UM3212
Dual bidirectional I2C-bus and SMBus voltage-level translator
UM3212M8 MSOP8
UM3212DA DFN8 2.1×1.6
General Description
The UM3212 is a dual bidirectional I2C-bus and SMBus voltage-level translator with an
enable(EN) input, and is operational from 1.0 V to 3.6 V (Vref(1)) and 1.8 V to 5.5 V(Vbias(ref)(2)).
The UM3212 allows bidirectional voltage translations between 1.0 V and 5 V without the use of a
direction pin. The low ON-state resistance (Ron) of the switch allows connections to be made with
minimal propagation delay. When EN is HIGH, the translator switch is on, and the SCL1 and
SDA1 I/O are connected to the SCL2 and SDA2 I/O, respectively, allowing bidirectional data
flow between ports. When EN is LOW, the translator switch is off, and a high-impedance state
exists between ports.
The UM3212 is not a bus buffer which provides both level translation and physically isolates the
capacitance to either side of the bus when both sides are connected. The UM3212 only isolates
both sides when the device is disabled and provides voltage level translation when active.
The UM3212 can also be used to run two buses, one at 400 kHz operating frequency and the other
at 100 kHz operating frequency. If the two buses are operating at different frequencies, the 100
kHz bus must be isolated when the 400 kHz operation of the other bus is required. If the master is
running at 400 kHz, the maximum system operating frequency may be less than 400 kHz because
of the delays added by the translator.
As with the standard I2C-bus system, pull-up resistors are required to provide the logic HIGH
levels on the translator’s bus. The UM3212 has a standard open-collector configuration of the
I2C-bus. The size of these pull-up resistors depends on the system, but each side of the translator
must have a pull-up resistor. The device is designed to work with Standard-mode, Fast-mode and
Fast-mode Plus I2C-bus devices in addition to SMBus devices. The maximum frequency is
dependent on the RC time constant, but generally supports > 2 MHz.
When the SDA1 or SDA2 port is LOW, the clamp is in the ON-state and a low resistance
connection exists between the SDA1 and SDA2 ports. Assuming the higher voltage is on the
SDA2 port when the SDA2 port is HIGH, the voltage on the SDA1 port is limited to the voltage
set by VREF1. When the SDA1 port is HIGH, the SDA2 port is pulled to the drain pull-up supply
voltage (Vpu(D)) by the pull-up resistors. This functionality allows a seamless translation between
higher and lower voltages selected by the user without the need for directional control. The
SCL1/SCL2 channel also functions as the SDA1/SDA2 channel.
All channels have the same electrical characteristics and there is minimal deviation from one
output to another in voltage or propagation delay. This is a benefit over discrete transistor voltage
translation solutions, since the fabrication of the switch is symmetrical.
The translator provides excellent ESD protection to lower voltage devices, and at the same time
protects less ESD-resistant devices.
Applications
I2C, SMBus and SPI Level Translation
Low-Voltage ASIC Level Translation
Smart Card Readers
Cell-phone Cradles
Portable POS Systems
Low-Cost Serial Interfaces
Cell-Phones
GPS
Telecommunications Equipment
Portable Communication Devices
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http://www.union-ic.com Rev.03 Dec.2013 1/11
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