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2014-01-0006 PT0475-1 02/18/14
8
PI4ULS3V502
280Mb/s Bi-directional Level Translator
for Push-Pull Applications
Functional Description
The PI4ULS3V502 is a 2-bit configurable dual-supply autosensing bidirectional level translator that does not require a
direction control pin. The B and A ports are designed to track two different power supply rails, VCCB and VCCA respectively.
The PI4ULS3V502 offers the feature that the values of the VCCB and VCCA supplies are independent. Design flexibility is
maximized because VCCA can be set to a value either greater than or less than the VCCB supply.
The PI4ULS3V502 has high output current capability, which allows the translator to drive high capacitive loads such as most
high frequency EMI filters. Another feature of the PI4ULS3V502 is that each An and Bn channel can function as either an input or
an output.
An Output Enable (EN) input is available to reduce the power consumption. The EN pin can be used to disable both I/O ports
by putting them in 3-state which significantly reduces the supply current.
Application Information
Level Translator Architecture
The PI4ULS3V502 auto-sense translator provides bi-directional logic voltage level shifting to transfer data in multiple supply
voltage systems. These level translators have two supply voltages, V
CCA
and VCCB, which set the logic levels on the input and
output sides of the translator. When used to transfer data from the I/O VCCA to the I/O VCCB ports, input signals referenced to
the VCCA supply are translated to output signals with a logic level matched to VCCB. In a similar manner, the I/O VCCB to I/O
VCCA translation shifts input signals with a logic level compatible to VCCB to an output signal matched to VCCA. The
PI4ULS3V502 translator consists of bi-directional channels that independently determine the direction of the data flow without
requiring a directional pin. One-shot circuits are used to detect the rising or falling input signals. In addition, the one-shots
decrease the rise and fall times of the output signal for high-to-low and low-to-high transitions.
Input Driver Requirements
Auto-sense translators such as the PI4ULS3V502 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 in the
opposite direction. For proper operation, the input driver to the auto−sense translator should be capable of driving 3mA of peak
output current. 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. Enable Input (EN) The PI4ULS3V502 translator 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 VCCB and I/O VCCA 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 VCCA supply and has Over-Voltage Tolerant (OVT) protection.
Uni-Directional versus Bi-Directional Translation
The PI4ULS3V502 translator 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
The values of the VCCA and VCCB supplies can be set to anywhere in range 0.85-2.7V and 1.35-3.6V. Design flexibility is
maximized because VCCA may be either greater than or less than the VCCB supply. In contrast, the majority of the competitive
auto sense translators have a restriction that the value of the VCCA supply must be equal to less than (VCCB - 0.4) V. The
sequencing of the power supplies will not damage the device during power-up operation. In addition, the I/O VCCB and I/O
VCCA pins are in the high impedance state if either supply voltage is equal to 0V. For optimal performance, 0.01 to 0.1μ F
decoupling capacitors should be used on the VCCA and VCCB power supply pins. Ceramic capacitors are a good design choice to
filter and bypass any noise signals on the 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. The
PI4ULS3V502 translators have a power down feature that provides design flexibility. The output ports are disabled when either
power supply is off (VCCA or VCCB = 0V). This feature causes all of the I/O pins to be in the power saving high impedance state.
