PCA9617A：低高压电平转换器，扩展I2C总线

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"PCA9617A 是一款CMOS集成电路，用于在低电压（0.8V到5.5V）和高电压（2.2V到5.5V）的Fast-mode Plus (Fm+) I²C总线或SMBus应用之间进行电平转换。它保留了I²C总线系统的所有操作模式和特性，同时提供数据线(SDA)和时钟线(SCL)的双向缓冲，使得总线在1MHz时能支持540pF的负载，或者在较低速度下支持高达4000pF的负载。PCA9617A允许系统设计者对电压和电容两个方面隔离总线的两半。SDA和SCL引脚具有过电压容忍能力，并在PCA9617A未供电时处于高阻态。" PCA9617A是一款关键的接口元件，主要用于解决不同电压域之间的通信问题。在I²C总线系统中，它能够确保低电压设备和高电压设备之间的兼容性。该器件的主要功能包括： 1. **电平转换**：PCA9617A能够在0.8V至5.5V的低电压系统与2.2V至5.5V的高电压系统之间转换信号，使得两种不同电压等级的设备可以相互通信，而不必担心电压不匹配导致的问题。 2. **双向缓冲**：PCA9617A提供了SDA和SCL线路上的双向缓冲，这增强了总线的驱动能力，使其能够在高速（如1MHz）或低速环境下支持较大的负载电容。这对于扩展I²C总线网络，连接更多设备至关重要。 3. **电压隔离**：通过PCA9617A，系统设计者可以将总线划分为两个独立的电压区域，每个区域可以有不同的电平标准，且不会相互干扰。这种隔离对于系统的稳定性和可靠性有显著提升。 4. **过电压保护**：SDA和SCL引脚设计为过电压容忍，即使在电源未开启的情况下，也能防止高电压信号对电路造成损害。这种特性增强了设备的安全性。 5. **静态偏置设计**：PCA9617A的Port B驱动器具有静态电压偏置，而可调电压的Port A驱动器则消除了静态偏移电压，使得Port B上的低电平信号可以转换为Port A上的早期0V低电平，适应更低电压逻辑的小幅电压摆动。 6. **防止互连问题**：Port B的PCA9617A输入/输出驱动器的设计防止了与其他总线缓冲器的静态或递增偏移连接，从而避免了潜在的信号质量下降或损坏。 PCA9617A是构建多电压环境下的I²C或SMBus系统中的关键组件，它的功能强大，能够确保系统的兼容性、稳定性和安全性。在设计需要跨越不同电压域的嵌入式系统时，PCA9617A是理想的解决方案之一。

Product data sheet Rev. 1 — 20 March 2013 5 of 23

NXP Semiconductors

PCA9617A

Level translating Fm+ I

C-bus repeater

6. Functional description

Refer to Figure 1 “Functional diagram of PCA9617A”.

The PCA9617A enables I

C-bus or SMBus translation down to V

CC(A)

as low as 0.8 V

without degradation of system performance. The PCA9617A contains two bidirectional

open-drain buffers specifically designed to support up-translation/down-translation

between the low voltage (as low as 0.8 V) and a 2.5 V, 3.3 V or 5 V I

C-bus or SMBus. All

inputs and I/Os are overvoltage tolerant to 5.5 V even when the device is unpowered

CC(B)

and/or V

CC(A)

= 0 V). The PCA9617A includes a power-up circuit that keeps the

output drivers turned off until V

CC(B)

is above 2.2 V and until after the internal reference

circuits have settled ~400 s, and the V

CC(A)

is above 0.8 V. V

CC(B)

and V

CC(A)

can be

applied in any sequence at power-up. After power-up and with the enable (EN) HIGH, a

LOW level on port A (below 0.3V

CC(A)

) turns the corresponding port B driver (either SDA

or SCL) on and drives port B down to about 0.55 V. When port A rises above 0.3V

CC(A)

the port B pull-down driver is turned off and the external pull-up resistor pulls the pin

HIGH. When port B falls first and goes below 0.4 V, the port A driver is turned on and

port A pulls down to ~0 V. The port A pull-down is not enabled unless the port B voltage

goes below 0.4 V. If the port B low voltage goes below 0.4 V, the port B pull-down driver is

enabled and port B will only be able to rise to 0.55 V until port A rises above 0.3V

CC(A)

then port B will continue to rise being pulled up by the external pull-up resistor. The V

CC(A)

is only used to provide the 0.35V

CC(A)

reference to the port A input comparators and for

the power good detect circuit. The PCA9617A includes a V

CC(A)

overvoltage disable that

turns the channel off if 0.4V

CC(A)

+0.8V>V

CC(B)

. The PCA9617A logic and all I/Os are

CC(B)

pin.

6.1 Enable

The EN pin is active HIGH with thresholds referenced to V

CC(B)

and an internal pull-up to

CC(B)

that maintains the device active unless the user selects to disable the repeater to

isolate a badly behaved slave on power-up until after the system power-up reset. It should

never change state during an I

C-bus operation because disabling during a bus operation

will hang the bus and enabling part way through a bus cycle could confuse the I

C-bus

parts being enabled. The enable does not switch the internal reference circuits so the

~400 s delay is only seen when V

CC(B)

comes up.

The enable pin should only change state when the global bus and the repeater port are in

an idle state to prevent system failures.

6.2 I

C-bus systems

As with the standard I

C-bus system, pull-up resistors are required to provide the logic

HIGH levels on the buffered bus (standard open-collector configuration of the I

C-bus).

The size of these pull-up resistors depends on the system, but each side of the repeater

must have a pull-up resistor. This part designed to work with Standard mode, Fast-mode

and Fast-mode Plus I

C-bus devices in addition to SMBus devices. Standard mode and

Fast-mode I

C-bus devices only specify 3 mA output drive; this limits the termination

current to 3 mA in a generic I

C-bus system where Standard-mode devices, Fast-mode

devices and multiple masters are possible. When only Fast-mode Plus devices are used

with 30 mA at 5 V drive strength, then lower value pull-up resistors can be used. The

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PCA9617A：低高压电平转换器，扩展I2C总线

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