SN74HCS238: Compatibility verification with CPLD(ICE40UP5K-SG48I)

Uthiravasagam I

Prodigy 30 points

Part Number: SN74HCS238
Other Parts Discussed in Thread: CD74HCT238, TXB0104

Hii

We are planning to drive the Decoder : SN74HCS238BQBR with the CPLD : ICE40UP5K-SG48I.

And the CPLD voltage levels are at LVTTL level (+3.3V) and the Decoder operating voltage with +5V-VCC.

Whether of the will compatible and the CPLD can able to drive Decoder(SN74HCS238BQBR).

over 2 years ago

0 Clemens Ladisch over 2 years ago

Guru 243220 points

It is not allowed to drive CMOS 5 V inputs with 3.3 V signals; those do not reach V_IH.

It might be possible to use the 3.3 V supply for the decoder. But if you need the decoder to output 5 V, then use a device with TTL-compatible inputs, i.e., CD74HCT238.

0 Emrys Maier over 2 years ago in reply to Clemens Ladisch

TI__Guru* 96591 points

I agree with Clemens.

HCT is probably the best solution for you, however I just wanted to mention that another option would be to add a voltage translator into the circuit such as TXB0104.

0 Uthiravasagam I over 2 years ago in reply to Clemens Ladisch

Prodigy 30 points

Sir,

Thank you for your reply

Can you please tell me the values of VIH and VIL (Max and min) of decoder : SN74HCS238BQBR with +5V-VCC ?

0 Clemens Ladisch over 2 years ago in reply to Uthiravasagam I

Guru 243220 points

You can use linear interpolation from the other supply voltages. For a Schmitt-trigger input, V_IH corresponds to the positive-going threshold voltage; at 5 V, V_T+(max) is 3.5 V.

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SN74HCS238: Compatibility verification with CPLD(ICE40UP5K-SG48I)