroller. If REG2 drops 0.3 VDC below its normal operating voltage, the Reset(a) pin

will go to a logic "0". Between the voltage levels of 4.65 VDC (min) and 5.10 VDC (max) on

REG2, a reset will occur. There is a hysteresis of 50mV on the Reset(a) pin.

Low Input Voltage Operation - If battery voltage level drops below 7.0V, the outputs are to

remain alive and ready for the return of normal voltage battery levels. The L5951 will be able

to retrieve data off the BUS and send it to the microprocessor when the supply voltage is as

low as 4.9 V. The regulators should stay the same voltage as the battery voltage down to

7.0 V minus operating headroom for the 7.8 V regulator. BUS VOH,min are not guaranteed

over all conditions below VBAT = 9.0 V.

a. denotes active low

Obsolete

Product(s)

- Obsolete

Product(s)