LTC4331 datasheet(15/22 Pages) AD

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LT3960

Rev. B

For more information www.analog.com

Supply Voltage Ranges

The LT3960 can be operated with or without using its

internal LDO. Tying VIN to VCC and powering directly from

a 3.3V or 5V supply will bypass the LDO. With a 5V supply

on VCC, transmitter common-mode voltage and receiver

common-mode input range are increased from their 3.3V

values. In this configuration, an internal comparator mon-

itors the supply voltage and switches internal reference

voltages and output drive strengths at approximately

4.1V. Operation with a supply between 3.6V and 4.5V is

not recommended, because of the discontinuity in the

internal voltages at this switch point.

When using the internal LDO to generate the 3.3V bus

supply on VCC, any VIN supply voltage between 4V and

60V is allowed. In this configuration, the switch point

mentioned above is avoided since VCC is regulated to a

fixed 3.3V.

An LT3960 operating with a VCC at 5V may share an I2CAN

bus with an LT3960 operating with VCC at 3.3V. However,

the fluctuation in common mode voltage between 1.95V

(when an LT3960 with VCC = 3.3V is dominant) and

2.5V (when an LT3960 with VCC = 5V is dominant) may

increase electromagnetic emissions.

Master and Slave Mode Configurations

The LT3960 connected to the I2C master must be oper-

ated in Master Mode, with the EN/MODE pin driven greater

than 2.5V. When operating in Master Mode, it is recom-

mended that VCC be tied to VIN and driven from a bus

voltage of 3.3V or 5V. Additionally, EN/MODE should be

driven from a digital output pin from the I2C Master as

shown below. In this configuration, EN/MODE can be held

low until the VCC cap is fully charged.

Do not tie the EN/MODE pin directly to VCC when oper-

ating in Master Mode. With EN/MODE and VCC shorted,

every power-up sequence will set the LT3960 into slave

mode for many microseconds while the VCC capacitor

charges between the enable threshold and the Master

Mode threshold.

APPLICATIONS INFORMATION

Figure 9.

LT3960

VIN

VCC

3.3V OR 5V

BUS VOLTAGE

EN/MODE

I/O

µCONTROLLER

30k

2.2µF

3960 F09

Recommended Master Mode Power Setup

An LT3960 connected to slave I2C devices must be oper-

ated in Slave Mode, with the EN/MODE pin between 0.7V

and 2V. When left floating, the EN/MODE pin will pull

up to approximately 1.2V, enabling the LT3960 and set-

ting it in Slave Mode, whenever the VIN pin is powered

above approximately 2V. It is recommended that the EN/

MODE pin be left floating for Slave Mode LT3960 devices,

regardless of whether the internal LDO is employed.

LT3960 and Standard CAN Transceivers

It should be noted that while the LT3960 uses the CAN

physical layer to conduct bidirectional I2C data, the

CANSCL and CANSDA buses created by the LT3960 are

not traditional CAN buses carrying traditional CAN data. As

such, the CANSCL and CANSDA buses between LT3960

devices cannot be shared with standard CAN transceivers

in a multidrop configuration.

±40V Fault Protection

The LT3960 provides ±40V fault protection on the

I2CAN interface pins (CANSCLH, CANSCLL, CANSDAH,

CANSDAL), allowing I2C communication in applications

where it was previously impractical. Addressing the need

the overvoltage tolerance in many industrial and auto-

motive applications, the driver outputs use a progressive

foldback current limit to protect against overvoltage faults

while still allowing high current output drive. The LT3960

is protected from ±40V faults powered or unpowered,

even in the case of VCC open or shorted to ground. When

VCC is open or shorted to GND, the transceivers are off and

the I2CAN bus pins remain in the high impedance state.

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