PCA9535: Difference with PCA9555

Jeffrey Lau

Prodigy 20 points

Part Number: PCA9535
Other Parts Discussed in Thread: PCA9555, , TCA9555, TCA9535

Tool/software:

Hi, there seems to be not much difference between PCA9535 and PCA9555 from the datasheet.

PCA9555 is recommended by IC vendor for hotplug support .

All the sideband signal from end device is connected to IO expander for isolation/safety purpose.

Is these 2 IO expander exchangeable?

What is the feature of this IO expander that aids in hotplug feature?

6 months ago

0 Clemens Ladisch 6 months ago

Guru 316940 points

The only difference is that the '55 has integrated pull-up resistors.

When you have pull-up/-down resistors, then the pin is in a defined state even if the other device is disconnected.

0 Tyler Townsend 6 months ago

TI__Mastermind 47748 points

Hi Jeffrey

CLemens is correct.

PCA9555 - internal 100kohm PU resistors on the IO's

PCA9535 - no internal PU resistors

I wanted to recommend the TCA9555 as the p2p drop in replacement to the PCA9555 as it has better cost, wider supply range, and can be used at fast mode (400kHz) I2C.

Regards,

Tyler

0 Jeffrey Lau 6 months ago in reply to Clemens Ladisch

Prodigy 20 points

Hi Clemens, thanks for the info.

is it safe to remove / insert the hotplug sidebands safety from this GPIO expander?

0 Jeffrey Lau 6 months ago in reply to Tyler Townsend

Prodigy 20 points

Thanks Tyler

May I know where do you found the 100kohm value? I could not spot it in the datasheet.

is it safe to remove / insert the hotplug sidebands safety from this GPIO expander?

0 Clemens Ladisch 6 months ago in reply to Jeffrey Lau

Guru 316940 points

See figure 8-2.

You need appropriate ESD/TVS protection on all lines that can be touched or are hotplugged.

What are the electrical characteristics (voltage, drive strength) of these sideband signals?

0 Tyler Townsend 6 months ago in reply to Jeffrey Lau

TI__Mastermind 47748 points

Hi Jeffrey,

Here is figure 23 from the TCA9555 datasheet:

Regards,

Tyler

0 Jeffrey Lau 6 months ago in reply to Clemens Ladisch

Prodigy 20 points

The voltage level is around 3.3V, it will be some logic high or low sideband signal

0 Tyler Townsend 6 months ago in reply to Jeffrey Lau

TI__Mastermind 47748 points

Hi Jeffrey,

What transients is the IO side expecting to face when hot-plugging the IO expander?

It might be best practice to include external ESD protection on the IO side if the transients are expected to exceed the maximum voltage input as listed in the datasheet:

If we expect a voltage spike from a hot-plug event to be >6V or < -0.5V, we need to clamp this voltage before it is seen by the IO expander, otherwise the IO port may have the potential of being damaged if the voltage exceeds the absolutely maximum ratings.

Regards,

Tyler

0 Woon Nee Tan 5 months ago

Prodigy 70 points

Hi,
Can I have difference power up sequence of 3.3V to PCA9555 and I2C pull up voltage rails ? as PCA9555 is used to support hot-pluggable IO to D1 and D2.
Can I have VCC rails powered up earlier than PCA9555 ?
Or, VCC, VDD1 and VDD2 can be powered up first, then hot-pluggable IO can be powered on later following to D1 and D2 ?

0 Tyler Townsend 5 months ago in reply to Woon Nee Tan

TI__Mastermind 47748 points

Hi Woon,

If using the PCA9555, there are internal 100k PU resistors from Pxx to VCC.

Say you power up VD1 and VD2 first, you will see back feeding into VDD1 and VDD2 power supplies.

IF you need this type of "hot swapping" capability, I would refer you to the TCA9535 which removes the internal 100k PU resistors.

The TCA9535 should be able to power sequence in any order. VCC can come up, then VDD1, then VD1.

Regards,

Tyler

0 Woon Nee Tan 5 months ago in reply to Tyler Townsend

Prodigy 70 points

Hi Tyler,

If change to TCA9535, it can support hot-pluggable of D1 and D2. Then I would power up VCC, VDD1, then VD1.

May I ask TCA9535 use 7-bit I2C address is 010X_XXXb ? and its addresses begin with the lowest address (0100000b) and increment
sequentially for each device ?

0 Tyler Townsend 5 months ago in reply to Woon Nee Tan

TI__Mastermind 47748 points

Hi Woon,

TCA9535 is p2p drop-in replacement upgrade to PCA9535.

The TCA9535 is the same or better in all specs.

It uses 7-bit i2c address too. Same software in terms of register map and fixed i2c address.

Regards,

Tyler

0 Woon Nee Tan 5 months ago in reply to Tyler Townsend

Prodigy 70 points

OK Thanks

0 Tyler Townsend 5 months ago in reply to Woon Nee Tan

TI__Mastermind 47748 points

Hi Woon,

Please let me know if you have any more questions.

If not, I will close the thread.

Regards,

Tyler

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PCA9535: Difference with PCA9555