“IO-Link is a communication standard for the point-to-point three-wire interface of smart sensors and actuators in industrial applications. IO-Link extends the traditional interface capabilities of these devices from a simple NC/NO switch interface (standard IO or SIO mode) to a bidirectional smart interface capable of kb/s or COM3 – 230.4kb/s) to transmit additional information.
“
IO-Link is a communication standard for the point-to-point three-wire interface of smart sensors and actuators in industrial applications. IO-Link extends the traditional interface capabilities of these devices from a simple NC/NO switch interface (standard IO or SIO mode) to a bidirectional smart interface capable of kb/s or COM3 – 230.4kb/s) to transmit additional information. In addition to the data pins (C/Q), the IO-Link Type A interface has a 24VDC power supply pin (L+) and a common return pin (LC).
When an IO-Link master is powered up, it interrogates each connected device to determine the correct operating mode for each device: SIO, COM1, COM2 or COM3. This allows older legacy devices and devices that support the IO-Link standard to work seamlessly in the same system.
The LTC2874 has a CQ output current rating of 110mA. Higher currents up to 440mA can be achieved by paralleling multiple channels. Although this exceeds the specification limits of the IO-Link standard, some non-standard SIO applications may require higher current supply and/or must maintain the functionality of 4 independent channels. This article will show how to repurpose the LTC2874’s hot-swap channels to deliver higher current to SIO loads (known as SIO+ mode) while maintaining the LTC2874’s IO-Link features and functionality.
circuit description
An arbitrarily large supply current can be provided in SIO+ mode by connecting the channel’s hot-swap controller output to its corresponding CQ pin, as shown in Port 1C3 in Figure 1. For high current ports, the hot-swap capability of the L+ is not available; however, for applications that desire this capability, an external hot-swap controller can be added. As shown at port 4 in Figure 1, the LTC2874 hot-swap controller not used for the SIO output can be used for normal L+ or other use.
In normal IO-Link or SIO operation, the L+ MOSFET is turned off and the CQ output operates normally through TXEN, TXD and RXD. All IO-Link functionality is maintained, including full-speed communication at COM3 speed and wake-up pulse generation.
During SIO+ operation, the L+ MOSFET is controlled through the SPI register interface and CQ is disabled (TXEN is low or under SPI register control). The upper nibble of Register 0xE controls the L+ MOSFET. In SIO+ mode, the switching frequency is limited to approximately COM1 speed.
While the LTC2874 will not be damaged if both the CQ and L+ outputs are running, this mode of operation is not recommended because the output waveform’s rising and falling trajectories are non-monotonic. These traces appear due to timing differences between channels and the interaction of various current limits and source resistances.
The maximum output current in SIO+ mode is determined by the choice of MOSFET and sense resistor RS. The current limit is set by 50mV/RS. The typical current limit for the circuit in Figure 1 is 500mA. Taking into account tolerances and variations, a port rated output current of 400mA results. The proper MOSFET must be selected to handle the voltage, current and safe operating area (SOA) requirements. See the LTC2874 data sheet for more details.
The output capacitance of the MOSFET contributes about 60pF to the 1nF maximum allowed by the IO-Link standard.
Since the circuit has two drivers in parallel, the idle driver acts as a capacitive load on the active driver. When the active driver changes state, it will generate a charging current in the idle driver. This effect is more pronounced during IO-Link operation due to the larger capacitance of the MOSFET and the faster edge rate of the CQ driver. To prevent ringing of the charge current pulse when the active driver is turned off, the parasitic inductance between the MOSFET source and the C/Q driver output should be minimized.
Figures 2 and 3 show the operating waveforms when a single port supporting SIO+ mode drives a resistive load while operating in either SIO+ or normal IO-Link mode. The supply voltage is 24V, and the resistive loads are 56Ω and 200Ω, respectively.
in conclusion
Operating the LTC2874 in SIO+ mode Arbitrarily large currents can be obtained by repurposing the hot-swap channels as higher current SIO drivers.
“IO-Link is a communication standard for the point-to-point three-wire interface of smart sensors and actuators in industrial applications. IO-Link extends the traditional interface capabilities of these devices from a simple NC/NO switch interface (standard IO or SIO mode) to a bidirectional smart interface capable of kb/s or COM3 – 230.4kb/s) to transmit additional information.
“
IO-Link is a communication standard for the point-to-point three-wire interface of smart sensors and actuators in industrial applications. IO-Link extends the traditional interface capabilities of these devices from a simple NC/NO switch interface (standard IO or SIO mode) to a bidirectional smart interface capable of kb/s or COM3 – 230.4kb/s) to transmit additional information. In addition to the data pins (C/Q), the IO-Link Type A interface has a 24VDC power supply pin (L+) and a common return pin (LC).
When an IO-Link master is powered up, it interrogates each connected device to determine the correct operating mode for each device: SIO, COM1, COM2 or COM3. This allows older legacy devices and devices that support the IO-Link standard to work seamlessly in the same system.
The LTC2874 has a CQ output current rating of 110mA. Higher currents up to 440mA can be achieved by paralleling multiple channels. Although this exceeds the specification limits of the IO-Link standard, some non-standard SIO applications may require higher current supply and/or must maintain the functionality of 4 independent channels. This article will show how to repurpose the LTC2874’s hot-swap channels to deliver higher current to SIO loads (known as SIO+ mode) while maintaining the LTC2874’s IO-Link features and functionality.
circuit description
An arbitrarily large supply current can be provided in SIO+ mode by connecting the channel’s hot-swap controller output to its corresponding CQ pin, as shown in Port 1C3 in Figure 1. For high current ports, the hot-swap capability of the L+ is not available; however, for applications that desire this capability, an external hot-swap controller can be added. As shown at port 4 in Figure 1, the LTC2874 hot-swap controller not used for the SIO output can be used for normal L+ or other use.
In normal IO-Link or SIO operation, the L+ MOSFET is turned off and the CQ output operates normally through TXEN, TXD and RXD. All IO-Link functionality is maintained, including full-speed communication at COM3 speed and wake-up pulse generation.
During SIO+ operation, the L+ MOSFET is controlled through the SPI register interface and CQ is disabled (TXEN is low or under SPI register control). The upper nibble of Register 0xE controls the L+ MOSFET. In SIO+ mode, the switching frequency is limited to approximately COM1 speed.
While the LTC2874 will not be damaged if both the CQ and L+ outputs are running, this mode of operation is not recommended because the output waveform’s rising and falling trajectories are non-monotonic. These traces appear due to timing differences between channels and the interaction of various current limits and source resistances.
The maximum output current in SIO+ mode is determined by the choice of MOSFET and sense resistor RS. The current limit is set by 50mV/RS. The typical current limit for the circuit in Figure 1 is 500mA. Taking into account tolerances and variations, a port rated output current of 400mA results. The proper MOSFET must be selected to handle the voltage, current and safe operating area (SOA) requirements. See the LTC2874 data sheet for more details.
The output capacitance of the MOSFET contributes about 60pF to the 1nF maximum allowed by the IO-Link standard.
Since the circuit has two drivers in parallel, the idle driver acts as a capacitive load on the active driver. When the active driver changes state, it will generate a charging current in the idle driver. This effect is more pronounced during IO-Link operation due to the larger capacitance of the MOSFET and the faster edge rate of the CQ driver. To prevent ringing of the charge current pulse when the active driver is turned off, the parasitic inductance between the MOSFET source and the C/Q driver output should be minimized.
Figures 2 and 3 show the operating waveforms when a single port supporting SIO+ mode drives a resistive load while operating in either SIO+ or normal IO-Link mode. The supply voltage is 24V, and the resistive loads are 56Ω and 200Ω, respectively.
in conclusion
Operating the LTC2874 in SIO+ mode Arbitrarily large currents can be obtained by repurposing the hot-swap channels as higher current SIO drivers.
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