AM26C31: AM26C31 can works on 3.3V VCC

Yee Wilson

Part Number: AM26C31
Other Parts Discussed in Thread: AM26LV31E-EP, AM26LV32E-EP, AM26LV31, AM26LS31

In my original design, I am using AM26LV31I to drive the receiver AM2632I with both 3.3V on its VCC. These two ICs are used in Delta-sigma modulator AM1303M2520D with a signal frequency 20 MHz. The total PCB traces length is less than 10 cm.

For some reason, the operating temperature of 85 oC is not enough. Then, I used AM26C31Q and AM26C32Q to replace onboard AM26LV31I and AM2632I. I have surprised that these two ICs are working well.

Can I supply 3.3V to the VCC of AM26C31Q and C32Q? Is there any effect I should aware of?

over 3 years ago

+1 Clemens Ladisch over 3 years ago

Guru 298840 points

At 5 V, correct operation is guaranteed. At 3.3 V, there is no guarantee. (And the guaranteed speed of the AM26C31 is only 10 Mbps.) I do not know what you mean with "working well", but you should check the waveform with an oscilloscope.

The cheapest alternative would be the AM26LV31E-EP/AM26LV32E-EP.

+1 Yee Wilson over 3 years ago in reply to Clemens Ladisch

Prodigy 40 points

This is the 1Y output of AM26C31Q with VCC 3.3V. There is a 120 Ohm termination resistor at the receiver's input.

+1 Clemens Ladisch over 3 years ago in reply to Yee Wilson

Guru 298840 points

This signal looks fine.

Try again at the highest temperature you actually need to support. And as I said, there is no guarantee.

+1 Hao L over 3 years ago in reply to Clemens Ladisch

TI__Mastermind 25705 points

Wilson,

Please note that the receiver threshold is about 200mV. Even the output voltage with a 3.3V supply doesn't meet the RS-422 standard. The system might still work. However like Clemens said, TI doesn't guarantee the performance with 3.3V.

0 Yee Wilson over 3 years ago in reply to Clemens Ladisch

Prodigy 40 points

What's factor makes the AM26LV31 can runs at 32 Mbps while AM26C31 runs at 10Mbps?

0 Clemens Ladisch over 3 years ago in reply to Yee Wilson

Guru 298840 points

The AM26C31 was designed as a replacement for the AM26LS31, so I guess nobody bothered to test it with more than 10 Mbps.

+1 Hao L over 3 years ago in reply to Clemens Ladisch

TI__Mastermind 25705 points

Wilson,

The maximum data rate is governed by the driver's rise/fall time. AM26C31 is 5ns typical, while AM26LV31 is 3ns.

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AM26C31: AM26C31 can works on 3.3V VCC