ISOW784x High-Performance, 5000-VRMS Reinforced Quad-Channel Digital Isolators With Integrated High-Efficiency, Low-Emissions DC-DC Converter (Rev. D)
SLLSEY2D – March2017 – revisedNovember 2017
UNLESS OTHERWISE NOTED, this document contains PRODUCTION DATA.
10 Application and Implementation
Information in the following applications sections is not part of the TI component specification, and TI does not warrant its accuracy or completeness. TI’s customers are responsible for determining suitability of components for their purposes. Customers should validate and test their design implementation to confirm system functionality.
10.1 Application Information
The ISOW784x devices are high-performance, quad channel digital isolators with integrated DC-DC converter. Typically digital isolators require two power supplies isolated from each other to power up both sides of device. Due to the integrated DC-DC converter in ISOW784x, the isolated supply is generated inside the device that can be used to power isolated side of the device and peripherals on isolated side, thus saving board space. The ISOW784x devices use single-ended CMOS-logic switching technology. When designing with digital isolators, keep in mind that because of the single-ended design structure, digital isolators do not conform to any specific interface standard and are only intended for isolating single-ended CMOS or TTL digital signal lines. The isolator is typically placed between the data controller (that is Microcontroller or UART), and a data converter or a line transceiver, regardless of the interface type or standard.
ISOW784x devices are suitable for applications that have limited board space and desire more integration. These devices are also suitable for very high voltage applications, where power transformers meeting the required isolation specifications are bulky and expensive.
10.2 Typical Application
| ||For step-by-step design procedure, circuit schematics, bill of materials, printed circuit board (PCB) files, simulation results, and test results, refer to TI Design TIDA-01333, Eight-Channel, Isolated, High-Voltage Analog Input Module With ISOW7841 Reference Design.|
Figure 36 shows the typical schematic for SPI isolation.
10.2.1 Design Requirements
To design with this device, use the parameters listed in Table 4.
Table 4. Design Parameters
|Input voltage||3 V to 5.5 V|
|Decoupling capacitor between VCC and GND1||0.1 µF to 10 µF|
|Decoupling capacitor between VISO and GND2||0.1 µF to 10 µF|
Because of very-high current flowing through the ISOW7841 VCC and VISO supplies, higher decoupling capacitors typically provide better noise and ripple performance. Although a 10-µF capacitor is adequate, higher decoupling capacitors (such as 47 µF) on both the VCC and VISO pins to the respective grounds are strongly recommended to achieve the best performance.
10.2.2 Detailed Design Procedure
The ISOW784x family of devices only requires external bypass capacitors to operate. These low-ESR ceramic bypass capacitors must be placed as close to the chip pads as possible.
The VCC power-supply input provides power to isolated data channels and to the isolated DC-DC converter. Use Equation 1 to calculate the total power budget on the primary side.
- ICC is the total current required by the primary supply.
- VISO is the isolated supply voltage.
- IISO is the external load on the isolated supply voltage.
- η is the efficiency.
- VCC is the supply voltage.
- Iinpx is the total current drawn for the isolated data channels and power converter when data channels are toggling at a specific data rate. This data is shown in the Electrical Characteristics—5-V Input, 5-V Output table.
10.2.3 Application Curve
|VCC = 3.3 V||IISO = 70 mA|
|Input current spike is because of charging the input supply decoupling capacitor|
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