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L5951

as well as a 10.6 kW + 5% pull down resistor to ground. The main node has a 3,300 + 10% pF capacitor on its

output for EMI suppression, as well as a 1.5 k

Ω + 5% pull down resistor to ground. With more than 26 nodes

there is no primary node , all nodes will have the 470 ±10% pF capacitor and the 10.6k

Ω ±5% pull down resistor.

No matter how many remote nodes are on the Class 2/IDR Bus, the RC of the Class 2/IDR Bus is maintained

at approximately 5ms. The minimum and maximum load on the Class 2/IDR Bus is given below :

1.5 Protection

The L5951 can survive under the following conditions: shorting the outputs to BAT and GND, loss of BAT, loss

of IC GND, double battery(+26.5V), 4000V ESD, 34V load dump. L5951 will not handle a reverse battery con-

dition. External components must be implemented for reverse battery protection.

Thermal Shutdown: thermal shutdown is broken down into two areas; V1 and V2 ouputs, and the other is V3

output and the Class 2 Bus Driver. V1 and V2 outputs shutdown at 160°C and returns to normal operation at

130°C. The V3 output and Class 2 Bus Driver shutdown at 150°C and return to normal operation at 120°C.

Current Limiting: each voltage regulator will contain its own current protection, and the maximum allowable cur-

rent for all three regulators is 280mA.

Short Circuit: If the outputs are short circuited, the IC will begin current limiting and eventually the thermal shut-

down will kick in. Current limiting will not disable the outputs.

Overvoltage: The IC will not operate if the BAT voltage reaches 30V or above. V1 and V2 will not be shutdown,

but all other outputs will not operate.

Loss of Ground & Loss of Battery Connection: in this conditions a very small leakage on BUS is generated.

1.6 Protocol Description

The L5951 uses a Variable Pulse Width (VPW) modulated protocol. One frame consists of an entire message

not containing more than 12 bytes. The first bit of each byte will be the most significant bit (MSB). A transmitted

message begins with a SOF signal and ends with the EOF signal.

The data to be transmitted has to be in a specific format as follows:

idle,SOF,DATA, CRC, EOD, NB, IFR, EOF, IFS, idle

Definitions below:

idle:

Logic level low on communication bus

SOF:

Start of Frame

DATA:

Data Bytes

CRC:

Cyclic Redundancy Check Error Detection Byte

EOD:

End of DATA(only when IFR is used)

NB:

Normalization Bit

IFR:

In-Frame Response Byte(s)

EOF:

End of Frame

IFS:

Inter-Frame Separation

BRK:

Break(can occur on network at any time)

Idle - Logic level low on bus any time after IFS.

Start of Frame (SOF) - The SOF signals the receiver that a new frame is beginning. SOF signal is a logic level

Capacitance

Resistance to Ground

Minimum Nodes

(3.33 · .9) + (.47 · .9) = 3.39 nF

(1.5 · 1.05) || (10.6 · 1.05) = 1.38 k

Ω

Maximum Nodes

(3.3 · 1.1) + 25·(0.47 · 1.1) = 16.55 nF (1.5 · 0.95) || (10.6 · 0.95) / 25 = 314

Ω