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전자부품 데이터시트 검색엔진 |
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전자부품 데이터시트 검색엔진 |
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CPC5002GSTR 데이터시트(PDF) 10 Page - IXYS Corporation |
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CPC5002GSTR 데이터시트(HTML) 10 Page - IXYS Corporation |
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10 / 14 page  INTEGRATED CIRCUITS DIVISION 10 www.ixysic.com R01 CPC5002 4.2 Application Example Shown below is an example of an isolated POE Controller SMBus where the SDA signal has been split into separate SDAIN and SDOUT signals on the isolated slave side of the barrier. In this example, the low power SMBus master, not shown, requires a buffer (U3) capable of driving the CPC5002 input LEDs. Although selection of the appropriate buffer is determined by the product definition and the ability to drive the LED’s, it is recommended the buffer have Schmitt trigger inputs to ensure clean bounce-free LED drive signals. A high power SMBus master with the ability to sink 4mA of pullup current may not require a buffer to drive the CPC5002 inputs. In this example, the POE Controllers are specified as SMBus high power and I2C compatible. This enables the POE Controllers to drive the CPC5002 LEDs directly without the need of an external buffer. Circuit design of the SMBus physical layer using the CPC5002 consists of two parts, one being the LED input drive current and the other being the buffered galvanically isolated logic output signals. The following design constraints are assumed for this example: • Supply Voltages: VDDx = 3.0V to 3.6V • Ambient Temperature: TA = 0°C to 70°C • VOL 0.4V for U3 and the POE Controllers • IOL 4mA for U3 and the POE Controllers • Resistors: • Tolerance = 1% • Temperature Coefficient = 100ppm Figure 3. Optically isolated SMBus for POE Controllers with Separate SDAIN and SDAOUT Pins To minimize pulse width distortion of the output signal, the input LED drive current needs to be set at the lower end of it’s operational range. Because the forward voltage of the LED has a negative temperature coefficient this will occur at the minimum operating temperature point with the minimum supply voltage. With VDD = 3.0V and VF = 1.442V at TA = 0°C and IF = 1.4mA, the calculated maximum value for the series input resistor RS is 826.8. Taking tolerance and value change due to temperature into account, the nearest E96 standard value sets RS = 806. Using VOL_Nominal = 0.25V and VOL_Minimum = 0.1V and calculating for the LED current range over the specified operating conditions with RS = 806, the LED input current IF will be 1.455mA to 3.212mA. At nominal operating conditions with TA = 25°C, the nominal LED input current is: IF_Nominal = 2.28mA. SCL M SDA M INT M SCL SDA IN SDA OUT SMBus POE Controllers 1 2 3 4 8 7 6 5 CPC5002 3.3V DDS 3.3V DDS 3.3V DDS 3.3V DDS GND M GND S 3.3V DDM 3.3V DDM 3.3V DDM 1 2 3 4 8 7 6 5 CPC5002 R1 806 Ω 3.3V DDM 3.3V DDM GND S GND M 3.3V DDS 3.3V DDS 3.3V DDS 3.3V DDS 0.1 μF 0.1 μF 0.1 μF 0.1 μF 3.3V DDM U3 U1 R2 806 Ω U2 R3 806 Ω R4 806 Ω R9* R10* INT SCL SDA IN SDA OUT INT R9 and R10 are not required for this design. See text for explanation. * R6 511 Ω R5 511 Ω R7 10k R8 10k |
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