PCA9517 电平转换 I2C 总线中继器

This dual bidirectional I2C buffer is operational at 2.7 V to 5.5 V.

The PCA9517 is a BiCMOS integrated circuit intended for I2C bus and SMBus systems. It can also provide bidirectional voltage-level translation (up-translation/down-translation) between low voltages (down to 0.9 V) and higher voltages (2.7 V to 5.5 V) in mixed-mode applications. This device enables I2C and similar bus systems to be extended, without degradation of performance even during level shifting.

The PCA9517 buffers both the serial data (SDA) and the serial clock (SCL) signals on the I2C bus, thus allowing two buses of 400-pF bus capacitance to be connected in an I2C application. This device can also be used to isolate two halves of a bus for voltage and capacitance.

The PCA9517 has two types of drivers—A-side drivers and B-side drivers. All inputs and I/Os are overvoltage tolerant to 5.5 V, even when the device is unpowered (VCCB and/or VCCA = 0 V).

The B-side drivers operate from 2.7 V to 5.5 V and behave like the drivers in the PCA9515A. The output low level for this internal buffer is approximately 0.5 V, but the input voltage must be 70 mV or more below the output low level when the output internally is driven low. The higher-voltage low signal is called a buffered low. When the B-side I/O is driven low internally, the low is not recognized as a low by the input. This feature prevents a lockup condition from occurring when the input low condition is released.

This type of design on the B side prevents it from being used in series with the PCA9515A and another PCA9517 (B side). This is because these devices do not recognize buffered low signals as a valid low and do not propagate it as a buffered low again.

The A-side drivers operate from 0.9 V to 5.5 V and drive more current. They do not require the buffered low feature (or the static offset voltage). This means that a low signal on the B side translates to a nearly 0-V low on the A side, which accommodates smaller voltage swings of lower-voltage logic. The output pulldown on the A side drives a hard low, and the input level is set at 0.3 VCCA to accommodate the need for a lower low level in systems where the low-voltage-side supply voltage is as low as 0.9 V.

The A side of two or more PCA9517s can be connected together to allow a star topography, with the A side on the common bus. Also, the A side can be connected directly to any other buffer with static- or dynamic-offset voltage. Multiple PCA9517s can be connected in series, A side to B side, with no buildup in offset voltage and with only time-of-flight delays to consider.

The PCA9517 drivers are enabled when VCCA is above 0.8 V and VCCB is above 2.5 V.

The PCA9517 has an active-high enable (EN) input with an internal pullup to VCCB, which allows the user to select when the repeater is active. This can be used to isolate a badly behaved slave on power-up reset. It should never change state during an I2C operation, because disabling during a bus operation hangs the bus, and enabling part way through a bus cycle could confuse the I2C parts being enabled. The EN input should change state only when the global bus and repeater port are in an idle state, to prevent system failures.

The PCA9517 includes a power-up circuit that keeps the output drivers turned off until VCCB is above 2.5 V and the VCCA is above 0.8 V. VCCB and VCCA can be applied in any sequence at power up. After power up and with the EN high, a low level on the A side (below 0.3 VCCA) turns the corresponding B-side driver (either SDA or SCL) on and drives the B side down to approximately 0.5 V. When the A side rises above 0.3 VCCA, the B-side pulldown driver is turned off and the external pullup resistor pulls the pin high. When the B side falls first and goes below 0.3 VCCB, the A-side driver is turned on and the A side pulls down to 0 V. The B-side pulldown is not enabled unless the B-side voltage goes below 0.4 V. If the B-side low voltage does not go below 0.5 V, the A-side driver turns off when the B-side voltage is above 0.7 VCCB. If the B-side low voltage goes below 0.4 V, the B-side pulldown driver is enabled, and the B side is able to rise to only 0.5 V until the A side rises above 0.3 VCCA. Then the B side continues to rise, being pulled up by the external pullup resistor. VCCA is only used to provide the 0.3 VCCA reference to the A-side input comparators and for the power-good-detect circuit. The PCA9517 logic and all I/Os are powered by the VCCB pin.

As with the standard I2C system, pullup resistors are required to provide the logic-high levels on the buffered bus. The PCA9517 has standard open-collector configuration of the I2C bus. The size of these pullup resistors depends on the system, but each side of the repeater must have a pullup resistor. The device is designed to work with Standard mode and Fast mode I2C devices in addition to SMBus devices. Standard mode I2C devices only specify 3 mA in a generic I2C system, where Standard mode devices and multiple masters are possible. Under certain conditions, higher termination currents can be used.

PCA9517
VCC(Min)(V) 0.9  
VCC(Max)(V) 5.5  
Technology Family PCA  
Pin/Package 8MSOP, 8SOIC  
Max Frequency(kHz) 400  
Vcc range(V) 0.9 to 5.5  
Channel Width 2  
Master Side I2C Bus Capacitance Supported(pF) 400  
Slave Side I2C Bus Capacitance Supported(pF) 400  
5V Tolerant I/O Yes  
Open–Drain I/O Type Yes  
Enable Pin Yes
PCA9517 特性
PCA9517 芯片订购指南
器件 状态 温度 价格 封装 | 引脚 封装数量 | 封装载体 丝印标记
PCA9517D ACTIVE -40 to 85 1.90 | 1ku SOIC (D) | 8 75 | TUBE  
PCA9517DG4 ACTIVE -40 to 85 1.90 | 1ku SOIC (D) | 8 75 | TUBE  
PCA9517DGKR ACTIVE -40 to 85 1.60 | 1ku MSOP (DGK) | 8 2500 | LARGE T&R  
PCA9517DGKRG4 ACTIVE -40 to 85 1.60 | 1ku MSOP (DGK) | 8 2500 | LARGE T&R  
PCA9517DR ACTIVE -40 to 85 1.60 | 1ku SOIC (D) | 8 2500 | LARGE T&R  
PCA9517DRG4 ACTIVE -40 to 85 1.60 | 1ku SOIC (D) | 8 2500 | LARGE T&R  
PCA9517 质量与无铅数据
器件 环保计划* 铅/焊球涂层 MSL 等级/回流焊峰 环保信息与无铅 (Pb-free) DPPM / MTBF / FIT 率
PCA9517D Green (RoHS & no Sb/Br)  CU NIPDAU  Level-1-260C-UNLIM PCA9517D PCA9517D
PCA9517DG4 Green (RoHS & no Sb/Br)  CU NIPDAU  Level-1-260C-UNLIM PCA9517DG4 PCA9517DG4
PCA9517DGKR Green (RoHS & no Sb/Br)  CU NIPDAU  Level-1-260C-UNLIM PCA9517DGKR PCA9517DGKR
PCA9517DGKRG4 Green (RoHS & no Sb/Br)  CU NIPDAU  Level-1-260C-UNLIM PCA9517DGKRG4 PCA9517DGKRG4
PCA9517DR Green (RoHS & no Sb/Br)  CU NIPDAU  Level-1-260C-UNLIM PCA9517DR PCA9517DR
PCA9517DRG4 Green (RoHS & no Sb/Br)  CU NIPDAU  Level-1-260C-UNLIM PCA9517DRG4 PCA9517DRG4
PCA9517 应用技术支持与电子电路设计开发资源下载
  1. PCA9517 数据资料 dataSheet 下载.PDF
  2. TI 德州仪器I2C 逻辑器件产品选型与价格 . xls
  3. Logic Guide 2009 (PDF 4263 KB)
  4. Shelf-Life Evaluation of Lead-Free Component Finishes (PDF 1305 KB)
  5. Understanding and Interpreting Standard-Logic Data Sheets (PDF 857 KB)
  6. TI IBIS File Creation, Validation, and Distribution Processes (PDF 380 KB)
  7. Implications of Slow or Floating CMOS Inputs (PDF 101 KB)
  8. CMOS Power Consumption and CPD Calculation (PDF 89 KB)
  9. Designing With Logic (PDF 186 KB)
  10. Live Insertion (PDF 150 KB)
  11. Input and Output Characteristics of Digital Integrated Circuits (PDF 1708 KB)
  12. Using High Speed CMOS and Advanced CMOS in Systems With Multiple Vcc (PDF 43 KB)
  13. HiRel Unitrode Power Management Brochure (PDF 206 KB)
  14. LOGIC Pocket Data Book (PDF 6001 KB)
  15. HiRel Unitrode Power Management Brochure (PDF 206 KB)
  16. Logic Cross-Reference (PDF 2938 KB)
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