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NLSX3012

2-Bit 100 Mb/s Configurable Dual-Supply Level Translator

ON Semiconductor 

NLSX3012

IMPORTANT APPLICATIONS INFORMATION

Level Translator Architecture

The NLSX3012 auto sense translator provides

bi−directional voltage level shifting to transfer data in

multiple supply voltage systems. This device has two

supply voltages, VL and VCC, which set the logic levels on

the input and output sides of the translator. When used to

transfer data from the VL to the VCC ports, input signals

referenced to the VL supply are translated to output signals

with a logic level matched to VCC. In a similar manner, the

VCC to VL translation shifts input signals with a logic level

compatible to VCC to an output signal matched to VL.

The NLSX3012 consists of four bi−directional channels

that independently determine the direction of the data flow

without requiring a directional pin. The one−shot circuits

are used to detect the rising or falling input signals. In

addition, the one shots decrease the rise and fall time of the

output signal for high−to−low and low−to−high transitions.

Input Driver Requirements

Auto sense translators such as the NLSX3012 have a

wide bandwidth, but a relatively small DC output current

rating. The high bandwidth of the bi−directional I/O circuit

is used to quickly transform from an input to an output

driver and vice versa. The I/O ports have a modest DC

current output specification so that the output driver can be

over driven when data is sent to in the opposite direction.

For proper operation, the input driver to the auto sense

translator should be capable of driving 2 mA of peak output

current with an output impedance less than 25 W. The

bi−directional configuration of the translator results in both

input stages being active for a very short time period.

Although the peak current from the input signal circuit is

relatively large, the average current is small and consistent

with a standard CMOS input stage.

Output Load Requirements

The NLSX3012 is designed to drive CMOS inputs.

Resistive pullup or pulldown loads of less than 50 kW

should not be used with this device. The NLSX3373 or

NLSX3378 open−drain auto sense translators are alternate

translator options for an application such as the I2C bus that

requires pullup resistors.

Enable Input (EN)

The NLSX3012 has an Enable pin (EN) that provides

tri−state operation at the I/O pins. Driving the Enable pin

to a low logic level minimizes the power consumption of

the device and drives the I/O VCC and I/O VL pins to a high

impedance state. Normal translation operation occurs

when the EN pin is equal to a logic high signal. The EN pin

is referenced to the VL supply and has Over−Voltage

Tolerant (OVT) protection.

Uni−Directional versus Bi−Directional Translation

The NLSX3012 can function as a non−inverting

uni−directional translator. One advantage of using the

translator as a uni−directional device is that each I/O pin

can be configured as either an input or output. The

configurable input or output feature is especially useful in

applications such as SPI that use multiple uni−directional

I/O lines to send data to and from a device. The flexible I/O

port of the auto sense translator simplifies the trace

connections on the PCB.

Power Supply Guidelines

It is recommended that the VL supply should be less than

or equal to the value of the VCC minus 0.4 V. The

sequencing of the power supplies will not damage the

device during the power up operation; however, the current

consumption of the device will increase if VL exceeds VCC

minus 0.4 V. In addition, the I/O VCC and I/O VL pins are

in the high impedance state if either supply voltage is equal

to 0 V.

For optimal performance, 0.01 to 0.1 mF decoupling

capacitors should be used on the VL and VCC power supply

pins. Ceramic capacitors are a good design choice to filter

and bypass any noise signals on the power supply voltage

lines to the ground plane of the PCB. The noise immunity

will be maximized by placing the capacitors as close as

possible to the supply and ground pins, along with

minimizing the PCB connection traces.

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