LLC-I2C Click
PID: MIKROE‐3276
Weight: 24 g
LLC I2C click can be utilized as the level converter for logic signals, which
makes it a very useful Click board™. The topology of this logic level
conversion (LLC) circuit is perfectly suited for the bi-directional I2C
communication. Although there are some specialized integrated circuits on
the market, sometimes it is more convenient to have a simple solution made
of just a few passive elements and four MOSFETs. Besides this, MOSFETs
can withstand up to 20V across their terminals (12V VGS), and they support
far greater currents than typical ICs, making them less likely to fail. The LLC
circuitry, also known as the level translator or level shifter, can be used in
virtually any application that utilizes the I2C communication protocol and
needs matching between the logic voltage levels.
It comes in the package which also includes the mikroSDK™ software and a
library with all the functions. The Click board™ comes as a fully tested and
approved prototype, making it a reliable device ready to use on the
development board.
How does it work?
LLC I2C click does not use an integrated circuit, as already mentioned. With
ICs avoided completely, there are some benefits gained: the overall cost of
the LLC circuit is greatly reduced, a more robust MOSFET solution reduces
the failure rate, and when powered off, both the low voltage and the high
voltage sides are isolated from one another (by non-conductive MOSFETs).
This type of circuit is sometimes referred to as a level shifting or level
translating circuit and it is often necessary when the I2C slave device
(typically a sensor IC) uses different logic voltage levels for the I2C
communication than the master device, which is a host microcontroller in
most cases. The conversion of this circuitry is bi-directional, which makes it
suitable to be used with the I2C communication protocol.
The I2C protocol was first introduced by NXP Semiconductors (formerly
Philips Semiconductors), in 1982. They also introduced an application note
that explains the operation of the LLC circuit in more details. The circuit is
divided into low‐side and high‐side sections for future reference, although the
circuit is symmetrical and can be used in both directions.
When there is no communication going on, both gates and sources of the
MOSFETs are pulled up to their specific reference voltage levels. This will
turn OFF both MOSFETs since there is no gate-source voltage difference
(e.g. VG=VS=VSL).
Since the I2C is operated by asserting its bus lines to a LOW logic level,
when the source terminal of the MOSFET on one side (e.g. high-side) is
driven to a LOW logic level, its VGS potential will rise since the gate voltage is
fixed. When the VGS reaches the threshold voltage (1.2V typically for the used
transistors), the MOSFET will turn ON, conducting current through the body
diode of the opposite-side (low-side) MOSFET, which will become directly
polarized. This mechanism can be used to convert signal levels in both
directions, within the whole operating range of the used MOSFETs.
The reference voltage for the high-side can be selected by using the SMD
jumper labeled as VCC SEL. The pull-up voltage for the high-side can be
selected from the mikroBUS™ power rails, so it can be either 3.3V or 5V. For
the low-side, an arbitrary reference voltage can be applied to the VSL pin of
the J1 header, respecting the maximum voltage rating. J1 is the standard,
2.54mm pin-header. The low-side I2C bus pins are also routed to the J1
header, allowing an external device to be connected (using the standard
wire-jumpers). As already mentioned, the low-side can actually use higher
voltage levels than the master, but in most usage scenarios, it will be lower
than the master, thus the terminology.
Specifications
Type
Port expander
Applications
I2C logic level conversion circuit has its use in many different
projects. It is used for the I2C logic voltage level matching
between the slave and the master device
Key Features
Very low cost achieved using only passive elements, and four
MOSFETs, ability to use an arbitrary voltage level conversion in the
range from 1.2V up to 10V
Interface
I2C
Input
Voltage
3.3V or 5V
Click board
size
M (42.9 x 25.4 mm)
Pinout diagram
This table shows how the pinout on LLC I2C Click corresponds to the pinout on
the mikroBUS™ socket (the latter shown in the two middle columns).
Notes
Pin
Pin
Notes
NC
1
AN
PWM
16
NC
NC
2
RST
INT
15
NC
NC
3
CS
RX
14
NC
NC
4
SCK
TX
13
NC
NC
5
MISO
SCL
12
SCL
I2C Clock
NC
6
MOSI
SDA
11
SDA
I2C Data
Power supply
3V3
7
3.3V
5V
10
5V
Ground
GND
8
GND
GND
9
GND
Power supply
Ground
Onboard settings and indicators
Label
Name
Default
Description
PWR
PWR
-
Power LED indicator
VCC
SEL
VCC SEL
Left
Logic voltage level selection (master): left
position 3.3V, right position 5V
J1
-
-
I2C bus with the converted voltage levels (I2C
slave)
Software support
We provide a library for the LLC I2C click on our LibStock page, as well as a
demo application (example), developed using MikroElektronika compilers.
The demo can run on all the main MikroElektronika development boards.
Library Description
The library contains functions for starting, writing data to I2C wires and
reading data from I2C wires.
Key functions:
void i2cllc_start() - The function executes start condition on I2C wires.
void i2cllc_write(uint8_t slaveAddress, uint8_t *pBuf, uint16_t nBytes, uint8_t
endMode) - The function should execute write sequence on I2C wires.
void i2cllc_read(uint8_t slaveAddress, uint8_t *pBuf, uint16_t nBytes, uint8_t
endMode) - The function should execute read sequence on I2C wires.
Examples description
The application is composed of the three sections :
System Initialization - Initializes I2C module
Application Initialization - Initialization driver init
Application Task - (code snippet) - Reads the temperature from the Thermo 7 click board and
logs data to UART.
Note: The start configuration chip is required at the beginning of each
program so that the chip wakes up and prepares for operation and
measurement. What is included and set in the start-up function can be
viewed in the help file.
void applicationTask()
{
// Thermo 7 measurement Temperature
uint8_t writeReg[ 1 ];
uint8_t readReg[ 2 ] = {0};
float Temp_msb;
uint8_t Temp_lsb;
char tempText[ 50 ];
writeReg[ 0 ] = 0x00;
i2cllc_start();
i2cllc_write( 0x48, &writeReg[0], 1, _I2CLLC_END_MODE_RESTART );
i2cllc_read( 0x48, &readReg[0], 2, _I2CLLC_END_MODE_STOP );
Temp_msb = readReg[ 0 ];
Temp_lsb = readReg[ 1 ] & 0xF0;
if( temp_lsb & 0x80 ) Temp_msb += 0.50;
if( temp_lsb & 0x40 ) Temp_msb += 0.25;
if( temp_lsb & 0x20 ) Temp_msb += 0.125;
if( temp_lsb & 0x10 ) Temp_msb += 0.0625;
FloatToStr(Temp_msb, tempText);
mikrobus_logWrite(" Ambient temperature : ", _LOG_TEXT );
mikrobus_logWrite(tempText, _LOG_TEXT);
mikrobus_logWrite(" C", _LOG_LINE);
Delay_ms( 1000 );
}
The full application code, and ready to use projects can be found on
our LibStock page.
Other mikroE Libraries used in the example:
I2C
Additional notes and information
Depending on the development board you are using, you may need USB UART
click, USB UART 2 click or RS232 click to connect to your PC, for development
systems with no UART to USB interface available on the board. The terminal
available in all MikroElektronika compilers, or any other terminal application
of your choice, can be used to read the message.
mikroSDK
This click board is supported with mikroSDK - MikroElektronika Software
Development Kit. To ensure proper operation of mikroSDK compliant click
board demo applications, mikroSDK should be downloaded from
the LibStock and installed for the compiler you are using.
For more information about mikroSDK, visit the official page.
https://www.mikroe.com/llc‐i2c‐click/1‐2‐19
